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ASME Conference Presenter Attendance Policy and Archival Proceedings

2017;():V002T00A001. doi:10.1115/SMASIS2017-NS2.
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This online compilation of papers from the ASME 2017 Conference on Smart Materials, Adaptive Structures and Intelligent Systems (SMASIS2017) 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presenter attendance policy, if a paper is not presented at the Conference by an author of the paper, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.

Commentary by Dr. Valentin Fuster

Modeling, Simulation and Control of Adaptive Systems

2017;():V002T03A001. doi:10.1115/SMASIS2017-3703.

There has been an increasing demand for force measurement in applications that are portable, wearable, have limited space, low power, or low cost requirements. Such applications cannot support the power and computing requirements of the load cells. Force sensing resistor (FSR) is a passive component that is composed of polymer thick films that change resistance between its terminals due to force applied at its surface. An FSR can provide a suitable alternative to the bulky load cell. However, it inherently exhibits many nonlinear behaviors. This paper evaluates five different FSR sensors (IEE FSR 151 NS, Interlink FSR 402, Sensitronics ShuntMode FSR. FlexiForce A201 FSR, and Sensitorincs ThruMode FSR). The FSRs were evaluated for sensitivity, minimum measurable force, repeatability, creep, and hysteresis. In addition, system identification techniques were used to model each FSR behavior so they can be used as calibrated standalone force sensors. Results show that the Sensitronics ThruMode FSR had the best repeatability and the least hysteresis, while the FlexiForce A201 had the lowest creep, and the Interlinks 402 FSR had the lowest threshold force.

Topics: Modeling , Resistors
Commentary by Dr. Valentin Fuster
2017;():V002T03A002. doi:10.1115/SMASIS2017-3725.

Shape memory alloys (SMA) can be used to create actuators for use in mechanical systems that carry pronounced benefits with their low weight, high strength, and low cost when coupled with advancements such as robust self-sensing. However, there exist drawbacks in the form of slow system response and complex material behavior. The design and implementation of controllers that drive SMA actuators successfully can pose a challenge, and accurate modelling of the material in software can help to optimize the system response time and power requirements. We have created a variety of tools to help implement these actuators into simulations that capture accurate thermal and mechanical responses of various SMA systems under a variety of control laws. In particular, thermo-electro-mechanical models of SMA behavior are implemented into software representations of mechanical systems such that the entire temperature, stress, and phase profiles of an SMA actuator can be accurately determined via simulation. Because analytical equations for modelling SMA behavior quickly become so complex to be untenable, we use stable numerical schemes to solve for these profiles. In particular, a finite difference scheme allows for spatial and temporally discretized temperature profiles along a shape memory actuator which can be solved for using empirically derived expressions for the heat transfer coefficient that dictated convective heat transfer. These types of models allow for a variety of boundary conditions to capture a number of SMA geometries, orientations, and applications. This paper presents the results of the numerical schemes for thermal cycling and a sliding mode controller used to drive a simple SMA actuator with varying boundary conditions and compares them to experimental results.

Commentary by Dr. Valentin Fuster
2017;():V002T03A003. doi:10.1115/SMASIS2017-3726.

Linear infinite dimensional systems are described by a closed, densely defined linear operator that generates a continuous semigroup of bounded operators on a general Hilbert space of states and are controlled via a finite number of actuators and sensors. Many distributed applications are included in this formulation, such as large flexible aerospace structures, adaptive optics, diffusion reactions, smart electric power grids, and quantum information systems. We have developed the following stability result: an infinite dimensional linear system is Almost Strictly Dissipative (ASD) if and only if its high frequency gain CB is symmetric and positive definite and the open loop system is minimum phase, i.e. its transmission zeros are all exponentially stable.

In this paper, we focus on infinite dimensional linear systems for which a fixed gain linear infinite or finite dimensional controller is already in place. It is usually true that fixed gain controllers are designed for particular applications but these controllers may not be able to stabilize the plant under all variations in the operating domain. Therefore we propose to augment this fixed gain controller with a relatively simple direct adaptive controller that will maintain stability of the full closed loop system over a much larger domain of operation. This can ensure that a flexible structure controller based on a reduced order model will still maintain closed-loop stability in the presence of unmodeled system dynamics. The augmentation approach is also valuable to reduce risk in loss of control situations.

First we show that the transmission zeros of the augmented infinite dimensional system are the open loop plant transmission zeros and the eigenvalues (or poles) of the fixed gain controller. So when the open-loop plant transmission zeros are exponentially stable, the addition of any stable fixed gain controller does not alter the stability of the transmission zeros. Therefore the combined plant plus controller is ASD and the closed loop stability when the direct adaptive controller augments this combined system is retained. Consequently direct adaptive augmentation of controlled linear infinite dimensional systems can produce robust stabilization even when the fixed gain controller is based on approximation of the original system. These results are illustrated by application to a general infinite dimensional model described by nuclear operators with compact resolvent which are representative of distributed parameter models of mechanically flexible structures. with a reduced order model based controller and adaptive augmentation.

Commentary by Dr. Valentin Fuster
2017;():V002T03A004. doi:10.1115/SMASIS2017-3734.

The technology of swarm intelligence has been applied to a mechanical vibration monitoring system composed of a network of units equipped with sensors and actuators. The expression of “swarm intelligence” was first used in 1988 in the context of cellular robotic systems, where lots of simple agents may generate self-organized patterns through mutual interactions. There are various examples of the swarm intelligence in the natural environment, a swarm of ants, birds or fish. In this sense, the network of agents in a swarm may have some kind of intelligence or higher function than those appeared in a simple agent, which is defined as the swarm intelligence. The concept of swarm intelligence may be applied in diverse engineering fields such as flexible pattern recognition, adaptive control system, or intelligent monitoring system, because some kind of intelligence may emerge on the network without any special control system. In this study, a simulation model of a five degree-of-freedom lumped mass-spring system was prepared as an example of a mechanical dynamic system. Five units composed of a displacement sensor and a variable damper as actuator were assumed to be placed on each mass of the system. Each unit was connected to each other to exchange the information of state variables measured by sensors on each unit. Because the network of units configured as a mutual connected neural network, a kind of artificial intelligence, the network of units may memorize the several expected vibration-controlled patterns and may produce the signal to the actuators on the unit to reduce the vibration of target system. The simulation results showed that the excited vibration was reduced autonomously by selecting the position where the damping should be applied.

Commentary by Dr. Valentin Fuster
2017;():V002T03A005. doi:10.1115/SMASIS2017-3740.

A cyber-physical system (CPS) combines active actuation, sensing, and a control algorithm to virtually replicate a physical structure with desired inertia, stiffness, and damping properties. The interaction of a CPS with a fluid flow can be used to study complex fluid-structure interaction phenomena. This paper highlights some of the control design challenges associated with the design of CPS and elaborates on issues pertaining to performance and lag. A model for including the interaction force and a potential work-around to inertia compensation are presented. Finally, a case study compares classical PID control with H based model-matching control design.

Commentary by Dr. Valentin Fuster
2017;():V002T03A006. doi:10.1115/SMASIS2017-3746.

In this paper we design an open-loop active normal force for dry friction dampers, aiming to enhance the damping effect. The active normal force is composed of a constant term plus a time-varying term with zero mean value. The constant term is the best constant normal force that minimizes the forced response in the resonant frequency band. The time-varying force can be expressed by the Fourier Series and here we assume that it is composed of four harmonics with respect to the excitation frequency. Overall eight unknown parameters are therefore to be determined, namely the combination coefficients of the fours harmonics and phase differences between them. First, the global sensitivity of these parameters with respect to the forced response are analysed, in order to select the most significant parameters and to eliminate the unimportant ones. To do that the Fourier Amplitude Sensitivity Test (FAST) is performed based on the Lumped Parameter Model, where the forced response of is calculated by the Multi-Harmonic Balance Method (MHBM) combined with Alternating Frequency/Time domain (AFT). The arc-length continuation technique is used to improve the convergence. We found that the interaction between the amplitude and phase of the second harmonic significantly impacts the forced response around resonance frequencies. Then only these two parameters are considered to minimize the forced response in the frequency band, rather than considering all eight parameters. Results show that a further 25% reduction of the response peak can be achieved by the designed time-varying normal force in comparison with the best constant normal force. The proposed design process is applicable for any dry friction dampers if it is possible to impose an open-loop active normal force.

Commentary by Dr. Valentin Fuster
2017;():V002T03A007. doi:10.1115/SMASIS2017-3753.

Dynamic range (ratio of the maximum on-state damping force to the off-state damping force), is an important index characteristic of the performance of the Magnetorheological Energy Absorbers (MREAs). In high speed impact, the dynamic range may fall into the uncontrollable zone (≤ 1) due to the increase in the off-state damping force which is associated with the transition of the flow from laminar to turbulent condition. Therefore, it is of paramount importance to design optimize the MREA in order to increase its dynamic range while accommodating the geometry, MR fluid flow and magnetic field constraints. In this study, a design optimization problem has been formulated to optimally design a bi-fold MREA to comply with the helicopter crashworthiness specifications for lightweight civilian helicopters. It is required to have a minimum dynamic range of 2 at 5 m/s impact velocity while satisfying the constraints imposed due to the geometry, volume of the device, magnetic field and the flow of the magnetorheological fluid in the MR valve. Meanwhile in order to comply with the helicopter crashworthiness requirement, the MREA device should be designed to generate 15 kN field-off damping force at the design impact velocity if the MREA is to be integrated with skid landing gear systems. The magneto-static analysis of the MREA valve has been conducted analytically using simplified assumptions in order to obtain the relation between induced magnetic flux in the MR fluid gaps in active regions versus the applied current and MREA valve geometrical parameters.

Both Bingham plastic models, with and without minor loss factors, have been utilized to derive the dynamic range and the results are compared in terms of the generated off-state damping force, on-state damping force, and dynamic range. The Bingham plastic model with minor loss coefficients was found to be more accurate due to the turbulent condition in the MREA caused by the impact. Finally, the performance of the optimized bi-fold MREA has been evaluated under different impact speeds.

Commentary by Dr. Valentin Fuster
2017;():V002T03A008. doi:10.1115/SMASIS2017-3754.

This research investigates a quasi-zero stiffness (QZS) property from the pressurized fluidic origami cellular solid, and examines how this QZS property can be harnessed for low-frequency base excitation isolation. The QZS property originates from the nonlinear geometric relations between folding and internal volume change, and it is directly correlated to the design parameters of the constituent Miura-Ori sheets. Two different structures are studied to obtain a design guideline for achieving QZS: one is identical stacked Miura-Ori sheets (ismo) and the other is non-identical stacked Miura-Ori sheets (nismo). Further dynamic analyses based on numerical simulation and harmonic balance method, indicate that the QZS from pressurized fluidic origami can achieve effective base excitation isolation at low frequencies. Results of this study can become the foundation of origami-inspired metamaterials and metastructures with embedded dynamic functionalities.

Commentary by Dr. Valentin Fuster
2017;():V002T03A009. doi:10.1115/SMASIS2017-3755.

