Rate-dependent molecular size effects govern the inverse thickness dependence of specific penetration energy in nanoscale thin films

HL White and W Chen and NM Pugno and S Keten, EXTREME MECHANICS LETTERS, 81, 102419 (2025).

DOI: 10.1016/j.eml.2025.102419

Laser-induced projectile impact tests (LIPIT) enable evaluation of thin film mechanical properties at strain rates on the order of 108 s-1. A popular metric for comparing material performance in LIPIT is the specific penetration energy (Ep*) which is meant to represent the microprojectile's energy loss normalized by the impacted film plug. However, recent LIPIT and LIPIT-like simulations have revealed in polymer-based films an inverse dependence of Ep* on nanoscale film thickness, indicating the presence of dissipative mechanisms unique to this scale. Here we report this same inverse thickness dependence in multilayered graphene oxide (GO) thin films subjected to LIPIT-like molecular dynamics simulations. A previously proposed analytical model is adjusted to suit layered materials such as GO. The influence of this model's parameters is probed with the aid of a Gaussian process metamodel, revealing that the aforementioned scaling is most dramatic when graphene oxide flakes are large and impact velocity is low. This work builds upon many theories pertaining to the mechanisms contributing to inverse dependence of Ep* on film thickness and will inform subsequent work on molecular design of ballistic impact-resistant thin films.

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