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ASME Conference Presenter Attendance Policy and Archival Proceedings

2011;():i. doi:10.1115/DETC2011-NS7.
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This online compilation of papers from the ASME 2011 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference (IDETC/CIE2011) represents the archival version of the Conference Proceedings. According to ASME’s conference presenter attendance policy, if a paper is not presented at the Conference, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in the ASME Digital Library and may not be cited as a published paper.

Commentary by Dr. Valentin Fuster

5th International Conference on Micro- and Nanosystems

2011;():3-9. doi:10.1115/DETC2011-47123.

The group 2 allergen, Der p2, has been reported to activate innate toll-like receptors (TLRs) on respiratory epithelial cells and thus aggravate respiratory diseases. In this study, a high sensitive nanobiosensor based on a 3D sensing element that has uniformly deposited gold nanoparticles for the detection of the dust mite antigen Der p2 is proposed. The barrier layer of an anodic aluminum oxide (AAO) film is used as the template in this highly sensitive nanobiosensor fabricated with a reducing agent and stabilizer-free method. Electrochemical deposition is utilized to synthesize uniformly distributed gold nanoparticles on the surface of the barrier layer. The size and the distribution density of the nanoparticles can be well controlled by the potential applied during electrochemical deposition. Following this procedure, monoclonal antibodies were immobilized against the dust mite antigen Der p2 by the gold nanoparticles through the 11-MUA (11-mercaptoundecanoic acid), EDC (1-Ethyl-3-(3-dimethyl-aminopropyl)-carbodiimide)/NHS (N-hydroxysuccinimide) self-assembled monolayer approach. The proposed nanobiosensor was successfully used to examine the Der p2 down to a concentration of 1pg/mL through the electrochemical impedance spectroscopy analysis. The high sensitivity of the proposed 3D nanobiosensor can be attributed to the high intensity and uniformity of the Au nanoparticles on the sensor. The proposed nanobiosensor would be useful for the fast detection of rare molecules in a solution.

Commentary by Dr. Valentin Fuster
2011;():11-15. doi:10.1115/DETC2011-47178.

The popular bio-marker for colon cancer is carcinoembryonic antigen (CEA). By conjugating anti-CEA onto magnetic nanoparticles, CEA can be specially labeled and detected by measuring magnetic signals via immunomagnetic reduction (IMR). The low detection limit and detection range of IMR on CEA are investigated. The results are compared with those by using the existing assay, such as enzyme-linked immunosorbent assay (ELISA). It is evidenced that IMR has sensitivity much higher than that of ELISA. The low detection limit is below the normal level of CEA concentration of clinic practice and is suitable for early-stage in-vitro diagnosis for colon cancer. Furthermore, the dynamic range of detection for the CEA concentration using IMR extends well above the threshold of high risk level of colorectal carcinoma in current diagnosing practice. Therefore, IMR is also suitable in other stages diagnosis for colon cancer development.

Commentary by Dr. Valentin Fuster
2011;():17-24. doi:10.1115/DETC2011-47320.

This paper outlines the adaptation of a mathematical computer model used to simulate the motion of DNA particles in order to determine the best geometry and setup for a prototype cell injection system. The model predicts DNA motion due to electrophoresis near micromachined electrodes. Ten key electrode parameters are identified to test for significance, and three key test measurements are identified to help compare the various setups. A simple design of experiment is used to organize and analyze the data collected from forty-one simulations of the DNA motion within the electric field. Based on the simulations of attracting DNA to the lance for injection, it is found that a compact ring electrode placed underneath an insulated lance will yield the optimal results. Two additional areas for research are recommended.

Topics: Electrodes
Commentary by Dr. Valentin Fuster
2011;():25-32. doi:10.1115/DETC2011-47528.

Usually microorganisms, molecules, or viruses in the fluidic environment are at very low Reynolds numbers because of tiny diameters. At very low Reynolds numbers, viscous forces of molecules and viruses will dominate. Those micro- or nanoparticles will stop moving immediately when flows cease and drag forces disappear, those phenomena were discovered by the fluorescent particle experiment. Of course, molecules and viruses are still subject to Brownian motion and move randomly. In order to increase the adhesion density of micro- and nanoparticles on sensor’s surface, designs of the flow movements in microfluidic channel is proposed. Adhesion density of linker 11-mercaptoundecanoic acid (MUA) and Turnip yellow mosaic virus (TYMV) with specific quantum dots were measured by confocal microscope. Fluorescent intensity and coverage of quantum dots are used to identify the adhesion density quantitatively. Results show that TYMV and MUA layers disperse randomly by dipping method. Fluorescent intensity of quantum dots; i.e. relative to the amount of MUA and TYMV; were 2.67A.U. and 19.13A.U., respectively, in W-type microfluidic devices to contrast just 1.00A.U. and 1.00A.U., respectively, by dipping method. Coverage of MUA and TYMV were 80∼90% and 70∼90%, respectively, in W-type microfluidic channel to contrast just 20∼50% and 0∼10%, respectively, by dipping method.

Commentary by Dr. Valentin Fuster
2011;():33-39. doi:10.1115/DETC2011-47532.

One of the continuing, persistent challenges confronting tissue engineering is the lack of intrinsic microvessels for the transportation of nutrients and metabolites. An artificial microvascular system can be a feasible solution to this problem. In this study, the femtosecond laser ablation technique was implemented for the fabrication of pillared microvessel scaffolds in PLGA. This novel scaffold enable the conventional cell seeding process to be implemented and the progress of cell growth to be observed in vitro by an optical microscopy. Hence, the milky and completely opaque problems of the conventional PLGA scaffold after cell seeding can be resolved. Currently, PLGA microvessel scaffolds consisting of 30μm×200μm pillared branches have been produced. Cell cultural results of BECs demonstrate that cells can well adhere and grow surrounding each branch of the proposed pillared microvessel networks. The promising results reveal that an artificial microvessel networks for tissue engineering can be completely realized.

Commentary by Dr. Valentin Fuster
2011;():41-49. doi:10.1115/DETC2011-47653.

Biological cell injection is a sensitive and important work which is implemented in injection of foreign materials into individual cells. Microinjection is significantly developed in the field of drug discovery and genetics so predicting the behavior of cell in microinjection is remarkably important because a tiny excessive manipulation force can destroy the tissue of the biological cell. There are a few analytical methods available to simulate the cell injection, hence the numerical methods such as FEM are suitable to be used to model the microinjection. In this study, a new spherical super element is presented to model the biological cells and deformation of a specific cell under an external force is performed. The relationship between the injection force and the deformation of biological cell is demonstrated by using super element formulations. For validating the model, results are compared with findings of analytical and experimental methods. The advantage of this element is that only a few super elements can predict the static behavior of biological cell in microinjection properly instead of implementing a large number of conventional elements, so using the super element to model the cell can decrease the run time with suitable accuracy.

Commentary by Dr. Valentin Fuster
2011;():51-62. doi:10.1115/DETC2011-48005.

Microfluidic devices are well suited for the study of biological objects because of their indirect nature of manipulation and high throughput. However, the cell manipulation process solely depends on the fluid flow and hence precise control is difficult to attain inside a microfluidic chamber. Utilizing optical tweezers as a complementary tool provides precise manipulation control. We have presented an automated cell manipulation approach using optical tweezers operating inside a microfluidic chamber. To test and demonstrate the effectiveness of the approach we have developed a physics-based simulator that is completely automated and allows high precision of manipulation.

Commentary by Dr. Valentin Fuster
2011;():63-69. doi:10.1115/DETC2011-48379.

This paper deals with electrostatically actuated Carbon NanoTubes (CNT) cantilevers for bio-sensing applications. There are three kinds of forces acting on the CNT cantilever: electrostatic, elastostatic, and van der Waals. The van der Waals forces are significant for values of 50 nm or lower of the gap between the CNT and the ground plate. As both forces electrostatic and van der Waals are nonlinear, and the CNT electrostatic actuation is given by AC voltage, the CNT dynamics is nonlinear parametric. The method of multiple scales is used to investigate the system under soft excitations and/or weakly nonlinearities. The frequency-amplitude and frequency-phase behavior are found in the case of primary resonance. The CNT bio-sensor is to be used for mass detection applications.

Commentary by Dr. Valentin Fuster
2011;():71-77. doi:10.1115/DETC2011-47116.

The opening and closing of a RF MEMS switch is simulated using the governing thermal and structural equations. The system is a bridge with a length of 250 microns, a width of 50 microns, and a thickness of 1 micron, in air with a pressure of 5 kPa. Simulations are performed for two different materials: silicon and silicon nitride. Three heating models are used: Distributed heat, concentrated heat at the center, and concentrated heat at the sides of the top plate. The steady state results show that the maximum deflection variation at the center of the bridge versus the total heat changes at the top corresponds to a linear system. For distributed heat, for a specific deflection at the center, closed bridge needs less heat at the top than the free bridge. Variation in the length of the contact results in negligible changes in the maximum deflection. Transient results show that silicon nitride has faster response in comparison with silicon. Silicon nitride has a smaller closing time and opening time in comparison with silicon for the same value of heat, due to the larger expansion coefficient of silicon nitride. Adding concentrated heat at the center yields a larger displacement than adding heat to the sides and show better dynamic behavior. When the heating is changed to a concentrated heat load at the center the required heat is an order of magnitude less than heat added to the sides.

Topics: Simulation , Switches
Commentary by Dr. Valentin Fuster
2011;():79-85. doi:10.1115/DETC2011-47125.

In the current paper, Extended Kantorovich Method (EKM) has been utilized to analytically solve the problem of squeezed film damping in micromirrors. A one term Galerkin approximation is used and following the extended Kantorovich procedure, the solution of the Reynolds equation which governs the squeezed film damping in micromirrors is reduced to solution of two uncoupled ordinary differential equation which can be solved iteratively with a rapid convergence for finding the pressure distribution underneath the micromirror. It is shown that the EKM results are independent of the initial guess function. It is also shown that since EKM is highly convergent, practically one iterate is sufficient for obtaining a precise response. Furthermore using the presented closed form solutions for the squeezed film damping torque, it is proved that when the tilting angle of the mirror is small, the damping is linear viscous one. Results of this paper can be used for accurate dynamical simulation of micromirrors under the effect of squeezed film damping.

Topics: Damping , Modeling
Commentary by Dr. Valentin Fuster
2011;():87-100. doi:10.1115/DETC2011-47260.

The goal of this paper is to elucidate the effects of device geometry and fabrication process variations on the statistical pull-in performance of an electrostatically-actuated capacitive radio frequency micro electro-mechanical system (RF-MEMS) switch through the use of uncertainty quantification. The prediction of switch dynamics and pull-in voltage involves the coupled interaction of elastodynamics, fluid dynamics, and electrostatics. A comprehensive computational framework based on the finite volume method (FVM) is developed to account for these effects. The immersed boundary method (IBM) is employed to couple the fluid, structure and electrostatics. A population of switches is fabricated, and geometry and material properties measured; these measurements provide the probabilistic input information needed for uncertainty quantification. Deterministic simulations are first made for a specific device, and the gap-versus-voltage and pull-in voltage predicted compare favorably with measurements and theoretical estimation. Uncertainty quantification of dynamic pull-in is performed next, using the stochastic collocation method for uncertainty propagation. Probability density functions (PDFs) of pull-in voltage and gap-versus-time are computed. The primary determinants of uncertainty in pull-in voltage are found to be the membrane thickness and gap size, with uncertainty in residual stress having a relatively small effect.

Commentary by Dr. Valentin Fuster
2011;():101-106. doi:10.1115/DETC2011-47271.

Micro-scale slender swimmers are frequently encountered in nature and recently in micro-robotic applications. The swimming mechanism examined in this article is based on small transverse axi-symmetrical travelling wave deformations of a cylindrical long shell. In very small scale, inertia forces become negligible and viscous forces dominate most propulsion mechanisms being used by micro-organisms and robotic devices. The present paper proposes a compact design principle that provides efficient power to propel and maneuver a micro-scale device. Shown in this paper is a numerical analysis which couples the MEMS structure to the surrounding fluid. Analytical results compare the proposed mechanism to commonly found tail (flagella) driven devices, and a parametric comparison is shown suggesting it has superior performance. Numerical studies are preformed to verify the analytical model. Finally, a macro-scale demonstrator swimming in an environment with similar Reynolds numbers to the ones found in small scale is shown and its behavior in the laboratory is compared to the theory.

Commentary by Dr. Valentin Fuster
2011;():107-116. doi:10.1115/DETC2011-47289.

Nanoscale resonators whose motion is measured through laser interferometry are known to exhibit stable limit cycle motion. Motion of the resonator through the interference field modulates the amount of light absorbed by the resonator and hence the temperature field within it. The resulting coupling of motion and thermal stresses can lead to self oscillation, i.e. a limit cycle. In this work the coexistence of multiple stable limit cycles is demonstrated in an analytic model. Numerical continuation and direct numerical integration are used to study the structure of the solutions to the model. The effect of damping is discussed as well as the properties that would be necessary for physical devices to exhibit this behavior.

Topics: Lasers , Cycles
Commentary by Dr. Valentin Fuster
2011;():117-123. doi:10.1115/DETC2011-47461.

This paper reports the development and implementation of a new method for tracking parameters at which dynamic bifurcations occur in MEMS. The underlying theory is developed for subcritical pitchfork bifurcations that occur near the subharmonic instability experienced near parametric resonance. The method relies on experimentally observed changes in response phase and amplitude just prior to the bifurcation, and these are used to forebode the bifurcation. These precursors are then employed in a feedback control scheme to stabilize a parametrically excited MEMS device at the edge of instability, making it highly sensitive to changes in device parameters. Implementation of the controller is shown through experimental validation. A comparison with the previous method of bifurcation detection for the same device shows that the new approach offers an improvement of over three orders of magnitude for the bifurcation point acquisition rate.

Commentary by Dr. Valentin Fuster
2011;():125-134. doi:10.1115/DETC2011-47506.

