Recent advances in microprojectile impact tests have opened a new route to explore the behaviors of nanomaterials under extreme dynamic conditions. For example, impact tests have revealed that the specific penetration energies of ultrathin polymer films are remarkably high compared to the energies of conventional protective materials. The current experimental techniques are, however, unable to elucidate some of the complex atomistic mechanisms associated with the penetration process, which can only be realized through atomistic simulations.

We conducted comprehensive molecular dynamics (MD) simulations using both density functional theory (DFT) and classical force fields to investigate the behavior of nanoscopic multilayers under shock loading. We first conducted DFT-based quantum MD simulations to compute the shock Hugoniot of polymers (i.e. polyurea and polyurethane) and compared them with the available experimental data. Subsequent comparisons of the DFT-based MD simulation results with the corresponding classical MD simulations revealed the upper limits of the shock speed that can be accurately modeled using non‑reactive force fields. Thereafter, we employed classical MD to explicitly model the dynamic shock wave propagation and spallation of isolated polymers, as well as polymer/ceramic and polymer/metal multilayers. Finally, we conducted large-scale MD simulations of ballistic impact tests on the multilayers to investigate the atomistic mechanisms associated with the penetration process.

Based on this work, we have published four journal articles [1-4], and another one is under review [5]. A one-minute overview of my presentation at the Mach 2021 conference last week, which highlights our work published in Ref. [3], is available here: https://youtu.be/WgtMYi20bRk; the full presentation is available here: https://youtu.be/DkPizzJ6_Hk

I have shared several MD and DFT models, used for this study, as well as some other useful information on my GitHub page. For example, MD (LAMMPS) input files to model a polymer-metal interface are available here: https://github.com/nuwan-d/polymer_metal_interface. Moreover, LAMMPS and DFT (VASP) models used to compute the parameters for modeling adhesion between SiC and polyurea in Ref. [3] are available here: https://github.com/nuwan-d/SiC_polyurea_interface

References

[1] Dewapriya, M. A. N. & Miller, R. E. Molecular Dynamics Study of the Mechanical Behavior of Ultrathin Polymer Metal Multilayers Under Extreme Dynamic Conditions. Comput. Mater. Sci. 184, 109951 (2020).

[2] Dewapriya, M. A. N. & Miller, R. E. Superior Dynamic Penetration Resistance of Nanoscale Multilayer Polymer/Metal Films. J. Appl. Mech. 87, 121009 (2020).

[3] Dewapriya, M. A. N. & Miller, R. E. Molecular dynamics study of the penetration resistance of multilayer polymer/ceramic nanocomposites under supersonic projectile impacts. Extreme Mech. Lett. 44, 101238 (2021).

[4] Dewapriya, M. A. N. & Miller, R. E. Energy Absorption Mechanisms of Nanoscopic Multilayer Structures Under Ballistic Impact Loading. Comput. Mater. Sci. 195, 110504 (2021).

[5] Dewapriya, M. A. N. & Miller, R. E. Molecular Dynamics Simulations of Shock Propagation and Spallation in Amorphous Polymers. J. Appl. Mech. (2021).