Crack nucleation and growth induced by thermal phase transition for polymer bonded energetic composite materials

Understanding thermophysical and thermomechanical damage behaviors of polymer-bonded energetic composite materials (PBECMs) is fundamental to the design of advanced safe munition structures. Herein, the effects of thermal expansion and phase transition in energetic crystal, thermal softening of binders, binder-crystal interface debonding, and heating rate on cracking damage in PBECMs are quantitated from the viewpoint of mechanics. An original thermomechanical crystal model integrating with anisotropic thermoelasticity, thermal expansion and phase transition is developed for energetic crystal. Damage and debonding at the interface and intracrystalline fracture are modelled by a bilinear traction-separation cohesive law. The results show that the occurrence of phase transition induces a prominent increase of volume deformation and contributes to mutual compression between crystals and mismatch shear deformation at the interface, thereby multiplying crack density. Inhomogeneous thermal stress field and crack distributions are related to anisotropic thermal expansion and phase transition behaviors of crystals. The predicted thermally cracking behaviors in PBECMs, including critical temperature to crack formation, crack nucleation position and growth mode, are consistent with experimental results.