The present study concerns with the performance of a skid landing gear (SLG) system of a rotorcraft impacting the ground at a vertical sink rate of 5.0 m/s. The impact attitude is per chapter 527 of the Airworthiness Manual (AWM) of Transport Canada Civil Aviation and FAR Part 27 of the U.S. Federal Aviation Regulation. A single degree of freedom helicopter model is investigated under two rotor lift factors 0.67 and 1.0. Three Configurations are evaluated: a) A conventional SLG; b) SLG equipped with a passive viscous damper and c) SLG incorporated with a magnetorheological energy absorber. The non-dimensional solutions of the helicopter model show that the passive damper system could reduce the maximum acceleration experienced by the helicopter occupants by 21% and 19.8% in comparison to the undamped system for the above rotor lift factors, respectively. However, the passive damper fails to constrain the non-dimensional energy absorption stroke of the damper within the given 18 cm maximum stroke and a bottoming out of the damper piston was noticed. Therefore, the alternative and successful choice was to employ a magnetorheological energy absorber (MREA). To improve the MREA controllability and to resettle the payload with no oscillations, i.e. in one cycle, two different Bingham numbers for compression stroke and rebound stroke were defined in the non-dimensional solution. Several simulations were conducted for different values of Bingham numbers. Among these numerical simulation results, the solution that implemented the optimum Bingham numbers was found to be the only one feasible solution. In this case the MREA with optimum Bingham number for compression could utilize the full energy absorption stroke to attain soft landing. In the rebound stroke, the generated optimal on-state damping force successfully controls the bounce of the payload until the payload settles down to its original equilibrium position with no oscillations.

Commentary by Dr. Valentin Fuster
2017;():V002T03A010. doi:10.1115/SMASIS2017-3759.

The paper presents results of finite element analysis of architectured iron-based shape memory alloy (SMA) samples consisting of bulk SMA and void combined to different proportions and according to different geometric patterns. The finite element simulation uses a constitutive model for iron-based SMAs that was recently developed by the authors in order to account for the behavior of the bulk material. The simulation of the architectured SMA is then carried out using a unit cell method to simplify calculations and reduce computation time. For each unit cell, periodic boundary conditions are assumed and enforced. The validity of this assumption is demonstrated by comparing the average behavior of one unit cell to that of a considerably larger sample comprising multiple such cells. The averaging procedure used is implemented numerically, by calculating volume averages of mechanical fields such as stress and strain over each finite element model considered as a combination of mesh elements.

Topics: Simulation , Modeling , Iron
Commentary by Dr. Valentin Fuster
2017;():V002T03A011. doi:10.1115/SMASIS2017-3763.

We propose an analytical model for a superelastic shape memory alloy (SMA) beam. The model considers reversible phase transformation between austenite and a single martensite variant driven by mechanical loading/unloading. In particular, we consider a cantilever beam subjected to a concentrated transverse force acting at the tip. The force is gradually increased from zero to a maximum value sufficient to cause complete transformation of the initially austenitic phase into martensite away from the beam core. The force is then gradually removed, resulting in complete strain recovery. In each stage of the loading/unloading process, an analytical relation is established between bending moment and curvature in terms of position along the axis of the beam. The model is compared to a uniaxial numerical beam model and to finite element analysis (FEA) results for the same beam in 3D, with very good agreement in each case. The moment-curvature relation is then integrated to obtain a nonlinear expression for the deflection and stress distribution in terms of position along the length of the beam. The expression is validated against 3D simulation results.

Commentary by Dr. Valentin Fuster
2017;():V002T03A012. doi:10.1115/SMASIS2017-3766.

In the development of high-performance hypersonic vehicles, the use of high lift and low drag concepts demonstrates improvements in thermal loading, vehicle accelerations and load factors, and total energy dissipation. The key design limitation of hypersonic waveriders is that the optimal waverider geometry is highly dependent on Mach number and deviations from the design point may significantly degrade performance. This paper addresses this fundamental limitation of waveriders by evaluating the ability to morph the bottom surface of a waverider to provide the optimal point-design performance across a broad operational range. This paper addresses the first step required to delivering this morphing capability by addressing the number of morphing control points required to accurately match the complex surfaces of the waverider for multiple Mach number designs. Additionally, the tradeoff between number of additional control points and surface error is investigated. To achieve this, a sensitivity analysis using a Q-DEIM algorithm is performed to identify and rank the optimal set of control. This control point set is verified through analysis and used to evaluate the performance of a morphing waverider structure. Future efforts will evaluate Mach number dependent pressure distribution, aerodynamic structural loading, and thermal loading. This work simply identifies the scale of the control problem and identifies a methodology to actuate a complex surface to enable viable waverider vehicles that maintain optimum performance across a range of Mach numbers.

Commentary by Dr. Valentin Fuster
2017;():V002T03A013. doi:10.1115/SMASIS2017-3777.

Time-space modulated structures (or dynamic structures) possess properties modulated both in time and space. They have been extensively studied in diverse areas. This presented work theoretically studies the unusual wave propagation phenomena induced by elastic waves incident on time-space modulated beams. The scattering matrix is developed to predict the characteristics of the reflected and transmitted waves. It is shown that the scattering matrix directly indicates the non-reciprocal wave transmission and frequency splitting phenomena caused by the dynamic beam, it also reveals a frequency conversion phenomenon, which is rarely noticed by researchers but has very significant influence on the application of dynamic structures.

Commentary by Dr. Valentin Fuster
2017;():V002T03A014. doi:10.1115/SMASIS2017-3781.

The key goal of prosthetic foot design is to mimic the function of the lost limb. A passive spring and damper system can imitate the behavior of an ankle for low level activity, e.g. walking at slow to normal speeds and relatively gentle ascents/descents. In light of this, a variety of constant stiffness prosthetic feet are available on the market that serve their users well. However, when walking at a faster pace and ascending/descending stairs, the function of the physiological ankle is more complex and the muscular activity contributes to the stride in different ways.

One of the challenges in prosthetic device design is to achieve the appropriate range of stiffness of the arrangement of joints and spring elements for different tasks, as well as varying loading of the prosthetic device. This calls for an adaptive mechanism that mimics the stiffness characteristics of a physiological foot by applying real-time adaptive control that changes the stiffness reactively according to user’s needs. The goal of this paper is to define the stiffness characteristics of such a device through modeling.

The research is based on a finite element model of a well-received prosthetic foot design, which is validated by mechanical measurements of the actual product. We further enhance the model to include a secondary spring/dampener element. Various smart material technologies are considered in the design to provide control of flexibility and damping rate of the ankle joint movement. The reactive control of the secondary element allows the simulated prosthetic foot to adapt the ankle joint to imitate the behavior of the physiological ankle during different activities and in different phases of the gait cycle.

Commentary by Dr. Valentin Fuster
2017;():V002T03A015. doi:10.1115/SMASIS2017-3782.

This paper discusses the semi-active control of helicopter ground resonance using magnetorheological (MR) damper. A dynamic model of a MR damper with bi-fold flow mode is built based on the hyperbolic tangent model and experimental data on mechanical properties; and its inverse model is derived for the control. An approximate analytical solution of a linear system is provided and a critical stability area is calculated according to the classical model of ground resonance and the method of determining the linear system stability. Then, Simulations are performed on the helicopter ground resonance model with three semi-active control strategies and the control performance is compared. Simulation results show that the comprehensive performance of the fuzzy skyhook control algorithm is superior to the on-off skyhook and continuous skyhook control algorithms.

Topics: Resonance
Commentary by Dr. Valentin Fuster
2017;():V002T03A016. doi:10.1115/SMASIS2017-3786.

Creating a multi-variance human pulsation simulator is crucial for deeper understanding of human pulsation system and developing useful medical devices. Current pulsatile systems are bulky, complex, and expensive. In order to address these disadvantages, this project intends to develop a simple and cost-effective pulsatile simulator using Magneto-Rheological fluids whose flow can be controlled by magnetic fields instantly. It also intends to evaluate its effectiveness in generating various arterial blood pulsation patterns. To this end, a test setup consisting of tubing, an electromagnet, and sensors along with MR fluids was constructed. Using Pulse Width Modulation (PWM) techniques, the electromagnet produced control signals to regulate the flow motion. The output pressure changes (perceived human pulsation) were measured using a pressure sensor installed in the tubing. Using the test setup, a series of testing was performed to measure arterial pulsations by varying the duty cycles of PWM signals. The results show that the pulsatile system was capable of replicating various human pulsation waveforms.

Topics: Fluids , Rheology
Commentary by Dr. Valentin Fuster
2017;():V002T03A017. doi:10.1115/SMASIS2017-3797.

In this communication, we first introduce the concept of programmable boundary conditions, and then use it to design a nonreciprocal acoustic device: an effective, broadband, acoustic diode.

Previous works showed that, using sufficiently small transducers, an active acoustic metasurface can be realized: a smart active acoustic skin with tunable acoustic properties. Using distributed control, these properties can be adapted or reconfigured in real-time. Or, it can even depend on the acoustic field itself, allowing for a programming of the (meta)surface properties: a programmable boundary condition. For instance, a partial derivative equation depending on the acoustic quantities can be imposed, in a discretized form, at the surface of such a programmable boundary. This type of non-standard boundary conditions have been shown to provide the necessary basis for nonreciprocal propagation for a plane wave interacting with a boundary with non grazing incidence, ie. for wavevectors that possess a component normal to the boundary. This restriction may appear problematic when the wavevector is then parallel to the boundary, e.g. when dealing with plane waves in a 1D waveguide, as in an acoustic diode.

An acoustic diode, or acoustic isolator, is a nonreciprocal device that let acoustic power pass only in one direction, hence breaking the reciprocity of normal acoustic propagation. We propose a new model of acoustic diode, based on active components: a continuous, distributed source inside the domain. However, based on the modeling of parietal sources in ducts, in the low frequency range, we show that the boundary control approach and the distributed domain sources are equivalent. The only difference is that, in the case of the programmable boundary condition, the near-field of the boundary also contains a component normal to the boundary. Hence our acoustic diode can be realized in practice using programmable boundary conditions. Moreover, the acoustic diode is effective on a broad frequency range, since it can work both on the fundamental mode (plane waves) and on higher-order mode of the waveguide.

Commentary by Dr. Valentin Fuster
2017;():V002T03A018. doi:10.1115/SMASIS2017-3810.

Origami-inspired mechanical metamaterials could exhibit extraordinary properties that originate almost exclusively from the intrinsic geometry of the constituent folds. While most of current state of the art efforts have focused on the origami’s static and quasi-static scenarios, this research explores the dynamic characteristics of degree-4 vertex (4-vertex) origami folding. Here we characterize the mechanics and dynamics of two 4-vertex origami structures, one is a stacked Miura-ori (SMO) structure with structural bistability, and the other is a stacked single-collinear origami (SSCO) structure with locking-induced stiffness jump; they are the constituent units of the corresponding origami metamaterials. In this research, we theoretically model and numerically analyze their dynamic responses under harmonic base excitations. For the SMO structure, we use a third-order polynomial to approximate the bistable stiffness profile, and numerical simulations reveal rich phenomena including small-amplitude intrawell, large-amplitude interwell, and chaotic oscillations. Spectrum analyses reveal that the quadratic and cubic nonlinearities dominate the intrawell oscillations and interwell oscillations, respectively. For the SSCO structure, we use a piecewise constant function to describe the stiffness jump, which gives rise to a frequency-amplitude response with hardening nonlinearity characteristics. Mainly two types of oscillations are observed, one with small amplitude that coincides with the linear scenario because locking is not triggered, and the other with large amplitude and significant nonlinear characteristics. The method of averaging is adopted to analytically predict the piecewise stiffness dynamics. Overall, this research bridges the gap between the origami quasi-static mechanics and origami folding dynamics, and paves the way for further dynamic applications of origami-based structures and metamaterials.

