ASME Conference Presenter Attendance Policy and Archival Proceedings

2018;():V002T00A001. doi:10.1115/SMASIS2018-NS2.

This online compilation of papers from the ASME 2018 Conference on Smart Materials, Adaptive Structures and Intelligent Systems (SMASIS2018) 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presenter attendance policy, if a paper is not presented at the Conference by an author of the paper, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.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

Mechanics and Behavior of Active Materials

2018;():V002T02A001. doi:10.1115/SMASIS2018-7952.

Electroactive polymers are a class of materials capable of reallocating their shape in response to an electric field while also having the ability to harvest electrical energy when the materials are mechanically deformed. Electroactive polymers can therefore be used as sensors, actuators, and energy harvesters. The parameters for manufacturing flexible electroactive polymers are complex and rate limiting due to number of steps, their necessity, and time intensity of each step. Successful 3D printing manufacturing processes for electroactive polymers will allow for scalability and flexibility beyond current limitations, improving the field, opening additional manufacturing possibilities, and increasing output. The goal for this research is to use additive manufacturing techniques to print conductive and dielectric substrates for building flexible circuits and sensors. Printing flexible conductive layers and substrates together allows for added creativity in design and application. In this work we have successfully demonstrated additive production of a simple flexible circuit using exclusively additive manufacturing.

Topics: Sensors , Circuits
Commentary by Dr. Valentin Fuster
2018;():V002T02A002. doi:10.1115/SMASIS2018-7964.

An electroactive polymer is a material capable of changing its size and shape when an electric field is present. It is composed of a thin film of dielectric elastomer and two electrodes placed on the top and bottom of the dielectric material. Since the rediscovery of their capabilities, electroactive polymers have been proposed as novel materials for use in numerous fields such as in bioengineering, electronics, hydraulics, and aerospace. It has been demonstrated that the actuation potential of electroactive polymer dielastomers can be significantly enhanced by mechanically pre-straining the material prior to application of an electric field. Application of uniform pre-strain is critical for uniform actuation and is challenging to achieve. This research details methods for constructing an automated uniform stretcher that resulted in the production of a LabView controlled iris stretcher for flexible materials. The high torque stretcher was capable of pre-straining materials with a minimum diameter of 1 inch mm) to a maximum diameter of 16 inches. The stretcher calculates the percent strain and has adjustable speed control through a high torque micro-stepper motor and controller. The stretcher’s capabilities were demonstrated on materials within varying tensile strengths up to 725 psi.

Commentary by Dr. Valentin Fuster
2018;():V002T02A003. doi:10.1115/SMASIS2018-7984.

Magnetorheological fluid is a special smart fluid which can show different rheological properties under different magnetic flux densities due to its magnetically sensitive structure. This makes the fluid able to be manipulated and semi-actively controlled for various applications such as dampers, clutches and brakes. To provide an effective damping it is necessary to create an appropriate control algorithm. In order to design a structure with magnetorheological fluid and to get an idea for a control approach, the physics of the fluid motion has to be modelled. Computational Fluid Dynamics is an effective tool to model any fluid behaviour or any fluid involved structure. For magnetorheological devices, despite number of numerical models available in the literature, a befitting model is not yet presented. In this study a mapped rheological model is proposed and used in a magnetorheological damper simulation. The results are compared with other models and experimental data. It is shown that the new mapped model is effective and better than old approaches. It also showed a good agreement with the experimental data.

Commentary by Dr. Valentin Fuster
2018;():V002T02A004. doi:10.1115/SMASIS2018-7987.

An exact solution that investigates the pre-buckling characteristics of nonlocal carbon nanotube (CNT)-based mass sensor subjected to thermal load under clamped-clamped boundary condition is determined. The uniform temperature rise is utilized to study thermal effects on the sensitivity of the mechanical resonator in pre-buckling configuration. Using Eringen’s nonlocal theory, along with the Hamilton’s principle, the governing equations considering small scale and geometric nonlinearity are derived. The influences of important parameters including nonlocal parameter, temperature change, length, and diameter of the CNT on the pre-buckling behavior and frequency shift of the CNT-based mass detector are also studied. Results show that these parameters have significant impact on the dynamic characteristics of the CNT-mass sensor.

Commentary by Dr. Valentin Fuster
2018;():V002T02A005. doi:10.1115/SMASIS2018-8005.

This paper presents the design, fabrication, and operation of a chemo-mechatronic system that changes its geometry and electrical functionality in the presence of specific chemical signals. To accomplish this, we integrated a protein hydrogel with an aluminum substrate and flexible circuit in a low-profile laminate. To demonstrate the concept, we have built and tested a sensor that lights an LED when actuated in the presence of polyethylene glycol (PEG).

Commentary by Dr. Valentin Fuster
2018;():V002T02A006. doi:10.1115/SMASIS2018-8011.

Dielectric electroactive polymers are materials capable of mechanically adjusting their volume in response to an electrical stimulus. However, currently these materials require multi-step manufacturing processes which are not additive. This paper presents a novel 3D printed flexible dielectric material and characterizes its use as a dielectric electroactive polymer (DEAP) actuator. The 3D printed material was characterized electrically and mechanically and its functionality as a dielectric electroactive polymer actuator was demonstrated. The flexible 3-D printed material demonstrated a high dielectric constant and ideal stress-strain performance in tensile testing making the 3-D printed material ideal for use as a DEAP actuator. The tensile stress-strain properties were measured on samples printed under three different conditions (three printing angles 0°, 45° and 90°). The results demonstrated the flexible material presents different responses depending on the printing angle. Based on these results, it was possible to determine that the active structure needs low pre-strain to perform a visible contractive displacement when voltage is applied to the electrodes. The actuator produced an area expansion of 5.48% in response to a 4.3 kV applied voltage, with an initial pre-strain of 63.21% applied to the dielectric material.

Commentary by Dr. Valentin Fuster
2018;():V002T02A007. doi:10.1115/SMASIS2018-8050.

Shape Memory Alloys (SMAs), known as an intermetallic alloys with the ability to recover its predefined shape under specific thermomechanical loading, has been widely aware of working as actuators for active/smart morphing structures in engineering industry. Because of the high actuation energy density of SMAs, compared to other active materials, structures integrated with SMA-based actuators has high advantage in terms of tradeoffs between overall structure weight, integrity and functionality. The majority of available constitutive models for SMAs are developed within infinitesimal strain regime. However, it was reported that particular SMAs can generate transformation strains nearly up to 8%–10%, for which the adopted infinitesimal strain assumption is no longer appropriate. Furthermore, industry applications may require SMA actuators, such as a SMA torque tube, undergo large rotation deformation at work. Combining the above two facts, a constitutive model for SMAs developed on a finite deformation framework is required to predict accurate response for these SMA-based actuators under large deformations.

A three-dimensional constitutive model for SMAs considering large strains with large rotations is proposed in this work. This model utilizes the logarithmic strain as a finite strain measure for large deformation analysis so that its rate form hypoelastic constitutive relation can be consistently integrated to deliver a free energy based hyper-elastic constitutive relation. The martensitic volume fraction and the second-order transformation strain tensor are chosen as the internal state variables to characterize the inelastic response exhibited by polycrystalline SMAs. Numerical experiments for basic SMA geometries, such as a bar under tension and a torque tube under torsion are performed to test the capabilities of the newly proposed model. The presented formulation and its numerical implementation scheme can be extended in future work for the incorporation of other inelastic phenomenas such as transformation-induced plasticity, viscoplasticity and creep under large deformations.

Commentary by Dr. Valentin Fuster
2018;():V002T02A008. doi:10.1115/SMASIS2018-8068.

Shape memory alloys (SMAs) are unique materials capable of undergoing a thermo-mechanically induced, reversible, crystallographic phase transformation. As SMAs are utilized across a variety of applications, it is necessary to understand the internal changes that occur throughout the lifetime of SMA components. One of the key limitations to the lifetime of a SMA component is the response of SMAs to fatigue. SMAs are subject to two kinds of fatigue, namely structural fatigue due to cyclic mechanical loading which is similar to high cycle fatigue, and functional fatigue due to cyclic phase transformation which typical is limited to the low cycle fatigue regime. In cases where functional fatigue is due to thermally induced phase transformation in contrast to being mechanically induced, this form of fatigue can be further defined as actuation fatigue. Utilizing X-ray computed microtomography, it is shown that during actuation fatigue, internal damage such as cracks or voids, evolves in a non-linear manner. A function is generated to capture this non-linear internal damage evolution and introduced into a SMA constitutive model. Finally, it is shown how the modified SMA constitutive model responds and the ability of the model to predict actuation fatigue lifetime is demonstrated.

Commentary by Dr. Valentin Fuster
2018;():V002T02A009. doi:10.1115/SMASIS2018-8091.

Future manned space missions will require thermal control systems that can adapt to larger fluctuations in temperature and heat flux that exceed the capabilities of current state-of-the-art systems. These missions will demand novel space radiators that can vary the heat rejection rate of the system to maintain the crew cabin at habitable temperatures throughout the entire mission. Current systems can provide a turndown ratio (defined as the ratio of maximum to minimum heat rejection) of 3:1 under adverse conditions. However, future missions are projected to demand thermal control systems that can provide a turndown ratio of more than 6:1. A novel radiator concept, known as the morphing radiator, varies the system heat rejection rate by altering the shape of the radiator that is exposed to space. This shape change is accomplished through the use of shape memory alloys, a class of active materials that exhibit thermomechanically-driven phase transformations and can be used as both sensors and actuators in thermal control applications. In past efforts, prototype morphing radiators have been tested in a relevant thermal environment, demonstrating the feasibility and scalability of the concept. This work summarizes the progress towards testing a high-performance morphing radiator in a relevant thermal environment and details the development of an efficient numerical model that predicts the mechanical response of an arbitrary morphing radiator configuration due to changes in temperature. Model predictions are then validated against previous experimental results, demonstrating the usefulness of the model as a design tool for future morphing radiator prototypes.

Topics: Alloys , Shapes
Commentary by Dr. Valentin Fuster
2018;():V002T02A010. doi:10.1115/SMASIS2018-8131.

Bone is a highly adaptive biological structure. Following Wolff’s law, bone realigns and grows to adapt to its mechanical environment. This leads to structural heterogeneity of trabecular bone and orthotropic symmetry of the elastic properties. Determining the bone alignment and material properties for living patients is difficult and involves implantation of force and displacement sensors on the bone to determine the compliance and stiffness properties. Micro-computed tomography along with finite element modeling have been limited to the vertebrae of donor cadavers to evaluate trabecular architecture, material properties, and density. Here, an adaptive structure topology optimization algorithm is presented and used to predict trabecular architecture. The algorithm predicts the optimal structure by minimizing the global compliance. The lumbar 1 (L1) vertebra is used as an example. Loads common to L1 vertebrae are applied and bone volume fraction measurements that can be taken easily from living patients through bone mineral density scans are used as the only inputs. The mathematical model is an adaptation of “99 Line Topology Optimization Code Written in Matlab” developed by Sigmund (2001). Bone is locally assumed to be isotropic with an elastic modulus of 13 GPa and the Poisson ratio of 0.3 applied to each element. The resulting structural heterogeneity results in global orthotropic relations. The model uses bone volume fraction and the loading orientation as inputs and gives the corresponding ideal bone structure geometry as an output. The trabecular structure can be predicted solely from the results of a bone mineral density scan. Finite element analysis of the optimized structure is then conducted and the global material properties are determined. While this model is for two-dimensional examples representing planes within the vertebral bone, it is extended to three-dimensional modeling to develop the cortical bone geometry and define the total volume. Matlab is then used to run the topology optimization simulation. The ideal structure is defined by optimizing for a prescribed displacement field of the system following the implementation of a gradient descent optimization method. The results are compared to published values from a combined experimental and numerical procedure. The procedure on sectioned vertebrae reported average ratios between elastic moduli of E1/E2 = 5.2, E1/E3 = 8.8, and E2/E3 = 1.4. Results between the models and the previously published data yield similar transversely isotropic symmetry in the elastic moduli of trabecular bone. However, the elastic moduli ratios are not quite in agreement. Improving the accuracy of the boundary conditions and loading of the finite element model may improve the correlation between the optimization models and published data.

