arXiv subjects

Thao D. Nguyen

Publications and source records attributed to Thao D. Nguyen.

4 recordsLinked to original sources

arXiv2026

A transient nonlinear finite element framework and implementation of coupled electro-chemo-mechanics of polyelectrolyte hydrogels

Polyelectrolyte (PE) hydrogels exhibit complex behavior characterized by large mechanical deformations, nonlinear stress response, solvent transport, and ion diffusion. The interplay between these mechanisms can lead to unexpected swelling dynamics, deformation patterns, and stress response. As such, advanced computational tools are needed for the efficient design of PE hydrogel-based devices, such as actuators and sensors for soft robotics, microfluidic valves, and drug delivery systems. In this work, we develop a numerical framework to simulate the coupled electro-chemo-mechanical behavior of PE hydrogels using finite element analysis. Applying this framework, an electro-chemo-mechanical model for PE hydrogels in a dilute ionic solution is implemented as a user element (UEL) subroutine in Abaqus/Standard. The model and UEL implementation are validated by comparing to experiments in the literature for transient free-swelling of a DMAEA gel in a solution of varying ionic strengths, then applied to study the consolidation behavior under confined compression and the transient bending behavior of a hydrogel bilayer. The simulations show that the ionic strength of the external solution, fixed charge density, and Flory-Huggins parameter play significant roles in the magnitude of the transient swelling and consolidation behavior.

cond-mat.soft↗

arXiv2025

Tension-Induced Soft Stress and Viscoelastic Bending in Liquid Crystal Elastomers for Enhanced Energy Dissipation

Architected materials that exploit buckling instabilities to reversibly trap energy have been shown to be effective for impact protection. The energy-absorbing capabilities of these architected materials can be enhanced further by incorporating viscoelastic material behavior into the buckling elements using liquid crystal elastomers (LCE). In addition to conventional viscoelastic behavior, LCEs also exhibit a highly dissipative rate-dependent soft stress response from mesogen rotation under a mechanical load. However, the buckling elements cannot take advantage of this dissipation mechanism because buckling occurs at strains below the threshold for mesogen rotation. In this study, we investigate tension-induced soft stress behavior as an additional dissipation mechanism in horizontal members of lattice structures composed of tilted LCE beams under compression. Viscoelastic properties of LCEs with two crosslinking densities were characterized experimentally, and a nonlinear viscoelastic model was implemented in Abaqus/Standard as a user-defined element to simulate finite-strain behavior of monodomain LCEs, including soft stress response. Simulations and experiments revealed a non-monotonic dependence of energy dissipation on the thickness ratio between horizontal and tilted LCE members. Optimized structures with stretchable horizontal bars dissipated 2-3 times more energy than rigid-bar counterparts by balancing tension-driven soft stress with viscoelastic beam bending. These findings demonstrate a new design strategy for LCE-based architected materials to enhance energy dissipation.

cond-mat.soft↗

arXiv2023

A Data-Driven Approach to Geometric Modeling of Systems with Low-Bandwidth Actuator Dynamics

It is challenging to perform system identification on soft robots due to their underactuated, high-dimensional dynamics. In this work, we present a data-driven modeling framework, based on geometric mechanics (also known as gauge theory) that can be applied to systems with low-bandwidth control of the system's internal configuration. This method constructs a series of connected models comprising actuator and locomotor dynamics based on data points from stochastically perturbed, repeated behaviors. By deriving these connected models from general formulations of dissipative Lagrangian systems with symmetry, we offer a method that can be applied broadly to robots with first-order, low-pass actuator dynamics, including swelling-driven actuators used in hydrogel crawlers. These models accurately capture the dynamics of the system shape and body movements of a simplified swimming robot model. We further apply our approach to a stimulus-responsive hydrogel simulator that captures the complexity of chemo-mechanical interactions that drive shape changes in biomedically relevant micromachines. Finally, we propose an approach of numerically optimizing control signals by iteratively refining models, which is applied to optimize the input waveform for the hydrogel crawler. This transfer to realistic environments provides promise for applications in locomotor design and biomedical engineering.

cs.RO↗

arXiv2021

Synergistic Energy Absorption Mechanisms of Architected Liquid Crystal Elastomers

Here, we report the rate-dependent energy absorption behavior of a liquid crystal elastomer (LCE)-based architected material consisting of repeating unit cells of bistable tilted LCE beams sandwiched between stiff supports. Viscoelastic behaviors of the LCE material cause the energy absorption to increase with strain rate according to a power-law relationship, which can be modulated by changing the degree of mesogens alignment during synthesis. For a strain rate of 600 s-1, the unit cell structure shows up to a 5 MJ/m3 energy absorption density, which is two orders of magnitude higher than the same structure fabricated from Polydimethylsiloxane (PDMS), and is comparable to the dissipation from irreversible plastic deformation exhibited by denser metals. For a stacked structure of unit cells, viscoelasticity also produces nonuniform buckling of the LCE beams, causing the energy absorption density to increase with the stacking number n up to n=3. Varying the beam geometry further promotes the nonuniform buckling behavior allowing the energy absorption density to increase with stacking number without bounds. We envision that our study can lead to the development of lightweight extreme energy-absorbing materials.

cond-mat.soft↗