In this study, a two-component auto-parametric resonator utilizing piezoelectric actuation is proposed. The resonator consists of a plate component which serves as the exciter and a beam component which serves as the oscillator. When an electric signal is applied, the plate component experiences in-plane oscillations which serve to provide axial excitation to the beam component. The system is designed to operate in auto-parametric resonance with a plate to beam principal frequency ratio of 1:2. Due to the oscillations of the beam component, a dynamic force and a moment are applied to the plate and can cause out-of-plane oscillations of the plate component. Internal-resonance can also exist between the beam oscillations and the out-of-plane vibrations of the plate component. A model is derived in order to describe these three motions and the coupling between them. By assuming single mode behavior for each motion, the model is discretized and represented with a three degree-of-freedom model. The model is solved analytically by using the method of multiple scales. Results of the perturbation method agree well with the numerical simulation. The results for the system with strong and weak coupling between the resonator components are presented and compared.

Commentary by Dr. Valentin Fuster
2011;():135-144. doi:10.1115/DETC2011-47575.

We report on the operational principle, modeling, fabrication and characterization of an electrostatically actuated force/acceleration sensor with mechanically nonlinear stiffening suspension. The suspension incorporates initially curved beams oriented in such a way that both the electrostatic and inertial forces applied to the beam’s ends are directed predominantly along the beam. Since the stiffness of the curved beam is significantly lower than that of the straightened beam, the force-displacement dependence of the suspension is of the self-limiting type while the suspension itself serves as a compliant constraint. Application of a softening electrostatic force, provided by a parallel-plate transducer, results in pull-in instability followed by the steep increase in the suspension stifftness and the appearance of an additional stable configuration of the device. In accordance with the model results the dependence between the acceleration and the shift of the pull-in voltage induced by the acceleration is nearly linear and the pull-in voltage monitoring can be used for the measurement of the acceleration. Model results show that using the suggested approach significantly improves device resolution, extends dynamic range, and improves reliability by eliminating contact. Devices of several configurations were fabricated from a silicon on insulator (SOI) substrate using a deep reactive ion etching (DRIE) based process. Preliminary experimental results imply that the suggested approach is feasible.

Topics: Sensors
Commentary by Dr. Valentin Fuster
2011;():145-151. doi:10.1115/DETC2011-47615.

Electrostatically actuated beams are fundamental blocks of many different nano and micro electromechanical devices. Accurate design of these devices strongly relies on recognition of static and dynamic behavior and response of mechanical components. Taking into account the effect of internal forces between material particles nonlocal theories become highly important. In this paper nonlinear vibration of a micro\nano doubly clamped and cantilever beam under electric force is investigated using nonlocal continuum mechanics theory. Implementing differential form of nonlocal constitutive equation the nonlinear partial differential equation of motion is reformulated. The equation of motion is nondimentioanalized to study the effect of applied nonlocal theories. Galerkin decomposition method is used to transform governing equation to a nonlinear ordinary differential equation. Homotopy perturbation method is implemented to find semi-analytic solution of the problem. Size effect on vibration frequency for various applied voltages is studied. Results indicate as size decreases the dimensionless frequency increases for a cantilever beam and decreases for a doubly clamped beam. Size effect is specially significant as the beam size tends toward nano scale in the analysis.

Commentary by Dr. Valentin Fuster
2011;():153-158. doi:10.1115/DETC2011-47791.

Accurate prediction of static and dynamic response of nano structures is one of the important interests of scientists in the last decade. Nano bearing as an important part of nano machines has been extensively implemented in recognizing and disassembling cancerous cells and building molecular support structures for strengthening bones. For this reason, Molecular Dynamic Method and some experimental methods are implemented in this area. As nano ball bearing is one of the most important components of nano machines, a large number of studies are concentrated to analyze it statically and dynamically. In this paper, a Fullerene is simulated by a spherical super element whose stress, deformation and natural frequency are calculated. The Fullerene is considered to be the C60 which is properly similar with a 66 surface-node spherical super element. In this study the mechanical properties of the fullerene and boundary conditions of the nano ball bearing under loading are introduced and stress and natural frequency of a fullerene under concentrated load is presented with two different strategies, super element and conventional elements. Compatible findings of these two methods validate and confirm the results. Findings indicate that applying 1 super element for the simulation of the fullerene leads to same results as implementing 154764 conventional elements.

Commentary by Dr. Valentin Fuster
2011;():159-166. doi:10.1115/DETC2011-47978.

This work investigates the impact of asymmetric cross-sectional geometry on the near-resonant response of electrostatically-actuated silicon nanowires. The work demonstrates that dimensional variances of less than 2% qualitatively alter the near-resonant response of these nanosystems, rendering a non-Lorentzian frequency response structure. Theoretical and experimental results demonstrate that this effect is independent of material properties and device boundary conditions and can be easily modeled using a two-degree-of-freedom system. Proper understanding of this phenomenon is believed to be essential in the characterization of the dynamic response of resonant nanotube and nanowire systems and thus the predictive design and development of such devices. Practical applications of the devices of interest include electrostatic force gradients and mass sensing, both of which can advantageously leverage the unique frequency response structure attendant to these systems.

Commentary by Dr. Valentin Fuster
2011;():167-176. doi:10.1115/DETC2011-48008.

As Micro and Nano Electro-Mechanical devices continue to find more applications, the electrostatically actuated micro-beam remains one of the most frequently used structures due to its usefulness and relative simplicity of fabrication. Accurate models of these devices which are valid under a wide range of circumstances are important both for design as well as metrology efforts. Often certain device parameters are implicitly extracted via a mathematical model when they are very difficult to measure directly. This work details the development and results of a reduced-order model for the behavior of an electrostatically actuated beam. The model accounts for arbitrary initial curvature, residual stress, flexible boundary conditions and contact, while including accurate sub-models for the electrostatic and damping forces. The equation of motion of the beam is discretized via the traditional Galerkin method. Static and dynamic solutions are found through specified displacement schemes and direct time integration, respectively. The rich behavior of these systems can easily be seen in the results. Arched doubly-clamped beams can show a variety of bi-stable configurations and tri-stable solutions can be seen in the post-contact behavior of cantilever beams. Dynamic solutions reveal phenomena such as dynamic pull-in, dynamic snap-through, and bouncing behavior. The widely valid model presented here generally converges quickly and is well suited for design, analysis and uncertainty quantification.

Commentary by Dr. Valentin Fuster
2011;():177-186. doi:10.1115/DETC2011-48199.

Microelectromechanical chemical and biological sensors have garnered significant interest over the past two decades due to their ability to selectively detect very small amounts of added mass. Today, most resonant mass sensors utilize chemomechanically-induced shifts in the linear natural frequency for detection. In this paper, an alternative, amplitude-based sensing approach, which exploits dynamic transitions across saddle-node bifurcations that exist in a microresonator’s nonlinear frequency response, is investigated. In comparison to their more traditional, linear counterparts, these bifurcation-based sensors have the ability to provide improved sensor metrics, eliminate power-consuming hardware from final sensor implementations, and operate effectively at smaller (e.g. nano) scales. The present work details the ongoing development of a bifurcation-based mass sensor founded upon the near-resonant response of piezoelectrically-actuated microcantilevers. Specifically, the work details the modeling and analysis of these devices, their functionalization, and proof-of-concept mass sensing experiments which not only validate the proposed technique, but allow for the direct evaluation of pertinent sensor metrics.

Commentary by Dr. Valentin Fuster
2011;():187-190. doi:10.1115/DETC2011-48286.

In this paper, we demonstrate Lead zirconate titanate (PZT) nanofibers as a transducer to generate and detect ultrasound acoustic waves. PZT nanofibers with average diameter of 102nm were fabricated by the electrospinning method. The as-fabricated nanofibers were collected and aligned across a 10 μm silicon trench with Au electrodes. After annealing, the device was tested with the pulse/delay method. Two resonant frequencies, 8 MHz and 13MHz, were detected respectively. By using the Hamilton’s principle for coupled electromechanical systems with properly assumed mode shape, the resonant frequency was caudated. Base on the current testing result, a broadband ultrasound transducer was envisioned.

Commentary by Dr. Valentin Fuster
2011;():191-196. doi:10.1115/DETC2011-48373.

In this paper, simple analytical expressions are presented for geometrically non-linear vibration analysis of thin nanobeams with both simply supported and clamped boundary conditions. Gurtin-Murdoch surface elasticity together with Euler-Bernoulli beam theory is used to obtain the governing equations of motions of the nanobeam with surface effects consideration. The governing nonlinear partial differential equation is reduced to a single nonlinear ordinary differential equation using Galerkin technique. He’s variational approach is employed to obtain analytical solution for the resulted nonlinear governing equation. The effects of different parameters such as vibration amplitude, boundary conditions, and beam dimensions on the natural frequencies of nanobeams are investigated and results are presented for future studies.

Commentary by Dr. Valentin Fuster
2011;():197-207. doi:10.1115/DETC2011-48501.

We present an investigation into the dynamics of MEMS arches when actuated electrically including the effect of their flexible (non-ideal) supports. First, the eigenvalue problem of a nonlinear Euler-Bernoulli shallow arch with torsional and transversal springs at the boundaries is solved analytically. Several results are shown to demonstrate the possibility of tuning the theoretically obtained natural frequencies of an arch to match the experimentally measured. Then, simulation results are shown for the forced vibration response of an arch when excited by a DC electrostatic force superimposed to an AC harmonic load. Shooting technique is utilized to find periodic motions. The stability of the captured periodic motion is examined using the Floquet theory. The results show several jumps in the response during snap-through motion and pull-in. Theoretical and experimental investigations are conducted on a microfabricated curved beam actuated electrically. Results show softening behavior and superharmonic resonances. It is demonstrated that non-ideal boundary conditions can have significant effect on the qualitative dynamical behavior of the MEMS arch, including its natural frequencies, snap-through behavior, and dynamic pull-in.

Commentary by Dr. Valentin Fuster
2011;():209-218. doi:10.1115/DETC2011-48544.

In this work we investigate the feasibility of two-directional switching of a pre-buckled electrostatically actuated micro beam operated by a single electrode fabricated from the same structural layer. The distributed electrostatic force, which is engendered by the asymmetry of the fringing fields in the deformed state, acts in the direction opposite to the deflection of the beam and is of a restoring nature. The reduced order model was built using the Galerkin decomposition and verified using the results of the numerical solution of the differential equation. The actuating force was approximated by fitting the results of the numerical solution of the electrostatic problem. Static stability analysis reveals that the presence of the restoring electrostatic force may result in the suppression of the snap-through instability. We show that two-directional switching of a pre-buckled beam between two stable configurations and bistability cannot be achieved using quasistatic loading but are possible through dynamic instability mechanism. We demonstrate that switching associated with the dynamic snap-through takes place within certain interval of actuation voltages and pulse durations. Theoretical results illustrate the feasibility of the suggested operational principle as an efficient mechanism with application to nonvolatile mechanical memory devices.

Commentary by Dr. Valentin Fuster
2011;():219-226. doi:10.1115/DETC2011-48552.

This paper summarizes a numerical analysis of an eigenmode-based approach for ultrasensitive mass detection via coupled microcantilevers. Mass detection using microcantilevers typically entails the observation of shifts in resonance frequency. Recently, detection systems have been proposed in which multiple cantilever sensors are coupled, either directly or by attachment to a single shuttle mass. Once sensors are coupled, however, mass adsorption on a single sensor alters all eigenmodes of the system. Thus, one disadvantage of the frequency-shift method in such cases is the need for strong mode localization, such that the shift of a single frequency can be associated with a mass change on a specific sensor. The consequent requirement for weak coupling limits the number of microcantilevers that can occupy a specific frequency band. The proposed eigenmode-based detection scheme involves solving the inverse eigenvalue problem to identify added mass, and can be used in cases where more than one eigenfrequency has shifted significantly. The method requires a single measured mode shape and corresponding natural frequency, selected from among those where a shift was observed. The fidelity of the identification of added mass and its location depends on the ability to accurately measure the mode shape, and on the amplitude with which each cantilever vibrates in the chosen mode (in modes without strong localization, multiple cantilevers respond with significant amplitude). Simulation results are presented that quantify, as a function of measurement noise, the ability of the method to accurately identify the cantilever(s) where mass adheres. In cases in which the resonance frequency-shift method is inappropriate due to non-localized modes, the inverse eigenvalue method proposed here can be used to identify both the amount and location of the added mass.

Commentary by Dr. Valentin Fuster
2011;():227-233. doi:10.1115/DETC2011-48562.

The use of micro- and nanoscale mechanical resonators for mass detection is a maturing concept. Recently, researchers have begun to consider coupled arrays of resonators and the notion of examining system eigenmodes as well as resonant frequencies to extract information about the system. This paper describes a method for the use of measured eigenmodes of a linear chain of nominally identical oscillators to identify the masses of the individual oscillators. This allows characterization of initial mass variation as well as changes due to the presence of one or more target analytes. This work uses numerical simulation to explore the sensitivity of this method to measurement noise. Mass identification is shown to be more accurate on oscillators with significant vibration amplitude in a given eigenmode. We discuss various averaging techniques for combining results from multiple eigenmodes to reduce sensitivity to noise.

Commentary by Dr. Valentin Fuster
2011;():235-243. doi:10.1115/DETC2011-48597.

Enhancing the sensitivity of an electrostatically actuated resonant switch (EARS) for earthquake detection is investigated. The resonator is proposed to operate close to instability bands of frequency-response curves, where it is forced to pull-in if operated within these bands. By careful tuning, the resonator can be made to enter the instability zone upon the detection of the earthquake signal, thereby pulling-in as a switch. Such a switching action can be functionalized for alarming purposes or can be used to activate a network of sensors for seismic activity recording. By placing such a resonator on a printed circuit board of a natural frequency close to that of the earthquake’s frequency, significant improvement on the detection limit of this switch is achieved. In this work, nonlinear Single-Degree-Of-Freedom (SDOF) and 2-Degree-Of-Freedom (2-DOF) models are used to simulate the performance of the switch concept.