Topics: Metamaterials
Commentary by Dr. Valentin Fuster
2017;():V002T03A019. doi:10.1115/SMASIS2017-3825.

The design of compliant mechanisms made of Nickel Titanium (NiTi) Shape Memory Alloys (SMAs) is considered to exploit the superelastic behavior of the material to achieve tailored high flexibility on demand. This paper focuses on two-stage design optimization of compliant mechanisms, as a systematic method for design of the composition of the functionally graded NiTi material within the compliant mechanism devices. The location, as well as geometric and mechanical properties, of zones of high and low flexibility will be selected to maximize mechanical performance. The proposed two-stage optimization procedure combines the optimization of an analytical model of a single-piece functionally graded unit, with a detailed FEA of a continuous compliant mechanism.

In the first stage, a rigid-link model is developed to initially approximate the behavior of the compliant mechanism. In the second stage the solution of the rigid-link problem serves as the starting point for a continuous analytical model where the mechanism consists of zones with different material properties and geometry, followed by a detailed FEA of a compliant mechanism with integrated zones of superelasticity.

The two-stage optimization is a systematic approach for compliant mechanism design with functional grading of the material to exploit superelastic response in controlled manner. Direct energy deposition, as an additive manufacturing technology, is foreseen to fabricate assemblies with multiple single piece functional graded components. This method could be applied to bio-inspired structures, flapping wings, flexible adaptive structures and origami inspired compliant mechanisms.

Commentary by Dr. Valentin Fuster
2017;():V002T03A020. doi:10.1115/SMASIS2017-3833.

Along with recent advancements in novel materials and manufacturing processes, the interest in morphing wings has increased in order to further improve the aerodynamic performance of flying bodies. The morphing wing can be tailored to deliver superior performance, compared to its non-morphing counterparts, for multiple operating conditions and in varying flows. In particular, the morphing wing is implemented for drag reduction and lift enhancement, and hence, the maneuverability, adaptability, and capability of the morphing wing can encompass an even wider spectrum by changing the wing shape. In this research, an existing morphing UAV wing design, Spanwise Morphing Trailing Edge (SMTE), actuated by bending Macro Fiber Composites (MFCs), is considered to generate the spanwise sinusoidal variations on the trailing edge of the morphing wing. A comparative aerodynamic study of the morphing wing by varying the spatial frequency (i.e., number of waves along the span) and the phase shift (i.e., wave shape along the span) at different angles of attack is conducted through analytical approaches and numerical Computational Fluid Dynamic (CFD) simulations, which are validated with previous experimental measurements. The analytical approach uses the three-dimensional (3D) Prandtl lifting line theory, and the CFD modeling in turbulence flow solves the 3D Reynolds-Averaged Navier-Stokes (RANS) equations with the k-ω Shear Stress Transport (SST) turbulence model. Note that the numerical simulations of a morphing wing focus on the pre-stall condition to estimate the aerodynamic performance. This work extends a prior study about a nominal flight condition testing a morphing wing at multiple flight conditions to evaluate multi-point 1 performance. The results show that there are governing aerodynamic efficiency zones of the lift-to-drag ratio, endurance, and aircraft range within a zone of angles of attack. Therefore, the morphing wing is shown to have a good aerodynamic performance as compared to the non-morphing wing.

Topics: Wings
Commentary by Dr. Valentin Fuster
2017;():V002T03A021. doi:10.1115/SMASIS2017-3837.

Periodic structures provide filtering behavior for vibrations, as a result of the repetition in space of unit blocks, or unit cells. In general, they are characterized by an internal mechanical impedance mismatch, so that waves are reflected and transmitted every time a discontinuity is present. The global behavior given by waves superposition is their cancellation, only for specific frequency ranges, generally called stop-bands or band-gaps. The variation of non-dimensional parameters shows how these attenuation regions move in the frequency domain: the correspondent diagrams are the main tools for the design problem and are known as band-maps. The selection of the geometrical, physical and elastic properties of the unit cell is therefore dependent on the designer experience and nothing can be said about the optimality of the proposed solution. Numerical methods are used for the selection of the best cell geometry, in order to get optimal attenuation. Generally, this is a time consuming approach. In this paper, an new method is presented, based on how the waves are reflected and transmitted at cells interface. Both beam and rod case studies are investigated. The algorithm allows matching between band-gap central frequency and the desired value, while the designed attenuation is optimal there, under certain physical and geometrical constraints. Moreover, the design of the bandgap location has been decoupled from the design of the magnitude of attenuation. This approach is purely analytic, therefore the computational efforts required are minimum. In order to validate the analytical model, a passive periodic beam has been manufactured. Its real frequency response is therefore compared to the expected one.

Commentary by Dr. Valentin Fuster
2017;():V002T03A022. doi:10.1115/SMASIS2017-3845.

We consider subset selection and active subspace techniques for parameters in a continuum phase-field polydomain model for ferroelectric materials. This analysis is necessary to mathematically determine the parameter subset or subspace critically affecting the response, prior to model calibration using either experimental or synthetic data constructed using density functional theory (DFT) simulations. For the 180° domain wall model, we employ identifiability analysis using a Fisher information matrix methodology, and subspace selection to determine the active subspace. We demonstrate the implementation and interpretation of techniques that accommodate the model structure and discuss results in the context of identifiable parameter subsets and active subspaces quantifying the strongest influence on the model output. Our results indicate that the governing domain wall gradient energy exchange parameter is most identifiable.

Commentary by Dr. Valentin Fuster
2017;():V002T03A023. doi:10.1115/SMASIS2017-3847.

In the paper, we discuss the development of a high-fidelity and surrogate model for a PZT bimorph used as an actuator for micro-air vehicles including Robobee. The models must quantify the nonlinear, hysteretic, and rate-dependent behavior inherent to PZT in dynamic operating regimes. The actuator dynamics are initially modeled using the homogenized energy model (HEM) framework. This provides a comprehensive high-fidelity model, which can be inverted and implemented in real time for certain control regimes. To improve efficiency, we additionally discuss the development of data-driven models and focus on the implementation of a surrogate model based on a dynamic mode decomposition (DMD). Finally, we detail the design and implementation of a PI controller on the surrogate and high-fidelity models.

Commentary by Dr. Valentin Fuster
2017;():V002T03A024. doi:10.1115/SMASIS2017-3848.

In this paper, we discuss the development and implementation of a 3-D electromechanically coupled homogenized energy model (HEM) for ferroelectric materials. A stochastic-based methodology is introduced and applied to problems involving large scale switching of ferroelectric and ferroelastic materials. Switching criteria for polarization variants are developed using density distributions in three dimensions to accommodate both electrical and mechanical loading and their coupled response. The theory accommodates non-proportional loading and major/minor loop hysteresis. Such formulations are known to accelerate computations for real-time control of nonlinear and hysteretic actuators. The proposed formulation maintains superior computational efficiency in the three dimensional case through the application of density formulations that are based on internal distributions of stress and electric field to produce a distribution of polarization switching events over a range of applied fields and stresses.

Commentary by Dr. Valentin Fuster
2017;():V002T03A025. doi:10.1115/SMASIS2017-3859.

We propose a finite element model which describes the dynamic behavior of hydrogels for step-responses and quasi-static regimes. The material properties are implemented in a fluid structure interaction (FSI) model which simulates the swelling behavior of hydrogels within a micro-valve. The resulting volume change effects the fluid domain describing the mass-flow behavior of the micro-valve. Furthermore, the concept is implemented in a high-level circuit and flow chart model to efficiently predict the response behavior of hydrogel-based micro-valves.

With these tools a foundation is set to efficiently simulate microfluidic systems with the aim to develop a fully computer-aided design process. The presented method will help to better understand, predict and visualize the behavior of hydrogels and support the development of highly integrated hydrogel-based microfluidic circuits.

Commentary by Dr. Valentin Fuster
2017;():V002T03A026. doi:10.1115/SMASIS2017-3876.

Periodic structures are the repetition of unit cells in space, that provide a filtering behavior for wave propagation. In particular, it is possible to tailor the geometrical, physical and elastic properties of the unit cells, in order to attenuate certain frequency bands, called band-gaps or stop-bands. Having each element characterized with the same parameters, the filtering behavior of the system can be described through the wave propagation properties of the unit cell. This is technologically impossible to obtain, therefore the Lyapunov factor is used, in order to define the mean attenuation of a quasi-periodic structure. Tailoring Gaussian unit cell properties potentially allows to extend the stop-bands width in the frequency domain. A drawback is that some unexpected resonance peaks may lie in the neighborhood of the extended regions. However, the correspondent mode-shapes are localized in a particular region of the structure, and they partially decrease the global attenuating behavior. In this paper, the aperiodicity introduced in the otherwise perfect repetition is investigated, providing an explanation for the mode-localization problem and for the stop-bands extension. Then, the proposed approach is applied to a passive quasi-periodic beam, characterized from a localized peak within a designed band-gap. The geometrical properties of its aperiodic parts are changed in order to deterministically move the localization peak in the frequency response. Numerical and experimental results are compared.

Commentary by Dr. Valentin Fuster
2017;():V002T03A027. doi:10.1115/SMASIS2017-3877.

Periodic systems have long been known for their peculiar characteristics in wave propagation and have been studied in many fields over the last century, going from electro-magnetics and optics to elastic structures, which drew an increasing interest in structural and mechanical engineering for vibration suppression and control spanning over broadband frequency ranges. Recently, on the stream of other studies conducted in different fields, spatiotemporal modulated elastic structures have been studied, showing promising results for wave control in that one-way propagation in the so called directional-bands can be achieved, constituting what may be called a mechanical diode. Despite of the fact that mathematical methods for the analysis of such structures have already been developed, often physics behind them is difficult to grasp. In this work, a simplified interpretation of the undergoing phenomena is thus given relating wave propagation in the mean to its physical characteristics as well as to modulation parameters. Exploiting Doppler effect and passive equivalent structures, it is shown that the broken reciprocity is due to the fact that opposite travelling waves effectively see two different periodic structures. To this aim the rod case is analysed for low modulation speeds and low modulation amplitudes; finally, in the light of the previous analysis, an explanation for First Brillouin Zone’s asymmetry is given.

Commentary by Dr. Valentin Fuster
2017;():V002T03A028. doi:10.1115/SMASIS2017-3889.

