Changes in limb volume and shape among transtibial amputees affects socket fit and comfort. The ability to accurately measure residual limb volume and shape and relate it to comfort could contribute to advances in socket design and overall care. This work designed and validated a novel 3D laser scanner that measures the volume and shape of residual limbs. The system was designed to provide accurate and repeatable scans, minimize scan duration, and account for limb motion during scans. The scanner was first validated using a cylindrical body with a known shape. Mean volumetric errors of 0.17% were found under static conditions, corresponding to a radial spatial resolution of 0.1 mm. Limb scans were also performed on a transtibial amputee and yielded a standard deviation of 8.1 ml (0.7%) across five scans, and a 46 ml (4%) change in limb volume when the socket was doffed after 15 minutes of standing.

Improving comfort is a paramount objective in the design process of a lower- limb prosthetic socket. A common issue with maintaining a comfortable socket fit during the day is that volume changes in the residual limb can result in regions of severe discomfort on the limb. These changes in residual limb volume can occur during both brief and long- term timescales. The objective of this research is to develop smart prosthetic sockets that can adjust for changes in the volume of the residual limb. Flexible Matrix Composites (FMCs) are high performance actuators that exhibit a high mechanical advantage when internally pressurized. FMCs are composed of symmetric layers of carbon fiber surrounding a flexible rubber tube. The actuators are then coiled into custom molds and filled with an elastomer, thus forming the active wafer. While FMCs are typically used for axial actuation, the FMC wafers take advantage of the radial expansion of the actuator to obtain actuation through the thickness of the wafer. Previous research characterized the effect of several design variables on the stiffness and actuation performance of wafer-style FMC actuators. Building upon the previous work, custom FMC wafers are fabricated and integrated into prosthetic sockets, thus forming a smart socket that can accommodate for volume changes. A socket was fabricated with custom wafers designed to target critical regions identified for the participant. An external gas canister and pressure regulation valve was used for precise control of the air pressure within the wafers. The participant was subjected to a physical activity regimen, recording their socket comfort every 150 seconds. The participant's socket comfort score improved using the FMC wafers after actuation.

The purpose of this paper is to explore shape change of a plate undergoing oscillatory heave motions. The shape change will be achieved using a panel embedded with Fluidic Flexible Matrix Composite ((FMC)-M-2) tubes for actuation. The active control of the plate is bio-inspired and is analyzed for propulsive characteristics. Classical Plate Theory and First-Order Shear Deformation Plate Theory will be used with a concentrated tip moment at the free edge to provide a means of modeling. The plate panel was constructed with Dragon Skin Silicone and embedded with two rows of five (FMC)-M-2 tubes which provide the means of shape actuation. Experimental results from actuating the panel in static conditions showed that (FMC)-M-2 tubes are an effective means of prescribing a repeatable shape change to a silicone panel. In comparing the static experimental results to the numerical models, it was found that the deflected plate shape could be most accurately predicted at lower pressures for upward deflection and higher pressures for downward deflections. This indicates a need for further comprehensive experimental analysis on the physics of the (FMC)-M-2 panel to obtain accurate results for larger deflections under an oscillatory motion. When tested in unsteady conditions in a heaving experiment (0.5 Hz to 2.3 Hz), the force measured at frequencies above 1.5 Hz were up to 3.6 times greater than those measured for frequencies below 1.5 Hz.

Honeycomb materials as reinforcements for shape memory polymers have been considered for their commercial availability, ease of geometric tailoring, and high in-plane stiffnesses. The design optimization of these honeycomb cells remains an open field of research, with many approaches taken in formulating the structural optimization problems. This investigation focuses on implementing a shape variable parametrization of the honeycomb to study the possible value of both cell asymmetry and spatially varying cell geometries in multicell networks. A unit cell finite element model framework was developed to predict the in-plane elastic properties of these composites, and two design objectives were selected to be optimized. Pareto fronts were estimated for multiple loading cases and cell wall material models, and experimental results were collected for model validation. The optimization results find that these composites can achieve a large range of performances, with maximum moduli as high as 17.2 GPa. Large asymmetry is found in the optimized cell geometries, and relationships are identified between loading cases and for different wall materials. Furthermore, the experimental results validate the finite element model predictions, with relative errors as low as 20% for the predicted maximum modulus and 2% for the modulus ratio.

