Session: 03-01-01: Mechanics of Penetration, Shockwaves, and High-Strain-Rate Events: Modeling and Experiments

Paper Number: 99977

99977 - Molecular Dynamics Simulations of the Shock Response of Homopolymers and Copolymers 

The shock wave response of various homopolymers and copolymers are investigated by large-scale all-atom Molecular Dynamics (MD) simulations. Polymers have been investigated for their energy dissipation capacity under high strain rates and have shown potential to attenuate shock waves.  During the high pressure state created by shock loadings, polymers can undergo complex phase transitions and morphological rearrangements that enhance the dissipative properties of the material.  Phase separated copolymers have been shown to attenuate shock wave through impedance mismatch between the hard and soft domains initiating a high number of wave reflections. However, the molecular structure-property-performance relationships for enhanced shock wave dissipation are not entirely understood.  In this work, we study the shock response of various homopolymers (polycarbonate, polymethyl methacrylate, polyethylene, polystyrene, etc.) that exhibit a wide range of molecular structures and mechanical properties to determine the molecular characteristics that produce enhanced shock wave attenuation.  Additionally, the shock response of a styrene-isobutylene-styrene phase separated copolymer is investigated to determine the effect of reflective shock waves due to impedance mismatched phases.

For this work, two methods are used to investigate the shock response: the equilibrium Multiscale Shock Technique (MSST) and the nonequilibrium piston method.  The MSST method well reproduces the experimental shock Hugoniot data for all polymers but does not give insight into the dynamics associated with shock waves, such as free surface wave reflection and tensile damage. The Hugoniot shock velocity (U_s) versus particle velocity (U_v) relationships are predicted and are in agreement with available experimental results.  The shock response produces a mostly linear U_s vs. U_v relationship that deviates slightly from experimental predictions at elevated shock pressures in polymers containing ring structures.    Using the piston method, the shock Hugoniot relationships are also well predicted. The damage (voids) accumulated during nonequilibrium shock is directly observed and the spall strength (tensile pressure failure) is related to the energy dissipation capacity.  The propagation of the shock wave is observed and tracked as it travels through the material.  The free surface velocity and reflected wave velocity is determined.  Many distinct methods for energy dissipation are observed, including shock induced phase transitions, chain conformation changes, and impedance mismatch.  This work provides insights into the mechanics of shock waves in polymers and provides a computational tool to investigate, design, and optimize novel shock resistance materials of the future.

Permission to publish was granted by Director, Geotechnical & Structures Laboratory.

Distribution A: approved for public release, distribution unlimited.

Presenting Author: Andrew Bowman U.S. Army Engineer Research and Development Center

Presenting Author Biography: Dr. Andrew Bowman is a Research Mechanical Engineer for the U.S. Army Engineer Research and Development Center (ERDC). He earned a Ph.D. from Mississippi State University in Mechanical Engineering (2019) and holds bachelor’s degrees in Biological Sciences (2010) and Mechanical Engineering (2014). <br/><br/>Dr. Bowman&#39;s research interest includes molecular dynamics simulation, Integrated Computational Materials Engineering (ICME), high rate damage and fracture modeling, and weapons effect simulations. He has demonstrated research expertise in the area simulation and modeling and has authored several publications including research articles, book chapters, and conference papers. He is a member of the American Society of Mechanical Engineers and serves as a member of the Joint AMD–MD Constitutive Equations Technical Committee.

Authors:

Andrew Bowman U.S. Army Engineer Research and Development Center
Michael Roth U.S. Army Engineer Research and Development Center
Manoj Shukla U.S. Army Engineer Research and Development Center