Airfoil camber adaptation may be the key for the performance improvement of wings for many specific applications, including shorter take-off distance, compensation of weight variation and so on. Following the successful experiences gained in SARISTU, where an adaptive trailing edge device was developed for medium to large size commercial aircraft, the authors propose to exploit the developed architecture to a small aircraft wing. The basic reasons behind that mainly rely on the associated possibility to access easier implementation onto a real aircraft instead of referring to wing segments for wind tunnel or ground tests. In this way, many operative problems are faced, that would be otherwise neglected in usual lab experimentation. First of all, the integration of the proposed device onto a flying machine, that in turn pose the problem of facing the interface with the existing systems. Secondly, the necessity of including the device into the flap while fully preserving its current functionality. Furthermore, the necessity of developing a robust design process that allows having the release of the permit-to-fly. Each of the above steps, non-exhaustive in illustrating the difficulty of the addressed challenge, is structured in many other sub-segments, ranging from a suitable FHA analysis to a full re-design of the existing high lift systems or the adaptation of the architecture of the reference morphing trailing edge itself. This last item poses the classical challenge of the scaling issues, requiring the structural and the actuation subsystems to entirely fit into the new geometry. The objective of the present research is then to verify the feasibility of applying a certain architectural morphing philosophy onto a real aircraft, taking into account all the operational difficulties related to such an operation. This paper reports the activities related to the exploitation of the reference adaptive structural architecture, to the geometry of a flap of a small aircraft. In detail, the system layout is presented, followed by a FE analysis of the structural system under the operational loads and an estimation of the weight penalty associated to this transformation. Interfaces of the flap system with the main aircraft body are considered as constraints to the design development, so that the only flap is affected.

Commentary by Dr. Valentin Fuster
2017;():V002T03A029. doi:10.1115/SMASIS2017-3892.

This manuscript investigates the flexural wave propagation behavior of a foldable metamaterial structure. Origami-inspired foldable structures are making inroads into many engineering applications — deployable solar cell arrays, foldable telescope lenses, foldable automotive airbags, to name a few; driven primarily by some of the remarkable mechanical properties (high stiffness, negative Poisson’s ratio, bistability etc.) of these structures. The chief motivation of this research is a comprehensive analysis of flexural wave propagation in such foldable structures. The repeating unit cell of the structure consists of an Euler-Bernoulli beam and a torsion spring. Transfer Matrix (TM) method is used to analyze the vibration attenuation properties of the structure and it is shown that the structure exhibits bandgap behavior. The obtained bandgaps are validated using Finite Element Analysis (FEA). Using the characteristic equation of the transfer matrix, we derive a transcendental equation for the bandgap edge frequencies. We show that for the nth band gap, the second band edge frequency is always equal to the natural frequency of the nth modeshape of the constituent beam under the simply supported condition. This frequency, therefore, is independent of the torsion spring constant. In addition, a detailed parametric study of the variation in band edge frequencies when the geometric and material parameters of the structure (Young’s modulus of beam, torsional spring constant, width and thickness of beam etc.) are varied is conducted. It is concluded that the ratio of flexural rigidity of the beam to the torsion spring constant (EI/kt) is an important parameter affecting the width of the bandgap. For low values of the ratio, i.e., low beam flexural rigidity and high torsional stiffness, the first band edge frequency is almost equal to the second band edge and, effectively, no bandgap exists. As the stiffness ratio increases, i.e. high flexural rigidity (EI of the beam) and low torsional stiffness kt, the first band edge frequency assumes progressively lower values relative to the second band edge and we obtain a relatively large bandgap over which no flexural waves propagate. This has important ramifications for the design of foldable metamaterial structures.

Commentary by Dr. Valentin Fuster
2017;():V002T03A030. doi:10.1115/SMASIS2017-3893.

This manuscript investigates one way sound propagation in Magnetorheological fluids (MRF) using spatio-temporal modulation of the applied magnetic field. One-way propagation of waves in a structure can have potential technological applications such as sound isolation, filtering and echo suppression. Several experimental works in the literature have shown that elastic properties of MRF’s (local speed of sound, in particular) are dependent on the applied magnetic field. Therefore, several fascinating possibilities regarding the manipulation of sound waves in MRF, by tailoring the applied magnetic field, exist.

A effective medium approximation (previously used in literature) is used to analyze sound propagation in a MRF composed of hydrogen-reduced Iron particles suspended in pure glycerine. Floquet-Bloch theory is used to obtain a quadratic eigenvalue problem that gives the band structure as a function of the material and modulation parameters. When the applied magnetic field is allowed to vary only in space, regular bandgaps are obtained as a result of Bragg scattering. In contrast, the temporal variation of the magnetic field to induce a traveling wave like variation of the modulated parameters, breaks the symmetry of the Brilloouin zones and we obtain directional bandgaps. The theoretical band structure is validated by numerical band diagrams obtained using a Finite Element code. This research has important applications in active sound manipulation.

Commentary by Dr. Valentin Fuster
2017;():V002T03A031. doi:10.1115/SMASIS2017-3897.

Vibrational Resonance (VR) is a nonlinear phenomenon which occurs when a bi-stable system is subjected to a bi-harmonic excitation consisting of a small-amplitude resonant excitation and a large-amplitude high-frequency excitation. The result is that, under some conditions, the high-frequency excitation amplifies the resonant response associated with the slow dynamics. While VR was studied extensively in the open literature, most of the research studies used optical and electrical systems as platforms for experimental investigation. This paper provides experimental evidence that VR can also occur in a mechanical bi-stable twin-well oscillator and discusses the conditions under which VR is possible.

Topics: Resonance
Commentary by Dr. Valentin Fuster
2017;():V002T03A032. doi:10.1115/SMASIS2017-3910.

To alleviate wave and vibration transmission in automotive, aerospace, and civil engineering fields, researchers have investigated periodic metamaterials with especially architected internal topologies. Yet, these solutions employ heavy materials and narrowband, resonant phenomena that are unsuitable for the many applications where broadband frequency vibration energy is a concern, such as that injected by impact forces, and weight is a performance penalty. To overcome these limitations, a new idea for lightweight, elastomeric metamaterials constrained near critical points is recently being explored, such that improved shock and vibration damping is achieved using reduced mass than conventional periodic metamaterials. On the other hand, the internal architectures of these metamaterials have not been explored beyond classical circular designs whereas numerous engineering structures involve square or rectangular geometries that may challenge the ability to realize critical point constraints due to the lack of rotational symmetry. The objectives of this research are to undertake a first study of square cross-section elastomeric metamaterials and to assess the impact tolerance of structures into which these metamaterials are embedded and constrained. Finite element simulations guide attention to design parameters for the metamaterial architectures, while experimental efforts quantify the advantages of constraints on enhancing impact tolerance metrics for engineering structures. It is seen that although the architected metamaterial leads to slightly greater instantaneous acceleration amplitude immediately after impact, it more rapidly attenuates the injected energy when compared to the solid and heavier elastomer mass from which the metamaterial is derived.

Topics: Metamaterials
Commentary by Dr. Valentin Fuster
2017;():V002T03A033. doi:10.1115/SMASIS2017-3920.

This paper presents the modeling, simulation and wind tunnel experimental verification of the aeroelastic behavior of a two-degree-of-freedom (pitch and plunge) typical airfoil section with superelastic shape memory alloy helical springs in the pitch degree-of-freedom. A linearly elastic spring is considered in the plunge degree-of-freedom. Although viscous damping is considered in both degrees-of-freedom, hysteretic damping simultaneously takes place in the pitch degree-of-freedom due to the (stress-induced) pseudoelastic behavior of the shape memory alloy springs. The shape memory alloy phase transformation kinetics and constitutive modeling are based on Brinsons model and the shape memory alloy helical spring behavior is based on classical spring design. The nonlinear effects of shape memory alloy phase transformation are included in the shape memory alloy spring modeling for the representation of hysteretic force-displacement behavior. A two-state linear aerodynamic model is employed to determine the unsteady pitching moment and lift. The aeroelastic behavior of the typical section is numerically and experimentally investigated for different preload levels applied to the shape memory alloys. Numerical predictions and experimental results show that for large enough preload levels (such that shape memory alloy phase transformations take place at small pitch angles) unstable post-flutter regime is replaced by stable limit-cycle oscillations. Moreover, the amplitudes of aeroelastic oscillations decrease with increasing preload levels since more expressive phase transformations are achieved at small pitch angles. Although the amplitudes of the post-flutter limit-cycle oscillations increase with increasing airflow speed (since aerodynamic loads increase with the square of the airflow speed), they remain bounded within acceptable levels over a range of airflow speeds due to hysteretic damping. Moreover, the cutoff airflow speed increases with increasing preload. The experimentally verified results show that the pseudoelastic behavior of shape memory alloy elements can passively enhance the aeroelastic behavior of a typical section.

Commentary by Dr. Valentin Fuster
2017;():V002T03A034. doi:10.1115/SMASIS2017-3927.

Macro-fiber composite (MFC) piezoelectric materials are used in a variety of applications employing the converse piezo-electric effect, ranging from bioinspired actuation to vibration control. Most of the existing literature to date considered linear material behavior for geometrically linear oscillations. However, in many applications, such as bioinspired locomotion using MFCs, material and geometric nonlinearities are pronounced and linear models fail to represent and predict the governing dynamics. The predominant types of nonlinearities manifested in resonant actuation of MFC cantilevers are piezoelectric softening, geometric hardening, inertial softening, as well as internal and external dissipative effects. In the present work, we explore nonlinear actuation of MFC cantilevers and develop a mathematical framework for modeling and analysis. An in vacuo actuation scenario is considered for a broad range of voltage actuation levels to accurately identify the sources of dissipation. Several experiments are conducted for an MFC bimorph cantilever, and model simulations are compared with nonlinear experimental frequency response functions under resonant actuation. The resulting experimentally validated framework can be used for simulating the dynamics of MFCs under resonant actuation, as well as parameter identification and structural optimization for nonlinear operation regime.

Commentary by Dr. Valentin Fuster
2017;():V002T03A035. doi:10.1115/SMASIS2017-3948.

Locally resonant metamaterials are characterized by bandgaps at wavelengths much larger than the lattice size, which enables low-frequency vibration attenuation in structures. Next-generation metastructures (i.e. finite metamaterial-based structures) hosting mechanical resonators as well as piezoelectric interfaces connected to resonating circuits enable the formation of two bandgaps, right above and below the design frequency of the mechanical and electrical resonators, respectively. This new class of hybrid metastructures proposed in this work can therefore exhibit a wider bandgap size and enhanced design flexibility as compared to using a purely mechanical, or a purely electromechanical metastructure alone. To this end, we bridge our efforts on modal analysis of mechanical and electromechanical locally resonant metastructures and establish a fully coupled framework for hybrid mechanical-electromechanical metastructures. Combined bandgap size is approximated in closed form for sufficient number of mechanical and electromechanical resonators. Case studies are presented to understand the interaction of these two locally resonating metastructure domains in bandgap formation, and conclusions are drawn for design and optimization of such hybrid metastructures. Numerical results from modal analysis are compared with dispersion analysis using the plane wave expansion method and the proposed analytical framework is validated succesfully.

Commentary by Dr. Valentin Fuster
2017;():V002T03A036. doi:10.1115/SMASIS2017-3966.

