Polymers behave differently than metals under high strain rate loading due to: 1) differing underlying deformation and failure mechanisms and 2) their morphological complexity (crystallinity and crystallite sizes/orientations, amorphous-crystalline interfaces, crosslinks and branch structures).
This work focuses on polyethylene because it is a simple model polymer, with a backbone chain comprised of only CH2 units. Our goal is to fundamentally understand its behavior under high strain rate and shock loading, including crystal phase transformations, and morphological and phase evolution during shock wave propagation. It is known that polyethylene undergoes a phase transformation from orthorhombic to monoclinic under loading, and this work will be used to to explore its strain rate dependence.
There are two components to this work:
1) Gas gun experiments
2) Molecular dynamics (MD) simulations
Once MD simulations can be used to accurately capture polyethylene’s experimental behavior, we will move on to other polymeric systems, leading to the possibility of rational design of polymers using machine learning models based on molecular dynamics and experimental data.