Numerical mesoscopic investigations of dynamic damage and failure mechanisms of polymer bonded explosives

A damage elasto-viscoplastic model has been developed for cyclotetramethylenetetranitramine (HMX) crystals, which considers the anisotropy nature of HMX crystals and dislocation-mediated plasticity as well as the cleavage damage. A damage viscoelastic model has been developed for the polymer binder and the interface, which captures rate dependent damage due to binder rupture and binder debonding during the loading process. The proposed models were implemented in the finite element code ABAQUS by the user subroutine VUMAT. Macroscopic mechanical responses of Polymer Bonded explosives (PBXs) 9501 homogenized across the microstructure is generally in agreement with Split Hopkinson Pressure Bar (SHPB) experimental stress-strain responses at the strain rate of 2000 s−1. Microstructural heterogeneity is responsible for the non-uniform stress, strain and damage fields. Crystal fracture is the dominant failure mechanism under dynamic compression while interfacial debonding plays a more important role under dynamic tension. Mesoscale modeling results along with macroscopic responses are significantly important to have a better understanding of deformation, damage and failure mechanisms of PBX samples under dynamic loading and to improve our predictive ability.