Variable performance characteristics in a multifunctional structure may be achieved by identifying suitable material candidates, and spatially varying, or grading, their material properties along the structures. Additive manufacturing (e.g. 3D printing) offers various possibilities to fabricate/manufacture such graded structures. The material properties of multifunctional composite structures, such as beams or plates, are often graded along their thickness (laminate/sandwich) or distributed in a material matrix (fibers/nanoparticles). In recent years, it has been demonstrated that by tailoring the materials in other directions (axially/radially), superior mechanical behavior and structural stability can be realized. In this research, the modeling and analyses of axially graded polymeric beams to maximize their vibration performance for a large bandwidth of frequencies and damping is presented. Polymeric materials have frequency and temperature dependent viscoelastic properties (complex modulus, glass transition temperature etc.) which can be leveraged for different applications. The goal is to spatially combine these materials such that desired longitudinal vibration characteristics (natural frequencies, damping and modes) can be achieved. To this end, the modeling for the free and forced vibration of beams with spatially varying properties, is carried out by a piecewise uniform continuous model. The spectral characteristics (natural frequency, damping ratios, and frequency response functions) of the axially graded beams are computed by solving associated transcendental eigenvalues problems. The parametric studies included the grading of polymers which are regularly used for additive manufacturing, such as ABS, PLA, etc. These results demonstrate that the response of the system can be manipulated by axial grading and optimal design/fabrication (3D printing) of multifunctional smart structures may be developed for vibration control applications.

Topics: Vibration
Commentary by Dr. Valentin Fuster
2017;():V002T03A037. doi:10.1115/SMASIS2017-3967.

Postbuckling response, long considered mainly as a failure limit state is gaining increased interest for smart applications, such as energy harvesting, frequency tuning, sensing, actuation, etc. Cylindrical shells have received less attention as structural form to harness elastic instabilities due to their increased modeling complexity and high imperfection sensitivity. Yet, preliminary experimental and computational evidence indicates that the elastic postbuckling response of cylindrical shells can be controlled and potentially managed. Further, cylindrical shells offer desirable features for the design of mechanical devices and adaptive structures that other forms cannot attain without additional external constraints. This paper presents a study on tailoring the elastic postbuckling response of thin-walled cylindrical shells under compression by means of non-uniform wall stiffness distributions. The pattern of stiffness distribution was designed by discretizing the shell surface into cells and thickening selected cells with respect to a baseline uniform wall thickness. Diverse patterns were characterized in the way of how they affect the postbuckling response through numerical simulations using the finite element method. Results show that the elastic postbuckling response can be tailored into three response types: softening, sustaining, and stiffening; and that number, sequence/time and location/space of localized buckling events can be designed. This work provides new knowledge on the means to design the cylindrical shells with controlled elastic postbuckling behavior for applications in smart materials, mechanical devices, and adaptive structures.

Commentary by Dr. Valentin Fuster
2017;():V002T03A038. doi:10.1115/SMASIS2017-3989.

One of the primary difficulties to implementing NiTi shape memory alloys as robotic actuators is reliably amplifying their low linear strain to large effective displacements. Bowden tubes, called “push-pull cables” in other industries, allow a long length of Shape Memory Alloy (SMA) wire to fit in a small space; this provides a method for increasing effective SMA actuator strain without compromising space or complexity of the entire mechanism. The mechanical advantage of the Bowden tube provides faster actuation speeds, but comes at a cost of increased thermal capacitance resulting in higher power consumption. A feedback control system has been formed comprising the Bowden tube actuator, a rotary platform, and a microcontroller. The controller heats the SMA by passing current through the SMA wire using pulse-width-modulation. After describing the creation of the electro-mechanical system, its capabilities and limitations are discussed. Linear Parameter Varying (LPV) models of SMA are used to determine the range of characteristics the inherently nonlinear SMA system will exhibit. A sliding mode controller is designed based on these characteristics, and implemented in the prototype. Sliding-mode control is shown to be a powerful tool for SMA control even when system parameters are uncertain.

Commentary by Dr. Valentin Fuster

Integrated System Design and Implementation

2017;():V002T04A001. doi:10.1115/SMASIS2017-3733.

This paper presents a summary of the ongoing research and development of a solid-state piezo-composite rotor design for use in rotary systems. The proposed hub-rotor system can be implemented in unmanned-aerial-vehicles such as single-rotor, tandem-rotor, multi-copter, and ducted-fan rotorcraft, or other rotating systems such as wind turbines, turbine engines and marine propellers. The preliminary feasibility of the solid-state rotor concept has been previously demonstrated through flight-testing a prototype on a quad-copter vehicle platform. This paper presents a summary of previous findings, and a new solid-state rotor prototype with the corresponding experimental results.

Topics: Rotors
Commentary by Dr. Valentin Fuster
2017;():V002T04A002. doi:10.1115/SMASIS2017-3735.

Piezocomposite beams are often modeled using linear constitutive equations describing the electromechanical coupling of the material. In nearly all experimental identification processes, nonlinearities in these equations are ignored, which can lead to significant errors in the identified models. Following a common practice in the literature, a piezocomposite cantilever beam is modeled as a single degree of freedom system, with strain induced harmonic excitation governed by linear piezoelectric constitutive relationships. The validity of the linear property assumptions is investigated. It is experimentally demonstrated that the relationship between input and response of the beam is significantly nonlinear. The impact of this nonlinear behavior on the parameter identification of the system is shown for three different testing methods, (1) Open Loop Excitation, (2) Constant Input, and (3) Constant Response. For each method, the command amplitude is varied which yields different parameter estimates for the single degree of freedom beam model. These results demonstrate that the assumed linear constitutive relationships lead to parameter estimates which are only accurate for the specific testing method and the specific commanded input or response amplitude, even under highly controlled testing procedures. The paper concludes with comments on the system identification of a single degree of freedom model given this nonlinear system behavior.

Commentary by Dr. Valentin Fuster
2017;():V002T04A003. doi:10.1115/SMASIS2017-3736.

Parameter estimation of a cantilever beam model typically involves estimating the effective parameters of the system for an assumed mode shape. This shape assumption, which is difficult to verify with traditional single-point sensors, can be validated through the distributed strain measurements available from optical Fiber Bragg Grating sensors. In this paper, the experimental mode shapes of a cantilever beam acquired from Fiber Bragg Grating sensors are compared with the analytical predictions of classical beam theory for the first two bending modes. A single degree of freedom model is also analyzed for the first bending mode and compared to the distributed parameter model and experimental data. It is shown that the distributed parameter model provides a good estimate of the strain profile at the first two natural frequencies, and that the single degree of freedom and distributed parameter models are in close agreement at the first natural frequency.

Commentary by Dr. Valentin Fuster
2017;():V002T04A004. doi:10.1115/SMASIS2017-3737.

The thermo-mechanical coupling of shape memory alloys has been modeled comprehensively using energy based constitutive models. These constitutive models describe the relationship of temperature, stress and strain in material and propose a solid methodology for system identification of model parameters. Equally important in the dynamics of shape memory alloy applications is the heat transfer model. Heat transfer models have been proposed but a complete resource for system identification of the model parameters is missing in the literature. Therefore, in this paper, the parameters for a low-order heat transfer model are identified experimentally. It is shown that for all parameters the measured parameters accurately model the system leading to the necessary values for use in predictive models. Furthermore, it is shown that using nominal values will produce inaccuracies in the predicted system response.

Commentary by Dr. Valentin Fuster
2017;():V002T04A005. doi:10.1115/SMASIS2017-3738.

A compliant hinge is proposed to replace conventional revolute joints for a shape memory alloy actuated arm-like mechanism. The arm-like mechanism is designed to replicate the articulation of the elbow joint, linking the humerus and radius, while being able to lift a dead load using a shape memory alloy wire as the biceps muscle. A parametric analysis on hinge geometry and Young’s modulus is performed to determine if a feasible geometric and material solution exists based on the application requirements. The results indicate optimum solutions are logarithmically correlated between modulus of elasticity and width-to-thickness ratio. Overlaying the results of the parametric study onto an Ashby chart indicates that large hinge widths are necessary. These results indicate more complex geometries are needed for arm-like manipulator applications.

Commentary by Dr. Valentin Fuster
2017;():V002T04A006. doi:10.1115/SMASIS2017-3739.

This paper investigates the heaving and pitching of a wing-like parameterized cantilevered plate with a leading edge stiffener and clamp variation when actuated with a surface-bonded piezoelectric actuator. The response is analyzed using a finite element model that is validated by comparison with known analytical solutions. The validated finite-element model is subjected to a harmonic excitation parametric analysis. The parameters varied in the model are the root clamped percentage, leading edge stiffener thickness, and the aspect ratio of the plate. The model is examined at the first two Eigen frequencies. Metrics of heaving and pitching are developed using surface fitting methods and their amplitudes and phases are reported throughout the parameter space. Emphasis is placed on the interaction and coupling of the first two modes of vibration with respect to the parameters. A piezo-composite wing prototype is fabricated and actuated harmonically with a Macro-Fiber Composite actuator while leading edge stiffener thickness and root clamped percentage is varied. The resulting experimental data is used to further validate the theoretical models.

Commentary by Dr. Valentin Fuster
2017;():V002T04A007. doi:10.1115/SMASIS2017-3750.

A control strategy called hybrid position feedback control is applied to a bistable system to prevent multiple crossovers during actuation from one stable equilibrium to the other. The hybrid controller is based on a conventional positive position feedback controller. The controller uses the inertial properties of the structure around the stable positions to achieve large displacements by destabilizing a positive position feedback controller. Once the unstable equilibrium is reached, the controller is stabilized to converge to the target stable equilibrium.

The bistable system under harmonic excitation and hybrid controller are investigated for its behavior. In addition, energy analysis of the system controlled by the hybrid controller is investigated using numerical time domain methods. The energy variance by parameters and the comparison between the open-loop system with harmonic excitation and the controlled system is investigated.

Commentary by Dr. Valentin Fuster
2017;():V002T04A008. doi:10.1115/SMASIS2017-3751.

Large loads due to fluid-structure interaction can lead to high bending stresses and fatigue failure in wings and wind turbine blades. A solution for the mentioned problem is using a bistable composite laminate for load alleviation. A bistable composite laminate is capable of attaining two statically stable shapes, and it can be designed to alleviate a critical load, such as wind gust, by snapping from one stable position to the other. Piezocomposite actuators can be used to reverse the snap-through and bring back the structure to its original optimal aerodynamic shape, after the gust load is alleviated. However, there will always be a limit on the size of the piezocomposite actuator used; hence, severe force and energy constraints exist to achieve the snap-through. In this context, this paper focuses on the minimum required actuation energy for performing snap-through of a bistable structure. The paper shows how the required energy for cross-well transfer varies as a function of damping ratio and frequency ratio at specific harmonic force amplitude when the system is externally disturbed with a band-limited noise signal. A band-limited noise signal is chosen to model external/ambient disturbances. This paper uses the Duffing-Holmes equation as a one-degree-of-freedom representative model of a bistable structure. This equation is numerically solved to calculate the required energy for cross-well oscillation under different system and forcing conditions. Various non-dimensional parameters are used to highlight interesting phenomena. It is found that the domain of low energy regions decreases by increasing the level of noise.

Topics: Noise (Sound)
Commentary by Dr. Valentin Fuster
2017;():V002T04A009. doi:10.1115/SMASIS2017-3752.

This paper presents the fatigue characterization of piezo-active beams in bending with surface bonded Macro-Fiber Composite actuators. Three substrate materials are considered: stainless steel, aluminum, and brass. First, the bending response is quantified theoretically using the classical laminate plate theory. The theoretical bending results indicate that the beam with the steel substrate had the largest curvature, and the specimen with the aluminum had the least. Next, midpoint deflection in a simply supported configuration in response to harmonic quasi-static actuation is experimentally measured. The results from the experiments showed no evidence of degradation of actuation for up to four million cycles at the harmonic excitation amplitude of 500 V; however, the results appeared highly sensitive to temperature.