Commentary by Dr. Valentin Fuster
2018;():V002T02A011. doi:10.1115/SMASIS2018-8166.

Dielectric electroactive actuators (DEAs) are polymer materials capable of reallocating their shapes mechanically due to an electric stimulus [1]. They can also be used as sensors by producing an electrical change from an induced mechanical deformation [2]. However, production of these materials using traditional manufacturing methods is a challenging process. The use of additive manufacturing promises to be an improved method to overcome those challenges. In addition, selection of dielectric materials that can function as DEAs and are capable of being produced through additive manufacturing is challenging.

The actuation capabilities of the DEA depend heavily on the electrical and mechanical material properties of the dielectric material used to build it, and not all dielectric materials have the capacity to function as DEAs. The likelihood of a material functioning as a DEA is difficult to predict due to the large number of variables. Therefore, this paper introduces a simple method for comparing materials, particularly 3-D printed materials for their viability to be used as DEAs.

The study proposes a method to compare 3-D printable materials by using coefficients calculated from the materials’ electromechanical properties. This value is then compared to an ideal DEA material. The higher the value, the better the 3-D printable material will be in comparison to a selected optimal DEA material. The coefficient is based on a linear elastic model that describes the strain of the material in relation to the electromechanical pressure applied as a result of supplied voltage.

This study tested three materials using a quantitative method along with experimental verification. The study demonstrates the relationship between the predictive coefficients and the physical actuation responses with disc-type actuators providing a simple method for predicting actuation potential of 3-D printable DEA material candidates.

Commentary by Dr. Valentin Fuster
2018;():V002T02A012. doi:10.1115/SMASIS2018-8168.

Shape memory alloys (SMAs) have tremendous potential use as actuators in mechanical systems due to their high specific energy density. Large recovery stresses can be generated when Nickel Titanium (NiTi), the most widely used SMA, undergoes constrained recovery where it is held in a deformed geometry and heated from a detwinned martensite phase to austenite phase. Recent experimental results have found that residual stresses can also be generated in NiTi after returning to a low temperature geometrically constrained state. This paper presents experimental results performed on NiTi wire samples where wire was: 1) deformed from a low temperature twinned martensite state to produce a strain that would be recoverable in an unloaded state 2) held at that strain state and heated above the austenite finish transition temperature and then cooled back below the martensite transition finish temperature while recording the forces generated. It was found that a residual load was produced in the low temperature state. Results from further testing beyond this point showed repeatability with application of small and large strains. Post constrained recovery stresses have the potential to be used to generate residual stresses in structures in a low energy, un-actuated state with a remaining potential for thermal actuation.

Commentary by Dr. Valentin Fuster
2018;():V002T02A013. doi:10.1115/SMASIS2018-8190.

Fracture behavior in nickel-titanium (NiTi) shape memory alloys (SMAs) subjected to mode-I, isothermal loading is studied using finite element analysis (FEA). Compact tension (CT) SMA specimen is modeled in Abaqus finite element suite and crack growth under displacement boundary condition is investigated for plane strain and plane stress conditions. Parameters for the SMA material constitutive law implemented in the finite element setup are acquired from characterization tests conducted on near-equiatomic NiTi SMA. Virtual crack closure technique (VCCT) is implemented where crack is assumed to extend when the energy release rate at the crack-tip becomes equal to the experimentally obtained material-specific critical value. Load-displacement curves and mechanical fields near the crack-tip in plane strain and plane stress cases are examined. Moreover, a discussion with respect to the crack resistance R-curves calculated using the load-displacement response for plane strain and plane stress conditions is presented.

Commentary by Dr. Valentin Fuster
2018;():V002T02A014. doi:10.1115/SMASIS2018-8234.

This paper presents the development process of an electrically insulating and liquid-impermeable coating for piezoelectric actuators. Against the background of flow investigations of an adaptive airfoil in a water tunnel the adaptive lip including PZT-ceramics for the active lip deformation must be insulated and sealed up against the ingress of moisture. Due to high electric field strength of 2 kV/mm between electrodes of multilayer actuators any ingress of moisture would lead to a reduction of the dielectric strength and may cause a short circuit. In order to prevent failure of the adaptive lip the electrical connections of the actuators have to be insulated by a waterproof coating. A service life of at least 107 load cycles at a frequency of 100 Hz is required for the actuators. Therefore the coating should be as ductile as possible otherwise it could crack and water could diffuse into the actuators. That is why the yield strength of the coating has to be higher than of the actuators, which is 0.3 %. For the investigation of the waterproofness several samples are coated with different materials in various processes. First the actuators are moulded in epoxy resin and then a diffusion-resistant PVF-foil is applied. After a screening of different materials, an additional coating with a two-component tar-epoxy resin in combination with a gold coating applied by a PVD process seems to be the most suitable process. Another promising waterproof coating is the atomic layer deposition (ALD). It is a slightly changed chemical vapor deposition (CVD) and referring to the studies of Abdulagatov et al. an ALD of aluminum oxide (Al2O3) and titanium dioxide (TiO2) can slow down the corrosion of static copper specimens in water for ∼80 days [1]. Through a redrying procedure during test intermissions an increased underwater service life of the piezoelectric actuators is achieved.

Commentary by Dr. Valentin Fuster
2018;():V002T02A015. doi:10.1115/SMASIS2018-8243.

This study uses the finite element method to analyze the sliding contact behavior between a rigid cylinder and a shape memory alloy (SMA) semi-infinite half-space. An experimentally validated constitutive model is used to capture the pseudoelastic effect exhibited by these alloys. Parametric studies involving the maximum recoverable transformation strain and the transformation temperatures are performed to analyze the effects that these parameters have on the stress fields during indentation and sliding contact. It is shown that, depending on the amount of recoverable transformation strain possessed by the alloy, a reduction of almost 40 % of the maximum stress in the pseudoelastic half-space is achieved when compared to the maximum stress in a purely elastic half-space. The studies also reveal that the sliding response is strongly temperature dependent, with significant residual stress present in the half-space at temperatures below the austenitic finish temperature.

Commentary by Dr. Valentin Fuster
2018;():V002T02A016. doi:10.1115/SMASIS2018-8244.

We present a mathematical model to guide and interpret ongoing Cell-in-Gel experiments, where isolated cardiac myocytes are embedded in a constraining viscoelastic hydrogel, to study mechano-chemo-transduction mechanisms at the single cell level. A recently developed mathematical model, based on the elastic Eshelby inclusion problem, is here extended to account for viscoelasticity of the inclusion (cell) and the matrix (gel). This provides a tool to calculate time-dependent 3D stress and strain fields of a single myocyte contracting periodically inside a viscoelastic matrix, which is used to explore the sensitivity of the cell’s mechanical response to constitutive properties and geometry. A parametric study indicates that increased gel crosslink concentration significantly alters the strain and stress fields inside the cell and creates an increased time-lag in the mechanical response of the cell during contraction.

It is also found that autoregulation at the cellular level in response to afterload, potentially in the form of increased cell stiffness, has a strong influence on cell contraction.

Commentary by Dr. Valentin Fuster

Structural Health Monitoring

2018;():V002T05A001. doi:10.1115/SMASIS2018-7908.

The focus of this study was to apply a robust inspection technique for monitoring damage nucleation and propagation in 7075 aluminum alloy specimens exposed to cyclic loading. A previously developed specimen, linearly tapered in width along the length, was subjected to a sinusoidal tension-tension load while conductivity and strain were measured in-situ. Ex-situ measurements of modulus, hardness, surface potential, digital image correlation strain field, and neutron diffraction were made as a function of fatigue cycles. It is hypothesized that varying levels of induced stress along the length due to equal-force but varying area along the length will create a record of damage which can be probed to intuit a temporal history for the specimen. Baseline, intermediate, and failure sensor measurements for several specimens were compared and analyzed as a function of applied stress (varied linearly along the length) and fatigue cycles (constant). Mechanisms of damage nucleation and propagation due to fatigue cycling are discussed with an emphasis on which inspection methods are most promising for improving structural durability and state monitoring.

Commentary by Dr. Valentin Fuster
2018;():V002T05A002. doi:10.1115/SMASIS2018-7936.

Structural health monitoring (SHM) of high-rate, mechanical systems in dynamically harsh environments presents many challenges over traditional SHM applications. Damage in these systems must be detected and quantified in tens to hundreds of microseconds in order to have sufficient time to react and mitigate damage. The computation speeds and robustness of sliding mode observers (SMOs) for state, parameter, and disturbance estimation for linear and nonlinear systems make them an attractive approach for real-time SHM of high-rate systems. This paper investigates a novel SMO combined with a recursive least squares parameter estimator to detect and track changing system parameters. The observer is simulated on a one degree-of-freedom system with time-varying model parameters to mimic damage. This paper focuses on practical considerations for SMOs for high-rate systems, such as the effects of measurement noise and sampling rates on the estimator’s accuracy and convergence speeds.

Commentary by Dr. Valentin Fuster
2018;():V002T05A003. doi:10.1115/SMASIS2018-7951.

An identification module is designed and studied to detect and evaluate the cracks at the welding joint area using a new smart coating sensor and entropy measurement. A new piezoelectric composite coating is applied at a welding joint to possibly charge the wireless data transmission module as an energy harvester. It also sends warning and dynamic signals for crack evaluation when the crack damage occurs. More specifically, entropy calculation is introduced to quantify the weak perturbations, which is caused by the material nonlinearity and crack breathing at the crack tip and hidden in the signal. In this paper, a finite element model (FEM) of a welded beam experiencing dynamic base motion is established as an example. The effects of material nonlinearity and crack breathing on structural dynamics response are simulated by creating nonlinear material property around the crack area and contact pair of crack walls, respectively. After obtaining the time domain vibration signal, crack severity is quantified using Sample Entropy. It is concluded that, even at very early stages of 5% of the beam thickness for the crack depth, the entropy variation is significant for a damaged beam compared with the healthy one.

Commentary by Dr. Valentin Fuster
2018;():V002T05A004. doi:10.1115/SMASIS2018-7965.

Polymers modified with conductive nanofillers have recently received considerable attention from the research community because of their deformation-dependent electrical resistivity. Known as piezoresistivity, this self-sensing capacity of nanocomposites has much potential for structural health monitoring (SHM). However, making effective use of the piezoresistive effect for SHM necessitates having a good understanding of the deformation-resistivity change relationship in these materials. While much insightful work has been done to model and predict the piezoresistive effect, many existing models suffer from important limitations such as being limited to microscales, over-predicting piezoresistive responses, and not considering complex deformations. We herein address these limitations by developing tensor-based piezoresistivity constitutive relations. The supposition of this approach is that resistivity changes due to small deformations can be treated as isotropic and be completely described by only two piezoresistive constants — one associated with volumetric strains and a second associated with shear strains. These piezoresistive constants can easily be discerned from simple experiments not unlike the process of determining elastic constants. We demonstrate the potential of this approach by deriving these piezoresistive constants for an experimentally-validated analytical model in the existing literature. This work can enable much more accurate and easily-obtained piezoresistive relations thereby greatly facilitating the potential of resistivity change-based SHM.

Commentary by Dr. Valentin Fuster
2018;():V002T05A005. doi:10.1115/SMASIS2018-7977.