Polymer-filled honeycomb composites are composite materials that exhibit effective in-plane moduli greater than either the honeycomb or polymer alone. Previous numerical modeling work by the authors has identified two key mechanisms by which this stiffness amplification is achieved. For thin honeycomb cells, the difference in Poisson's ratio between the infill and honeycomb drives the in-plane composite behavior. For large cell depths, the volume change of the hexagonal cells, acting on the infill polymer, is the dominant factor in stiffness amplification. This work aims to extend these findings to thick walled honeycombs, and to experimentally validate the model predictions while making comparisons to existing analytic models. A unit cell finite element model is created for the composite, with isotropic material properties for the honeycomb and infill obtained from characterization tests on 3D printed honeycomb wall material and polyurethane elastomer infill materials. An experimental investigation is completed, where both empty and polymer filled honeycomb samples are 3D printed and tested for a range of cell geometries, varying the cell angle, cell depth, and infill polymer, and are testing in two in-plane loading directions. The results support both the model predictions of the effective Young's moduli and the mechanisms of stiffness amplification previously found, with a maximum percent error of 16.9% found and an amplification factor of the infill modulus of up 16 demonstrated. The improved understanding demonstrated in this work supports the use of these composites in applications where reinforcement of the honeycomb by a polymer, or vice versa, is desired.

The subject of this paper is part of a larger project where plates subjected to oscillatory heave motion will undergo active reconfiguration, or controlled shape change, to better understand complex fluid structure interactions. The plates will be placed in water near a free surface interface. In this paper, Fluidic Flexible Matrix Composites (F2MC) are explored as an option for active reconfiguration. To assist in designing future panels, both Euler-Bernoulli beam and Timoshenko beam models were used to estimate the plate deflections due to shape change actuation. The F2MC loads were modeled as both a concentrated tip moment and a distributed moment for the Euler-Bernoulli model and as a distributed moment in the Timoshenko model. A plate panel was then constructed with Dragon Skin Silicone with embedded F2MC tubes to validate the models. It was found that the Euler-Bernoulli beam model better predicted the experimental results when the F2MC forces were modeled as concentrated tip moments in both air and under water. Oscar Johansson is a senior undergraduate student studying Ocean Engineering in the Kevin T. Crofton Department of Aerospace and Ocean Engineering at Virginia Polytechnic Institute and State University. He is set to graduate with a B.S. in Ocean Engineering in 2023. Oscar will then continue his studies in the Fall of 2023 towards a Master's degree in Ocean Engineering. He currently serves as the Head of Design for the Human Powered Submarine Team at Virginia Tech. Oscar also worked at Newport News Shipbuilding where he worked on future aircraft carrier concept designs. He is a student member of AIAA. Blake Armstrong is an undergraduate researcher in the Kevin T. Crofton Department of Aerospace and Ocean Engineering at Virginia Polytechnic Institute and State University. Blake is currently enrolled at Virginia Tech studying Aerospace Engineering, with an expected graduation in 2024. He is currently employed with The Boeing Company, in the Accelerated Leadership Program, and is working on the 787 Dreamliner family. Prior to his current position, Blake worked at Mathnasium (2019-2021) as a Math Instructor. Christine Gilbert is an associate professor in the Kevin T. Crofton Department of Aerospace and Ocean Engineering at Virginia Polytechnic Institute and State University. Dr. Gilbert received her PhD from the University of Maryland in Mechanical Engineering in 2012. Prior to her appointment at Virginia Tech, Dr. Gilbert has worked at the U.S. Naval Academy (assistant research professor, 2012 to 2014) and the University of New Orleans (tenure track assistant professor, 2014 to 2016). Dr Gilbert has received both the ONR Young Investigator Award (YIP, 2015) and the NSF CAREER award (2020). She is a member of the American Physical Society (APS) Division of Fluid Dynamics and AIAA.