Topics: Earthquakes , Switches
Commentary by Dr. Valentin Fuster
2011;():245-253. doi:10.1115/DETC2011-48601.

This study is motivated by the growing attention, both from a practical and a theoretical point of view, toward the nonlinear behavior of microelectromechanical systems (MEMS). We analyze the nonlinear dynamics of an imperfect microbeam under an axial force and electric excitation. The imperfection of the microbeam, typically due to microfabrication processes, is simulated assuming the microbeam to be of a shallow arched initial shape. The device has a bistable static behavior. The aim is that of illustrating the nonlinear phenomena, which arise due to the coupling of mechanical and electrical nonlinearities, and discussing their usefulness for the engineering design of the microstructure. We derive a single-mode-reduced-order model by combining the classical Galerkin technique and the Padé approximation. Despite its apparent simplicity, this model is able to capture the main features of the complex dynamics of the device. Extensive numerical simulations are performed using frequency response diagrams, attractor-basins phase portraits, and frequency-dynamic voltage behavior charts. We investigate the overall scenario, up to the inevitable escape, obtaining the theoretical boundaries of appearance and disappearance of the main attractors. The main features of the nonlinear dynamics are discussed, stressing their existence and their practical relevance. We focus on the coexistence of robust attractors, which leads to a considerable versatility of behavior. This is a very attractive feature in MEMS applications. The ranges of coexistence are analyzed in detail, remarkably at high values of the dynamic excitation, where the penetration of the escape (dynamic pull-in) inside the double well may prevent the safe jump between the attractors.

Commentary by Dr. Valentin Fuster
2011;():255-261. doi:10.1115/DETC2011-48862.

One of the most important phenomena related to electrically actuated micro and nano electromechanical systems (MEMS\NEMS) is dynamic pull-in instability which occurs when the electrical attraction and beam inertia forces are more than elastic restoring force of the beam. According to failure of classical mechanics constitutive equations in prediction of dynamic behavior of small size systems, nonlocal theory is implemented here to analyze the dynamic pull-in behavior. Equation of motion of an electrostatically actuated micro to nano scale doubly clamped beam is rewritten using differential form of nonlocal theory constitutive equation. To analyze the nonlocal effect equation of motion is nondimentionalized. Governing partial differential equation is transformed to an ordinary differential equation using the Galerkin decomposition method and then is solved implementing differential quadrature method (DQM). Change of dynamic pull-in voltage with respect to size change is investigated. Results indicate as the beam length decreases dynamic pull-in voltage increases due to nonlocal effect and the difference with clasical mechanics results is up to 20% for nano beams.

Commentary by Dr. Valentin Fuster
2011;():263-267. doi:10.1115/DETC2011-48888.

MEMS devices typically have moving or oscillating mechanical parts, and characterization of their dynamics, including their modal parameters, is highly desirable. This paper is concerned with experimental implementation of a Stochastic Subspace Identification (SSI) algorithm as well a base excitation based identification algorithm for experimental modal analysis of a micro-cantilever switch. A white noise signal applied to the built-in electrostatic actuator in the switches excited a response measured using microscanning Laser Doppler Vibrometry (LDV). In the case of identification via the SSI, only the output response was used while the base excitation based algorithm employed the input and the output signals. The modal parameters found using MACEC matched well with those predicted by theory, and the results obtained via the two experimental identification approaches are in good agreement, thus providing confidence in using the SSI approach for experimental modal analysis of MEMS structures.

Commentary by Dr. Valentin Fuster
2011;():269-277. doi:10.1115/DETC2011-47512.

Lead Zirconate Titanate (PbZrx Ti1−x O3 or PZT) is a piezoelectric material widely used as sensors and actuators. For microactuators, PZT often appears in the form of thin films to maintain proper aspect ratios. One major challenge encountered is accurate measurement of piezoelectric coefficients of PZT thin films. In this paper, we present a simple, low-cost, and effective method to measure piezoelectric coefficient d33 of PZT thin films through use of basic principles in mechanics of vibration. We use a small impact hammer with a tiny tip to generate an impulsive force acting perpendicularly to the surface of a PZT film. In the meantime, we measure the impulsive force via a load cell and the responding charge of the PZT thin film via a charge amplifier. Then the piezoelectric coefficient d33 is obtained from the measured force and charge based on piezoelectricity and a finite element modeling. We also conduct a thorough parametric study to understand the sensitivity of this method on various parameters, such as substrate material, boundary conditions, specimen size, specimen thickness, thickness ratio, and PZT thin-film material. To demonstrate the feasibility, we calibrate the new method via a PZT thick film disk resonator with a known d33 . Experimental results show that d33 measured via this method is as accurate as those from the manufacturer’s specifications within its tolerance. We then apply the new method to PZT thin films deposited on silicon substrate, and successfully measure the corresponding piezoelectric coefficient d33 .

Commentary by Dr. Valentin Fuster
2011;():279-286. doi:10.1115/DETC2011-47902.

This paper presents a new model and test device for determining piezoresistive response in long, thin polysilicon beams with axial and bending moment inducing loads. If the piezoresistive coefficients are known, the Integrated Piezoresistive Flexure Model (IPFM) is used to find the new resistance of a beam under stress. The IPFM first discretizes the beam into small volumes represented by resistors. The stress that each of these volumes experiences is calculated, and the stress is used to change the resistance of the representative resistors according to a second-order piezoresistive equation. Once the resistance change in each resistor is calculated, they are combined in parallel and series to find the resistance change of the entire beam. If the piezoresitive coefficients are not initially known, data are first collected from a test device. Piezoresistive coefficients need to be estimated and the IPFM is run for the test device’s different stress states giving resistance predictions. Optimization is done until changing the piezoresistive coefficients provides model predictions that accurately match experimental data. These piezoresistive coefficients can then be used to design and optimize other piezoresistive devices. A sensor is optimized using this method and is found to increase voltage response by an estimated 10 times.

Commentary by Dr. Valentin Fuster
2011;():287-290. doi:10.1115/DETC2011-48029.

We study the use of a time-dependent potential barrier to control quantum wave packets, in a discretization of the Schroedinger equation. We consider computational issues in solving for a control which steers an initial single peak wave packet to a terminal double peak wave packet.

Commentary by Dr. Valentin Fuster
2011;():291-299. doi:10.1115/DETC2011-48467.

This article explores nonlinear position plus integral (PI) feedback for controlling an optical trap used in single-molecule experiments. In general, nonlinearities in the spatial dependence of the optical force complicate feedback control for optical traps. Furthermore, the extension of a molecule creates an additional feedback path that puts constraints on the PI control gains. The nonlinear PI control presented here is shown to provide all of the benefits of integral control: disturbance rejection, servo tracking, and force estimation. The ability of nonlinear PI control to lower the measurement SNR is evaluated. Finally, constraints on the pulling rate are given to ensure the system trajectory remains in a quasi-static condition, stable, and the bead remains held in the trap.

Commentary by Dr. Valentin Fuster
2011;():301-308. doi:10.1115/DETC2011-48472.

In many optical trapping experiments, exogenous forces are estimated by assuming the exogenous force is balanced with the optical force. These optical forces are measured using Hooke’s law, and the displacement of the particle is low-pass filtered to minimize the effects of Brownian noise. This paper explores a different approach that uses a disturbance model approach for estimating exogenous forces using a Kalman filter. The state estimate is then used in a LQG structure to manipulate the relative position of a dielectric particle within an optical trap. The exogenous force estimate using a Kalman filter has been shown to have a higher SNR than the force estimation using Hooke’s Law. In addition to force estimation, the control structure can also manipulate the relative displacement of the particle to satisfy experimental conditions. A simulation is presented to demonstrate the performance of the LQG control structure.

Topics: Force , Modeling
Commentary by Dr. Valentin Fuster
2011;():309-316. doi:10.1115/DETC2011-48734.

MEMS and NEMs devices benefit many applications due to their unique performance and tiny size. We have researched replacing components of a Wireless Sensor Network (WSN) mote with several such devices. In this paper, we present an energy conversion and storage circuit that can be used with piezoelectric nanogenerators for self powered motes. Energy from external vibration or environmental acoustics is capacitively stored and released at certain time intervals according to the application. Stored and lost power is compared against a detailed WSN mote power budget to size the generator and capacitor.

Commentary by Dr. Valentin Fuster
2011;():317-325. doi:10.1115/DETC2011-48848.

Modeling and measurement of stiction or adhesion due to van der Waals force between microstructures and micro-gripper tools are important for contact-based manipulation and assembly of microstructures. Microfabricated structures commonly feature rough tapered curved surfaces due to undercutting and surface alterations inherent in the microfabrication processes. While several theoretical models exist for calculating adhesive forces between microstructures featuring spherical, cylindrical and flat surfaces, a model for estimating adhesive forces between microstructures featuring tapered curved surfaces is lacking in the literature. This paper presents experimentally measured values of adhesion or pull-off force between a rough tapered curved microstructure from a rough plane surface using a custom micro-cantilever beam as a force sensing mechanism. The paper also introduces an approach to estimate adhesive force between a tapered curved surface and a flat surface by considering the tapered curved surface as a frustum of a cone bound between two cylinders and using the van der Waals force model for cylinders. It is shown that the experimentally measured adhesive force values lie within the upper and lower values of the theoretically estimated van der Waals force values for the two cylinders that define the tapered curved surface geometry.

Topics: Force , Stiction
Commentary by Dr. Valentin Fuster
2011;():327-334. doi:10.1115/DETC2011-47717.

The purpose of this research is trying to design a 6 degree-of-freedom micro-precision positioning stage with monolithic mechanism. It is hoped that this stage can reach 10 μm strokes along linear axis and with rotational angle no less than 50 μrad. The dimension of this positioning stage should be less than 200 mm × 200 mm × 50 mm. By using flexure hinge and piezoelectric actuator, this stage can achieve nanometer resolution. From the experimental results, it is found that the stage can achieve a maximum displacement of 29.3 μm in X axis; 11.94 μm in Y axis; and 6.74 μm in Z axis. The stage can also achieve a maximum rotation of 405.41 μrad around Z axis; 57.18 μrad around X axis; and 63.72 μrad around Y axis. With open loop control, we have shown that the minimum step for the stage is 110 nm in X-axis; 45 nm in Y axis; and 30 nm in Z-axis.

Topics: Design
Commentary by Dr. Valentin Fuster
2011;():335-344. doi:10.1115/DETC2011-47914.

The 6 × 6 Cartesian stiffness matrix obtained through finite element analysis for structures designed with material and geometric symmetries may lead to unexpected coupling that stems from discretization error. Hence, decoupling of the Cartesian stiffness matrix becomes essential for design and analysis. This paper reports a numerical method for decoupling the Cartesian stiffness matrix, based on screw theory. With the aid of this method, the translational and rotational stiffness matrices can be analyzed independently. The mechanical properties of the decoupled stiffness submatrices are investigated via their associated eigenvalue analyses. The decoupling technique is applied to the design of two accelerometer layouts, uniaxial and biaxial, with what the authors term simplicial architectures. The decoupled stiffness matrices reveal acceptable compliance along the sensitive axes and high off-axis stiffness.

Commentary by Dr. Valentin Fuster
2011;():345-354. doi:10.1115/DETC2011-48810.

This paper presents the work conducted towards the realization of a novel tactile display system composed of miniature thermo-fluidic actuators. An application of the system particularly relevant to blind individuals is communication with computers through touch. The development of programmable spatio-temporal pattern of touch actuation based on bubble formation and vapor pressure has remarkable scope, not only because of the flexibility and wearability but also the high levels of motion amplitude and force of actuation not achieved so far by other means. The design specifications of the tactile display involved packaging of the miniature actuators in such a manner that the display can be conveniently attached at the tip of the human finger with desirable spatial resolution, and achieving the optimum force that can be felt through the human finger. However, there were challenges that were faced by the authors while miniaturizing the actuators for suitability in sub-millimeter spatial resolution desirable for the tactile display. The paper reports on the design, prototype development and experimental results and brings out the limitations along with possible solutions being pursued by the authors. The progressive efforts through fabrication and testing of different prototype thermo-fluidic actuators ranging from 3mm diameter bore to sub-millimeter sizes and the corresponding difficulties faced in the form of cooling requirements, hysteresis effects, and fabrication challenges are elucidated. The paper reports on packaging of actuators as an array of tiny tubes spaced as close as possible, and establishment of parameters, namely, amplitude of actuation and switching frequency, along with force generation adequate for tactile perception.

Commentary by Dr. Valentin Fuster
2011;():355-364. doi:10.1115/DETC2011-48842.

This paper presents the work conducted towards the realization of a novel tactile display system, first using block type piezoelectric actuators and later using cantilever type piezoelectric actuators. The system is particularly useful for blind users to communicate with computers through touch, but also has many potential applications in several other fields such as virtual reality, gaming, and other general communication interfaces for sighted users. Although piezoelectric actuators have been used in the past in electronic Braille and other systems, there is no reported configuration that can achieve sub-millimeter center-to-center resolution in an array of programmable actuation pins that act as interfaces in contact with a human body part such as a finger. This paper reports development of a wearable tactile display device: (a) built of block type actuators and its characterization showing that the perception was not adequate for certain purposes; (b) further, a novel arrangement with considerable improvement in perception wherein- (i) two or more vibrating stimulation pins can be located close to each other at the plane of contact with a finger, and (ii) actuated by means of piezoelectric bending elements arranged in a cantilever configuration partially overlapping each other in multiple planes. A significant feature of the unique configuration reported in this paper is that vibratory stimulation can be achieved at finer spatial resolutions than hitherto achieved.

Commentary by Dr. Valentin Fuster
2011;():365-370. doi:10.1115/DETC2011-47112.