Engineering systems subject to high-rate extreme environments can often experience a sudden plastic deformation during a dynamic event. Examples of such systems include civil structures exposed to blast or aerial vehicles experiencing impacts. The change in configuration through deformation can rapidly lead to catastrophic failures resulting in intolerable losses in investments or human lives. A solution is to conduct fast system estimation enabling real-time decisions, in the order of microseconds, to mitigate such high-rate changes. To do so, we propose a model-driven observer coupled with a data-driven adaptive wavelet neural network to provide real-time stiffness estimations to continuously update a system’s model. This real-time system identification method offers adaptability of the system’s parameters to unforeseeable changes. The results of the simulations demonstrate accurate stiffness estimations in milliseconds for three different excitation conditions for a one degree-of-freedom spring, mass, and damper system with variable stiffness.

Commentary by Dr. Valentin Fuster
2018;():V002T05A006. doi:10.1115/SMASIS2018-7997.

Nondestructive inspection (NDI) is an effective technique to inspect, test, or evaluate the integrity of materials, components, and structures without interrupting the serviceability of a system. Despite recent advances in NDI techniques, most of them are either limited to sensing structural response at their instrumented locations or require multiple sensors and measurements to localize damage. In this study, a new NDI system that could achieve distributed sensing using a single measurement was investigated. Here, piezoresistive carbon nanotube (CNT)-polymer thin film sensors connected in a transmission line setup were interrogated using electrical time-domain reflectometry (ETDR). In ETDR, an electromagnetic signal is sent from one end of the transmission line. When the signal encounters the sensor, it can partially reflect and be captured at the same point. The characteristics of the reflected signal depend on the sensor’s impedance, which is correlated to structural response, deformation, or damage. The advantage of this is that distributed sensing along the entire transmission line can be achieved using a single measurement point. To validate this concept, CNT-polymer thin films that were integrated with a transmission line are subjected to uniaxial tensile strains applied using a load frame. The ETDR signals were analyzed to assess the system’s sensing performance.

Commentary by Dr. Valentin Fuster
2018;():V002T05A007. doi:10.1115/SMASIS2018-8008.

Conductive nanofiller-modified composites have received a lot of attention from the structural health monitoring (SHM) research community in recent years because these materials are piezoresistive (i.e. they have deformation and damage-dependent electrical conductivity) and are therefore self-sensing. To date, the vast majority of work in this area has utilized direct current (DC) interrogation to identify and/or localize damage. While this approach has been met with much success, it is also well known that nanofiller-modified composites possess frequency-dependent electrical behavior. This behavior can be roughly modeled as a parallel resistor-capacitor circuit. However, much less work has been done to explore the potential this frequency-dependent behavior for damage detection. To this end, the work herein presented covers some preliminary results which leverage high-frequency electrical interrogation for damage detection. More specifically, carbon nanofiber (CNF)/epoxy specimens are produced and connected to an external inductor in both series and parallel configurations. Because the CNF/epoxy electrically behaves like a resistor-capacitor circuit, the inclusion of an inductor enables electrical resonance to be achieved. Changes in resonant frequency are then used for rudimentary damage detection. These preliminary results indicate that the potential of SHM via the piezoresistive effect in nanofiller-modified composites can be considerably expanded by leveraging alternating current (AC) interrogation and resonant frequency principles.

Commentary by Dr. Valentin Fuster
2018;():V002T05A008. doi:10.1115/SMASIS2018-8012.

Total Knee Replacement (TKR) is an important and in-demand procedure for the aging population of the United States. In recent decades, the number of TKR procedures performed has shown an increase. This pattern is expected to continue in the coming decades. Despite medical advances in orthopedic surgery, a high number of patients, approximately 20%, are dissatisfied with their procedure outcomes. Common causes that are suggested for this dissatisfaction include loosening of the implant components as well as infection. To eliminate loosening as a cause, it is necessary to determine the state of the implant both intra- and post-operatively. Previous research has focused on passively sensing the compartmental loads between the femoral and tibial components. Common methods include using strain gauges or even piezoelectric transducers to measure force. An alternative to this is to perform real-time structural health monitoring (SHM) of the implant to determine changes in the state of the system. A commonly investigated method of SHM, referred to as the electromechanical impedance (EMI) method, involves using the coupled electromechanical properties of piezoelectric transducers to measure the host structure’s condition. The EMI method has already shown promise in aerospace and infrastructure applications, but has seen limited testing for use in the biomechanical field. This work is intended to validate the EMI method for use in detecting damage in cemented bone-implant interfaces, with TKR being used as a case study to specify certain experimental parameters. An experimental setup which represents the various material layers found in a bone-implant interface is created with various damage conditions to determine the ability for a piezoelectric sensor to detect and quantify the change in material state. The objective of this work is to provide validation as well as a foundation on which additional work in SHM of orthopedic implants and structures can be performed.

Commentary by Dr. Valentin Fuster
2018;():V002T05A009. doi:10.1115/SMASIS2018-8035.

Piezoresistive strain sensors can be manufactured by embedding carbon nanotubes (CNTs) in an insulating polymer matrix, by taking advantage of CNTs superior electromechanical properties. In particular, the electromechanical properties find their roots in the conductive network formed by the randomly dispersed CNTs, through which the current can flow. When a mechanical strain occurs the conductive network configuration varies, changing the overall material conductivity. In this study this concept is being exploited to form a CNTs-based functional paint that allows to monitor ultra-large structural areas, in multiple directions, with an easy to assemble and processing approach. In particular, CNTs are dispersed in a PolymethylMethacrylate (PMMA) matrix following a carefully designed process to achieve a proper viscosity for direct painting onto a large in scale structure. Electromechanical tests are performed to characterize the piezoresistive behaviour of the coating in static and dynamic loading conditions. The results showed the great sensitivity of the coating to strain. The proposed approach to directly paint a sensitive coating onto the structure to be monitored has the advantages of: ultra-low weight, direct contact with the structure to be monitored and an extremely simple installation procedure.

Commentary by Dr. Valentin Fuster
2018;():V002T05A010. doi:10.1115/SMASIS2018-8112.

Passive infrared (PIR) sensors are the most popular deployed sensors in building lighting control for individual presence detection. However, PIR sensors are motion detectors in nature, responding only to incident radiation variation, which lead to false negative detections, inaccurate occupancy estimation, and uncomfortable lighting swings, short lifetime of the equipment, and waste of energy. In this study, a shutter driven by a Lavet motor PIR (LAMPIR) sensor is developed for presence detection for both stationary and moving occupants. Building off our previous work on chopped PIR (C-PIR) and rotationally-chopped PIR (Ro-PIR) sensors, Lavet motor, a single-phase electro-mechanical vibrator, is introduced, which has many advantages over traditional servo motors and stepper motors in terms of power consumption, size, weight and noise level. Driven by pulsed signal from a microcontroller unit (MCU), the electro-mechanical vibrator drives a semi-transparent long-wave infrared (LWIR) optical shutter to shutter the field of view (FOV) of a PIR sensor periodically. Output voltage generated by a LAMPIR senor for occupied and unoccupied scenarios can be monitored and analyzed to identify presence accurately. Parametric studies are conducted to find the optimal setting of driving signal frequency, shutter width and shuttering period. The LAMPIR sensor reaches an accuracy of 100% for detecting stationary occupants up to a range of 4.5 m and moving occupants up to a range of 10 m, which improves the detection range of both C-PIR and Ro-PIR sensors (4.0 m for stationary and 8.0 m for moving occupancy detection). LAMPIR has a FOV of 90° in horizontal and 100° in vertical, which is reasonable for most applications. For a 17-hour-long presence detection test, LAMPIR can reach an accuracy of 93.52% to classify unoccupied, stationary and moving occupant scenarios. More importantly, the average power consumption of LAMPIR is 0.19 W, which is 82% less than that of the C-PIR sensor and 89% less than that of the Ro-PIR sensor.

Topics: Sensors
Commentary by Dr. Valentin Fuster
2018;():V002T05A011. doi:10.1115/SMASIS2018-8182.

In many structural applications the use of composite material systems in both retrofit and new design modes has expanded greatly. The performance benefits from composites such as weight reduction with increased strength, corrosion resistance, and improved thermal and acoustic properties, are balanced by a host of failure modes whose genesis and progression are not yet well understood. As such, structural health monitoring (SHM) plays a key role for in-situ assessment for the purposes of performance/operations optimization, maintenance planning, and overall life cycle cost reduction. In this work, arrays of fiber Bragg grating optical strain sensors are attached to glass-epoxy solid laminate composite specimens that were subsequently subjected to specific levels of fully reversed cyclic loading. The fatigue loading was designed to impose strain levels in the panel that would induce damage to the laminate at varying numbers of cycles. The objectives of this test series were to assess the ability of the fiber Bragg grating sensors to detect fatigue damage (using previously developed SHM algorithms) and to establish a dataset for the development of a prognostic model to be applied to a random magnitude of fully reversed strain loading. The prognostic approach is rooted in the Failure Forecast Method, whereby the periodic feature rate-of-change was regressed against time to arrive at a failure estimate. An uncertainty model for the predictor was built so that a probability density function could be computed around the time-of-failure estimate, from which mean, median, and mode predictors were compared for robustness.

Commentary by Dr. Valentin Fuster
2018;():V002T05A012. doi:10.1115/SMASIS2018-8223.

High-speed railway plays critical roles in public safety and the country’s economy. Visual detection of components and damages can reflect the health conditions of high-speed railway. Human-based visual inspection is a difficult and time-consuming task and its detection results significantly rely on subjective judgement of human inspectors. Image-based detection methods abandon the weakness of human-based visual inspection. However, in practice, the complex real-world situations, such as lighting and shadow changes, can lead to challenges to the wide adaptability of image process techniques. To overcome these challenges, this paper provides a Faster Region-based Convolutional Neural Network (Faster R-CNN)-based detection method of component types and track damage for high-speed railway. To realize the method, a database including 575 images labeled for three component types and one track damage type of high-speed railway is built. A Faster R-CNN architecture based on ZF-Net is modified, then trained and validated using the built database. The performance of the trained Faster R-CNN is evaluated using 50 new images which are not be used for training process. The results show that the proposed method can indeed detect the component types and track damage for high-speed railway.

Commentary by Dr. Valentin Fuster
2018;():V002T05A013. doi:10.1115/SMASIS2018-8226.

In the last couple of years, advancements in the deep learning, especially in convolutional neural networks, proved to be a boon for the image classification and recognition tasks. One of the important practical applications of object detection and image classification can be for security enhancement. If dangerous objects or scenes can be identified automatically, then a lot of accidents can be prevented. For this purpose, in this paper we made use of state-of-the-art implementation of Faster Region-based Convolutional Neural Network (Faster R-CNN) based on the monitoring video of hoisting sites to train a model to detect the dangerous object and the worker. By extracting the locations of them, object-human interactions during hoisting, mainly for changes in their spatial location relationship, can be understood whereby estimating whether the scene is safe or dangerous. Experimental results showed that the pre-trained model achieved good performance with a high mean average precision of 97.66% on object detection and the proposed method fulfilled the goal of dangerous scenes recognition perfectly.

Commentary by Dr. Valentin Fuster
2018;():V002T05A014. doi:10.1115/SMASIS2018-8232.

Scour is one of the most important problems lead to submarine pipeline failure. In this paper, several scour monitoring techniques based on active thermometry method was introduced. Firstly, DS18B20 digital temperature sensor was used to monitor the surface heat change pattern in the heating process in different media like sand and water. The test results validated the feasibility of the active thermometry method. Then, the submarine pipeline scour monitoring system based on Brillouin distributed optical fiber sensing technique was developed. Due to the high cost of monitoring system of distributed Brillouin fiber optical sensing technology. In order to reduce costs, common armed fiber optic cable was used as both heating and sensing unit, and Raman sensing with relatively lower cost was utilized for distributed temperature sensing for scour monitoring. Laboratory test results shown there is good potential of active thermometry method for scour monitoring in practical field.

Commentary by Dr. Valentin Fuster
2018;():V002T05A015. doi:10.1115/SMASIS2018-8265.