Topics: Fatigue
Commentary by Dr. Valentin Fuster
2017;():V002T04A010. doi:10.1115/SMASIS2017-3764.

Additive Layer Manufacturing is offering tremendous oportunities for manufacturing. Many complex structures, which could not be manufactured by conventional methods can be produced additive. This paper gives three examples of how additive manufacturing can be used to built smart structures with integrated actuators and sensors. The integration of piezoceramic actuators into FDM and SLM processes is described as well as the design of structures with integrated pneumatic actuators printed with the PolyJet method.

Commentary by Dr. Valentin Fuster
2017;():V002T04A011. doi:10.1115/SMASIS2017-3788.

Material handling is a crucial part of manufacturing and assembly in industry. In state-of-the-art handling systems, robots use various end-effectors to grip and transport different shapes of workpieces. The exchange process of fitted end-effectors to appropriate workpieces, often requires to interrupt the manufacturing process. From the prospective of economic efficiency, there is an inherent benefit creating a reconfigurable end-effector that is able to adjust automatically to different workpiece geometries. In this work a novel end-effector prototype based on shape memory alloys (SMA’s) is developed and experimentally validated. The end-effector prototype has four arms with two SMA driven reconfigurable degrees of freedom (DOF’s) to allow gripping of different workpiece shapes and geometries. Each arm is rotatable by 90 degrees (1. DOF) and uses a counterweight to relieve the SMA wire. The tip of the arm is driven by a separate SMA in a 20 degree range and it has a special locking mechanism to hold different positions without any flowing current. The designs of the actuator constructions are presented and a prototype is produced via rapid-prototyping. Future work will include the characterization of the second DOF and controlling the positions of both DOF’s by using a PID controller based on the SMA self-sensing ability.

Commentary by Dr. Valentin Fuster
2017;():V002T04A012. doi:10.1115/SMASIS2017-3802.

Smart Memory Alloys have brought a range of new capabilities to existing and novel designs due to their unique properties and ability to induce stress and strain in the material due to thermomechanical loading. Shape memory alloy-based smart material has widely been used and studied for biomedical applications. This includes smart needle for percutaneous procedures, self-expanding Nitinol grafts, stents, and other permanent internal devices. The smart needle is a needle in which deflection/path of the insertion in tissues can be controlled by incorporating Nitinol wire actuators on the body of the needle. However, smart needle designs proposed in the past lack both flexibility for multidirectional angles, and they do not allow for multiple martensitic phase transformations and are thus not repeatable. Each time the Nitinol wire is actuated, the wire would have to be manually reset to its initial length. Active materials like Nitinol require a bias force or mechanism that reverts the activated form of the needle back to its original martensitic form, which in the case of active needles is a straight wire. The lack of a recovery mechanism means that subsequent austenite transformations for deflection in opposing or similar trajectories cannot be performed as the system will not fully reset itself once cooled. In our proposed design, four Nitinol wires are embedded into a needle and act independently of one another to provide multi directional needle deformations. By providing tension onto a flexible 3D printed needle shaft, they can pivot a hard needle tip into any given direction. Once the needle’s deformation is complete, the material’s natural rigidity coupled with other Nitinol wires pulling resistance will restore the initial length of the actuated wire as it cools. This allows the needle to undergo a martensitic transformation and then subsequent cooling followed by additional phase transformation in a different direction. This makes the needle’s mechanism repeatable and functional for multiple insertions.

Topics: needles
Commentary by Dr. Valentin Fuster
2017;():V002T04A013. doi:10.1115/SMASIS2017-3826.

This work presents the design, optimization, manufacturing, and experimental characterization of a swept, camber-morphing, flying wing. By virtue of a novel actuation concept, combined with a compliant structural concept, camber deflections of sufficient amplitude to achieve controllability in roll and pitch are attained. The optimization, which accounts for aeroelastic interactions in the assessment of the wing behaviour, concurrently optimizes the variables describing the aerodynamic shape, the inner structure, and the actuation strategy. The aerodynamic shape is optimized for a longitudinally stable flying wing, which solely relies on morphing deflections to control its attitude. The morphing deflection can be varied along the span, enabling to attain optimized deformed shapes for any flight condition. To validate the concept and assess its structural characteristics and actuation capabilities, an experimental demonstrator was fabricated. The wing has a total span of 3.2m and a maximum chord length of 23cm. Its structural integrity was assessed through a wing up-bending test, permitting to both characterize its load-carrying capacity and validate the structural model. The actuation capability was assessed by measuring the deformed shapes through a digital image correlation system, enabling to successfully confirm the predictions obtained through a detailed FE model.

Topics: Design , Testing , Aircraft , Wings
Commentary by Dr. Valentin Fuster
2017;():V002T04A014. doi:10.1115/SMASIS2017-3832.

Controlled drug delivery (CDD) technology has received extensive attention in the past three decades due to numerous advantages of this technology when compared to the conventional methods. Despite recent efforts and substantial achievements, controlled drug releasing systems still face major challenges in practice, including chemical issues with synthesizing biocompatible drug containers and releasing the pharmaceutical compounds at the targeted location with a controlled time rate. In this work, we present experimentally-validated acoustic-thermoelastic mathematical modeling to show the feasibility of using shape memory polymers (SMPs) and focused ultrasound (FU) technology for designing a novel drug-delivery system. SMPs represent a new class of materials that have the ability of storing a temporary shape and returning to their permanent or original shape when subjected to external stimuli such as heat. FU is used as a trigger for noninvasively stimulating SMP-based drug capsules. FU has a superior capability to localize the heating effect, thus initiating the shape recovery process only in selected parts of the polymer. A multiphysics model is developed, which optimizes the design of a SMP-based CDD system using acoustic-thermoelastic analysis of a filament as the constituting base structure and quantifies its activation through FU. The analytical and numerical models are divided into three parts. The first part studies the acoustic behavior of SMPs using Khokhlov-Zabolotskaya-Kuznetsov (KZK) model. The equation solves for acoustic pressure field in a hybrid time-frequency domain using operator-splitting method and examines the effects of absorption, diffraction and nonlinear distortion on the propagating wave in the medium. The second part provides a numerical model based on Penne’s Bioheat equation to estimate the thermal field developed in SMPs as a result of focused acoustic pressure field. The third part provides a numerical framework to predict the mechanical stresses developed in SMPs under FU and consequent shape recovery. The mechanical model is formulated by a compressible neo-Hookean constitutive equation, which assumes the SMPs behave as a thermoelastic material and predicts the shape memory effect under FU. Experimental validation is performed using a FU transducer in a water tank. The recovery of thermally responsive SMPs under FU predicted by our model shows a good accordance with the experiments. The modeling results are used to optimize parameters such as nonlinear properties, input frequency, source power and dimensional effects to achieve maximum shape recovery.

Commentary by Dr. Valentin Fuster
2017;():V002T04A015. doi:10.1115/SMASIS2017-3838.

Biopsy involves removing a piece of tissues for further medical examination. Brain biopsy is generally performed using different techniques, such as open biopsy, stereotactic core biopsy, and needle biopsy. Open biopsy is the most common and the most invasive form of the brain biopsy. During the procedure, a piece of the skull is removed and the brain is exposed. Stereotactic core and needle biopsies are minimally invasive. In these procedures, a hole is usually drilled into the skull and a needle is inserted through the hole to extract the tissue. Brain biopsy has its risks and complications due to the vulnerability of the brain tissue. Although using needle or stereotactic biopsies reduce the risks, brain biopsy may cause swelling or bleeding in the brain, and in some cases, can result in infection, stroke, seizure or even coma. A needle biopsy with conventional needles involves pulling or pushing the cutting stylet inside the needle hollow body (cannula). The manual pulling and pushing procedure induces lateral movement of the needle, which increases the damage in brain tissue. The goal here is to completely remove the needle harmful lateral movement. In this work, design of smart biopsy needles is proposed and demonstrated by incorporating nitinol wires and springs to control the lateral movement of the cutting stylet. The first design comprises of two parts. The first part of the needle is a 360° tissue cutting stylet, and the second part is the cannula. The cutting stylet can slide inside the cannula and a nitinol wire is embedded at the end of the stylet and the end of the cannula. As the electric current is applied on the nitinol wire, it shrinks and pulls the cutting stylet. The second design is almost similar to the first design, but it has a 180° tissue cutting stylet with a similar actuating mechanism. The last design uses a nitinol torsion spring that is attached to the cutting stylet. It cuts tissue samples by activating the nitinol spring to rotate the cutting stylet.

Topics: Design , Brain , needles
Commentary by Dr. Valentin Fuster
2017;():V002T04A016. doi:10.1115/SMASIS2017-3853.

Respiratory diseases such as asthma or chronic obstructive pulmonary disorder (COPD) affect millions of people around the world. The most common treatment approach is to take an inhaled corticosteroid as needed with a dry-powder inhaler or a metered-dose inhaler. Unfortunately, rates of inhaler mishandling and misuse are staggeringly high and as a result, the majority of those suffering from asthma and COPD are not receiving proper treatment. There are a myriad of ways inhalers are mishandled and misused, but one significant challenge results from the timing miscoordination of the medicine dispersion and inhalation breath. To address this, the current study successfully demonstrates the feasibility of automating the timing of the medicine dispersion by the addition of a Shape Memory Alloy (SMA) actuator and a differential pressure sensor into the casing of a traditional metered-dose inhaler. To meet actuation requirements and reliably depress the inhaler cartridge, the SMA wire was routed around a set of miniature bearings within the casing of the inhaler. By demonstrating that a metered-dose inhaler may be actuated by SMA without a significant increase of its weight or size, this study provides a practical technological approach to reducing the improper treatment of asthma and COPD due to inhaler misuse.

Commentary by Dr. Valentin Fuster
2017;():V002T04A017. doi:10.1115/SMASIS2017-3891.

Patterned liquid crystal elastomer (LCE) has been shown to have significant promise in surface topography control. Large and diverse shapes and surface adaptive responses have been shown using LCE materials with patterned director profiles. Using various techniques, crystal orientation across the surface of the material as well as through the thickness can be achieved yielding the capability to design out-of-plane deformation. These topological features can be used as active flow effectors manipulating, among other things, drag on an object in cross-flow.

It is well known that surface topography can have a large effect on skin friction drag by effecting the boundary layer transition, separation, and interfering with the shedding of vortices. In regards to a cylinder in a cross-flow, spatially manipulating surface topography, and thus drag, in this way gives rise to forces exerted by the fluid on the body. An imbalance of forces due to non-uniform surface topography can then be used to control the cylinder.

Designing such a system requires optimization of the surface topography via optimization of the crystal orientation pattern over a wide range of environments. Key to this optimization, described in detail in the presented work, is an accurate material model validated against experimental data. By representing the strain energy of the material as a combination of contributions of the elastomer backbone and the liquid crystals separately, unique material properties can be properly modeled. This is achieved by combining a traditional isotropic 3 chain Arruda-Boyce hyperelastic equation modeling the elastomer backbone with an anisotropic extension modeling the patterned liquid crystals, resulting in an anisotropic hyperelastic material model. The model can then be used to predict the material response of various patterns and investigate the design space of possible surface topographies.