Atomic force microscopy (AFM) has been a field driving at exploring nanoscale surfaces and measuring both topography as well as material properties. One of the phenomena that has attracted significant interest is tip-sample dissipation, which was initially investigated by Cleveland and coworkers [Appl. Phys. Lett. 72, 2613–2615 (1998)]. In this paper we expand on that work by developing a method to map the total conservative and non-conservative forces simultaneously in space and as a function of relative tip-sample velocity. This is accomplished through Fourier analysis performed on the response of a torsional harmonic cantilever (THC) probe, previously developed by Sahin and coworkers [Nature Nanotechnology 2, 507–514 (2007)]. The effect of a select group of AFM parameters (cantilever resonant frequency, force constant, quality factor, amplitude set point and excitation amplitude) is simulated in a feasible range of experimental conditions, which maximizes the spatial and velocity range of the oscillating tip, such that useful maps of the total force as a function of tip velocity and position can be acquired. We analyze the observed trends and propose an approach to acquire analytical models of the local tip-sample dissipative and conservative forces.

Commentary by Dr. Valentin Fuster
2011;():371-377. doi:10.1115/DETC2011-47152.

Characterization and simulation of carbon nanotube-reinforced composites at large scale have been a concern of researchers in the past decade. This is due to the computational complication of considering many embedded carbon nanotubes (CNTs). However a simple meshing of organized CNT distribution in the matrix can ease this obstacle. In this study, a finite element approach is employed to investigate the elastodynamic behavior of a wavy CNT-reinforced composite structure. A three dimensional structure with up to 6400 uniformly distributed wavy CNTs is embedded in a polymer matrix. Each wavy nanotube is represented by a set of beam elements. The effect of nanotube waviness and volume fraction on the effective modulus of nanocomposite is evaluated and verified by previous studies. The results demonstrate that waviness tends to decrease the effective modulus of the structure. Furthermore, the natural frequencies of a nano structure at different boundary conditions are examined. The results reveal that the natural frequencies increase with volume fraction of CNT, while a nominal increase of CNT waviness decreases the natural frequencies sharply.

Commentary by Dr. Valentin Fuster
2011;():379-385. doi:10.1115/DETC2011-47167.

We present numerical simulations of a recently developed atomic force microscopy (AFM) technique known as the Band Excitation Method, developed by Jesse et al. [2007 Nanotechnology 18 435503]. With this technique an AFM microcantilever is simultaneously excited and the response measured over a continuum band of frequencies. The purpose of this work is to introduce an analytical model providing insight into the dynamics of the Band Excitation Method, which can help in the translation of the acquired signals into sample properties. As an initial step we examine the cantilever response to two distinct excitation signals, the chirp and sinc functions, both of which have uniform frequency content, differing only in the phase content.

Commentary by Dr. Valentin Fuster
2011;():387-390. doi:10.1115/DETC2011-47226.

We present an electrical measurement of elastic modulus of single electrospun lead zirconate titanate (PZT) nanofibers under harmonic vibration using in situ scanning electron microscopy (SEM) equipped with a nanomanipulator. The PZT nanofiber was fabricated using an electrospinning process and collected on a silicon substrate with 10 μm trenches. The individual PZT nanofibers were excited with an oscillating electric field applied by a network analyzer and the resonant frequency was observed through the SEM along with the transfer frequency spectra simultaneously. The elastic modulus was calculated as ∼70 GPa from this resonant frequency using Euler-Bernoulli equation.

Commentary by Dr. Valentin Fuster
2011;():391-396. doi:10.1115/DETC2011-47616.

In this paper, size dependent static behavior of micro and nano cantilevers actuated by a static electric field including deflection and pull-in instability, is analyzed implementing nonlocal theory. Euler-bernoulli assumptions are made to model the relation between deflection of the beam and bending moment. Differential form of the constitutive equation of nonlocal theory is used to find the revised equation for bending moment and substituting in the equilibrium equation of electrostatically actuated beams final nonlinear ordinary differential equation is arrived. Also the boundary conditions for solving the equation are revised and to analyze the size effect better governing equation is nondimetionalized. The one parameter Galerkin method is used to transform this equation to a nonlinear algebraic equation. Arrived algebraic equation is solved utilizing Newton-Raphson method. Size effect on the maximum deflection and deflection shape for various applied voltages is studied. Also effect of beam size on the static pull-in voltage is studied. Results indicate that the dimensionless beam deflection decreases as size decreases while the pull-in voltage increases and specially change of deflection and pull-in voltage is significant for nanobeams.

Commentary by Dr. Valentin Fuster
2011;():397-399. doi:10.1115/DETC2011-47681.

The Lorenz number of metals has been considered constant according to the Wiedemann-Franz law. But this has been questioned by the most recent research in nano-scale thermal transfer. To study the size effect of Lorenz number for thin film metals, a MEMS tester was designed and fabricated. The tester is capable of measuring the Lorenz number of thin films or nanowires with various dimensions. The ANSYS simulation showed the measurement error generated by the non-uniformity in the heating area is below 2%.

Commentary by Dr. Valentin Fuster
2011;():401-404. doi:10.1115/DETC2011-47856.

Load bearing conjunctions are never perfectly flat. They are covered by surface features, which may be either unintentional roughness inherent in the manufacturing process or a combination of such roughness with intentionally introduced surface texture. In either case, only a small proportion of load bearing surfaces are in contact and carry load. This depends on the surface topography, material properties and contacting conditions. Simple surface roughness characterisation parameters such as Ra , Rp etc. although commonly used do not give an adequate description, particularly where surfaces are deliberately textured. Furthermore Imaged surface topographies commonly exhibit features below the resolution of the imaging apparatus. We demonstrate the application of a fractal geometry analysis to honed internal combustion engine cylinder liners, imaged by Atomic Force Microscopy and Confocal Laser Scanning Microscopy. This method enables anisotropic surfaces to be characterised by five parameters which can then be used to generate model surfaces whose characteristics follow very closely those of the measured surface. Analysis of the structure function allows the determination of length scales and roughness features relevant at a given contact length. The reconstruction of anisotropic surfaces is demonstrated. Results from modelled contacts between these surfaces reveal the likely asperity contact geometry to be used in modelling contact and friction in these interfaces.

Commentary by Dr. Valentin Fuster
2011;():405-412. doi:10.1115/DETC2011-47883.

This paper describes a fully analytic solution method for the displacements and sub-surface stresses within a graded elastic layered solid. This method can be utilised to predict the local deformation of nano or micro-scale depositions under contacting conditions. The solid consists of two distinct layers which are considered to be perfectly bonded and comprise of a graded elastic coating whose shear modulus varies exponentially with the depth coordinate and an infinitely deep homogeneously elastic substrate. The solution given in this paper is generic and easily utilised to solve real problems as it requires only known physical characteristics of the solid under study and an applied surface pressure. As a result, this model is very cheap to use and can be easily integrated into tribological codes to predict local deflections.

Commentary by Dr. Valentin Fuster
2011;():413-416. doi:10.1115/DETC2011-48999.

In the interest of understanding contact mechanics, friction and wear processes where plastic deformation occurs between rough surfaces, significant effort has and continues to be applied to understand single asperity elastic-plastic contacts. The main tools used in obtaining experimental data with which to inform and validate simulation methods in this area of study are nano and micro indenters. This article presents some of the less commonly considered phenomena which may affect the interpretation of experimental data from such apparatus. The interpretation of AFM pull off data is briefly discussed and invasive effects of electron imaging are highlighted.

Commentary by Dr. Valentin Fuster
2011;():417-424. doi:10.1115/DETC2011-47298.

Micro-Electrical Discharge Machining (μEDM) has become a widely accepted non-traditional material removal process for micro-manufacture of conductive materials considered difficult to be cut using traditional machining technologies. Moreover, EDM is an ideal process for obtaining burr-free micron-size apertures with high aspect ratios. Aim of this work was to investigate the feasibility of drilling micro holes on titanium using μ-EDM technology. Titanium plates having a thickness equal to 0.5 mm were taken into account and the holes were performed using a carbide electrode having a diameter equal to 0.3 mm. The Design Of Experiment (DOE) method was used for planning the experimental campaign and ANOVA techniques were applied to study the relationship between process parameters and final output. In particular, the most important process parameters such as peak current, pulse duration, frequency and electrode rotation speed were investigated as a function of material removal rate, wear rate and machining accuracy. Geometrical and dimensional analyses were carried out on micro-holes using both optical and scanning electron microscopes to evaluate both the over cut and the rate of taper.

Commentary by Dr. Valentin Fuster
2011;():425-431. doi:10.1115/DETC2011-47945.

Traditional microelectromechanical MEMS fabrications such photolithography and deep reactive ion etching (DRIE) are expensive and time consuming. This limits the types and designs of MEMS devices that can be produced cost effectively since in order to overcome the high startup costs and times associated with traditional MEMS fabrication techniques tens of thousands of each type of MEMS device must be produced and sold. In this paper, we will present a method for placing carbon nanotube (CNT) based piezoresistive sensors onto metallic flexural elements that are created via micromachining. This method reduces the fabrication time from over 3 months to less than 3 days. In addition, the fabrication cost is reduced form over $500 per device to less than $20 per device. This flexible, low cost fabrication method enables rapid prototyping of MEMS devices which is an important step in the design and development process for electromechanical systems. Also, the development of this type of low cost fabrication method will help to make low volume manufacturing of MEMS devices feasible from a cost prospective. In this fabrication method, a micromill is used to fabricate the flexure beams. Electron beam evaporation is then used to deposit (1) an insulating ceramic thin film layer and (2) metal traces on the flexure. A shadow mask is used to define the wire patterns. Either a tungsten wire or a focused ion beam (FIB) is used to define a 1–5 μm gap in the wire traces. Dielectrophoresis is then used to orient/position the CNT sensors across the gap. Finally, the structure is coated with a thin ceramic layer to protect the sensor and mitigate noise. When the flexure element is deflected, the CNTs strain which results in a measurable change in resistance. Several meso-scale test devices were produced using this fabrication method. The devices that were fabricated using a FIB to create the gap in the wire traces have the same strain sensitivity as devices fabricated using traditional cleanroom based techniques. However, the devices that were fabricated using the tungsten wire have a strain sensitivity that is almost 7 times lower than the devices fabricated using traditional cleanroom based fabrication techniques. This is because the gap size for the tungsten wire fabrication method is about an order of magnitude larger than for the FIB cut or lithography based gap fabrication methods. Therefore, the CNT are not able to stretch across the entire gap. This creates CNT-CNT junctions in the electrical pathway of the sensors which significantly increases the sensor resistance and decreases the strain sensitivity of the sensor. Overall, these results show that functional CNT-based piezoresistive MEMS sensors may be fabricated without conventional integrated circuit (IC) microfabrication technologies but that tight control over the gap size is needed in order to ensure that the sensor performance is not degraded.

Commentary by Dr. Valentin Fuster
2011;():433-439. doi:10.1115/DETC2011-48301.

Due to its high efficiency for the large scale production of polymeric parts, micro injection moulding is one of the key technologies of the new millennium. Although a lot of researches have been conducted to identify the most effective processing conditions for micro injection moulding, the comprehension of the influence of all parameters on the quality, the properties and the reliability of the moulded parts is still an issue. In this context, this study aims to evaluate the effects of the micro injection moulding process conditions on the tensile properties of micro parts, investigating the influence of three main process parameters: the injection speed, the mould temperature and the melt temperature. A full factorial plan has been applied to study the contributions of these parameters and a second study has been performed to understand the synergic interaction between the two temperatures on the tensile strength. Due to its high level of potential crystallinity, a typical semi-crystalline thermoplastic resin was used in the experiments. The results of the analysis showed a great influence of the mould temperature (Tmould ) on the ultimate tensile strength and of the melt temperature (Tmelt ) on the deformation at the point of breaking; whereas the injection speed was significant on the overall mechanical performance. A new studied factor (Tmelt -Tmould ) could affect the resulting molecular structure and consequently the mechanical behaviour, but itself is not sufficient to thoroughly explain the observed behaviour. Moreover, the visual inspection of the deformation mechanism at break shows three distinctive trends demonstrating the great variability of the mechanical properties of micro-injected specimens due to process conditions.

Commentary by Dr. Valentin Fuster
2011;():441-446. doi:10.1115/DETC2011-48331.

Micro Electrical Discharge Machining (μEDM) technology is widely used to process conductive materials, regardless to their hardness and strength, and realize micro-sized feature components for industrial application. μEDM proves to be a very competitive fabrication technology since micro-sized features within 1 μm of accuracy and with high surface quality (<0.1 μm Ra) can be attained. When High Aspect Ratio (HAR) micro-features are machined via μEDM milling, the main problem is to identify the technological parameters and settings mainly affecting the process performance. In the present study the influence of the adjustment factor and flushing conditions are investigated and discussed for the machining of HAR cavities with different Fill Factor (FF). Material Removal Rate (MRR) and Tool Wear Ratio (TWR) are evaluated when deep cavities having variable square sections are machined on Ni-Cr-Mo steel workpiece. All tests are performed using a state of the art micro-EDM milling machine, with a Tungsten Carbide electrode tool and a dielectric oil for flushing. The experimental results presented here highlight different trends in the machining performance in dependence of AR and FF. In particular, MRR exhibits a decreasing trend where the curve slopes are strictly related to the FF and the initial adjustment factor. On the contrary, TWR, for higher FF, displays two distinct trends characterized by opposite slopes in each curve. Finally a nozzle for micro-injection with varying Aspect Ratio and Fill Factor is machined and presented as demonstrator.

Topics: Milling
Commentary by Dr. Valentin Fuster
2011;():447-457. doi:10.1115/DETC2011-48619.

Building a two degree-of-freedom (2 DOF) MEMS nanopositioner with decoupled X-Y motion has been a challenge in nanopositioner design. In this paper a novel design concept on making the decoupled motion of the MEMS nanopositioner is suggested. The suggested nanopositioner has two electrothermal actuators and employs a fully nested motion platform with suspended anchors. The suggested MEMS nanopositioner is capable of delivering displacement from the electrothermal actuator to the motion platform without coupled motion between the two X-Y axes. The design concept, finite element analysis (FEA) results, fabrication procedures and the performance of the 2 DOF nanopositioner is presented. In order to test the nanopositioner moving platform decoupled motion, one actuator moves the platform by 60 μm, while the other actuator is kept at the same position. The platform position cross talk error was measured to be less than 1 μm standard deviation.