Due to the particularity of texture features in ancient buildings, which refers to the fact that these features have a high historical and artistic value, it is of great significance to identify and count them. However, the complexity and large number of textures are a big challenge for the artificial identification statistics. In order to overcome these challenges, this paper proposes an approach that uses smartphones to achieve a real-time detection of ancient buildings’ features. The training process is based on SSD-Mobilenet, which is a kind of Convolutional Neural Network (CNN). The results show that this method shows well performance in reality and can indeed detect different ancient building features in real time.

Commentary by Dr. Valentin Fuster
2018;():V002T05A016. doi:10.1115/SMASIS2018-8266.

With the rapid development of rail traffic, the importance of railway overhaul is becoming increasingly prominent. Making an inventory on tools is an important step that railway workers must take before and after railway inspection. The tools left on the railway will cause great harm to train safety. To avoid this happening, the commonly used method is manual inventory at present, which is time-consuming, laborious and easily leads to omissions. In order to overcome these shortcomings, this paper proposes a Faster Region-based Convolutional Neural Network (Faster R-CNN)-based method for tools inventory. To realize the method, a Faster R-CNN architecture based on ZF-Net is modified and a database including a large number of images for 10 types of tools is built. Then the Faster R-CNN is trained and validated using the built database. The performance of the trained Faster R-CNN is evaluated using some new images which are not be used for training process. The result shows 95.0325% average precision (AP) ratings for 10 different types of tools and proves the proposed method is effective.

Commentary by Dr. Valentin Fuster
2018;():V002T05A017. doi:10.1115/SMASIS2018-8268.

Bridge management and maintenance work is an important part for the assessment the health state of bridge. The conventional management and maintenance work mainly relied on experienced engineering staffs by visual inspection and filling in survey forms. However, the human-based visual inspection is a difficult and time-consuming task and its detection results significantly rely on subjective judgement of human inspectors. To address the drawbacks of human-based visual inspection method, this paper proposes an image-based comprehensive maintenance and inspection method for bridges using deep learning. To classify the types of bridges, a convolutional neural network (CNN) classifier established by fine-turning the AlexNet is trained, validated and tested using 3832 images with three types of bridges (arch, suspension and cable-stayed bridge). For the recognition of bridge components (tower and deck of bridges), a Faster Region-based Convolutional Neural Network (Faster R-CNN) based on modified ZF-net is trained, validated and tested by utilizing 600 bridge images. To implement the strategy of a sliding window technique for the crack detection, another CNN from fine-turning the GoogLeNet is trained, validated and tested by employing a databank with cropping 1455 raw concrete images into 60000 intact and cracked images. The performance of the trained CNNs and Faster R-CNN is tested on some new images which are not used for training and validation processes. The test results substantiate the proposed method can indeed recognize the types and components and detect cracks for a bridges.

Commentary by Dr. Valentin Fuster

Bioinspired Smart Materials and Systems

2018;():V002T06A001. doi:10.1115/SMASIS2018-7925.

In this article, a novel wall-climbing locomotion mechanism, which can adapt multiple wall surfaces is developed to imitate the special animals, such as geckoes or flies. The spiny and adhesive belts are adopted in this robot to implement climbing on different kinds of wall surfaces instead of the vacuum generator for moving quietly and quickly. The switching mechanism is brought out to realize the belts switching between different surfaces, and a tail made up of two torsional springs and a supporting part is designed to overcome the robot’s overturning moment. So the mechanical system of the robot consists of four parts: the power and drive system, the moving mechanisms (spiny and adhesive), the switching system and the tail. Then the virtual prototyping of the robot with multi-locomotion modes is brought out, and the different gaits on the rough surface, the smooth surface and the transition process are analyzed. During the spine gait using the spine belts, the adhesive force should overcome the robot gravity and drive it, so the drive torque can obtained by building the force balance equations of the robot, which include the supporting forces of the spine belts and the tail. During the adhesive gait using the adhesive rubber belts, the force balance equations should include the supporting forces of the adhesive belts and the tail. And during the transition gait, the force balance equations include all of the above forces. So the mechanical model of the robot can be built according to the above analysis. Finally, the experimental prototype of the wall-climbing robot is manufactured and the wall-climbing experiments are carried out to testify its functions. The experiments show that the robot can adapt to different wall surfaces, and the torque parameters obtained based on the dynamics model can ensure the robot to locomote stably.

Topics: Robots , Design , Biomimetics
Commentary by Dr. Valentin Fuster
2018;():V002T06A002. doi:10.1115/SMASIS2018-7983.

A novel bridged-microfluidic for cell-based assays was developed by combining a microstructured optical fiber (MOF) with a microfluidic network with the purpose of continuously monitoring the state of hepatocellular carcinoma (HepG2) cells. In this configuration a solid core MOF with channels in the cladding serves as a bridge for cell transport as well as an evanescent wave-based monitoring system to detect cells labeled with fluorescent nanomaterials. The device was fabricated by positioning an MOF to bridge two polydimethylsiloxane (PDMS) microfluidic networks. Alignment strategies and pressurization considerations to produce this system are presented. Pump systems that support fluid transport through the MOF demonstrated the tendency of flow rate fluctuations even for constant microfluidic pump rates. Spectroscopic measurements confirm the delivery and motion of cells between the two neighboring microfluidic chips. The linewidth of the spectra demonstrated oscillations that were consistent with pressure broadening caused by hydrodynamic fluctuations. Fluctuations in the microfluidic flow ranging from 0.005 to 0.016 Hz were observed. These results are consistent with theoretical principles and provide important information regarding syringe pump artifacts, i.e. fluctuations, observed during spectroscopic measurements in MOF/microfluidic systems.

Commentary by Dr. Valentin Fuster
2018;():V002T06A003. doi:10.1115/SMASIS2018-7986.

Unlike most modern aircraft, which have a vertical tail component, birds fly utilizing a purely horizontal tail. In order to provide control normally associated with a vertical rudder, bird’s tails are incredibly mobile, twisting, pitching, and widening to perform necessary aerial maneuvers. This research primarily focuses on the development and testing of a mechanical planform morphing horizontal control surface, aiming to emulate the tail-spread control action of birds. This horizontal control surface is implemented on a small, tailless, avian inspired unmanned aerial vehicle (UAV). In this research, the horizontal control surface, made entirely of 3D printed material, comprises a rigid overlapping top layer held together by a soft and elastic honeycomb bottom layer, allowing for shape morphing without compromising structural integrity required to withstand aerodynamic forces. Using the relatively large strain and strength offered by shape memory alloy (SMA) springs, the 3D printed horizontal tail undergoes a notable and consistent geometric change. To quantify the system’s performance, the tail width and center was measured while actuating the springs through a range of frequencies from 0.01 to 10 Hz. Preliminary experiments were conducted in a 1ft. × 1 ft. open loop wind tunnel at the University of Michigan at wind speeds of 5, 10 and 15 m/s to quantify the effects of aerodynamic loading on actuation magnitude and speed.

Commentary by Dr. Valentin Fuster
2018;():V002T06A004. doi:10.1115/SMASIS2018-8037.

In the United States, Total Knee Replacement (TKR) is a surgery many people go through, but frequently, patients find that they are unhappy post-surgery due to misalignment and loosening of the knee. An estimated 20% of knee replacement recipients report discomfort or undesired functionality within their first few years after surgery. Surgical techniques currently rely heavily on experience and tactile feedback to correctly align the knee replacement. If surgical teams were to have access to data regarding compartmental forces within the knee over the life of the implant, then a more precise balancing procedure could be implemented. As it stands, the only way to obtain this in vivo data is for patients to undergo post-operative fluoroscopy procedures; unfortunately, patients have no incentive to undergo this process. This study tests the capabilities of knee bearings embedded with piezoelectric transducers to estimate the magnitude and location of loading given certain inputs. The prototype is fabricated from ultra high molecular weight (UHMW) polyethylene using Computer Numerical Control (CNC) machining. For this study, to simulate loads under both normal and irregular knee positions, a custom fixture is designed and fabricated for use in a uniaxial load frame. The problem at hand necessitates a more realistic knee testing environment that can simulate the loading types of both balanced and imbalanced knees. Thus, the fixture permits various degrees of internal and external rotation. Additionally, through use of an X-Y translational table, the setup allows for in-plane translation between the condyles of the femoral component and the bearing prototype. This study compares values of force location from the piezoelectric sensors to measurements from pressure sensitive film. The piezoelectric knee bearing is tested to lay the groundwork for in vivo testing. Future work expanding upon this research would include designing and optimizing an in vivo knee bearing replacement to facilitate force location and magnitude data collection in a system free from external power sources by utilizing the energy harvesting capabilities of piezoelectrics.

Commentary by Dr. Valentin Fuster
2018;():V002T06A005. doi:10.1115/SMASIS2018-8038.

This study aims to examine the coiling and uncoiling motion of a soft pneumatic actuator reinforced with tilted helix fibers. Coiling motion can be quite useful for robotic manipulation and locomotion purposes. This research proposes and investigates a novel actuator that is inspired and derived from the unique cell wall architecture in the seed appendage of Stork’s Bill plant (Erodium Gruinum). These plant cells are reinforced by cellulose fibers distributed in a tilted helix pattern — helixes that are tilted at a certain angle with respect to the longitudinal axis of the cell. As a result, the seed appendage can coil and uncoil via a combination of twisting and bending. This paper discusses the design, fabrication, and testing of a soft actuator that can mimic this sophisticated motion. This actuator consists of Kevlar fiber thread wrapped around a silicon rubber body that has the shape of a tube. The tube will be capped at both ends so that it can be pressurized internally to induce motion. Once the design parameter has been chosen, the soft actuator are fabricated by 1) designing and 3D printing molds, 2) tube casting and fiber wrapping, and 3) creating the end caps for pressure sealing. Carefully executing these fabrication steps is essential because any errors could give undesired deformation. Several soft actuators prototypes are fabricated based on different design choices regarding the actuator radius, tube wall thickness, and the number of tilted helix fibers (aka. fiber coverage). Proof-of-concept tests show that these actuator prototypes can indeed exhibit a combined twisting and bending under internal pressurization: all are the necessary receipts to achieve the coiling and uncoiling motion. Result of this paper can pave the way for a new family of soft actuators capable of unprecedented and sophisticated actuation motions, which are particularly appealing for soft robot application.

Topics: Fibers , Actuators
Commentary by Dr. Valentin Fuster
2018;():V002T06A006. doi:10.1115/SMASIS2018-8054.

Several biological creatures represent a great inspiration for the realization of advanced morphing materials. For instance, bat wing is extremely interesting because of its unique ability of drastically changing shape and size thanks to an embedded distributed array of ultra-small-in-size muscles. This is obviously done as a response to continuously detected external stimuli. Novel ultra-lightweight and non-invasive artificial muscles that can exploit a dual functionality and that can be integrated into hosting materials, are here investigated. The muscles are made of a piezoelectric (PVDF) single micro-fibre and a micro-fibre rope created using a simple electrospinning technique. The advantage of this technique is the less-complex in-situ fibres poling during electrospinning which makes them an attractive alternative compared to thin PVDF films that require an additional complicated poling step to achieve their piezoelectric properties. Muscles that possess an active and passive electromechanical response based on a ∼ 3-micron thick single PVDF fibre and ∼ 150-micron thick PVDF fibred rope, were realized. Preliminary results prove that these PVDF fibres have a highly accurate electromechanical response over an extremely wide frequency range. Fully constrained single fibres and fibre ropes, when actuated with the corresponding electric fields, show a midpoint displacement of ∼ 36 μm.

Topics: Biomimetics , Muscle
Commentary by Dr. Valentin Fuster
2018;():V002T06A007. doi:10.1115/SMASIS2018-8077.