Commentary by Dr. Valentin Fuster
2017;():V002T04A018. doi:10.1115/SMASIS2017-3926.

Shape memory alloy (SMA) knitted actuators are a type of functional fabric that uses shape memory alloy wire as an active fiber within a knitted textile. Through intentional design of the SMA knitted actuator geometry, various two- and three-dimensional actuation motions, such as scrolling and contraction [1], can be accomplished. Contractile SMA knitted actuators leverage the unique thermo-mechanical properties of SMA wires by integrating them within the hierarchical knitted structure to achieve large distributed uniaxial contractions and variable stiffness behavior upon thermal actuation. During the knit manufacturing process, the SMA wire is bent into a network of interlacing adjacent loops, storing potential energy within the contractile SMA knitted actuator. Thermal actuation above the wire-specific austenite finish temperature leads to a partial recovery of the bending deformations, resulting in large distributed uniaxial contraction (15–40% actuation contraction observed) of the SMA knitted actuator. The achievable load capacity and %-actuation contraction are dependent on the geometric loop parameters of the contractile SMA knitted actuator. While exact descriptions of the geometric loop parameters exist, a reduction of the geometric complexity is advantageous for high-level contractile SMA knitted actuator design procedures. This paper defines a simple geometric measure, the non-dimensional knit density, and experimentally correlates the contractile SMA knitted actuator performance to this measure. The experimentally demonstrated dependency of relevant actuator metrics on the knit density and the wire diameter, suggests the usability of the simplified geometry definition for a high-level contractile SMA knitted actuator design.

Topics: Actuators , Design
Commentary by Dr. Valentin Fuster
2017;():V002T04A019. doi:10.1115/SMASIS2017-3943.

Black box design is a constraint driven design approach that distills essential elements of a physical process into inputs and outputs. This paper details the black box design implementation and validation of shape memory alloy (SMA) coil actuators as active members in a Watt I six bar avian-inspired wearable morphing angel wing mechanism. SMA coil actuators leverage the unique characteristics of high energy density SMA wire by providing a compact structural platform for large actuation displacement applications. The moderate force and displacement performance of low spring index coil actuators paired with their virtually silent actuation performance made them an attractive actuator solution to an avian-inspired wearable morphing wing mechanism for the University of Minnesota Department of Theatre Arts and Dance production of ‘Marisol’. The wing design constraints (extended span of 7.5 ft, a closed span of 3 ft) required a tailorable actuator system with capacity to perform at particular target force and strain metrics cyclically. A low spring index parameter study was conducted to facilitate an accelerated phase of design prototyping. The parameter study featured six SMA coil actuator prototypes made with 0.012” diameter Dynalloy Flexinol® wire of varying spring indexes (C = 2.5–4.9). The coil actuators were manufactured through a CNC winding process, shape set in a furnace at 450 °C for 10 minutes, and water quenched for hardening. A series of thermomechanical actuation tests were conducted to experimentally characterize the low spring index actuation performances. The coil actuation characterizations demonstrated increased force and decreased actuator displacement corresponding to decreased spring indexes. Scaling these results aided an accelerated design of an actuator system. The actuator system consisted of four C = 3.05 coil actuators wound with 0.02” diameter SMA that were integrated into each Watt I mechanism. The characterization of the force-displacement profiles for low index SMA coil actuators provides an effective empirical design strategy for scaling actuator performance to mechanical systems requiring moderate force, moderate displacement actuators.

Topics: Design , Wings
Commentary by Dr. Valentin Fuster
2017;():V002T04A020. doi:10.1115/SMASIS2017-3976.

Light-weight, compact actuators capable of delivering large linear stroke based compliant structures offer interesting potential for adaptive structures and robotics given their capability to carry a load and to be geometrically scalable. Furthermore, the utilization of compliant structures replacing mechanisms and moving parts offers the possibility for reducing losses due to friction. Solid state actuators have been proposed as a means to attain such capabilities with particular success for smart systems based on piezoelectric, shape memory, and electroactive polymer materials. Despite this success, smart material systems do not concurrently offer large strokes, high blocking force and wide response bandwidth. Recently, a new class of multi-stable structures that generate large linear strokes from twisting have been introduced. Furthermore, the snap-through action characterizing the changes between stable states of multi-stable systems has been shown to be a viable mechanism for inducing controlled actuation at high rates. In this paper, the novel design of a linear actuator adapted from twisting multi-stable structures is tailored to have geometric instability that is exploited to achieve large axial strokes under the action of small deformations from a single structural component. Finite element modeling is used for analysis of the structure, where parameter studies of composite layup and structure geometry are conducted to adjust equilibrium positions and stroke length of the actuator design. Different smart actuator topologies demonstrating the ability for compliant multi-stable systems are coupled with smart materials to produce large linear deformations and wide actuation bandwidth. The herein presented unconventional design serves as a useful linear actuator, as well as a load carrying component. The introduced multi-functional light-weight load-carrying actuators relevant for aerospace and robotics applications.

Topics: Actuators , Design
Commentary by Dr. Valentin Fuster
2017;():V002T04A021. doi:10.1115/SMASIS2017-4007.

In this contribution the conceptual development of a two-speed transmission utilizing coupling elements based on magnetorheological fluids (MRF) will be presented. The transmission concept is based on a mechanical power split. The transmission ratios are optimized for an appropriate utilization of MRF coupling elements. This transmission concept can be applied in several applications, like vehicles or industrial use. Besides, the electrical feeding power of the coupling elements will be investigated for certain scenarios considering the proposed transmission concept. MRF coupling elements provide a highly dynamical and continuously adjustable torque transmission. In combination with the MR fluid movement control to avoid viscous losses, a very energy efficient operation in contrast to conventional coupling elements can be achieved. For a reduction of the weight, space and feeding energy also a novel design with serpentine flux guidance will be introduced. Due to this design, combined arrangements of MRF coupling elements can be achieved, to create a very compact dual coupling element for the proposed transmission concept.

Commentary by Dr. Valentin Fuster
2017;():V002T04A022. doi:10.1115/SMASIS2017-4009.

Compared to clinic-based systems, rehabilitation robots designed for home use could enable increased accessibility and intensity of therapy for stroke survivors. To move upper extremity rehabilitation robots from the clinic to the home, the designs must become smaller, lighter, and less complex. One path to reducing the size of the robot’s hardware is to replace conventional actuators with smaller designs utilizing the unique properties of smart materials. As a first step towards reducing the size of upper extremity rehabilitation robots, this paper presents results from a characterization study of a prototype electrorheological fluid. The fluid’s dynamic yield stress was first measured using a modified controlled stress rheometer. A testbed was then developed to analyze the mechanical performance of a custom brake filled with the fluid. System parameters measured included braking torque at varying electric field strengths as well as the fluid’s speed of response. Maximum torque output was 4.80 N-m at an electric field strength of 3 kV/mm. Experimental results also indicate that the fluid’s activation and relaxation times will enable sufficient control bandwidth for the desired application. However, non-linear effects, such as field-dependent hysteresis, are significant and may require compensation from the controller supervising interaction between the robot and patient.

Commentary by Dr. Valentin Fuster

Structural Health Monitoring

2017;():V002T05A001. doi:10.1115/SMASIS2017-3780.

Traditionally, most mechanical testing is conducted on specimens of uniform cross-section and stress magnitude, or only a single position along the specimen length is of interest. Investigations of various stress levels therefore requires separate tests with a unique specimen at each stress level of interest. The impetus of the current work was to develop a method for the design and monitoring of a specimen that simultaneously experiences a continuum of stress magnitudes across various positions. A linearly-tapered specimen was developed and subjected to sinusoidal tension-tension fatigue until specimen failure, with the expectation that a record of damage exists along the length of the specimen due to the varying level of induced stress. Baseline and post-failure scans of x-ray diffraction, electrical resistance via four point probe, nano-indentation, eddy current, and geometric changes were compared. Attempts were made to characterize the pre- and post-test property behaviors as a function of the applied stress, which varied linearly along the specimen, and as a function of fatigue cycles, which were the same along the length of the specimen. The mechanisms of specimen damage due to fatigue cycling were investigated and analyzed to improve durability and damage tolerance understanding.

Topics: Damage
Commentary by Dr. Valentin Fuster
2017;():V002T05A002. doi:10.1115/SMASIS2017-3839.

Strain sensors are one of the most widely used transducers for structural health monitoring, since strain can provide rich information regarding structural integrity. Recently, it has been shown that thin film sensors that incorporate nanomaterials can be engineered to possess unique properties, such as flexibility, high sensitivity, and distributed sensing capabilities, to name a few. To date, a plethora of different nanomaterials have been explored for fabricating strain sensors, such as by using conductive polymers, metal nanowires, and carbon nanotubes, among others. The aim of this work is to leverage the unique properties of graphene to fabricate next-generation thin film strain sensors. While graphene exhibits impressive mechanical and electrical properties, it remains challenging to harness these properties for sensing, primarily because of difficulties associated with high-quality synthesis and to incorporate them in a scalable fashion. In this study, few-layered graphene nano-sheets (GNS) were first synthesized using a low-cost, liquid-phase exfoliation technique. Second, GNS was dispersed in an aqueous solution with a low-concentration polymer acting as the dispersing agent. Third, the dispersion was printed onto flexible polymer substrates to form complex geometrical patterns, such as strain rosettes. Then, the electrical and electromechanical properties of the printed thin film sensors were characterized. It was found that the strain rosettes could resolve multi-axial strains applied during coupon tests. Overall, the GNS-based strain sensors showed excellent signal-to-noise ratio, stable sensing performance, high strain sensitivity, and remarkable reproducibility.

Commentary by Dr. Valentin Fuster
2017;():V002T05A003. doi:10.1115/SMASIS2017-3840.

Embedded fiber Bragg grating (FBG) sensors are attractive for in-situ structural monitoring, especially in fiber reinforced composites. Their implementation in metallic structures is hindered by the thermal limit of the protective coating, typically a polymer material. The purpose of this study is to demonstrate the embedding of FBG sensors into metals with the ultimate objective of using FBG sensors for structural health monitoring of metallic structures. To that end, ultrasonic additive manufacturing (UAM) is utilized. UAM is a solid-state manufacturing process based on ultrasonic metal welding that allows for layered addition of metallic foils without melting. Embedding FBGs through UAM is shown to result in total cross-sectional encapsulation of the sensors within the metal matrix, which encourages uniform strain transfer. Since the UAM process takes place at essentially room temperature, the industry standard acrylate protective coating can be used rather than requiring a new coating applied to the FBGs prior to embedment. Measurements presented in this paper show that UAM-embedded FBG sensors accurately track strain at temperatures higher than 400 °C. The data reveals the conditions under which detrimental wavelength hopping takes place due to non-uniformity of the load transferred to the FBG. Further, optical cross-sectioning of the test specimens shows inhibition of the thermal degradation of the protective coating. It is hypothesized that the lack of an atmosphere around the fully-encapsulated FBGs makes it possible to operate the sensors at temperatures well above what has been possible until now. Embedded FBGs were shown to retain their coatings when subjected to a thermal loading that would result in over 50 percent degradation (by volume and mass) in atmospherically exposed fiber.