Commentary by Dr. Valentin Fuster
2011;():459-467. doi:10.1115/DETC2011-47082.

Recent reports of sub-atomic resolution AFM images acquired using transition metal tips have sparked debate within the AFM community. However, an in-depth theoretical feasibility study of this work has yet to be produced. We focus on the tungsten/graphite system investigated by Hembacher and coworkers [Science 305 , 380–383 (2004)] in which experimental higher-harmonics images revealed four-leaf clover symmetry features within the tungsten atom diameter. The authors interpret these features as the footprint of four bonding lobes of increased charge density at the tip apex atom, thought to be caused by covalent-like bonding in the bulk. Here we present our development of a computational method ranging from density functional theory to continuum dynamics for simulating the imaging process. We find that four lobes of increased electronic density are indeed present for W(001) tips and demonstrate the ability of the chemical forces on the tip apex atom to produce higher harmonics images.

Commentary by Dr. Valentin Fuster
2011;():469-473. doi:10.1115/DETC2011-47199.

We have recently reported on experimental observations of silk-elastin-like protein polymers (SELPs) that self-assembled into 1-dimensional nanofibers on mica surfaces upon application of a mechanical stimulus with atomic force microscopy (AFM) in water. SELPs are genetically engineered block co-polymers made of silk-like blocks (Gly-Ala-Gly-Ala-Gly-Ser) from Bombyx mori (silkworm) and elastin-like blocks (Gly-Val-Gly-Val-Pro) from mammalian elastin. The experiment consisted of adsorbing the protein polymer onto a freshly cleaved mica surface, followed by AFM characterization under different sets of imaging parameters, each of which led to different nanofiber coverage rates. In order to gain further understanding of the factors governing the self-assembly process, we utilized multimodal AFM simulation to formulate and guide the implementation of a suitable force modulation strategy, which allowed us to observe trends of the surface coverage rate as a function of the applied peak forces. The simulations suggest that a nearly linear control of the peak tapping forces can be achieved by following simple scaling laws based on the harmonic oscillator model.

Commentary by Dr. Valentin Fuster
2011;():475-480. doi:10.1115/DETC2011-47455.

We present a new servo controllable force sensor that exploits photon momentum forces for the identification, calibration, and control of its dynamic properties. The sensor comprises a millimeter-scale glass cantilever, a low-noise fiber interferometer for detection of the cantilever deflection, and a high-power, intensity-modulated fiber laser to apply optical actuation forces. Combined with appropriate digital and analog signal processing, the sensor has been operated as a feedback-cooled low-noise force sensor, and as a self-excited oscillator governed by the familiar Rayleigh equation. Operated in this self-excited Quber mode, it appears well suited for noncontact, frequency modulated force gradient detection such as in atom discrimination. Here, we briefly lay out the principles of the sensor and provide examples of its performance, including the demonstration of feedback cooling and the ability to induce controlled limit cycle oscillations with atomic scale amplitudes.

Commentary by Dr. Valentin Fuster
2011;():481-490. doi:10.1115/DETC2011-47503.

The atomic force microscope (AFM) is a high-resolution measurement tool for sample topography and material properties in nano-scale and micro-scale research. The dynamics of the cantilever probe in AFM is affected by the intrinsically nonlinear interaction between the probe tip and the sample. Previous works have shown that in off-resonance excited intermittent-contact AFM, a period-doubling bifurcation occurs as a result of the nonlinearity. The sub-harmonic amplitude of the response is used as the source of contrast to measure the effective modulus of the sample. This paper further investigates the performance of this proposed measurement method on more complicated 1-D samples and 2-D samples. The nonlinear relationship between the sub-harmonic amplitude and the tip-sample separation raises new challenges to the traditional PI controller. The design of the controller is revisited and modified in this paper to improve measurement accuracy.

Commentary by Dr. Valentin Fuster
2011;():491-500. doi:10.1115/DETC2011-47543.

In last decades, control of nonlinear dynamic systems became an important and interesting problem studied by many authors, what results the appearance of lots of works about this subject in the scientific literature. In this paper, an Atomic Force Microscope micro cantilever operating in tapping mode was modeled, and its behavior was studied using bifurcation diagrams, phase portraits, time history, Poincare maps and Lyapunov exponents. Chaos was detected in an interval of time; those phenomena undermine the achievement of accurate images by the sample surface. In the mathematical model, periodic and chaotic motion was obtained by changing parameters. To control the chaotic behavior of the system were implemented two control techniques. The SDRE control (State Dependent Riccati Equation) and Time-delayed feedback control. Simulation results show the feasibility of the both methods, for chaos control of an AFM system.

Commentary by Dr. Valentin Fuster
2011;():501-506. doi:10.1115/DETC2011-47668.

Multifrequency Atomic Force Microscopy (AFM) techniques, where the cantilever oscillation is measured and sometimes driven at multiple frequencies, have become an active research topic in recent years. This is in part because these methods can provide increased compositional contrast during surface characterization. Since 2004 bimodal AFM imaging has been used extensively to complement the information that can be obtained using the standard single-frequency tapping-mode operation. More recently we have implemented a trimodal tapping-mode scheme, in which we have incorporated a frequency-modulated third eigenmode into bimodal tapping-mode operation in order to acquire topography, phase and frequency shift information simultaneously. We have also studied numerically the effect of different levels of sample stiffness, tip-sample dissipative forces, oscillation amplitudes for each of the eigenmodes and cantilever rest positions above the sample on the frequency response of the higher eigenmodes in bimodal and trimodal operations. Here we explore the ability to separate conservative and dissipative effects using the different channels available in trimodal operation.

Commentary by Dr. Valentin Fuster
2011;():507-524. doi:10.1115/DETC2011-47730.

Base-excitation of microcantilevers using a dither piezoelectric element, also known as acoustic excitation, is one of the most popular methods for dynamic atomic force microscopy (AFM) because it is inexpensive, easy to use and does not require special cantilevers. However, in liquid environments there are problems using this method for quantitative force spectroscopy. The problems arise due spurious peaks in the driving spectrum (also known as “forest of peaks”) caused by piezo and fluid cell resonances, as well as a large base motion, which make it very hard to quantify the exciting forces. Although some groups have tried to overcome these limitations, it is has generally been accepted that acoustic excitation is unsuitable for quantitative force spectroscopy in liquids. In this work the authors show that a thorough understanding of the excitation forces and base motions reveals a method by which quantitative analysis is in fact possible with acoustic excitation in liquid environments, thus opening this popular method for quantitative dynamic AFM in liquids. This method is validated by experiments using a scanning laser Doppler vibrometer, which can measure the actual base motion. Finally, the method is demonstrated by performing force spectroscopy on solvation shells of octamethylcyclotetrasiloxane (OMCTS) molecules on mica.

Commentary by Dr. Valentin Fuster
2011;():525-534. doi:10.1115/DETC2011-47955.

In this article, the authors study the effects of Gaussian white noise on the dynamics of an atomic force microscope (AFM) cantilever operating in a dynamic mode by using a combination of numerical and analytical efforts. As a representative system, a combination of Si cantilever and HOPG sample is used. The focus of this study is on understanding the stochastic dynamics of a micro-cantilever, when the excitation frequencies are away from the first natural frequency of the system. In the previous efforts of the authors, period-doubling bifurcations close to grazing impacts have been reported for micro-cantilevers when the excitation frequency is in between the first and the second natural frequencies of the system. In the present study, it is observed that the addition of Gaussian white noise along with a harmonic excitation produces a near-grazing contact, when there was previously no contact between the tip and the sample with only the harmonic excitation. Moment evolution equations derived from a Fokker-Planck system are used to obtain numerical results, which support the statement that the addition of noise facilitates contact between the tip and the sample.

Commentary by Dr. Valentin Fuster
2011;():535-542. doi:10.1115/DETC2011-47985.

Micro-Cantilever Sensors (MCS) have caught a widespread attention during past couple of years for offering label free biodetection. Amongst many current MCS-based measurement platforms, piezoresistive MCS offer a great advantage over other types of MCS especially when compared with optical measurements where sample preparation and laser alignment and adjustment are serious limitations. In order to address the uncertainties and nonlinearities inherent in nanoscale, a comprehensive modeling of the system is required. In almost all of the studies targeting piezoresistive MCS, the system is modeled as a simple lumped-parameters system which does not describe all phenomena and dynamics of the system. In the first part of this study, a comprehensive distributed-parameters modeling is proposed for the piezoresistive MCS. A new method of excitation is developed and modeled through cantilever tip instead of the commonly used techniques such as base excitation or excitation through piezo-layers deposited over cantilever surface. In the second part of this study, a comprehensive distributed-parameters modeling is proposed for the piezoresistive MCS-based force microscopy in contact with a piezoelectric sample. The output voltage of the piezoresistive layer is determined and utilized as a function of cantilever deflection through a piezoresistive modeling framework. Extensive numerical simulations are performed to demonstrate the effectiveness of the modeling framework presented here.

Commentary by Dr. Valentin Fuster
2011;():543-549. doi:10.1115/DETC2011-48653.

Atomic-scale wear is one of the main factors that hinders the performance of probes for atomic force microscopy (AFM) [1–6], including for the widely-used amplitude modulation (AM-AFM) mode. To conduct consistent and quantitative AM-AFM wear experiments, we have developed a protocol that involves controlling the tip-sample interaction regime, calculating the maximum contact force and normal stress over the course of the wear test, and quantifying the wear volume using high-resolution transmission electron microscopy imaging (HR-TEM). The tip-sample interaction forces are estimated from a closed-form equation that uses the Derjaguin-Müller-Toporov interaction model (DMT) accompanied by a tip radius measurement algorithm known as blind tip reconstruction. The applicability of this new protocol is demonstrated experimentally by scanning silicon probes against ultrananocrystalline diamond (UNCD) samples. The wear process for the Si tip involved blunting of the tip due to tip fragmentation and plastic deformation. In addition, previous studies on the relative contributions of energy dissipation processes to AFM tip wear are reviewed, and initial steps are taken towards applying this concept to AM-AFM.

Commentary by Dr. Valentin Fuster
2011;():551-555. doi:10.1115/DETC2011-48737.

Graphene has attracted great interest due to its exceptional electrical, mechanical, and chemical properties since its discovery in 2004. Since its first realization, the substrate of choice for graphene exfoliation has been Si wafer with approximately 300 nm thick SiO2 dielectric layer, because it allows 1) direct optical detection of monolayer flakes, and 2) a convenient back gate with dielectric for controlling carrier density in the graphene. However, the amorphous structure of SiO2 and its associated surface roughness has led to ongoing controversy in determining the structure of SiO2 -supported graphene. The conductivity of graphene allows scanning tunneling microscopy (STM) to be used to measure its topography, generally allowing its structure to be atomically resolved. In contrast, the insulating SiO2 must be probed with atomic force microscopy (AFM), and this is often done using ambient tapping-mode AFM. STM measurements of graphene on SiO2 generally show greater roughness and finer corrugation than is seen in AFM measurements of SiO2 , and this has been interpreted as evidence for “intrinsic” corrugation of the graphene. However, when the energetics of adhesion and elasticity are considered, the idea of intrinsic structure becomes quite controversial for graphene supported on a substrate. Here we show that UHV non-contact AFM (NC-AFM) measurement of SiO2 reveals structure unresolved in previous measurements, and shows both greater roughness and smaller lateral feature size than seen for graphene measured by STM. High-resolution measurement of the SiO2 topography enables an analysis based on the energetics of graphene bending and adhesion, showing that the graphene structure is highly conformal to the SiO2 beneath it. The topographies reported here contrast the atomically-flat crystalline surfaces used in benchmark NC-AFM measurements. They pose unique challenges for measurement resolution, and highlight the very different physical mechanisms which determine resolution in STM vs. NC-AFM. We discuss these issues and our recent efforts at quantitative modeling of the imaging process, with particular focus on the role of van der Waals forces and their contribution to the image signal.

Commentary by Dr. Valentin Fuster

8th International Conference on Design and Design Education

2011;():559-568. doi:10.1115/DETC2011-47154.

It is desirable that the graduating engineering students possess the skills of formulating and solving engineering problems to design solutions that meet the established requirements. However, the current literature has noticeable gaps pertaining to understanding how the formulation of design problems and establishment of requirements affect the final design solution. The ultimate goal of this research is to understand the influence of the level of detail of problem statement and requirements on the level of detail of final solution. In order to accomplish this goal a coding scheme is developed to systematically code the information in the final design reports from capstone design class collected over a period of ten years from 1999 to 2008. The coded information is used to develop mappings between problem statement and final solution. To this end, this paper describes the scheme for systematically coding the problem statement and final design solution.

Topics: Design
Commentary by Dr. Valentin Fuster
2011;():569-578. doi:10.1115/DETC2011-47471.

Formulating and solving engineering problems and designing solutions that meet the established requirements are important skills that graduating engineering students need to possess. However, there are noticeable gaps in the literature with respect to understanding how the formulation of design problems and establishment of requirements affect the final design solution in undergraduate design education. This paper is an initial step to understand the influence of level of detail of problem statement and requirements on the level of detail of final solution in capstone design projects. In doing so, a document analysis of final reports from capstone design class collected over a period of ten years, 1999 to 2008, is conducted. A data compression approach is developed to allow for the mapping of level of detail of problem statement and requirements to the level of detail of final solution. The findings of this research indicate that a low level of detail problem statement and requirements leads to no greater than a medium level of detail in the final solution. A high level of detail of final solution is more likely to result from either a high or medium level of detail of problem statement and requirements. Additionally, it was found that a high level of detail final solution is more likely to result in a high percentage of requirements satisfied. These findings are used to make several recommendations to improve the level of detail of the problem statement and requirements so a high level of detail final solution is developed while satisfying a great number of requirements. This assists in ensuring that students possess the skills needed before entering the professional workforce.