Squid are the fastest aquatic invertebrates through jetting locomotion. This done through a mantle that quickly compresses an internal fluid, forcing fluid out through a funnel. The squid mantle has a complex collagen fiber and muscular system and squid propulsion is primarily done through circumferential muscles (90°) contracting around the mantel, forcing fluid out of the mantel. However, jetting is also increased through elastic energy stored in the helically-wound IM-1 collagen fibers, which have been measured between 28° to 32° in different species of squid. Inspired by the muscular and collagen fiber configuration found in the squid mantel, new composite pumps with active fibers oriented at precise angles around a cylindrical tube are proposed. An analytical model of the active fiber composite pump is developed. Results show that maximum pumping power and efficiency is achieved with a wind angle of 90° and a matrix modulus that is equal to the fiber modulus.

Commentary by Dr. Valentin Fuster
2018;():V002T06A008. doi:10.1115/SMASIS2018-8078.

Computational modeling, instrumented linkages, optical technologies, MRI, and radiographic techniques have been widely used to study knee motion after total knee replacement (TKR) surgery. Information provided by these methods has helped designers to develop implants with better clinical performance and surgeons to obtain an improved understanding of the stability and mobility of the joint. Correspondingly, overall patient satisfaction with respect to the reduction in pain and recovery of normal functioning of the joint has been improving. However, about 20% of patients are still not fully satisfied with their surgical outcomes. The main obstacle in the current state-of-the-art is that a comprehensive post-operative understanding of knee balance is still unavailable, mostly due to a lack of in vivo data collected from the joint after surgery. This work presents an attempt to develop a self-powered instrumented knee implant for in vivo data acquisition. The knee sensory system in this study utilizes several embedded piezoelectric transducers in the tibial bearing of the knee replacement in order to provide sensing and energy harvesting capabilities. Through a series of analytical modeling, finite element simulation, and experimental testing, the performance of the suggested system is evaluated and a dimensionally optimized design of an instrumented TKR is achieved. More specifically, a comprehensive platform is established in order to combine the knowledge of embedded piezoelectric sensors and energy harvesters, musculoskeletal modeling of the knee joint, multiphysics finite element modeling, additive manufacturing techniques, image processing, and experimental knee loading simulation in order to achieve the experimentally validated and optimized instrumented knee implant design. The cumulative work presented in this article encompasses three main studies performed on the sensing performance of the proposed design: first, preliminary parametric studies of the effect of local dimensional and material parameters on the electromechanical behavior of the embedded sensory system; second, investigation of the ability to sense total force and center of pressure location; and third, evaluation of an enhanced system with the ability to sense compartmental forces and contact locations. Additionally, the energy harvesting capacity of the system is investigated to ensure the achievement of a fully self-powered sensory system. Results obtained from the experimental analysis of the system demonstrate the successful sensing and energy harvesting performance of the designs achieved in this study.

Commentary by Dr. Valentin Fuster
2018;():V002T06A009. doi:10.1115/SMASIS2018-8123.

Silicon anodes in lithium ion batteries have high theoretical capacity and large volumetric expansion. In this paper, both characteristics are used in a segmented unimorph actuator consisting of several Si composite anodes on a copper current collector. Each unimorph segment is self-actuating during discharge and the discharge power can be provided to external circuits. With no external forces and zero current draw, the unimorph segments will maintain their actuated shape. Stress-potential coupling allows for the unimorph actuator to be self-sensing because bending changes the anodes’ potential. An analytical model is derived from a superposition of pure bending and extensional deformation forces and moments induced by the cycling of a Si anode. An approximately linear relationship between axial strain and state of charge of the anode drives the bending displacement of the unimorph. The segmented device consists of electrically insulated and individually controlled segments of the Si-coated copper foil to allow for variable curvature throughout the length of the beam. The model predicts the free deflection along the length of the beam and the blocked force. Tip deflection and blocked force are shown for a range of parameters including segment thicknesses, beam length, number of segments, and state of charge. The potential applications of this device include soft robots and dexterous 3D grippers.

Commentary by Dr. Valentin Fuster
2018;():V002T06A010. doi:10.1115/SMASIS2018-8139.

This paper presents a method to measure gripping force of a bipedal wall-climbing robot (WCR) with spiny toe pads. The spiny toe pad is designed based on inspiration of an insect’s tarsal system. Each foot of the robot consists of a pair of opposed linear spiny arrays. The foot employs a pulley system to actuate the arrays via four pairs of tension and compression springs. Two Hall effect sensors are embedded into the robot feet to sense the gripping force by detecting the linear deformation of the springs. The two Hall effect sensors are calibrated and the relationship between the voltage signal output of the sensors and displacement is established before measuring gripping force. Then the consistency and accuracy of Hall effect sensor measurement method are verified by comparing with a commercial force sensor. A horizontal crawling test of the WCR is carried out and the gripping force verse time when the WCR moves. The experimental results show that the measured force history is in accordance with the actual movement states.

Commentary by Dr. Valentin Fuster
2018;():V002T06A011. doi:10.1115/SMASIS2018-8170.

Even though Unmanned Aerial Vehicles (UAVs) operating at low Reynolds numbers are becoming common, their performance and maneuverability are still greatly limited due to aerodynamic phenomena such as stall and flow separation. Birds mitigate these limitations by adapting their wings and feather shapes during flight. Equipped with a set of small feathers, known as the alula, located near the leading edge and covering 5% to 20% of the span, bird wings can sustain the lift necessary to fly at low velocities and high angles of attack. This paper presents the effect on lift generation of different placements of a Leading-Edge Alula-inpsired Device (LEAD) along the span of a moderate aspect-ratio wing. The device is modeled after the alula on a bird, and it increases the capability of a wing to maintain higher pressure gradients by modifying the near-wall flow close to the leading-edge. It also generates tip vortices that modify the turbulence on the upper-surface of the wing, delaying flow separation. The effect of the LEAD can be compared to traditional slats or vortex generators on two-dimensional wings. For finite wings, on the other hand, the effect depends on the interaction between the LEADs tip vortices and those from the main structure. Wind tunnel experiments were conducted on a cambered wing at post-stall and deep-stall angles of attack at low Reynolds numbers of 100,000 and 135,000. To quantify the aerodynamic effect of the device, the lift generated by the wing with and without the LEAD were measured using a 6-axis force and torque transducer, and the resulting lift coefficients were compared. Results show that the location of the LEAD yielding the highest lift enhancement was 50% semi-span away from the wing root. Lift improvements of up to 32% for post stall and 37% for deep stall were obtained at this location, demonstrating that the three-dimensional effects of the LEAD are important. The lift enhancement was also more prominent on a finite moderate aspect-ratio wing (3D) than on an airfoil (2D), confirming that the LEAD is a three-dimensional device. Identifying the configurations and deployment parameters that improve lift generation the most is needed to design an adaptive LEAD that can be implemented on a UAV wing for increased mission-adaptability.

Commentary by Dr. Valentin Fuster
2018;():V002T06A012. doi:10.1115/SMASIS2018-8175.

Cellular contact-aided compliant mechanisms (C3M) are cellular structures with integrated self-contact mechanisms, i.e. the segments can come into contact with each other during deformation. The contact changes the load path and can influence on the mechanism’s performance. Cellular contact-aided compliant mechanisms can be tailored for a specific structural application, such as energy absorption. Nickel Titanium compliant mechanisms can exploit the superelastic effect to improve performance and increase energy absorption. The potential for compliant mechanisms designed specifically for metal additive manufacturing opens the possibility of functional grading and tailoring the material properties locally for achieving overall performance. The combined effort of the geometry and the nonlinear material property increases the local compliance of the unit cell, resulting in higher energy absorption. A functionally graded 3D energy absorbing contact-aided compliant mechanisms cell with curved walls is analyzed. Functionally graded zones of higher flexibility are explored with different superelastic material properties. Introducing different moduli of elasticity as a function of the critical transformation stress results in different energy absorption. This approach can be used for tailoring the overall performance based on the application.

Commentary by Dr. Valentin Fuster
2018;():V002T06A013. doi:10.1115/SMASIS2018-8176.

Functionally graded compliant mechanisms can be fabricated with additive manufacturing technology by engineering the microstructural and compositional gradients at selected locations resulting in compositionally graded zones of higher and lower flexibility. The local compliance depends on the geometry of the structure as well as the material property in the selected region. As Nitinol (NiTi) is well suited for applications requiring compliance, the critical transformation stress and the superelastic modulus of elasticity are crucial parameters for defining the local compliance. To understand the behavior at the interface between two different material compositions, three models of gradient change between the alloys are analyzed: step change, linear and polynomial gradients. In addition to localize the deformation in the interface, three different flexure designs in the interface are analyzed. This paper will address a methodology for modeling and parametrization of material properties and transition at the interface, for different flexure designs. The combined effort in the interface of the functional grading and the geometry will be used for the design of monolithic self-deployable structures, initially folded in compact shape. The design motivation comes from the self-deploying mechanisms inspired by insects’ wings.

Topics: Modeling
Commentary by Dr. Valentin Fuster
2018;():V002T06A014. doi:10.1115/SMASIS2018-8177.

Arthropod animals like scorpions with modular body parts can be an inspiration for a robot’s structure. The design presented here relays on inter-connected origami towers, but could also be easily disassembled. Each origami tower is fully autonomous and at the same time is part of the robot as a whole. The towers are positioned between two platforms that enable modularity. The scorpion’s tale shape is achieved by the varying platform diameter resulting in cone-like form. Each tower is actuated independently to enable multiple degrees of freedom. Maneuvering with separated units, assists in easier reparation as well as replacement. Detaching the towers into separate parts makes this structure develop more precise movements, since every unit will move autonomously. Therefore, having a higher number of separated movements combined leads to a smooth bionic movement. So, the overall hierarchy will be modular contributing to a greater curvature bending of the whole structure. Actuating and maneuvering the robot in the main concept is done by separated electro motors, built in the platform. The basic structure will be built from thick paper with plastic coatings. The thick paper itself is lightweight, but at the same time flexible. To protect the paper towers, double plastic foil is placed as an outer coating which acts as an origami cover. This transparent layer is elastic hence it can follow and support the individual units’ movements.

This work is focused on understanding origami towers kinematics and different combinations of inter-connected towers to achieve multiple degrees of freedom. A conceptual model is developed, supported by CAD and mathematical models. At the end a prototype is presented.

Topics: Robots
Commentary by Dr. Valentin Fuster
2018;():V002T06A015. doi:10.1115/SMASIS2018-8203.

This paper presents an initial step towards a new class of soft robotics materials, where localized, geometric patterning of smart materials can exhibit discrete levels of stiffness through the combinations of smart materials used. This work is inspired by a variety of biological systems where actuation is accomplished by modulating the local stiffness in conjunction with muscle contractions. Whereas most biological systems use hydrostatic mechanisms to achieve stiffness variability, and many robotic systems have mimicked this mechanism, this work aims to use smart materials to achieve this stiffness variability. Here we present the compositing of the low melting point Field’s metal, shape memory alloy Nitinol, and a low melting point thermoplastic Polycaprolactone (PCL), composited in simple beam structure within silicone rubber. The comparison in bending stiffnesses at different temperatures, which reside between the activation temperatures of the composited smart materials demonstrates the ability to achieve discrete levels of stiffnesses within the soft robotic tissue.

Commentary by Dr. Valentin Fuster
2018;():V002T06A016. doi:10.1115/SMASIS2018-8248.

This paper reports on the realistic color generation and color change due to cyanosis which refers to the blue coloration around the lips’ area. The design requirements for the manikin were identified based on the color measurement and corrections of cyanosis in images of real babies. The classification of the literature study is according to physics working principles based on energy. A reversible color changing mechanism is achievable by stimuli of external energy such as electric, heat, mechanical, light and magnetic energy. Here, the overview of cyanosis coloration is presented to serve as a basis for a new design of a physiologically-inspired color change actuator for cyanosis in a baby manikin. A state-of-the-art review of color change actuators in the desired color ranges, switching time, dimensions and shape, including the safety issues of each actuating working principle, is presented. Employing a simplified version of the Weighted Objectives method, the practical value of the actuator types was evaluated by assigning scores to each actuator’s type, which indicates their criteria. This work highlights the design’s specifications which aim to design a cyanosis color change actuator in the near future. Ultimately, the envisioned system will increase the efficiency of the visual evaluation and assessment of cyanosis coloration in medical training.

