Session: 04-09-01: Design of Engineering Materials

Paper Number: 167114

Molecular Dynamics Investigation: High Strain-Rate Response of Polyurea 

Polyurea is increasingly recognized for its ability to mitigate energy from high-velocity impacts and blasts, making it a strategic choice for advanced protective applications ranging from ballistic armor to infrastructure reinforcement. This unique thermoplastic elastomer consists of alternating hard and soft segments, providing a balance of rigidity, strength, and flexibility. Despite being well suited for protective applications, the underlying molecular mechanisms responsible for its exceptional energy mitigating capabilities are not well understood. Bridging this knowledge gap is essential to inform the rational design and optimization of tomorrow’s protective materials.

In this study, we present an investigation of polyurea at the atomistic scale using molecular dynamics (MD) simulations with the LAMMPS software package. Our computational model incorporates the polymer consistent force field (PCFF) and interface force field (IFF), capturing the role of hydrogen bonding in the hard segments and the flexibility of the soft segments. Following a multistage equilibration and annealing procedure, we subject the polymer to a flyer-plate-style compression at a strain rate on the order of 10^10 s⁻¹, simulating a high-velocity impact equivalent to a piston speed of approximately 1 km/s. Global and per-atom quantities—such as temperature, stress, and energy—are tracked over time, while radial distribution functions and positional binning are utilized to evaluate morphological changes at the nanometer scale.

Our preliminary results show pronounced adiabatic heating at the impact interface, effectively dispersing a portion of the kinetic energy through localized temperature deltas of up to 140 K. Stress propagation within the material extends to several GPa before a rapid tensile unloading wave triggers the onset of spallation—marked by void nucleation and coalescence in the polyurea matrix. Additionally, hydrogen bonding among the hard segments exhibits partial dissociation under extreme loading, an effect that is largely reversible during unloading, suggesting a mechanism for energy storage and dynamic recovery. These atomistic observations align with macro-scale trends reported in limited experimental and lower-strain-rate literature, reinforcing the validity of our simulation parameters.

Our findings advance scientific understanding of how polyurea dissipates energy at the molecular level. By expanding on the roles of adiabatic heating, reversible hydrogen-bond dissociation, and polymer densification, this work contributes insights for tailoring polymeric systems to perform optimally under extreme loads. Future directions include parameter validation against emerging ultrafast experimental techniques and comparative analyses with alternative block co-polymers. Ultimately, these results highlight the potential for targeted computational approaches to guide material design, enabling improved performance and safety in a broad range of high-velocity impact scenarios.

Presenting Author: Tyler Collins San Diego State University

Presenting Author Biography: Tyler Collins is a doctoral student in the joint Computational Science program at San Diego State University and the University of California, Irvine. His recent research directions center on computational materials science, leveraging high-performance computing, data-driven modeling, and advanced simulation methods to investigate how materials behave under extreme conditions. He earned his M.S. in Bioengineering from SDSU and B.S. Bioengineering from the University of California, Merced. His interdisciplinary background spans computational modeling, HPC resource optimization, and collaborative research in material design. By bridging fundamental science with practical applications, Tyler aims to guide the development of next-generation protective and functional materials.

Authors:

Tyler Collins San Diego State University
George Youssef San Diego State University
Sara Adibi San Diego State University