Topics: Design
Commentary by Dr. Valentin Fuster
2011;():579-587. doi:10.1115/DETC2011-47498.

This paper presents an analysis of design team characteristics and design activities that are significantly associated with design outcomes (i.e., project performances) in sophomore-level project-based design courses. Besides efficient team work, a team needs to successfully perform three design activities: concept generation, concept selection, and prototyping. In the design course, teams are formed based on students’ choice of teammates as well as on instructor assigned teams which maximize cognitive mode diversity among members. A regression analysis is performed to find variables that are significantly associated with design outcomes. These variables include team size, teaming preference, diversity of cognitive modes among team members, the average number of power tools team members have used in the past, whether or not a team experienced a team-working difficulty, the number of concepts generated before and after using creativity techniques, whether or not a team had the most successful strategy (called “winning” concept in this study) in a set of concepts from which one concept is chosen for prototyping, and timing of selecting the winning concept (at concept selection, at proof-of-concept testing, or at final testing). Design strategies used by teams, the winning concepts, results of regression analysis (variables significantly associated with design outcomes) are discussed.

Topics: Design , Performance , Teams
Commentary by Dr. Valentin Fuster
2011;():589-598. doi:10.1115/DETC2011-48168.

This paper presents lessons learned from a project-based approach for teaching new cognitive product development to multi-disciplinary student teams. Within the class, interdisciplinary teams with students from mechanical engineering, electrical engineering and computer science are formed. To date, the class has been run five semesters using different themes and developing more than 15 new products. Cognitive products are tangible and durable things with cognitive capabilities that consist of a physical carrier system with embodied mechanics, electronics, microprocessors and software. The surplus value is created through cognitive capabilities, e.g. perceiving, learning and reasoning, that are enabled by flexible control loops and cognitive algorithms. Common product development processes are often not applicable to this high level of interdisciplinarity and require extension and refinement. Therefore, project-focused, technical lectures, balancing technology-push and market pull, are given and specifically tailored to cognitive product design. Additionally, software and hardware prototyping workshops and toolkits are provided in combination with the support of technical and process coaches to assist the teams. Attention is especially paid to giving students hands-on experience in developing their own cognitive product starting with the generation of ideas, turning the best idea into a product concept and finally building a functional and a design prototype. Lessons learned through the refinement of the product development process and methods used as well as from student questionnaires are presented and discussed.

Commentary by Dr. Valentin Fuster
2011;():599-606. doi:10.1115/DETC2011-48310.

Due to its focus in project-based learning, design educators must provide individual coaching and mentoring of student teams as they progress through their design efforts. In order to increase the quantity and quality of design mentoring, the authors have implemented the use of Wiki websites as a medium for providing formative assessment for student design teams enrolled in a sophomore-level Mechanical Engineering design course. Wiki websites, which allow for easy creation and editing of interlinked webpages, were created for each design team in order to provide a virtual space for the creation, compilation, and editing of their design project report submissions. With access to each team’s Wiki site, the mentor is able to observe each team’s product design process unfold and provide feedback using an embedded commenting system. The public presentation of design reports also affords the facilitation of a peer-review of student work. In this paper the authors present details of the implementation of a Wiki for preliminary assessment data for this tool. Results show that the students found the tool and the associated activities to be easy to use, helpful in developing better design reports and a contributing factor to their development of critical and analytical thinking skills. In addition, students who used the tool reported receiving more meaningful formative feedback from the instructor and reported giving more formative feedback to their peers when compared to other sections of the class that were not using the Wiki.

Commentary by Dr. Valentin Fuster
2011;():607-614. doi:10.1115/DETC2011-48357.

In this paper, the authors report on progress of a longitudinal study on the impact of design education on students’ design thinking and practice. Using innovations in cognitive science and new methods of protocol analysis, the authors are working with engineering students to characterize their design cognition as they progress through engineering curricula. In this paper, the results from a protocol study of sophomore Mechanical Engineering students are presented. Specifically, data gathered from two experimental sessions (conducted before and after the students’ introductory design course) are analyzed to identify changes in design thinking cognition. Design cognition is determined using protocol analysis with the coding of the protocols based on a general design ontology, namely, the Function-Behavior-Structure (FBS) as a principled coding scheme (as opposed to an ad hoc one). Preliminary results indicate that statistically significant changes in students’ design cognition occur over the course of their sophomore year. The change manifests itself in an increase in focus on the purposes of designs being produced, which is often a precursor to the production a higher quality designs, and an increase in the design processes associated with the introduction of purposes of designs.

Commentary by Dr. Valentin Fuster
2011;():615-623. doi:10.1115/DETC2011-48724.

Capstone courses are an integral part of the educational experience in undergraduate engineering programs. However, such courses tend to be challenging in nature for course instructors as many of the features of the capstone course contrast starkly with typical courses in the engineering curriculum. As in any field, communication of effective strategies is crucial as the capstone course community seeks to better their practices. With this goal in mind, the question arises: How does one instructor convince her or his colleagues that a teaching practice implemented at the home university is (i) truly effective, and (ii) can be transferred to other universities with similar results? While effectiveness may be measured in other more traditional courses by simply looking at assignment and test grades, the complexity associated with the capstone course adds ambiguity and complex interrelations that require a more thoughtful and detailed inquiry. This work explains such a framework for evaluating the effectiveness of capstone course changes implemented over the past seven years at Oregon State University. The evaluation framework relies on results from faculty, sponsor, and student surveys as well as sponsor participation data, student work products, course evaluations, and student grades over the period of the past seven years. This work outlines the framework and discusses future plans of implementation of the research project.

Commentary by Dr. Valentin Fuster
2011;():625-636. doi:10.1115/DETC2011-47852.

This paper reviews functional representation and modeling across multiple domains of engineering as well as function recognition and modeling in the engineering design field. Various modeling techniques are presented along with approaches to model realization published in common engineering design text books. Specifically, within the field of engineering design, seven published approaches for modeling function are presented: 1.) Glass Box Method; 2.) Function Analysis System Technique; 3.) Systematic Processes; 4.) Enumeration; 5.) Zen Approach; 6.) Reverse Engineering; and 7.) Function-Means Trees. Through discussion of the modeling approaches the authors pose questions on how function should be taught in undergraduate engineering curriculum. Finally, the potential benefits of function-based design approaches are reviewed and discussed.

Topics: Modeling , Teaching
Commentary by Dr. Valentin Fuster
2011;():637-643. doi:10.1115/DETC2011-48163.

Learning and teaching procedures need to evolve, regarding the high technological profile most students have. The Teacher might consider that in some cases, outdated teaching methods create barriers for students who are used to interaction with modern technological gadgets and computers. Augmented Reality technology emerges as a great potential tool in the teaching environment. Augmented reality (AR) is a cost-effective technology which has the ability to coexist with paper books supplying students with more attractive and didactic contents meaning rebirth of classic textbooks. In this work we present the developed didactic material supported by AR technology for learning sketching, designation and rules of standard mechanical elements. This book has been included in the curriculum of engineering graphics subject of the Mechanical Engineering Degree in a Spanish University for performing a pilot study seeking comparison of academic performance acquired and motivation for study between two groups of students. One group uses AR based material meanwhile the other uses traditional class notes.

Topics: Students
Commentary by Dr. Valentin Fuster
2011;():645-654. doi:10.1115/DETC2011-48439.

Mechanix is a sketch recogniton tool that provides an efficient means for engineering students to learn how to draw truss free-body diagrams (FBDs) and solve truss problems. The system allows students to sketch these FBDs into a tablet computer or by using a mouse just as they would by hand. Mechanix is then able to provide immediate feedback to the students and tells them if they are missing any components of the FBD, without providing answers. The program is also able to tell them whether their solved reaction or member forces are correct or not. This paper presents studies to evaluate the effectiveness and advantages of using Mechanix in the classroom, as a supplement to traditional teaching and learning methods. Current results demonstrate that students believe Mechanix enhances their learning and are highly engaged when using it. Future work on the refinement of the program is also discussed.

Commentary by Dr. Valentin Fuster
2011;():655-660. doi:10.1115/DETC2011-48571.

Biomimetic design, the use of nature to inspire solutions to engineering problems, has been practiced on an ad hoc basis throughout human history. Only recently, however, have researchers sought to develop formal tools and principles to effectively tap the wealth of design solutions found within nature. Texas A&M University is developing an undergraduate course to introduce interdisciplinary engineering students to the current concepts, principles, and methods of biomimetic design, as found in published literature. This paper seeks to concisely present the results and conclusions of the many research efforts that will be incorporated into the developing course. The research reviewed in this paper is discussed with some emphasis on its pedagogical implications. Research efforts in applying design tools such as functional modeling, analogical reasoning, and the Theory of Inventive Problem Solving (TRIZ) to biomimicry are summarized. This paper also discusses the efforts to develop effective tools to search biological information for design inspiration. As similar courses in biomimetic design have been conducted at the Georgia Institute of Technology and the University of Maryland, the published findings from those courses are also presented.

Commentary by Dr. Valentin Fuster
2011;():661-670. doi:10.1115/DETC2011-47796.

Engineering is a technical profession that seeks to solve open problems. The practice of engineering spans design, manufacture, operation and maintenance and these in themselves offer wide ranging opportunities for routine and novel approaches. In preparing engineering students through a university education, it has been observed that they have differing reactions to open ended project activities intended to model their chosen profession. For example, not all mechanical or even automotive engineering students desire to be involved in a Formula SAE Team. If students engaged in their engineering education are preparing to deal with future issues not yet perceived (open problems), why do students make the choices they do and what motivates them? Why have they chosen an engineering pathway and what do they find exciting about this prospect? With a view to strengthening educational outcomes, some initial findings from an investigation of student choices and motivations are presented.

Commentary by Dr. Valentin Fuster
2011;():671-681. doi:10.1115/DETC2011-47933.

Historically, the teaching of design theory in an engineering curriculum was relegated to a senior capstone design experience. Presently, however, engineering design concepts and courses can be found through the entirety of most engineering programs. Educators have recognized that engineering design provides a foundational platform that can be used to develop educational strategies for a wide array of engineering science principles. More recently, educators have found that product archaeology provides an effective platform to develop scalable learning materials, strategies, and educational innovations across these design courses. In this paper, we focus on the upper level design experience and present a set of innovative strategies aimed at teaching design in a global perspective. Moreover, this approach facilitates meeting the challenging requirements of ABET’s Outcome h. The effectiveness of the strategies is assessed using a benchmark national survey on the Engineer of 2020. Results demonstrate a significant increase in student perception across a number of skill and knowledge areas, which are critical to the next generation of engineers.

Commentary by Dr. Valentin Fuster
2011;():683-695. doi:10.1115/DETC2011-48078.

Along with theoretical knowledge acquisition, knowledge application and professional competence acquisition must be important teaching objectives in any engineering subject. This is especially remarkable for subjects aiming the acquisition of product design knowledge, provided that, in actual professional practice, product design is done in multidisciplinary teams, taking into account technical and non-technical criteria, and with tight deadlines and budgets. This work describes the contents and teaching planning and execution for the subject “product design methodology” at the Mechanical Engineering Department of Universidad Politécnica de Madrid, aiming for the student acquisition of important professional competences to be used on professional product design practice, such as systematic decision making, global company view, task prioritizing, internal and external entrepreneurship, or teamwork, as well as hard competences such as design procedures, quality or project economics. Student teamwork examples from the problem-based learning (PBL) experience, together with internal and external surveys are shown to check the validity of the proposal.

Commentary by Dr. Valentin Fuster
2011;():697-703. doi:10.1115/DETC2011-48242.

Many engineering departments often struggle with meeting “the broad education necessary to understand the impact of engineering solutions in a global, economic, environmental, and societal context” (outcome h) that is required by ABET. The already packed curricula provide few opportunities to offer meaningful experiences to address this outcome, and most departments relegate this requirement to an early cornerstone or later capstone design experience as a result, making these courses an ineffective “catch all” for many ABET requirements. We address this issue by using the paradigm of product archaeology, defined as the process of reconstructing the lifecycle of a product — the customer requirements, design specifications, and manufacturing processes used to produce it — to understand the decisions that led to its development. By considering products as designed artifacts with a history rooted in their development, we embed context as a central component in developing design solutions. Specifically, in our work we have implemented several approaches to integrate contextual thinking into a senior level engineering design course. Following Kolb’s model of experiential learning and an instructional framework adapted for product archaeology (inclusive of evaluate-explain-prepare-excavate activities) we have restructured the course to embed specific and targeted reflection, dissection, and analysis activities so that students teams effectively address the global, economic, environmental, and societal factors in their design solutions. This paper provides the theoretical framework of our instructional approach, describes the specific instructional activities we implemented, and results from our pre and post survey assessments that describe the impact on students’ understanding of contextual as well engineering design topics.

Commentary by Dr. Valentin Fuster
2011;():705-716. doi:10.1115/DETC2011-48258.

The competitiveness of the U.S., which is linked to our standard of living, is dependent on our ability to produce a large number of sufficiently innovative engineers prepared to address issues related to complex systems. Hence, our focus is on research and the associated development of curriculum and instructional activities that address the engineering competencies related to innovation. In this paper, we present a hierarchical curriculum design model, grounded in experiential learning. The model addresses curriculum design from multiple levels: design of experiential activities to provide targeted scaffolding and support for engineering students to develop competencies, then mapping the competencies at course, course sequence, and curriculum levels, for systemic development of competencies at higher order cognition. We illustrate the hierarchical approach for the design of a three-course sequence around the Formula Society of Automotive Engineers (FSAE) Racing team at University of Oklahoma, Norman, to foster meaningful learning, innovation, systems-level thinking, and the attainment of career-sustaining skills through authentic experiences. With a view to stimulating discussion, in this paper we highlight some of the salient features of our plan and some issues that warrant further investigation.