Topics: Actuators , Design
Commentary by Dr. Valentin Fuster

Energy Harvesting

2018;():V002T07A001. doi:10.1115/SMASIS2018-7902.

This paper proposes a novel idea of a combined piezoelectric energy harvesting and torsional vibration absorber for rotating system. In particular, among possible alternative solutions for durable power sources useable in mechanical components, vibration represents a suitable method for the amount of power required to feed a wireless sensor network. For this purpose energy harvesting from structural vibration has received much attention in the past few years. Suitable vibration can be found in numerous mechanical environments including automotive moving structures, household applications, but also buildings and bridges. Similarly, a dynamic vibration absorber (DVA) is one of the most used devices to mitigate the vibration structures. This device is used to transfer the primary structural vibration to the auxiliary system. Thus, vibration energy is effectively localized in the secondary less sensitive structure and it can be harvested. This paper describes the design process of an energy harvesting tuned vibration absorber for rotating system using piezoelectricity components. Instead of being dissipated as heat, the energy of vibration is converted into electricity. The device proposed is designed to mitigate torsional vibrations as a rotational vibration absorber and to harvest energy as a power source for immediate use. The initial rotational multi degree of freedom system is initially reduced in equivalent single degree of freedom (SDOF) systems. An optimization method is used for evaluating the optimal mechanical parameters of the initial absorber for the SDOF systems defined. The design is modified for the integration of the active patches without detuning the absorber. In order to estimate the real power generated, a complex storage circuit is implemented. A fixed voltage is obtained as output. Through the introduction of a big capacitor, the energy stored is measured at different frequencies. Finally, the simultaneously achievement of the vibration reduction function and the energy harvesting function is evaluated.

Commentary by Dr. Valentin Fuster
2018;():V002T07A002. doi:10.1115/SMASIS2018-7958.

This paper presents mathematical modeling of an energy harvester (EH) for a wireless structure health monitoring (SHM) system in wind turbine blades. The harvester consists of a piezoelectric energy harvester (PEH) beam, a gravity-induced disk, and magnets attached to both the beam and the disk. An electromechanical model of the proposed EH is developed using the energy method with repelling magnetic force considered. The three coupled equations — the motion of the disk, the vibration of the beam, and the voltage output — are derived and solved using ODE45 in MATLAB software. The result showed the blade rotation speed affects the output angular velocity of disk and the output PEH voltage. That is, as the blade speed increases, the disk angular velocity becomes nonlinear and chaotic which is more beneficial to generate larger power.

Commentary by Dr. Valentin Fuster
2018;():V002T07A003. doi:10.1115/SMASIS2018-7967.

This paper presents a special piezoelectric energy harvester system which is obtained by separating the end of the upper piezoelectric layer of the traditional piezoelectric cantilever beam from its basic layer. A mass I is located at the end of the separated upper piezoelectric layer (SUPL), a mass II and a permanent magnet I are located at the end of the separated lower piezoelectric beam (SLPB) and a permanent magnet II is added in the opposite position of the permanent magnet I and they face each other with same polarities. A nonlinear magnetic force which can broaden the frequency bandwidth of the system is generated mutually on the two permanent magnets. Studies find that this special piezoelectric energy harvester has extremely high energy capture efficiency. In order to further explore the reason of high efficiency, experimental research on its dynamic behavior is carried out. The experimental results show that the vibrations of the SUPL and the SLPB are relatively simple. The dynamic behaviors of the SUPL, the SLPB and the unseparated part are different. The unseparated part of the piezoelectric shows relatively complex nonlinear phenomenon due to the interaction of nonlinear magnetic force and the collision. With the increase of the external excitation frequency, period doubling motion and almost periodic motion appear alternately.

Commentary by Dr. Valentin Fuster
2018;():V002T07A004. doi:10.1115/SMASIS2018-7968.

Nonlinear energy sink (NES) is employed to passively reduce vibration transmission in this study. A two-degree-of-freedom system, comprising a primary structure coupled with a grounded piezoelectric NES possessing essential nonlinearity, is investigated for both harmonic force excitation and base excitation. The piezoelectric NES acts as not only a vibration isolator but also an energy harvester when connected to an alternating current circuit. Approximate analysis is carried out by the harmonic balance method and validated by numerical solutions using ODE45 in Matlab and equivalent circuit simulation. The effectiveness of the nonlinear vibration isolation system is evaluated by the force (displacement) transmissibility defined as the root-mean-square ratio of transmitted force (displacement) to the excitation force (displacement), which is compared with that of its linear counterparts. Output voltage of the piezoelectric transducer is also derived. By and large, it is found that the piezoelectric NES could reduce the force (displacement) transmissibility while collecting electric energy efficiently in a relatively broad frequency range.

Commentary by Dr. Valentin Fuster
2018;():V002T07A005. doi:10.1115/SMASIS2018-7979.

Impulsive energy provides a promising source for energy harvesting techniques due to their high amplitude and abundance in a living environment. The sensitivity to excitation of bistable energy harvesters makes them feasible for impulsive-type events. In this paper, a novel impulsively-excited bistable energy harvester with rotary structure and plectrum is proposed to achieve plucking-based frequency up-conversion. The input excitation is converted to plucking force on the bistable energy harvester, so as to help it go into the high-energy orbit. The piezoelectric and electromagnetic transduction mechanisms are combined by incorporating a coil to the structure in order to overcome the increase of damping introduced by the bistable configuration. As a result, high-energy output and broadband performance could be realized. Impact mechanics is employed to develop a comprehensive model, which could be used to analyze the nonlinear dynamics and predict the system responses under various plucking velocities and overlap lengths. Numerical simulation shows that the bistable energy harvester could experience large-amplitude oscillation under impulsive excitation and the hybrid configuration outperforms the standalone ones under high damping ratio and low coupling coefficient. The proposed design is targeted to be applied on the turnstile gates of the subway station. Less human effort would be needed when passengers pass the turnstile gate due to the snap-through motion of bistability.

Commentary by Dr. Valentin Fuster
2018;():V002T07A006. doi:10.1115/SMASIS2018-8022.

In this paper, a high performance micro piezoelectric energy harvester (PEH) fabricated on stainless substrates is presented. A PZT piezoelectric active layer with a thickness of about 10 μm was deposited on a stainless steel substrate by the aerosol deposition method. The cantilever beam-shaped PEH was then fabricated by metal-MEMS processing of the PZT/stainless steel composite structure. The size of the cantilever PEH transducer developed was about 1 cm2 and a proof mass was attached to tune its resonant frequency to around 120 Hz for harvesting mechanical vibrations from direct drive AC motors. The PEH transducer showed an output voltage and an output power of 8.9 Vp-p and 107.8 μW, respectively, when connected with optimal load and excited under 0.5 g acceleration level. In order to realize the fatigue behavior and reliability of the PEH in field applications, the PEH transducer was driven at its own resonant frequency and tested under 1.0 g acceleration level for millions of cycles and the vibration modes were measured with a laser scanning vibrometer. The PEH transducer had an operating lifetime of about 1.8 million cycles at 1.0 g cyclic loading based on the shift of its resonant frequencies and the decrease in electrical output. The experimental results show the resonant frequencies of the first, second and third modes were all shifted to lower frequencies with increasing operation cycle number due to the development of microcracks in the ceramic PZT active layer. However, the same PEH transducer could survive millions of cycles (in the high millions) at 0.5 g cyclic loading without any significant changes in the resonant frequencies and electrical output. The results confirm the operating limits of the PEH transducer and suggest further protection and reinforcement are required for the transducer to operate at high acceleration loadings.

Commentary by Dr. Valentin Fuster
2018;():V002T07A007. doi:10.1115/SMASIS2018-8029.

This paper proposes a broadband rotational energy harvesting setup by using micro piezoelectric energy harvester (PEH). When driven in different rotating speed, the PEH can output relatively high power which exhibits the phenomenon of frequency up-conversion transforming the low frequency of rotation into the high frequency of resonant vibration. It aims to power self-powered devices used in the applications, like smart tires, smart bearings, and health monitoring sensors on rotational machines. Through the excitation of the rotary magnetic repulsion, the cantilever beam presents periodically damped oscillation. Under the rotational excitation, the maximum output voltage and power of PEH with optimal impedance is 28.2 Vpp and 663 μW, respectively. The output performance of the same energy harvester driven in ordinary vibrational based excitation is compared with rotational oscillation under open circuit condition. The maximum output voltage under 2.5g acceleration level of vibration is 27.54 Vpp while the peak output voltage of 36.5 Vpp in rotational excitation (in 265 rpm).

Commentary by Dr. Valentin Fuster
2018;():V002T07A008. doi:10.1115/SMASIS2018-8031.

A piezoelectric-coupled finite element model for a THUNDER harvester (THin layer UNimorph DrivER) is developed and studied in this work. THUNDER is a curved piezoelectric energy generator developed by NASA Langley Research Center, which has better vibration absorption and higher energy recovery efficiency at low-frequency vibration compared to a flat PZT harvester. To apprehend the piezoelectric effect of the THUNDER harvester, finite element method was used to perform the piezoelectric coupled field analysis. Piezoelectric THUNDER harvester was studied under cantilever boundary condition. In the model, the excitation forces are distribution force allied on the top of the dome line. An electric circuit element was used to create load resistance across the electrodes to obtain the generated voltage and power. The effect of the geometric parameter was investigated via the varying radius of curvature, which affects the resonance frequency, voltage, and power output of the THUNDER. Good agreement between finite element analysis and experimental results were also observed. In finite element analysis: Modal analysis was carried out to find the resonance frequency at which maximum performance characteristics of the THUNDER can be achieved. Then, the harmonic analysis was performed to distinguish the voltage and power output variation as the load resistance changes. The effects of the varying radius of curvature on the power efficiency of the THUNDER were summarized.

Commentary by Dr. Valentin Fuster
2018;():V002T07A009. doi:10.1115/SMASIS2018-8041.

Portable, wearable, and mobile devices are becoming more and more popular in the past two decades. Those devices rely on batteries heavily as power source. However, the limited life span of batteries constitutes a limitation. Human body energy harvesting has the potential to power those devices, thus replacing batteries or extending battery life. Harvesting positive muscle work from human body can be a burden, and exhausts the wearer. In this paper, we developed a biomechanical energy-harvesting device that generates electricity by harvesting negative work during human walking. The energy harvester mounts on the ankle and selectively engages to generate power between the middle stance phase and terminal stance phase, during which the calf muscles do negative work. The device harvests negative energy by assisting muscles in performing negative work. Test subjects walking with the device produced an average of 0.94 watts of electric power. From treadmill test, the device was shown to harvest energy only during the negative work phase, as a result it has the potential to not to increase the metabolic cost. Producing substantial electricity without burden on the wearer makes this harvester well suited for powering wearable, portable, and mobile devices.

Commentary by Dr. Valentin Fuster
2018;():V002T07A010. doi:10.1115/SMASIS2018-8043.

Energy harvesting from low frequency cyclic motion is possible in a variety of applications, but generating power with piezoelectric stacks at low, off-resonance frequencies is challenging. In this study, Compliant Layer Adaptive Composite Stacks (CLACS) were investigated as a toughened piezoelectric generator to increase efficiency at low frequencies and match the compliance of many commercial devices.

CLACS were manufactured with PZT discs, interdigitated epoxy layers of varying thicknesses, and encapsulated in epoxy. Energy production of each CLACS type as a function of compliant layer thickness was characterized. Power amplification of CLACS was modeled assuming discs remain planar, volume of epoxy was conserved, and total epoxy deformations were small. Shear lag theory demonstrated increases in positive in-plane strains induced by external through-thickness compression. This amplified sensitivity of the entire stack to through-thickness compressions, substantially increases power generation capability.