This study aims at elucidating the synergistic effect of the hybridization of two piezoelectric materials: zinc oxide nanowires (ZnO NWs) and a thin film of lead zirconium titanate (PZT), on the mechanical and energy harvesting performance of carbon fiber reinforced polymer composites beams. Novel synthesis techniques were utilized to develop energy-harvesting composite beams with surface-grown ZnO NWs and sputtered PZT thin films. While not an extraordinarily strong piezoelectric material, ZnO NWs enhanced the strength and damping parameter of the composite due to the increased surface area and mechanical interlocking. The composite comprising two piezoelectric materials showed a substantial gain in stiffness, a 25.8% increase compared to plain composite without piezoelectric materials. The hybrid composite energy harvester based on PZT/ZnO NWs exhibited a significant electric power gain of 733.94% more than that for beams with ZnO NWs compared to 44% improvement for a beam utilizing only PZT. Using PZT thin films with ZnO NWs on carbon fiber could yield a high-performance hybrid composite with excellent mechanical properties and energy harvesting capabilities.

Flexible Matrix Composites (FMCs) are high performance actuators that exhibit a high mechanical advantage when pressurized. These actuators rely on symmetric layers of carbon fiber surrounding a flexible rubber tube. When the fiber angle is less than 55 degrees with respect to the longitudinal axis, these actuators expand radially and contract in length when pressurized. When these actuators are coiled in a disk-shaped wafer, the radial volume change within the composite actuator can be utilized to create a compressive force through the thickness. By varying the actuation pressure, matrix material, fiber winding angle, and inner tubing diameter, the actuation and stiffness properties can be widely varied and suited to the desired application. This research aims to determine the impact on wafer performance by the variation of design parameters. It has been found that increasing the matrix material modulus will increase the overall stiffness of the wafer, while also increasing the maximum load that can be applied. Inversely, a lower modulus matrix will decrease the overall stiffness of the wafer, with the benefit of greater actuation volume. For each combination of fiber and matrix selection, there exists a stratum of pressures allowing for active stiffness and force management during use. From this comprehensive evaluation, a characterization of the wafer performance through experimentation will be reported.

Variable stiffness structures and materials have been considered for many applications, including active vibration control and shape morphing. With regards to shape morphing, variable stiffness materials and composites have been considered for reconfigurable skin materials in aerospace vehicles. Of the many concepts that have been developed for such applications, shape memory polymers (SMPs) are one such promising materials for shape morphing. SMPs exhibit both high modulus ratios and recoverable strains but suffer from a low overall modulus and often require reinforcements, such as honeycomb. This work investigates the design space of such honeycomb reinforced SMPs as variable stiffness materials. Unit cell finite element models are developed for the material, and parametric studies are completed for varying honeycomb cell geometries. A multiobjective, constrained Pareto front optimization is completed for two honeycomb material models and in two loading directions using selected sizing design variables. Pareto fronts are established, and cell geometries are selected and fabricated to experimentally verify the optimized model predictions. The results both predict and demonstrate the advantages of using honeycomb reinforcements for SMPs. Effective in-plane moduli as high as 45 GPa are predicted while achieving a change in modulus of 450X. Compared to existing reinforcement strategies for shape memory polymers, these composites exhibit favorable combinations of both high stiffness and high changes in stiffness with a high degree of tailorability through the honeycomb cell geometry and predicted performances that meet and exceed the state of the art.