Topics: Competencies
Commentary by Dr. Valentin Fuster
2011;():717-727. doi:10.1115/DETC2011-48298.

Product dissection activities have been very successful used in engineering courses to help anchor the knowledge and practice of engineering in students’ minds. Unfortunately, most product dissection activities tend to stress form, functionality, and fabrication, missing opportunities to explore the broader impacts of engineering design decisions. In this paper, we present initial efforts to transform product dissection activities into product archaeology exercises wherein students “dig” to uncover not only the manufacturing (i.e., economic) issues of a product, but also the global and societal context that influenced its development as well as the environmental impact of the product during its life cycle. We introduce two new classes of exercises—competitive “digs” and collaborative “digs”—to engage students in similar, yet different, ways in product archaeology. Competitive “digs” pit teams of students in a time-based competition to unearth the global, societal, economic, and environmental impact of a product while collaborative “digs” allow students to work together to dig more deeply into these issues over an extended period of time. Results from pilot offerings of both of these types of exercises are summarized and discussed along with a preliminary educational assessment of one of the collaborative “digs”. Improvements to the exercises and future work to formalize this new paradigm of product archaeology are also discussed.

Topics: Students
Commentary by Dr. Valentin Fuster
2011;():729-739. doi:10.1115/DETC2011-48438.

Design education has traditionally been incorporated into the engineering curriculum in the junior or senior year through upper level mechanical design courses and capstone design projects. However, there is a general trend in engineering education to incorporate design activities at the freshman and sophomore level. The design aspects of these courses provide a unique opportunity to integrate global, economic, environmental, and societal factors with traditional design considerations. Incorporating these early in an engineering curriculum supports a broad engineering education in accordance with ABET required Outcome h. In this paper we introduce global, economic, environmental, and societal factors into a sophomore level engineering design course using strategies adapted from a Product Archaeology paradigm. Specifically, functional modeling is synthesized with a product dissection platform to create a foundation to demonstrate the broader impacts of engineering design decisions. The effectiveness of using Product Archaeology-based educational strategies to facilitate the learning objectives of Outcome h is evaluated using student surveys taken over a two year period.

Commentary by Dr. Valentin Fuster
2011;():741-750. doi:10.1115/DETC2011-48817.

Engineering design involves a series of steps that lead to the creation of a product, a system, or a service to meet desired needs. The design and creation of innovative solutions to challenging engineering design problems require young engineers to be immersed in an education environment which challenges and nurtures the thought process and provides the necessary hands-on experience in design. There is increasing convergence in opinions that problem-based and experiential learning should be more integrated with the science-based engineering programs. Experiential learning is the key to engaging students to learn effectively. This paper describes an experiential learning experience for a group of undergraduate students in National University of Singapore (NUS) to design a competition fuel efficient vehicle. The students started with engineering design process and went through a series of steps to design, manufacture, assemble, test and compete in a specifically built prototype urban concept car for the competition with the experiential learning experience. Components of the competition vehicle, from chassis to diminutive parts, such as wheel uprights and motor mounts, have been carefully designed, properly analyzed and fabricated in a teamwork environment. The result is a futuristic fuel efficient urban concept car that won many awards in the competition. The team also took the initiative to promote eco-friendliness and raise awareness with the design of fuel efficient car to battle environmental issues like climate change, pollution, and energy crisis.

Commentary by Dr. Valentin Fuster
2011;():751-761. doi:10.1115/DETC2011-47837.

In this paper, we report on the results from a qualitative study of six exemplary engineering programs focusing on the ways and the extent of nurturing creativity in engineering students. The study (P360: Prototyping the Engineering of 2020) included data collection from students, faculty, and administrators at the six institutions. This data collection focused mainly on three student outcomes, including design and problem solving. Creativity and how creativity was nurtured, both inside the classroom and outside, often emerged as a major theme. We also support our qualitative findings with quantitative data. Overall, the results indicate that although students improve their creativity in design settings, this result is mostly a by-product of design teaching, and creativity is not taught per se. Quantitative results show that program emphasis on creativity and innovation significantly correlates to skill levels in design problem solving, interdisciplinarity, contextual awareness, and recognizing perspectives. Qualitative data provide supporting evidence for this.

Topics: Creativity , Design , Teaching
Commentary by Dr. Valentin Fuster
2011;():763-772. doi:10.1115/DETC2011-48265.

It is well documented that students learn more effectively when they are actively involved in the learning process. Interactive scenario-based education is a novel concept expected to stimulate active learning and provide an engaging learning experience. Recently we have developed a Create your Scenario Interactively (CSI) module to teach metal casting and have implemented it in manufacturing engineering courses at the University of Oklahoma. In this paper, we discuss the impact of the CSI on students’ learning in manufacturing engineering education. The pedagogical effectiveness of the CSI instruction has been evaluated in several areas such as students’ engaging and active learning through pre-test and post-test format and survey questionnaires. Our preliminary results suggest that a majority of the students feels that the CSI module is very effective in keeping them engaged. Results also indicate that the CSI instructions help improve their understanding of the metal casting process. The details of the CSI module, implementation details, and assessment results are discussed.

Topics: Casting , Teaching
Commentary by Dr. Valentin Fuster
2011;():773-782. doi:10.1115/DETC2011-48402.

Experiments in engineering design creativity have the general objective of increasing the understanding of the creative design process, for example, experiments on the use of brainstorming, or a new ideation method or software to increase idea generation. This type of experiments is most of the time difficult to perform. In general, the difficulty is derived from the nature of the experiment which involves human subjects in a creative process solving design problems. The subjects, creative process, method involved, and design problem, each brings an abundance of variables some of which are qualitative (e.g. subject’s personality). Based on the extensive experience running engineering design creativity experiments, the authors present a review of major issues related to the design of experiments (DOE) of engineering design creativity experiments. First, an overview of creativity experimentation is presented; this includes the identification of key elements: subject, design process, treatment, controls, output and environment. Second, an overview of the design of experiment (DOE) steps is presented: hypothesis, factors, responses, etc. Third, for each step in the DOE the authors identify typical issues related to engineering design creativity. Each issue is analyzed, referred to other experiments in the literature, and a series of practical recommendations are made. The scope of the paper is limited to engineering design creativity experiments, more specifically, when the assessment is performed on the outcome. Also, the focus is on the “conceptual model” (i.e. planning stage) of DOE. Future papers will focus on the execution of the experiment and the assessment process. The authors hope that these guidelines help designologists improve the relevance, significance, and accuracy of creativity experiments.

Commentary by Dr. Valentin Fuster
2011;():783-792. doi:10.1115/DETC2011-48609.

This paper introduces a new approach named Design for Patentability (DFP) and presents the preliminary formulation of a formal methodology to attempt consideration of patentability aspects during the early stages of design including conceptual design and initial implementation of detailed design and manufacturing. Design for Automation (DFAM) approach formulated earlier by the first author based on Axiomatic Design Theory originated by Suh et. al. at MIT is adapted, suitably modified and customized for inclusion of patentability aspects such as anticipation, functionality, utility, and obviousness. Highlighting the complexity in incorporation of legal aspects in an engineering methodology, the paper presents the possibilities of improving the patentability of a design by a systematic and considered approach. The proposed methodology introduces a Patentability Evaluation phase in-between the Product Design, Process Design and Automation System Design phases of DFAM. The paper reviews mapping of parameters between different domains, namely, Functional Requirements Domain, Design Parameters Domain, Process Requirements Domain, and Design Automation Parameters Domain encompassed in the DFAM methodology and includes Patentability Parameters Domain in parallel to the last three domains to enable possible consideration of patentability aspects during Product Design, Process Design, and Automation System Design. Further, the paper briefly discusses the relevance of the Information Axiom of the Axiomatic Design Theory in the context of preparation of preliminary drafts of invention disclosure and potential claims for perusal by patent agents or attorneys. The approach reported in the paper is expected to have broad applications in the growing field of innovation based entrepreneurship in which design for patentability is an essential requirement for success of a business venture.

Topics: Design
Commentary by Dr. Valentin Fuster
2011;():793-804. doi:10.1115/DETC2011-48378.

The presented study demonstrates the enormous potentials of translating mathematical expressions into their relevant physical meanings. In the past, such translations have proven capable of explaining the cause(s) of phenomena, which seemed to defy all principles of common sense. In other cases, they were able to rectify deeply rooted misconceptions, which haunted the engineers for many decades. Among others, they have revealed the need for revising everything what has been done in the last eight decades in relation to the head developed by an impeller. All the above conclusions are here supported by actual case histories from past experience. The discussions presented in this study relate directly to the design of centrifugal and other rotodynamic pumps. However, there exist strong indications, that such translations may prove equally useful also in other fields of engineering.

Commentary by Dr. Valentin Fuster
2011;():805-813. doi:10.1115/DETC2011-48446.

In today’s world, it is critical to continually improve and develop new educational practices. Compared to developed and developing countries around the world, especially in science, mathematics, and engineering, the United States is falling behind. One of the most prominent reasons is the lack of interest in these subjects. In order to reverse this trend, it is important to develop new ways to creatively spark interest in engineering and natural sciences early on in a student’s educational career. The scope of this project was to develop a children’s book that introduced mechanical dissections. Along with the book, an in class presentation was developed for early elementary students in Kindergarten and 1st grade, with the goal of inspiring interest in engineering as a whole. This presentation was then used in local elementary school classrooms to gauge how such a program would fare in a typical elementary level classroom. Overall the project produced successful results. Not only were the students intrigued and excited to see the presentation, but they also learned more of the information than was originally expected. Through different media, the students were able to explore and question how and why a household appliance worked. This interaction with engineering concepts at a young age could prove to be very beneficial in the future.

Commentary by Dr. Valentin Fuster
2011;():815-822. doi:10.1115/DETC2011-48648.

Engineering educators and practitioners have suggested that collaborative-competitive team design events promote innovation. These competitions are popular, and they attract sponsors and participants. Beyond being popular, they are believed to provide rich learning opportunities for students. In this paper we present a peer-to-peer learning environment for student centered learning to have a more appropriate mix of theory and experience (hands-on activities) to provide a complete experiential learning environment for collaborative-competitive student design teams. A student-taught seminar course on designing an FSAE vehicle is being offered to new members of the team to address issues in collaborative-competitive student design teams, which addresses the concrete experience and active experimentation element of the experiential model, but has deficiencies in the reflective observation and abstract conceptualization elements of the cycle. In this paper we will present the structure of the seminar course and how it tries to support and enhance the experiential learning in the FSAE team.

Topics: Design , Teams , Students
Commentary by Dr. Valentin Fuster
2011;():823-832. doi:10.1115/DETC2011-47577.

Due to a demand for more sustainability, with as ultimate goal Zero Emission Buildings, building design becomes more complex. Building design transfers from a mainly architect led process into a approach for multi-disciplinary design teams to cope with the growing complexity of the process. A supportive design method was developed in cooperation with the Dutch professional organizations of architects and consulting engineers. The design method provides overview and helps to structure the communication and reflection between design team members. The design method is focused on sustainability and the creation of sustainable solutions in the conceptual phase of building design. After testing the method in workshops as part of a training program in industry, the design method was transferred and applied at the department of architecture for master students for their multidisciplinary Master project Integral Design. The workshops became part of the permanent professional education program of the Dutch society of architects, several in-company workshops for industry were held and a course is now being developed for the Dutch society of building services engineers. So the partnership with building industry let to the developed design support method which acted as a kind of bridge for engineering education.

Commentary by Dr. Valentin Fuster
2011;():833-843. doi:10.1115/DETC2011-47847.

In order for our future engineers to be able to work toward a sustainable future, they must be versed not only in sustainable engineering but also in engineering design. An engineering education must train our future engineers to think flexibly and to be adaptive as it is unlikely that their future will have them working in one domain. They must, instead, be versatilists. The School of Engineering at James Madison University has been developed from the ground up to provide this general engineering training with an emphasis on engineering design, systems thinking, and sustainability. Students take courses in math and science, business and liberal arts, engineering science, sustainability, and design. In this paper, we discuss how sustainability is taught in a multi-context perspective through the School’s curriculum and pedagogy. We do not mean to present the School’s approach as an all or nothing model, but instead as a collection of approaches of which hopefully one or more may be appropriate at another university.

Commentary by Dr. Valentin Fuster
2011;():845-849. doi:10.1115/DETC2011-48454.

Sustainability is gaining national and global prominence as a key external constraint in engineering design. Courses in solar energy and wind energy have been common offerings, but due to their power production focus, do not address sustainability in the broader context of design. The question becomes, are undergraduate mechanical engineering programs evolving to introduce design for sustainability concepts, such as life cycle assessment, the triple bottom line, and carbon balance, in the broader context of mechanical engineering design? A review of mechanical engineering programs at well recognized universities indicates that most course offerings with definable sustainable design content remain focused on sustainable energy production. In addition, most of these courses are primarily graduate level offerings, indicating a substantial population of recent graduate engineers with limited knowledge of the scope of design for sustainability. Isolated efforts to broaden awareness of sustainability concepts were also identified and will be reported. These programs may serve as models for integration of sustainability into the general mechanical design education.

Commentary by Dr. Valentin Fuster
2011;():851-859. doi:10.1115/DETC2011-48859.

The ability to solve engineering design problems using academic knowledge flexibly is essential for mechanical engineering students and is also quality that employers look for. This paper introduces how students could explore and experience the process of mechanical design in the course project of Theory of Machines and Mechanisms (TMM) in Dalian University of Technology (DUT) through sharing the design process of accelerator (gear-box) in wind power generator by one representative team of students in the course project. Firstly, design requirements are set based on industrial need and the choosing of the best scheme of multi-stage gear train is conducted. Following that is the design of kinematic parameters of gears and the evaluation of selected system. Then, a possible solution to control the input speed of the generator is proposed. In the end, a survey to 279 students who participate in the course project shows the importance of course project in cultivating their ability to apply knowledge in design.