Experimental data showed that increases in compliant layer thickness resulted in increased power generation in all loading conditions. The shear lag structural mechanics model showed good correlation with theoretical predictions, assuming small deformation of the compliant layer. In addition to reducing composite stiffness, the CLACS generated 61% more power than conventional stack actuators with the same PZT volume via lateral strain amplification effects.

Commentary by Dr. Valentin Fuster
2018;():V002T07A011. doi:10.1115/SMASIS2018-8086.

In this study, a dual-beam piezoelectric energy harvester is proposed. This harvester consists of a main beam and an auxiliary beam with a pair of magnets attached to couple their motions. The potential energy of the system is modeled to understand the influence of the potential wells on the dynamics of the harvester. It is noted that the alignment of the magnets significantly influences the potential wells. A theoretical model of the harvester is developed based on the Euler-Bernoulli beam theory. Frequency sweeps are conducted experimentally and numerically to study the dynamics of the harvester. It is shown that the dual-beam harvester can exhibit hardening effect with different configurations of magnet alignments in frequency sweeps. The performance of the harvester can be improved with proper placement of the magnets.

Commentary by Dr. Valentin Fuster
2018;():V002T07A012. doi:10.1115/SMASIS2018-8162.

Heat is often lost unused in industry, commerce and households and is considered a waste product — while there is a lot of energy potential in waste heat. As part of the project “Theasmart”, scientists and companies are exploring just these potentials to find out how the waste product heat can be used for further purposes through the use of an innovative smart materials technology. The goal of the project is the further qualification of shape memory alloys with special focus on thin hysteresis applications for energy harvesting. In certain applications, these metals can be used as a thermal drive, for example for thermal valves or as thermal air flow regulators. Energy efficiency in processes in industrial companies or households could be improved by their use of waste heat. By 2020, the development of thermally driven generators, so-called “energy harvesters”, and the identification of other areas of application is planned. This publication focuses on first steps towards a process tool which can be actuated by waste heat of a thermal annealing sub-process directly, or used as mechanical energy charging device combined with a releasing mechanism.

Commentary by Dr. Valentin Fuster
2018;():V002T07A013. doi:10.1115/SMASIS2018-8188.

One major problem of implantable biomedical devices is the source of their power. Batteries, as the main source of current implantable devices, deplete after a few years and either the battery or the whole device needs to be replaced. Usually, this procedure involves a new surgery which is costly and could cause some risks for the patient. In this paper, we study the energy harvesting at small scale for powering implantable biomedical devices. The device consists of a layer of cultured cardiac muscle cells (cardiomyocytes) and a layer of piezoelectric polymer polyvinylidene fluoride (PVDF). The cardiac muscle cells with the desired thickness are grown over the PVDF layer and as the cardiac cells contract the piezoelectric layer deforms and produces electricity. The proposed device uses both piezoelectric and flexoelectric effects of the PVDF layer. At the smaller thicknesses the flexoelectric effect becomes dominant. The amount of power is on the order of multiple microwatts and is sufficient to power variety of sensors and implantable devices in the body. Unlike the battery technology, the proposed energy harvester is autonomous and lasts for the lifetime of patients. In this article, we explain the configuration of the proposed energy harvester, the natural frequency of the device is calculated, the power output is optimized with respect to the thickness of the PVDF, and a resistance sweep is performed to find the optimized resistive load.

Commentary by Dr. Valentin Fuster
2018;():V002T07A014. doi:10.1115/SMASIS2018-8197.

In this paper, we report a low-frequency and wide-bandwidth piezoelectric energy transducer. The transducer is designed based on a piezoelectric plate, a truss mechanism, a spring-mass system and a stopper. The spring-mass system receives kinetic energy from excitation and induces forces, which are further transmitted, amplified by the truss mechanism and applied onto the piezoelectric plate. The stopper is added to truncate the amplitude of the mass. The mass and the stopper interact through impacts. The impact force triggers dynamic bifurcation in the transducer. By taking advantage of the superharmonic resonances and nonlinearity born from the bifurcation, the transducer is able to work efficiently with a wide bandwidth. Through experiment studies on a fabricated prototype, the lowest resonant frequency is around 3.2Hz with the peak-peak voltage output up to 55V. The bandwidth of the transducer is approximately 4.5Hz out of our targeted frequency domain [2.5Hz, 10Hz], broadened by up to 20 times compared to that of the linear system without the stopper.

Commentary by Dr. Valentin Fuster
2018;():V002T07A015. doi:10.1115/SMASIS2018-8199.

In this paper, a new prototype is proposed for accelerated orthodontic tooth treatment. In contrast to conventional methods, where heavy vibration generators are used, the proposed design is light and small and may remain into patient’s mouth without obstructing his daily activities. To do that, a PVDF Piezoelectric actuator layer is incorporated into a bio-compatible flexible structure which is to be excited by an external electric source. Generally, application of cyclic loading (vibration) reverses bone loss, stimulates bone mass, induces cranial growth, and accelerates tooth movement. This reduce the pain experience and discomfort associated with the treatment and also enhances the patient compliance with the treatment. Vibration has the advantage of minimal side effects in comparison to medicinal treatments. This configuration enables the operator to adjust the vibration frequency as well as the orthodontic force exerted on the tooth.

Commentary by Dr. Valentin Fuster
2018;():V002T07A016. doi:10.1115/SMASIS2018-8212.

The main goal of this paper is to investigate the feasibility of a triboelectric mechanism to harvest electrical energy for powering a knee implant load measurement sensor under walking activity of daily living. A triboelectric energy harvester is proposed to be placed in between the tibial tray and the UHMWPE bearing of the TKR. To characterize the triboelectric generator, the walking tibiofemoral axial load is approximated as a 1 Hz sine wave signal. An MTS 858 II servo-hydraulic load frame setup is used to transfer the axial load to the triboelectric generator. The optimal resistance is extracted experimentally and found to be 58MΩ. With an applied cyclic load of 2.3 kN at 1 Hz, which is equivalent to the load from normal walking, the generator generated a maximum output of 18 V, and 6 μW of power at the optimal resistance. A power management and digitization circuit is designed based on the harvester output that consumes about 4.74 μW power, which is less than the generated power. Thus, the power harvested from the triboelectric energy harvester can power the load sensing circuitry.

Commentary by Dr. Valentin Fuster

Emerging Technologies

2018;():V002T08A001. doi:10.1115/SMASIS2018-7932.

Acoustic metamaterials display unusual mechanical wave manipulation behavior not seen in natural materials. In this study, nonlinear metamaterials with passive, amplitude-activated directional bandgaps are investigated. Test articles are constructed by installing periodic arrays of mass-loaded dome resonators on a square polycarbonate substrate. These resonators display nonlinear softening response with increase in excitation amplitude. Experiments conducted by mounting the test articles on low-stiffness boundaries along two adjacent sides and applying mechanical excitations at the opposite corner. A mechanically-staged laser vibrometer mounted overhead was used to make noncontact measurements at discrete plate and resonator locations. Measured displacement transmissibility verify the existence and extent of bandgap frequency ranges as well as amplitude-activated shifts in their bounds. Moreover, by tailoring the pattern of resonators within the array, preferential steering, focusing and selective beaming of waves within tunable frequency ranges depending on their amplitude are shown to be possible. Steady-state spatial maps depicting the displacement transmissibility field were generated from experiments and correlated with simulations to bring out underlying mechanisms. In addition, both lumped parameter and continuum models are considered to aid the design of scalable, passive adaptive metamaterial waveguides for applications ranging from seismic wave mitigation to MEMS transduction.

Commentary by Dr. Valentin Fuster
2018;():V002T08A002. doi:10.1115/SMASIS2018-7935.

Shape-memory polymers (SMPs) as stimuli-responsive shape-changing materials gained significant interest in recent years. Their developments have challenged the conventional understanding of the polymer effect and have further enhanced and broadened the applications of the smart materials. Nowadays, 4D printing is seen as an emerging technology that combines smart materials and additive manufacturing, which can be used to design active mechanical structures. It provides tremendous potential for engineering applications which is capable of producing complex, stimuli-responsive 3D structures. While many “ad hoc” designs of 4D printed solutions have been progressively developed for a specific process, the general approach of additive manufacturing that integrates smart materials in real time across an entire product development process is not pervasive in the industry. To solve this issue, the authors propose a general 4D printing oriented framework for the design of multi-functional SMPs architectures. This framework is not intended to be an exhaustive and specific instruction but is instead a means to motivate these designers to seek the process of applying these unique functional materials to their own designs and applications. It will be useful and give more insight into the design process of the SMP device.

Commentary by Dr. Valentin Fuster
2018;():V002T08A003. doi:10.1115/SMASIS2018-7960.

Bayesian statistics is a quintessential tool for model validation in many applications including smart materials, adaptive structures, and intelligent systems. It typically uses either experimental data or high-fidelity simulations to infer model parameter uncertainty of reduced order models due to experimental noise and homogenization of quantum or atomistic behavior. When heterogeneous data is available for Bayesian inference, open questions remain on appropriate methods to fuse data and avoid inappropriate weighting on individual data sets. To address this issue, we implement a Bayesian statistical method that begins with maximizing entropy. We show how this method can weight heterogeneous data automatically during the inference process through the error covariance. This Maximum Entropy (ME) method is demonstrated by quantifying uncertainty in 1) a ferroelectric domain structure model and 2) a finite deforming electrostrictive membrane model. The ferroelectric phase field model identifies continuum parameters from multiple density functional theory calculations. In the case of the electrostrictive membrane, parameters are estimated from both mechanical and electric displacement experimental measurements.

Commentary by Dr. Valentin Fuster
2018;():V002T08A004. doi:10.1115/SMASIS2018-7963.

This document condenses the results obtained when 3D printing lenses and their potential use as diffraction gratings using Digital Light Processing (DLP), as an additive manufacturing technique. This project investigated the feasibility of using DLP additive manufacturing for producing custom designed lenses and gratings. DLP was identified as the preferred manufacturing technology for gratings fabrication. Diffraction gratings take advantage of the anisotropy, inherent in additive manufacturing processes, to produce a collated pattern of multiple fringes on a substrate with completely smooth surfaces. The gratings are transmissive and were manufactured with slit separations of 10, 25 and 50 μm. More than 50 samples were printed at various build angles and mechanically treated for maximum optical transparency. The variables of the irradiance equation were obtained from photographs taken with an optical microscope. These values were used to estimate theoretical irradiance patterns of a diffraction grating and compared against the experimental 3-D printed grating. The resulting patterns were found to be remarkably similar in amplitude and distance between peaks when compared to theoretical values.

Commentary by Dr. Valentin Fuster
2018;():V002T08A005. doi:10.1115/SMASIS2018-7982.

Elastocaloric cooling is a novel environment-friendly alternative to vapor compression-based cooling systems. This solid-state cooling technology uses NiTi shape memory alloys (SMAs) as cooling medium. SMAs are well known for lightweight actuator systems and biomedical applications, but in addition, these alloys exhibit excellent cooling properties. Due to the high latent heats activated by mechanical loading/unloading, large temperature changes can be generated in the material. Accompanied by a small required work input, this also leads to a high coefficient of performance superior to vapor compression-based systems. In order to access the potential of these alloys, the development of suitable thermodynamic cooling cycles and an efficient system design are required. This paper presents a model-based design process of an elastocaloric air-cooling device. The device is divided into two parts, a mechanical system for continuously loading and unloading of multiple SMA wire bundles by a rotary motor and a heat transfer system. The heat transfer system enables an efficient heat exchange between the heat source and the SMA wires as well as between the SMA wires and the environment. The device operates without any additional heat transfer medium and cools the heat source directly, which is an advantage in comparison to conventional cooling systems. The design of this complex device in an efficient manner requires a model approach, capable of predicting the system parameters cooling power, mechanical work and coefficient of performance under various operating conditions. The developed model consists of a computationally efficient, thermo-mechanically coupled and energy based SMA model, a model of the system kinematics and a heat transfer model. With this approach, the complete cooling system can be simulated, and the required number of SMA wires as well as the mechanical power can be predicted in order to meet the system requirements. Based on the simulation results a first prototype of the elastocaloric cooling system is realized.