Commentary by Dr. Valentin Fuster
2017;():V002T05A004. doi:10.1115/SMASIS2017-3858.

Current acoustoelastic-based stress measurement techniques operate at the high-frequency, weakly-dispersive portions of the dispersion curves. The weak dispersive effects at such high frequencies allow the utilization of time-of-flight measurements to quantify the effects of stress on wave speed. However, this comes at the cost of lower sensitivity to the state-of-stress of the structure, and hence calibration at a known stress state is required to compensate for material and geometric uncertainties in the structure under test.

In this work, the strongly-dispersive, highly stress-sensitive, low-frequency flexural waves are utilized for stress measurement in structural components. A new model-based technique is developed for this purpose, where the acoustoelastic theory is integrated into a numerical optimization algorithm to analyze dispersive waves propagating along the structure under test. The developed technique is found to be robust against material and geometric uncertainties. In the absence of calibration experiments, the robustness of this technique is inversely proportional to the excitation frequency. The capabilities of the developed technique are experimentally demonstrated on a long rectangular beam, where reference-free, un-calibrated stress measurements are successfully conducted.

Topics: Stress , Waves
Commentary by Dr. Valentin Fuster
2017;():V002T05A005. doi:10.1115/SMASIS2017-3882.

This paper presents a pan-tilt sensor fusion platform for activity tracking and fall-detection which can work as a reliable surveillance system with long-term care function. A low cost thermal array sensor and a distance sensor are integrated together as the sensor module. The sensor module is installed on a pan-tilt orienting mechanism with two rotation degrees of freedom to increase the field of view while reducing the number of sensors used on-board. The performance of the sensor test platform is analyzed. The location of the indoor object as well as its size can be estimated based on a novel sensor fusion algorithm. The support vector machine (SVM) based machine learning algorithm is applied for fall detection. The preliminary experiment result shows a 95% accuracy to identify falling action from similar normal indoor activity such as sitting and picking up stuff.

Topics: Sensors
Commentary by Dr. Valentin Fuster
2017;():V002T05A006. doi:10.1115/SMASIS2017-3930.

Owing to the unique features of passive sensing, low cost, large detection range and wide field of view (FOV), the pyroelectric infrared (PIR) sensors are widely used for smart home applications based on motion detection, such as light control, intrusion detection. However, due to the pyroelectricity on which their sensing principles are based, PIR sensors cannot detect stationary objects, which confines their applications to advanced sensing systems, e.g. stationary occupancy sensing. To address this issue, this paper develops a novel chopped PIR (C-PIR) sensor for detecting the presence of both moving and stationary occupants, which consists of a chopper, a servo motor, a Fresnel lens, PIR sensing elements and a controller. Theoretical analysis is conducted to reveal the working principles of the proposed C-PIR sensor. A prototype of the C-PIR sensor is fabricated and experiments are conducted to find the optimal option of the chopper material, and the optimal values of the thickness, and the chopping frequency. Results show that the proposed C-PIR sensor can sense human presence no matter if the occupant is moving or not. In experiments, the preliminary prototype shows its detection range up to 4.0 m for stationary occupant sensing and 8.5 m for moving occupant sensing. Meanwhile, the C-PIR sensor maintains the same performance of the field of view as its traditional PIR sensor counterpart. Thus, the C-PIR sensor has great potential to provide accurate occupancy information for smart building energy management.

Topics: Sensors
Commentary by Dr. Valentin Fuster
2017;():V002T05A007. doi:10.1115/SMASIS2017-3936.

During the last decades, extensive research has been conducted on structural health monitoring (SHM) techniques based on the changes of coupled structure properties, e.g. piezoelectric impedance, which enjoys high detection sensitivity due to high-frequency actuation/sensing nature. However, the actual identification of fault locations and severities remains to be challenging owing to underdetermined underling mathematics. Recently, compressed sensing, a signal processing technique originally developed to recover signals from the compressed measurements, has shown its potential to address some of the mathematical challenges encountered in SHM practices. In this research, we morph the impedance-based SHM problem into a compressed sensing scheme such that the impedance change are used as measured data to reconstruct the damage locations and severities through convex optimization, e.g. l1 optimization. The proposed approach offers practical attractions of only requiring a small number of measurements and a short amount of computational time, and the results are promising if certain properties are fulfilled. Finally, the proposed approach is applied to and validated by several test problems.

Topics: Damage
Commentary by Dr. Valentin Fuster
2017;():V002T05A008. doi:10.1115/SMASIS2017-3941.

Recent advances in energy harvesting technologies have led to the development of self-powered monitoring techniques that are energy-efficient. This study presents an intelligent damage identification strategy for plate-like structures based on the data provided by a network of self-powered sensors that communicate through a pulse switching protocol, which has been demonstrated as an effective means for minimizing communication energy demands. The energy-aware pulse switching communication architecture uses single pulses instead of multi-bit packets for information delivery, resulting in discrete binary data. A system employing such an energy-efficient technology requires dealing with power budgets for sensing and communication of binary data, which leads to time delay constraints. In this paper, a novel machine learning framework incorporating low-rank matrix decomposition, pattern recognition, and a statistical approach is proposed to overcome challenges inherent in algorithm design for damage identification using time-delayed binary data. Performance and effectiveness of the proposed energy-aware damage identification strategy was examined for the case of a dynamically loaded plate. Damage states were simulated on a finite element model by reducing stiffness in a region of the plate. Results show that the presence and location of the damage can be effectively identified even with noisy features and missing data. The performance and applicability of the proposed localized damage detection strategy for plate-like structures using discrete time-delayed binary data from a novel wireless sensor network is thus demonstrated.

Commentary by Dr. Valentin Fuster
2017;():V002T05A009. doi:10.1115/SMASIS2017-3965.

Mechanically induced light emission, termed mechanoluminescence (ML) has been a potential candidate for stress sensing, stress visualization, damage detection and crack propagation applications. In this work, we demonstrate utilizing ML from elastic loading, termed elastico-mechanoluminescence (EML), for structural health monitoring and failure prediction applications. EML from ZnS:Cu phosphors impregnated in elastomeric matrix is shown to correlate with the structural health of the matrix as well as indicate impending failure of the matrix. Indicators for real-time monitoring to predict impeding failure are also identified. EML based SHM system can be implemented to monitor health of several existing engineering devices that depend on functional elastomeric components for reliable operation.

Commentary by Dr. Valentin Fuster
2017;():V002T05A010. doi:10.1115/SMASIS2017-3977.

Aerospace mechanical structures encounter various forms of damage throughout their operation due to mechanical stimuli. Structural health monitoring (SHM) is suggested as a way to actively check the integrity of a component by using a system of sensors. However, these conventional sensors can often require external power that is not always readily available in aerospace, thus the development of self-powered sensors could prove beneficial for SHM applications. In this study, the design of multifunctional mechano-luminescent-optoelectronic (MLO) composites strain sensor is suggested. The MLO composites sensor is composed of two transformative materials: 1) mechano-luminescent (ML) copper-doped zinc sulfide (ZnS:Cu) and 2) mechano-optoelectronic (MO) poly(3-hexylthiophene) (P3HT). ML ZnS:Cu emits light in response to mechanical stimuli. MO P3HT showed self-sensing capability by generating direct current (DC) sensor signal under light. First, ZnS:Cu ML crystals will be embedded in polydimethylsiloxane (PDMS) matrix to fabricate ZnS:Cu/PDMS elastomeric composites. ML light emission characteristics of ZnS:Cu/PDMS will be studied by subjecting the ZnS:Cu/PDMS to cyclic tensile strain loadings while videos are recorded of the light emission. The data are analyzed using a statistical factorial methodology so that a regression model to predict light emission based on loading strain and frequency can be calculated. Second, MO P3HT-based self-sensing thin films will be fabricated on glass slides using a spin-coating technique. Last, self-powered sensing capability of the MLO composites strain sensor will be validated by measuring DC voltage (DCV) in close proximity of the ZnS:Cu/PDMS subjected to cyclic tensile loadings.

Commentary by Dr. Valentin Fuster
2017;():V002T05A011. doi:10.1115/SMASIS2017-3980.

The objective of this study is to develop three dimensional (3D) impact self-sensing composites capable of localizing impact damage in through-the-thickness direction. The 3D impact self-sensing composites (3D-ISSC) are designed by embedding fracto-mechanoluminescent (FML) crystals in cells of honeycomb-cored fiber reinforced polymer (FRP) structural composites. FML crystals were shown to emit light resulting from cleavage of crystalline structures due to external mechanical stimuli. Unlike other conventional sensor networks, without supplying external electrical source, the 3D-ISSC is envisioned to monitor impact occurrences and detect damage. Instead, the emitted light will be utilized for informing severity of impact occurrences and 3D locations of the impact damage. First, FML europium-doped dibenzoylmethide triethylammonium (EuD4TEA) crystals are synthesized. Second, the synthesized EuD4TEA crystals are embedded in the honey-cored FRP structural composites to fabricate 3D-ISSC. Third, to validate its 3D self-sensing capability, Kolsky bar is employed to apply high strain-rate compressive loading to simulate impact occurrences while taking high-speed video footage for quantifying intensity of FML light emission through image processing technique.

Commentary by Dr. Valentin Fuster
2017;():V002T05A012. doi:10.1115/SMASIS2017-3981.

Railroads carry 40% of the U.S.’ freight tonnage. Railroad bridges are the most critical component of this network. Measuring transverse displacement of railroad bridges under train-crossing load is essential for the safe and cost-effective operation of railroad network. However, bridge displacement is difficult to collect in the field with traditional sensors due to the lack of fixed reference frame. Although reference-free sensors provide flexibility overcoming the aforementioned challenge, they often fail to capture pseudo-static components observed in timber bridges. This study proposes a novel reference-free sensing system to measure the total displacements of railroad bridges under train-crossing loads. A novel passive-servo electro-magnetic-induction (PSEMI) sensing technology provides accurate direct reference-free dynamic displacement measurement. Furthermore, researchers utilize two reference-free accelerometers to record inclination measurement and transform to pseudo-static displacement. Total bridge displacement is obtained by adding dynamic and pseudo-static responses together. Shake table experiments employing a bridge pier model excited by bridge displacements measured in the field has validated the effectiveness and accuracy of the novel sensing system.

Commentary by Dr. Valentin Fuster
2017;():V002T05A013. doi:10.1115/SMASIS2017-3999.

Reliable operation of next generation high-speed complex structures (e.g. hypersonic air vehicles, space structures, and weapons) relies on the development of microsecond structural health monitoring (μSHM) systems. High amplitude impacts may damage or alter the structure, and therefore change the underlying system configuration and the dynamic response of these systems. While state-of-the-art structural health monitoring (SHM) systems can measure structures which change on the order of seconds to minutes, there are no real-time methods for detection and characterization of damage in the microsecond timescales.

This paper presents preliminary analysis addressing the need for microsecond detection of state and parameter changes. A background of current SHM methods is presented, and the need for high rate, adaptive state estimators is illustrated. Example observers are tested on simulations of a two-degree of freedom system with a nonlinear, time-varying stiffness coupling the two masses. These results illustrate some of the challenges facing high speed damage detection.

Commentary by Dr. Valentin Fuster

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