Commentary by Dr. Valentin Fuster

21st Reliability, Stress Analysis, and Failure Prevention Conference

2011;():863-870. doi:10.1115/DETC2011-47343.

Compressor blades are a major component of an aeroengine. Failure mode and effects analysis (FMEA), especially, the risk priority order of failure modes, is essential in its design. The risk priority number (RPN) has been extensively used to the risk priority order of failure modes. When multiple experts give their different risk evaluation information to one failure mode, which may be imprecise and uncertain, the traditional RPN cannot deal with the problem. In this paper, the modified Dempster-Shafter (D-S) is adopted to aggregate the different evaluation information by considering multiple experts’ evaluation opinions, multiple failure modes and three risk factors respectively. The simplified discernment frame is proposed according to the practical application. Moreover, the mean value of the new RPN is used to risk priority order of multiple failure modes. Finally, the method is used to deal with the risk priority evaluation of the failure modes of compressor blades of an aeroengine under multiple sources of different and uncertain evaluation information. The consequence of the method is rational and efficient.

Commentary by Dr. Valentin Fuster
2011;():871-875. doi:10.1115/DETC2011-47378.

Most of new products evolve based upon existing products. The reliability indices and maintenance records of existing products are very important to provide useful information for the reliability allocation of the new evolutionary products. In this paper, a fuzzy similarity-based reliability allocation method which considers not only the similarity between the new product and old ones, but also the judgments from domain experts, is proposed to realize a reasonable reliability allocation at the initial design stage of diesel engines. The new method allows for using both the objective information from the old products and the subjective judgments from experts simultaneously, and it is more comprehensive and objective compared to the traditional reliability allocation method.

Commentary by Dr. Valentin Fuster
2011;():877-885. doi:10.1115/DETC2011-47485.

Observed failures, rather than first principles, are used to estimate fatigue rates probabilistically conditioned on operating conditions. The method developed assumes that a normal random variable may be used to approximate the damage limit (remaining lifetime) of components subjected to cumulative damage and that when a component fails, its damage limit has vanished at a rate proportional to the amount of time spent at each operating condition experienced during its lifetime. By considering differences in cumulative damage between pairs of failed components, we obtain the relative rates at which damage is accumulated for each observed operating condition. When the differences in component lifetimes are dominated by variations in experienced conditions, it is possible to estimate absolute rates. Otherwise, variations in initial damage limits dominate and it is only possible to estimate the mean and variance of this distribution. We demonstrate the procedure on synthetic data, including a test for the dominant source of lifetime variations.

Topics: Failure
Commentary by Dr. Valentin Fuster
2011;():887-892. doi:10.1115/DETC2011-47583.

Fault tree analysis (FTA), as an effective reliability assessment tool, is a widely used in analyzing the risk and reliability of large scale and complex engineering systems. Dynamic fault tree analysis (DFTA) extends the static fault tree by defining additional gates to model the complicated interactions, and in most case, Markov models can be used to solve dynamic gates. In many real systems, it is quite difficult to evaluate the probability of failure events preciously due to many uncertainty factors. To account for the uncertainty resulting from the lack of sufficient data or the subjective adjustments from experts, a fuzzy dynamic fault tree model is proposed to assess the system reliability when acquiring precious probability of failure event is impossible. With the aim of obtaining the membership function of the fuzzy probability of the top event, the extension principle is employed. The proposed method and algorithm are demonstrated by a case study of the hydraulic system of a specific CNC machining center.

Commentary by Dr. Valentin Fuster
2011;():893-898. doi:10.1115/DETC2011-48413.

In this work, a novel framework is proposed for the risk based design optimization of engineering systems by minimizing the demand on the system components’ accuracy (which directly relates to their cost). The fundamental development of this work is an analytical upper bound for calculating the probability of failure. This is in contrast with First Order Reliability Method (FORM), where a lower bound is used in calculating the probability of failure. FORM is one of the most popular methods for reliability analysis of engineering systems. In this paper, we show that FORM results in an optimistic measure of risk, hence potentially catastrophic in engineering design. A more accurate measure of failure is proposed by utilizing an analytical upper bound for the distribution of reliability index (the length of the most probable point vector to origin). This distribution is a function of the eigenvalues of the linearized limit state function in the normal space which results in a better understanding of failure phenomenon. The proposed formulation is computationally efficient and straightforward to solve, since it only involves finding eigenvalues in each iteration. This algorithm is applicable to any linearizable continuous limit state function with any type of distribution for the design variables. The method is applied to two examples and its accuracy is compared with the Monte Carlo simulation and FORM, demonstrating its effectiveness and value.

Commentary by Dr. Valentin Fuster
2011;():899-908. doi:10.1115/DETC2011-47080.

Thin walled cellular structures have the ability to absorb impact energy during crashing thus it is important to enhance the crashing efficiency and optimise the structural reliability. This paper discusses the honeycomb cell configuration optimization procedure. For the design optimization, the response surface method (RSM) is used to formulate the complex design where the energy absorption (EA) representing the structure’s ability of absorbing energy was selected as objective, the Y split side parting length w1 , w2 , and thickness T1 are defined as three design variables, and the maximum crushing force (Max.F) occurs as constraint. During this distinctive optimization, the (RSM) was combined with detailed geometrically simplified finite element (FE) model using ANSYS/LS-DYNA (pre-processor), LS-DYNA (solver) and LS-Opt (optimiser). RSM combined with (FE)model without user intervention, was the effective tool to optimize non-linear impacted cellular structures. Optimal design achieved through LS-OPT is compared to the validated results for accuracy and effectiveness.

Commentary by Dr. Valentin Fuster
2011;():909-914. doi:10.1115/DETC2011-47265.

This paper investigates the effects of nanoclay (Organically Modified Montmorillonite -OMMT) dispersion state and morphology of nanocomposites on laser induced surface micro/nano structure formation and modification of Polystyrene-Clay Nanocomposites at various OMMT concentrations. Injection molded sample surfaces were irradiated by a 248 nm KrF excimer laser in air. Scanning electron microscopy, atomic force microscopy and Fourier Transform Infrared (FTIR) spectroscopy with attenuated total reflectance accessory were utilized to analyze the ablated surface. Results show that, in general, better dispersion of OMMT leads to less continuous surface structures and more pronounced carbonyl regions on FTIR spectra. Clay nanoparticles are exposed on ablated surfaces and affect surface structure formation after irradiation by laser. A mechanism for the formation of excimer laser induced surface structures on injection molded parts is thus proposed.

Commentary by Dr. Valentin Fuster
2011;():915-919. doi:10.1115/DETC2011-47375.

An S-N curve is a traditional tool for design against fatigue. Because there is often a considerable amount of scatter in fatigue performance of specimens, The P-S-N curves capturing the probability of failure should be employed instead of S-N curves. In order to minimize the time and the number of specimens required for fatigue test, many researches had been done. Most studies were focused on a three-parameter S-N curve model; lognormal distribution and maximum likelihood estimation were employed to estimate unknown parameters. In this paper, a three-parameter Weibull distribution is used to describe the scatter of fatigue life. The relationship among survival probability, stress level and fatigue life is considered. A method for estimating parameters of P-S-N curves is proposed. According to this method, three groups of specimens are needed. Each group is submitted to a stress level. The parameters of P-S-N curves can be estimated by solving a set of nonlinear equations. And a numerical example shows that the method is effective.

Commentary by Dr. Valentin Fuster
2011;():921-925. doi:10.1115/DETC2011-48002.

Due to the degradation, input loading and uncertainty in the design parameters usually involve random variables and random processes, reliability analysis for engineering design problems are usually time dependent. Many problems related to degradation have been treated as monotonic or statistically independent, therefore, the probability of failure only at the end of the lifetime of the structure are considered. To the issues of parameters with stochastic process, the outcrossing rate methods have been extensively developed to calculate the upper bound of time-dependent reliability. In these methods, the issue of proper choice of time interval is crucial and difficult. In this paper, a new method for time dependent reliability optimization based on the total probability theory and universal generating function is proposed. In the proposed method, firstly, Parameters with stochastic processes are discretized into some discrete random variables. Secondly, the discrete parameters are reformed into a new random process by the operation of the universal generating functions. Finally, based on the total probability theory, the probability of failure for each limit state function is analyzed using sequential optimization and time invariant reliability assessment method. Only the time invariant reliability method is needed in the proposed method, by conditioning the continuous random variables on the discrete random parameters. Numerical example is presented to demonstrate the performance of the proposed method.

Commentary by Dr. Valentin Fuster
2011;():927-932. doi:10.1115/DETC2011-48650.

Monte-Carlo (MC) methods are often used to carry out reliability based design of structures. Methods that improve the accuracy of MC simulation include Separable Monte Carlo (SMC), Markov Chain Monte-Carlo, and importance sampling. We explore the utility of combining SMC and importance sampling for improving accuracy. The accuracy of the estimates is compared for crude MC, SMC, importance sampling and combined method for a composite plate example and a tuned mass damper example. For these examples SMC and importance sampling reduced the error individually by factors of 2 to 5, and the combination reduced it further by about a factor of 2. The results were also compared with the first order reliability method (FORM). FORM was grossly inaccurate for the tuned mass-damper example which has a failure region bounded by safe regions on either side.

Commentary by Dr. Valentin Fuster
2011;():933-938. doi:10.1115/DETC2011-47076.

In this paper a new protective structure is designed to save human life, in the event of the structural collapse due to an earthquake, terrorist attack or other catastrophic events. The life-saver device discussed here is a moment resisting 3-D steel or composite frames that encapsulates a single or double bedstead, board in the kitchen, worktable in the office or other cases as appropriate. The frame consists of a number of beam-columns of angle cross-section bolted together by gusset plates and topped with a thin steel plate or a rectangular rebar mesh. The collapse of walls and ceiling on top of this structure will result in large plastic deformations in various sections of the frame whereby the energy of the falling debris is dissipated. Despite these large deflections, no harm is inflicted upon the people sleeping inside the frame. The physical behavior of this new life-saving device under real situation of structural collapse also is modeled in ANSYS LS-DYNA software. Combined nonlinear analysis of the frame is performed under dynamic loads developed; the stresses and deformations are carried out. Austenitic twinning induced plasticity (TWIP) steel which has a good combination of both strength and ductility also has been used for modeling and designing this structure and the results has been compared with ordinary steels. The design is verified for the emergency limit state considering the safety of people inside the protective structure.

Topics: Collapse
Commentary by Dr. Valentin Fuster
2011;():939-944. doi:10.1115/DETC2011-48222.

The effects of the strain rate sensitivity on the stress propagations of bonded shrink fitted joint, in which a ring is fitted using an adhesive layer at the middle part of a shaft, subjected to impact push-off loadings are examined. The plastic flow deformation behaviors of structural adhesive under some strain rates are examined experimentally. In addition, the stress wave propagations in the joint are analyzed using finite element method (FEM). The experimental results show that the yield stress of the adhesive increases as the strain rate increases nonlinearly. It is observed that the maximum equivalent von Mises stress occurs in the adhesive layer at the upper interfaces, which causes the rupture of the joint based on the numerical calculations. Furthermore, the strain responses obtained from numerical and experimental methods are compared with each other. A fairly good agreement is obtained between FEM calculations and experiments. In addition, the joint strength is predicted by impact energy using experimental results, which is about 20.85 J in the present study.

Topics: Stress
Commentary by Dr. Valentin Fuster
2011;():945-952. doi:10.1115/DETC2011-48247.

In designing bolted joints, it is necessary to know the stress distributions in bolted joints. Recently, high strength bolts have been used with a higher bolt preload. As the results, the permanent set occurs sometimes at the bearing surfaces of clamped parts in a bolted joint. In addition, when an external load is applied to the bolted joint, the permanent set can be extended at the bearing surfaces. As the permanent set increases, the reduction in the bolt preload increases. Thus, it is important to estimate the reduction in the bolt preload from the reliability stand point. However, no study on the permanent set at the bearing surface under the external loading has been carried out. In this study, the stress distribution and the extension of the permanent set at the bearing surface of the bolted joint under the external tensile loading are examined using finite element Method (FEM), where two hollow cylinders are clamped with a hexagon bolt and a nut. The spring constants for the hexagon bolt and the clamped parts are analyzed using an axi-symmetrical theory of elasticity. Using the obtained results, an increment in the axial bolt force and the reduction in the bolt preload are estimated. For verification of the FEM stress analysis, the load factor of hexagon bolt was measured. The FEM results of the load factor (the increment in the axial bolt force) and the axial bolt force are in a fairly good agreement with the experimental results and the reduction of the axial bolt force. Finally, discussion is made on the appreciate bolt preload.

Commentary by Dr. Valentin Fuster
2011;():953-959. doi:10.1115/DETC2011-48807.

The severe operating conditions required Logging While Drilling (LWD) devices to withstand the high temperatures and pressures. And the seal capability is one of the most important factors to determine the performance and reliability of LWD device directly. O-shaped seal ring is generally used for mechanical sealing in most LWD devices. To precisely predict the behavior of O-shaped seal ring, in this paper, a Finite Element Analysis (FEA) method is proposed to expose the stress and strain of O-shaped seal ring worked under rigorous conditions. An analysis model, which considers all parts are non-rigid components, is established and the contact balance equation is presented. By using ANSYS, the stress distribution and the deformation of O-shaped seal ring is analyzed and a test case is given.

Commentary by Dr. Valentin Fuster
2011;():961-965. doi:10.1115/DETC2011-48874.

Concrete-filled steel structures (SC), or called steel concrete composite structures are composed of steel plates and reinforced concrete. This kind of structures has demonstrated more effective against blast and impact loads, and has been used in risk-sensitive structures such as the nuclear electric power plant and other critical constructions. The comprehensive modeling and analysis is performed in this paper for the full scale SC panel against aircraft impact after the testing results of 1/7.5 scaled model was reviewed and correlated. The methodology, modeling approach, and mesh density sensitivity investigation is presented.

Commentary by Dr. Valentin Fuster

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