Commentary by Dr. Valentin Fuster
2018;():V002T08A006. doi:10.1115/SMASIS2018-8007.

Liquid metal (LM) alloys such as eutectic gallium indium (EGaIn) and gallium-indium-tin (Galinstan) have been used in the fabrication of soft and stretchable electronics during the past several years. The liquid-phase and high electrical conductivity of these materials make them one of the best candidates for fabrication of deformable electronics and multifunctional material systems. While liquid metals are highly reliable for fabrication of simple circuits and stretchable microfluidic devices, their application for producing complex circuits faces fabrication challenges due to their high surface tension and surface oxidization. In this study, we propose a scalable, cost-effective, and versatile technique to print complex circuits using silver nanoparticles and transform them into stretchable electronics by incorporating eutectic gallium indium alloys to the circuit. As a result, the deposited liquid metal considerably increases the electrical conductivity and stretchability of the fabricated electronics. The reliability and performance of these stretchable conductors are demonstrated by studying their electromechanical behavior and integrating them into skin-like electronics, termed electronic tattoos.

Commentary by Dr. Valentin Fuster
2018;():V002T08A007. doi:10.1115/SMASIS2018-8032.

Twenty-two years ago, adaptive munitions using piezoelectric actuators were conceived. The Barrel-Launched Adaptive Munition (BLAM) program used piezoelectric elements to articulate a 10 deg. half-angle conical section on the nose of a 73 mm caliber supersonic wind tunnel model. The test article was designed to pivot the forward portion of the round about the aerodynamic center (which was collocated with the forward section center of gravity). While effective in trim articulation, the majority of actuator power was expended resisting nose inertia rather than manipulating air loads. Adaptive actuators for guided munitions have progressed greatly since that time. In 2001, major advances canard articulation for guided bullets were achieved. These were followed by the Shipborne Countermeasure Range-Extended Adaptive Munition (SCREAM) program. While the piezoelectric effectors designed for these historic programs would allow for respectable deflections, the invention of post-buckled piezoelectric (PBP) actuation would dramatically boost total deflection levels while maintaining full blocked force capabilities. These PBP actuators would be used in a variety of flight control mechanisms for different classes of UAVs. In addition to these applications, the high bandwidth of piezoelectric actuators are particularly well suited to guided munitions. This paper describes the structural mechanics and dynamics of the PBP-class actuator as integrated in guided munitions. As a critical element in ultra-high bandwidth flight control actuation, PBP actuators have been shown to possess pseudo-corner frequencies in excess of 1 kHz. Additionally, PBP actuators have been integrated into tight packing volumes in guided cannon shells while demonstrating setback acceleration tolerances of tens of thousands of g’s. Previous work illustrates several different actuation configurations as well as integration methods with canards and fins. This study links the structural mechanics of previous authors with aeromechanics to arrive at performance predictions in aerial combat. The paper lays out a guided aerial round based on the PBP concept, then uses circular error probable (CEP) predictions in a standard atmosphere quantify the required deflections for engagement of a variety of targets. The results show one order of magnitude fewer rounds being expended per kill in direct air-to-air engagements with peer aircraft. The paper shows that PBP-class actuators could be used for defensive engagements as well with the engagement of oncoming hostile missiles. The paper concludes with prediction of engagement improvements for modern aircraft like the F-35 with 25 mm rounds as well as aircraft like the F-15 with 20 mm guided ammunition.

Topics: Munitions
Commentary by Dr. Valentin Fuster
2018;():V002T08A008. doi:10.1115/SMASIS2018-8048.

Fused deposition modeling (FDM) is highly commercialized Rapid Prototyping (RP) technology for its ability to build complex parts with low cost in a short period of time. The process parameters in the FDM play a vital role in the mechanical properties of the polymeric parts. Most of the research studies show that the variable parameters such as orientation, layer thickness, raster angle, raster width, and air gap are some of the key parameters that affect the mechanical properties of FDM-processed polymeric parts. However, no reports have been made regarding the influence of nozzle diameter with raster width on the tensile properties of FDM fabricated polymeric parts.

This work was devoted to achieving improved and isotropic mechanical properties in polycarbonate (PC) and PC/carbon nanotube (PC/CNT) nanocomposites by investigating the effect of printing parameters in FDM process. The nozzle diameter to raster width ratio, α was found to significantly affect the mechanical properties. The printing direction dependency in tensile properties were studied with the ratio α < 1 and α≥ 1 at three different raster angles of 0°, 45°/−45° and 90°. For α < 1, Ultimate tensile strength and modulus of elasticity were higher for 0°, compared to 45°/−45° and 90° raster angles. However, for α ≥ 1, the ultimate tensile strength and the modulus of elasticity showed little dependency to print direction. This certainly determines the decrease in anisotropy at higher values of α. Mesostructure characterization with microscopy and image analysis were used to further explain the printing behavior and the resultant properties of the printed samples.

Commentary by Dr. Valentin Fuster
2018;():V002T08A009. doi:10.1115/SMASIS2018-8049.

This paper presents a motor driven wrist brace that can adjust its stiffness by changing its mesoscale geometry. The design involves a plate structure that folds from a flexible flat shape to a stiff corrugated shape by means of a motor driven tendon. The structure is built using a laminate of rigid and flexible layers, with embedded flexural hinges that allow it to fold. The paper proposes a simplified analytical model to predict stiffness, and physical three-point bending tests indicate that the brace can increase its stiffness up to fifty times by folding.

Commentary by Dr. Valentin Fuster
2018;():V002T08A010. doi:10.1115/SMASIS2018-8087.

Since its inception by Richard Feynman in 1982, quantum computing has provided an intriguing opportunity to advance computational capabilities over classical computing. Classical computers use bits to process information in terms of zeros and ones. Quantum computers use the complex world of quantum mechanics to carry out calculations using qubits (the quantum analog of a classical bit). The qubit can be in a superposition of the zero and one state simultaneously unlike a classical bit. The true power of quantum computing comes from the complexity of entanglement between many qubits. When entanglement is realized, quantum algorithms for problems such as factoring numbers and solving linear algebra problems show exponential speed-up relative to any known classical algorithm. Linear algebra problems are of particular interest in engineering application for solving problems that use finite element and finite difference methods. Here, we explore quantum linear algebra problems where we design and implement a quantum circuit that can be tested on IBM’s quantum computing hardware. A set of quantum gates are assimilated into a circuit and implemented on the IBM Q system to demonstrate its algorithm capabilities and its measurement methodology.

Commentary by Dr. Valentin Fuster
2018;():V002T08A011. doi:10.1115/SMASIS2018-8169.

The ability to sense neural activity using electrodes has allowed scientists to use this information to temporarily restore movement in paralyzed individuals using brain-computer interfaces (BCI). However, current electrodes do not provide chronic recording of the brain due to the inflammatory response of the immune system caused by the large (∼ 20–80 μm) size of the shanks, and the mechanical mismatch of the shanks relative to the brain. Electrode designs are evolving to use small (< 15 μm) flexible neural probes to minimize inflammatory responses and enable chronic use. However, their flexibility limits the scalability — it is challenging to assemble 3D arrays of such electrodes, to insert the arrays of flexible neural probes into the brain without buckling, and to uniformly distribute them into large areas of the brain. Thus, we created Shape Memory Alloy (SMA) actuated Woven Neural Probes (WNPs). A linear array of 32 flexible insulated microwires were interwoven with SMA wires resulting in an ordered array of parallel electrodes. SMA WNPs were shaped to an initial constricted profile for reliable insertion into a tissue phantom. Following insertion, the SMA wires were used as actuators to unravel the constricted WNP to distribute electrodes across large volumes. We demonstrated that the WNPs could be inserted into the brain without buckling and record neural activity. In separate experiments, we showed that the SMA could mechanically distribute the WNPs via thermally induced actuation. This work thus highlights the potential of actuatable WNPs to be used as a platform for neural recording.

Commentary by Dr. Valentin Fuster
2018;():V002T08A012. doi:10.1115/SMASIS2018-8208.

Using fused deposition modeling (FDM) 3D printing, we combine a bio-inspired bilayer architecture with distributed pre-stress and the shape memory behavior of polylactic acid (PLA) to manufacture shells with switchable bistability. These shells are stiff and monostable at room temperature, but become elastic and bistable with fast morphing when heated above their glass transition temperature. When cooled back down, the shells retain the configuration they were in at the elevated temperature and return to being stiff and monostable. These programmed deformations result from the careful design and control of how the filament is extruded by the printer and therefore, the resulting directional pre-stress. Parameter studies are presented on how to maximize the pre-stress for this application. The shells are analyzed using nonlinear finite element analysis. By leveraging the vast array of geometries accessible with 3D printing, this method can be extended to complex, multi-domain shells, including bio-inspired designs.

Commentary by Dr. Valentin Fuster
2018;():V002T08A013. doi:10.1115/SMASIS2018-8225.

Knitted Textiles made from Nickel-Titanium (NiTi) shape memory alloy wires are a new structural element with enhanced properties for a variety of applications. Potential advantages of this structural form include enhanced bending flexibility, tailorable in-plane, and through-thickness mechanical performance, and energy absorption and damping. Inspection of the knit pattern reveals a repeating cell structure of interlocking loops. Because of this repeating structure, knits can be evaluated as cellular structures that leverage their loop-based architecture for mechanical robustness and flexibility. The flexibility and robustness of the structure can be further enhanced by manufacturing with superelastic NiTi. The stiffness of superelastic NiTi, however, makes traditional knit manufacturing techniques inadequate, so knit manufacturing in this research is aided by shape setting the superelastic wire to a predefined pattern mimicking the natural curve of a strand within a knit fabric. This predefined shape-set geometry determines the outcome of the knit’s mechanical performance and tunes the mechanical properties. In this research, the impact of the shape setting process on the material itself is explored through axial loading tests to quantify the effect that heat treatment has on a knit sample. A means of continuously shape setting and feeding the wire into traditional knitting machines is described. These processes lend themselves to mass production and build upon previous textile manufacturing technologies. This research also proposes an empirical exploration of superelastic NiTi knit mechanical performance and several new techniques for manufacturing such knits with adjustable knit parameters. Displacement-controlled axial loading tests in the vertical (wale) direction determined the recoverability of each knit sample in the research and were iteratively increased until failure resulted. Knit samples showed recoverable axial strains of 65–140%, which could be moderately altered based on knit pattern and loop parameters. Furthermore, this research demonstrates that improving the density of the knit increases the stiffness of the knit without any loss in recoverable strains. These results highlight the potential of this unique structural architecture that could be used to design fabrics with adjustable mechanical properties, expanding the design space for aerospace structures, medical devices, and consumer products.

Commentary by Dr. Valentin Fuster
2018;():V002T08A014. doi:10.1115/SMASIS2018-8245.

Robotic Materials are materials that have sensing, computation and, possibly actuation, distributed throughout the bulk of the material. In such a material, we envision semiconducting polymer based sensing, actuation, and information processing for on-board decision making to be designed, in tandem, with the smart product that will be implemented with the smart material. Prior work in printing polymer semiconductors for sensing and cognition have focused on highly energetic inkjet printing. Alternatively, we are developing liquid polymer extrusion processes to work hand-in-hand with existing solid polymer extrusion processes (such as Fused Deposition Manufacturing - FDM) to simultaneously deposit sensing, computation, actuation and structure. We demonstrate the successful extrusion printing of conductors and capacitors to impedance-match a new, higher-performance organic transistor design that solves the cascading problem of the device previously reported and is more amenable to liquid extrusion printing. Consequently, these printed devices are integrated into a sheet material that is folded into a 3-D, six-legged walking machine with attached electric motor.

Commentary by Dr. Valentin Fuster

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