Deformation and fracture of LLM-105 molecular crystals studied by nanoindentation

Abstract

Mechanical deformation of crystalline high explosives plays an important role in both the fabrication of polymer-bonded explosives and controlling their sensitivity to mechanically-induced decomposition. Here, we study the deformation behavior of (010)-oriented LLM-105 and β-HMX molecular crystals by nanoindentation with pyramidal (Berkovich) and spherical (19 μm-diameter) indenters. Results reveal indentation elastic moduli of 21 and 18 GPa and Berkovich hardness of 0.73 and 0.65 GPa for LLM-105 and HMX, respectively. For LLM-105 (but not for HMX), indentation stress remains essentially unchanged for spherical indentation strains of ∼10–25%, suggesting that inelastic deformation above a certain strain proceeds via flow at constant stress. Both materials exhibit highly anisotropic surface fracture patterns after Berkovich and spherical indentation, consistent with fracture along (011) cleavage planes. No deformation-induced material decomposition is observed in either material for the indentation conditions used.