Shape Memory Polymer (SMPs) have been of interest for use in morphing structures. Owing to their low cost and density, large stiffness change in excess of 1000X, and easy tailorability, they are an attractive option as a variable stiffness material and in variable stiffness structures. One limitation of these polymers, however, is that they are generally too compliant for high force applications, with maximum moduli less than 3 GPa. It is of interest then to develop methods to increase the modulus of these materials while preserving their stiffness change. In this research a novel multimaterial smart carbon fiber honeycomb is designed as a reinforcement for a styrene SMP infill, creating a variable modulus honeycomb composite. A unit cell finite element model is created, and parametric studies are completed to explore the design space of the composite. Selected cell geometries are fabricated and tested to validate the fabrication method and determine their the in-plane effective modulus, Poisson’s ratio, and stiffness change through SMP activation. The results find increases in modulus over the SMP alone of up to 400%, and modulus close to those of the SMP are found to be possible. Modulus changes of nearly 450X are demonstrated, which is found to be an underprediction owing to experimental uncertainty. The predicted and measured performance of this type of composite, along with the ease of tailoring the cell geometry, represent a potentially attractive option for variable stiffness SMP composites and morphing structures.

Squid possess a mantle that is able to quickly compress an internal fluid, thus providing a jetting locomotion that enables them to be the fastest aquatic invertebrates. The mantle possesses a complex collagen fiber and muscular system, and the primary propulsion is accomplished through circumferential muscles (90°) contracting around the mantel. In addition, jetting is enhanced through elastic energy stored in the helically-wound IM-1 collagen fibers. The angles of these fibers have been measured between 28° and 32° in different species of squid. Inspired by the muscular fiber configuration found in the mantle of squid, novel pumps that use shape memory alloy (SMA) active fibers oriented at precise angles around a cylindrical shell are investigated through experiments and analytical studies. A thermomechanical model of an SMA fiber is presented and the parameters are identified through experiments. Using the thermomechanical model of the SMA fiber, an analytical model of the SMA active fiber pump is presented and is validated through experiments. Results show that maximum pumping power and efficiency is achieved for pumps when the matrix modulus is less than the fiber modulus and the optimal fiber wind angle is ±55°. When the matrix modulus is similar to the fiber modulus, maximum pumping performance is achieved with a wind angle of ±90°, similar to the angle of the circumferential muscles in the squid mantel.

Honeycomb composites are now common materials in applications where high specific stiffness is required. Previous research has found that honeycombs with polymer infills in their cells, here referred to as honeycomb-polymer composites (HPCs), exhibit effective stiffnesses greater than the honeycomb or polymer alone. Currently, the state of analytic models for predicting the elastic properties of these composites is limited, and further research is needed to better characterize the behavior of these materials. In this research, a nonlinear finite element analysis was employed to perfor2m parametric studies of a filled honeycomb unit cell with isotropic wall and infill materials. A rigid wall model was created as an upper bound on the deformable wall model’s performance, and an empty honeycomb model was employed to better understand the mechanisms of stiffness amplification. Parametric studies were completed for infill material properties and cell geometry, with the effective Young’s modulus studied in two in-plane material directions. The mechanisms by which the stiffness amplification occurs are studied, and comparisons to existing analytic models are made. It has been observed that both the volume change within the honeycomb cell under deformation and the mismatch in Poisson’s ratios between the honeycomb and infill influence the effective properties. Stiffness amplifications of over 4000 have been observed, with auxetic behavior achieved by tailoring of the HPC geometry. Additionally, the effect of large effective strains up to 10% is explored, where the cell geometry changes significantly. This research provides an important step toward understanding the design space and benefits of HPCs.

