Research Projects
In general, our research group aims to characterize the behavior of novel and classical materials and structures and derive mathematical models and/or simulation tools that accurately reflect the observed mechanical behavior. We focus on deriving these models from fundamental principles of mechanics and thermodynamics. Accurate and reliable models for the mechanical behavior of materials and structures are increasingly important as engineers have more computational power and can analyze more complex conditions, but such analyses are only as good as the underlying model. Better understanding and predictions can lead to safer, cheaper, more reliable, and more efficient design of structures and machines. Research projects are constantly evolving; however, below are a few examples of current/past projects.
Childbirth Mechanics
An episiotomy, in which a doctor or midwife makes a small incision from the back of the vagina through the perineum towards the anus to widen the vaginal opening, is sometimes used during childbirth to create more room for the fetus to be extracted. However, an episiotomy also creates very high internal stresses in the perineum at the tip of the incision. The objective of this work is to calculate the stress at the tip of the episiotomy under a wide range of conditions, including the geometry and length of the incision, the size of the fetal head, and the properties of the muscle and tissue of the pelvic floor, and to determine when an episiotomy will lead to further tearing of the perineum during childbirth. As such, this work will help guide clinicians and reduce the risk of additional tearing. This work is being done in collaboration with the bMECH Lab at UC Riverside.
Plastic Deformation
Plastic deformation occurs when a material is loaded beyond the elastic limit, and it is especially difficult to predict because it is highly non-linear and history-dependent. We are currently using the models for yield surface distortion to try to improve predictions of multi-axial ratcheting, the accumulation of plastic deformation due to cyclic plastic loading. Predicting ratcheting is especially difficult because any small errors in one cycle accumulate over several cycles, and predicting ratcheting is especially important to foresee and prevent material failure in any structure subject to earthquakes, extreme weather, and/or cyclic mechanical and thermal service conditions.
Mechanics of Ion-Exchange Polymers
Ion-exchange polymers have many uses, including in moisture swing (MS) materials for direct air capture (DAC). We are mechanically characterizing the behavior of these materials and developing a nonlinear, rate-dependent constitutive model to predict the hygro-thermomechanical behavior and damage. This model will be coupled with the transport mechanism to fully capture the chemo-mechanical behavior of these MS materials during DAC. This work is being done with the Climate Solutions Engineering Lab at NAU, as well as ASU and UT Austin.
Magnetic Shape Memory Alloys
Magnetic shape memory alloys (MSMAs) can undergo a recoverable deformation in the presence of a magnetic field or mechanical load as internal martensitic variants reorient. The deformation can be recovered by a magnetic field and/or mechanical load in an orthogonal direction. Our group has developed several thermodynamic-based models to predict the magneto-mechanical behavior of MSMAs, the most recent of which is fully three-dimensional. While this model predicts general trends, it lacks accuracy, so we are currently trying to identify what it is missing and how to improve it. This research is being performed in conjunction with the Multifunctional Materials and Adaptive Systems Lab.
NOTE: This project is not currently active.
Artificial Muscles
Artificial muscle systems have the potential to impact industries ranging from advanced prostheses to miniature robotics. Our group is currently developing and experimentally validating analytic models, manufacturing processes, and applications of twisted polymer actuators, as well as new actuators we developed called "cavatappi". The challenges associated with developing this model include the material's asymmetric nature, the complex twisted geometry, and temperature and load variations. This research is being performed in conjunction with the Dynamic and Active Systems Lab (DASL).
NOTE: This project is not currently active.
Making Cavatappi Actuators
Actuation Mechanism for Cavatappi
Precision Control of Cavatappi Actuator
Cavatappi Energy Storage
Select Publications
Sara Sarbaz, Zhi Xin Liu, Heidi Feigenbaum, Samaneh Bayati, Winston Wang, Jennifer Wade, Husain Mithaiwala, Matthew D. Green, "Characterizing and modeling the mechanical behavior of an anion exchange membrane for carbon capture applications," Polymer Testing, Volume 153, 2025, https://doi.org/10.1016/j.polymertesting.2025.109024
Glen J. D’Silva, Heidi P. Feigenbaum, and Constantin Coicanel, “On the Power and Efficiency of Ni2MnGa Magnetic Shape Memory Alloy Energy Harvesters”, Smart Materials and Structures, 31(7), 075013, 2022. https://doi.org/10.1088/1361-665X/ac72da
Diego R. Higueras-Ruiz, Kiisa Nishikawa, Heidi Feigenbaum, Michael Shafer, “What is an artificial muscle? A comparison of soft actuators to biological muscles”, Bioinspiration & Biomimetics, 17(1), 2021, https://iopscience.iop.org/article/10.1088/1748-3190/ac3adf.
Diego R. Higueras-Ruiz, Michael W. Shafer, and Heidi P. Feigenbaum “Cavatappi Artificial Muscles”, Science Robotics, 6, 53, 2021, https://doi.org/10.1126/scirobotics.abd5383.
Diego R. Higueras-Ruiz, Charles J. Center, Heidi P. Feigenbaum, Amy M. Swartz, and Michael W. Shafer, “Finite Element Analysis of Straight Twisted Polymer Actuators Using Precursor Properties”, Smart Materials and Structures, 30, 20, 025005, 2021, https://doi.org/10.1088/1361-665x/abcaad.
Diego R. Higueras-Ruiz, Heidi P. Feigenbaum, and Michael W. Shafer, “Moisture's significant impact on twisted polymer actuation”, Smart Materials and Structures, 29, 12, 125009, 2020, https://doi.org/10.1088/1361-665X/abc061.
Parma, S., Plesek, J., Marek, R., Hruby, Z., Feigenbaum, H. P., Dafalias, Y. F., “Calibration of a simple directional distortional hardening model for metal plasticity,” International Journal of Solids and Structures, 143(15): 113-124, 2018, https://doi.org/10.1016/j.ijsolstr.2018.02.037.
Welling, C. A., Marek, R., Feigenbaum, H. P., Dafalias, Y. F., Plesek, J., Hruby, Z., Parma, S., “Numerical Convergence in Simulations of Multiaxial Ratcheting with Directional Distortional Hardening,” International Journal of Solids and Structures, 126-127: 105-121, 2017, DOI: 10.1016/j.ijsolstr.2017.07.032.
Feigenbaum, H. P., Ciocanel, C., Eberle, J. L., and Dikes, J. L., “Experimental Characterization and Modeling of a Three-Variant Magnetic Shape Memory Alloy” Smart Materials and Structures, 25(10), 104004, 2016.
Marek, R., Plesek, J., Hruby, Z., Parma, S., Feigenbaum, H.P., and Dafalias, Y.F., “Numerical Implementation of A Model With Directional Distortional Hardening,” ASCE Journal of Engineering Mechanics, page 04015048, 2015.
LaMaster, D.H., Feigenbaum, H.P., Ciocanel, C., and Nelson, I.D., “A 3D Thermodynamic-Based Model for Magnetic Shape Memory Alloys,” Journal of Intelligent Material Systems and Structures, 1-17, 2014.
Feigenbaum, H.P., and Dafalias Y. F., “Directional Distortional Hardening at Large Plastic Deformations,” International Journal of Solids and Structures, 51(23-24): 3904-3918, 2014