About

Professor Michael Philen is an Assistant Department Head for Laboratory Facilities in the Kevin T. Crofton Department of Aerospace and Ocean Engineering at Virginia Tech. He holds a Ph.D. in Mechanical Engineering from The Pennsylvania State University, earned in 2006, and a B.S. in Mechanical Engineering from Texas A&M University. His research expertise encompasses structures and materials, structural dynamics and control, adaptive structures, and smart materials. He is the director of the Aerospace Structures and Materials Laboratory (ASML) and is actively involved in research related to aerospace structures and materials, including bio-inspired structures and systems. Professor Philen has contributed significantly to the field through his leadership roles in professional societies such as the American Society of Mechanical Engineers (ASME) and the American Institute of Aeronautics and Astronautics (AIAA). He has served as chair and co-chair for various technical committees and conferences, and as an associate editor for prominent journals including the Journal of Intelligent Material Systems and Structures and Smart Materials and Structures. His work has earned him multiple awards, including the Dean's Award for Excellence in Service and Teaching, the AIAA Associate Fellow designation, and the Ralph E. Powe Junior Faculty Enhancement Award. His research and service activities reflect a strong commitment to advancing aerospace structures, smart materials, and adaptive systems.

Research topics

• Composite material
• Materials science
• Structural engineering
• Computer Science
• Engineering
• Nanotechnology

Selected publications

• A Transtibial Prosthetic Socket with Integrated Pneumatic Flexible Matrix Composite Actuators to Accommodate for Volume Change: Proof of Concept

  JPO Journal of Prosthetics and Orthotics · 2026-03-16

  article

  Background: Accommodating for residual limb volume change among lower limb prosthesis users remains a persistent challenge. Pressurizing a pneumatic flexible matrix composite actuator (P-FMC) increases the thickness of the P-FMC. Thus, when a P-FMC is integrated into the interior wall of a prosthetic socket, increasing the P-FMC pressure effectively decreases the volume of the socket and enables accommodation for limb volume change. Importantly, the P-FMCs maintain high stiffness when pressurized, thus retaining stiff interface with the limb. Objective: The aim of this study was to evaluate socket comfort during the use of a transtibial socket with integrated novel P-FMCs. Methods: A single male participant had a custom P-FMC socket fabricated with three integrated P-FMCs for localized volume accommodation. The participant used the P-FMC socket while completing three cycles of a physical activity regimen involving 5 minutes of walking, 5 minutes of sitting, and 10 minutes of standing. During each cycle, a different P-FMC pressure control scheme was used. Cycle 1 involved maintaining the P-FMC pressure at a fixed 20 psi throughout all three activities and served as a baseline. Cycle 2 involved adjusting the P-FMC pressure according to the activity. Cycle 3 involved adjusting the P-FMC pressure according to the participant’s preference. Results: Socket comfort scores improved in Cycles 2 and 3 compared to Cycle 1, suggesting the P-FMC socket’s ability to modulate P-FMC pressure improved socket comfort. Conclusions: These results support further investigation of P-FMCs to accommodate for residual limb volume change. Clinical Relevance: A novel pneumatic composite actuator integrated into the interior wall of a prosthetic socket has the potential to help maintain socket fit and user function despite limb volume change. Key attributes of these actuators are that they maintain a high stiffness when actuated and are amenable to automatic control in future applications.

  PublisherDOI

• A high precision laser scanning system for measuring shape and volume of transtibial amputee residual limbs: Design and validation

  PLoS ONE · 2024-07-11 · 1 citations

  articleOpen accessSenior authorCorresponding

  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.

  PublisherOA PDFDOI

• Shape Change of a Flapping Plate using Fluidic Flexible Matrix Composite through Modeling and Experiments

  2024-01-04

  article

  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 (F2MC) 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 F2MC tubes which provide the means of shape actuation. Experimental results from actuating the panel in static conditions showed that F2MC 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 F2MC 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.

  PublisherDOI

• Flexible Matrix Composite Wafers in Smart Prosthetic Sockets for Improved Socket Comfort and Fit

  2024-09-09

  articleSenior author

  Abstract 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.

  PublisherDOI

• Investigation of single and multicell honeycomb reinforced shape memory polymer composites: Shape optimization and experimental characterization

  Journal of Intelligent Material Systems and Structures · 2023-10-07

  articleSenior author

  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.

  PublisherDOI

• Sizing optimization and experimental characterization of a variable stiffness shape memory polymer filled honeycomb composite

  Smart Materials and Structures · 2023 · 5 citations

  Senior authorCorresponding
  • Computer Science
  • Materials science
  • Composite material

  Abstract 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.

  PublisherOA PDFDOI

• Control of a Flapping Plate Shape with Fluidic Flexible Matrix Composites

  AIAA SCITECH 2023 Forum · 2023-01-19 · 2 citations

  articleSenior author

  View Video Presentation: https://doi.org/10.2514/6.2023-0828.vid 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.

  PublisherDOI

• Fabrication and Characterization of Flexible Matrix Composite Wafers

  2023-09-11

  articleSenior author

  Abstract 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.

  PublisherDOI

• Design and Testing of a Variable Stiffness Honeycomb Composite

  2022-09-12

  articleSenior author

  Abstract 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.

  PublisherDOI

• <scp>In‐plane</scp> mechanical properties of <scp>thick‐walled polymer‐filled</scp> honeycomb composites: Analysis and experiments

  Polymer Composites · 2022-09-12 · 6 citations

  articleSenior author

  Abstract 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.

  PublisherDOI

Recent grants

• Cells as an Intelligent Material: An integrated multiscale modeling approach based on coupled responses to chemical, electrical, and mechanical stimuli

  NSF · $561k · 2013–2017

• Smart Prosthetic Sockets: Improved Prosthesis Comfort and Performance Through Adaptive Fluidic Flexible Matrix Composite Technology

  NSF · $402k · 2019–2023

• EFRI-BSBA: Multifunctional materials exhibiting distributed actuation, sensing, and control: Uncovering the hierarchical control of fish for developing smarter materials

  NSF · $2.2M · 2009–2014

Frequent coauthors

• Eric C. Freeman

  University of Georgia

  21 shared

• Carson Squibb

  Virginia Tech

  13 shared

• Ashok K. Kancharala

  Virginia Tech

  12 shared

• Amir Barati Farimani

  9 shared

• N. R. Aluru

  Walker (United States)

  9 shared

• Donald J. Leo

  University of Georgia

  8 shared

• Kon‐Well Wang

  7 shared

• Zhiye Zhang

  First Affiliated Hospital of Henan University of Science and Technology

  6 shared

Labs

• Aerospace Structures and Materials Laboratory (ASML)PI

Education

• Ph.D., Mechanical Engineering

  Pennsylvania State University

  2006

• B.S., Mechanical Engineering

  Texas A&M University

  1998

Awards & honors

• Dean's Award for Excellence in Service (2020)
• AIAA Associate Fellow (2015)
• Dean’s Award for Excellence in Teaching (2011)
• Dean’s Award for Outstanding New Assistant Professor (2010)
• ASME Adaptive Structures and Material Systems Best Paper Awa…