Hexagonal honeycombs and their use in composite structures has become commonplace in aerospace design and other fields. Polymer-filled honeycomb structures, where the hexagonal cells are filled with an elastomer, are of interest for their ability to increase the stiffness of the composite over that of the elastomer or honeycomb individually. Previous research by the authors has demonstrated that the effective behavior of such composites is determined by both the honeycomb geometry as well as the material properties of the infill and cell wall. Infill stiffness amplifications of over three orders of magnitude have been predicted, which could be an attractive option for improving the performance of smart materials such as shape memory polymers. Considering the benefits of such composites, it is of interest to optimize the honeycomb cell geometry to maximize the stiffness increase observed in the infill material. To meet this objective, in this work a unit cell finite element model was created for a hexagonal, thin walled honeycomb. Six design variables describing the honeycomb geometry were selected, and parametric studies of these design variables in the objective have been generated. Informed by these studies, an estimation of the Pareto front has been completed, with chosen objectives of the maximum composite in-plane modulus and modulus ratio, in one material direction. Promising designs are identified, and the range of effective composite properties if discussed. While this problem considers fixed infill properties, the methods applied could readily be extended to smart material infills. The contour plots and performance estimation employed in this research provides an important step in the design of improved smart composites for use in morphing and variable stiffness structures.

Honeycomb composites are common materials in applications where a high specific stiffness is required. Previous research has found that honeycombs with polymer infills in their cells exhibit effective stiffnesses greater than the honeycomb or polymer alone. Currently, the state of analytic models for predicting the effective properties of these honeycomb polymer composites is limited, thus further research is needed to better characterize the behavior of these materials. In this work, a nonlinear finite element analysis was employed to perform parametric studies of a filled honeycomb unit cell with isotropic wall and infill materials. A pinned rigid wall model was created as an upper bound on the deformable wall model's performance, and an empty honeycomb model was employed to better understand the mechanisms of stiffness amplification. Mechanisms by which the stiffness amplification occurs is studied through parametric studies, and the results are compared to current analytic models. It has been observed that both the volume change within the honeycomb cell under deformation, and the mismatch in Poisson's ratios between the honeycomb and infill influence the effective properties. Stiffness amplifications of over 4,000 have been observed, with auxetic behavior achieved by tailoring of the HPC geometry. This research provides an important step toward understanding the design space and benefits of honeycomb polymer composites, and demonstrates the possibilities for variable stiffness structures when considering smart material infill materials.

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.

In the current paper, phospholipid bilayers are modeled using coarse-grained molecular dynamics simulations with the MARTINI force field. The extracted molecular trajectories are analyzed using Fourier analysis of the undulations and orientation vectors to establish the differences between the two approaches for evaluating the bending modulus. The current work evaluates and extends the implementation of the Fourier analysis for molecular trajectories using a weighted horizon-based averaging approach. The effect of numerical parameters in the analysis of these trajectories is explored by conducting parametric studies. Computational modeling results are validated against experimentally characterized bending modulus of lipid membranes using a shape fluctuation analysis. The computational framework is then used to estimate the bending moduli for different types of lipids (phosphocholine, phosphoethanolamine, and phosphoglycerol). This work provides greater insight into the numerical aspects of evaluating the bilayer bending modulus, provides validation for the orientation analysis technique, and explores differences in bending moduli based on differences in the lipid nanostructures.

The remarkable performance of various species of fish in propulsion and maneuvering has motivated the design and analysis of flexible, biomimetic underwater propulsors, which may be particularly suitable to small-scale, unmanned vehicles. In this work, we employ a novel fluid-structure coupled computational framework, referred to as FIVER (a Finite Volume method based on Exact Riemann solvers), to simulate the flapping motion of a fin-and-joint system, which mimics the caudal peduncle and caudal fin of fish, and serves as a simplified engineering model of tail-dominated fish propulsion. This problem is dominated by fluid-structure interaction, featuring a three-dimensional, unsteady fluid flow, large structural motion and deformation, and strong added-mass effect. To handle these challenges, we apply an embedded boundary method and a numerically-stable partitioned procedure to couple a hybrid finite volume finite element computational fluid dynamics (CFD) solver and a nonlinear finite element computational structural dynamics (CSD) solver. First, we validate the CFD and CSD models using experimental data in fundamental vibration frequency, hydrodynamic forces, and structural displacement. Next, we investigate the fluid and structural dynamics, as well as the propulsive performance, focusing on the two-way fluid-structure coupling and the three-dimensional flow variation, which supplements the existing body of literature on biological and bio-inspired fluid dynamics. Further, by comparing a wide, trapezoidal fin and a narrow, forked fin, we investigate the various effects of fin geometry, and more generally, also demonstrate the use of observations and knowledge of biological diversity in the design of engineering systems. (C) 2018 Elsevier Ltd. All rights reserved.

Fluidic flexible matrix composites (F2MCs) are composite tubes that consist of multiple layers of oriented, high performance fibers, such as carbon, precisely placed in a flexible matrix resin to form high-mechanical advantage actuators and variable stiffness materials. Unique to the F2MC tube is its ability to generate high pressures and volume change with a small external load as a result of the stiff reinforcement fiber orientation in the wall of the tube and the soft supporting elastomer. When a load is applied to the tubes, the volume of the F2MC tube is reduced and fluid is forced out of the tube by the reinforcing fibers. This is the first reported research on the design, fabrication, and characterization of F2MC tubes as power take-off (PTO) mechanisms for ocean wave energy conversion where the heaving motion of a floating body in waves provides the axial load that drives fluid through the pumps. An analytical model is developed to predict the performance of F2MC pumps in a variety of test conditions, and 1/50th scale F2MCs pumps are tested in a water basin. The scaled pumps are mechanically cycled between 0 Hz and 2 Hz at up to 17 percent strain replicating ocean waves of varying period and amplitude. Instantaneous input mechanical power and output fluid power values are calculated from force, velocity, pressure, and flow rate measurements, and the actuator efficiency is subsequently determined and compared with the prediction of the analytical model. At 1/50th scale, a maximum power conversion efficiency of 40 percent is obtained for a single pump and a peak output power of 0.21 W is recorded. At full scale, the predicted peak output power is 180 kW, suggesting that F2MC pumps are a promising class of fluid power takeoff (PTO) mechanisms for ocean wave energy conversion, representing a substantial improvement over hydraulic cylinders.

The ninth annual meeting of the ASME Smart Materials, Adaptive Structures and Intelligent Systems Conference ( SMASIS ) was held at the beautiful Stowe Mountain Resort in Stowe, Vermont, USA. It is the conference ’ s objective to provide an up-to-date overview of research trends in the fi eld of smart materials and adaptive structures in a casual forum conducive to the exchange of ideas and latest results. The cross-disciplinary emphasis was re fl ected in keynote presenta-tions by Professor Ralph Smith ( North Carolina State University ) on ‘ Uncertainty Quanti fi cation for Smart Materials and Adaptive Structures ’ , by Dr James Mabe ( Technical Fellow, Boeing Research and Technology ) on ‘ Shape Memory Alloys in Aerospace: Breakthroughs and Roadblocks to Innovation ’ , and by Professor Markus J. Buehler ( Massachusetts Institute of Technology ) on ‘ Multiscale Smart Materials by Design — Connecting Simulation, Design, Synthesis across Multiple Scales ’ . SMASIS 2016 was divided into seven symposia, which span basic research, applied technological design and development, and industrial and governmental integrated system and application demonstrations.

A full-scale commercial aircraft morphing control surface using flexible matrix composite actuators was designed and demonstrated in this research. The muscle-like flexible matrix composite actuator is ideal for morphing structures as it deforms while actuating with the structure, and the hydraulically driven actuator can operate at pressures similar to existing aircraft hydraulic systems. Through a series of parameter studies performed with finite element models, an active spoiler was designed to control the gap between a spoiler and deployed Fowler flap. A full-scale prototype was then fabricated and tested under pseudo-aerodynamic loads. The prototype demonstrated that it can achieve the necessary deflections under the given loading condition. A closed-loop control system that allows the tip deflection of the spoiler to be precisely controlled under loading was designed.