Study on friction behavior of HMX crystals based on peridynamic theory

The friction behavior of HMX crystals has attracted significant attention since friction is proven to be a critical factor in causing local heating and even accidental ignition. But the friction mechanisms of HMX single crystals remain elusive. Classical continuum mechanics faces challenges in modeling discontinuities. In contrast, peridynamic (PD) theory has emerged as an effective approach for investigating discontinuous phenomena such as damage evolution. In this study, a frictional contact model for HMX crystals is developed based on the state-based PD theory. The effects of indenter shape, size, scratching depth and scratching velocity on the tribological response of HMX crystals, particularly regarding damage and crack propagation, are investigated. The results indicate that the tribological response is insensitive to changes in scratching velocity. As the scratching depth increases, longer lateral cracks develop for both the spherical and conical indenters, but the median crack propagation depth increases for only the spherical indenter. And the combined action of radial and lateral cracks plays a crucial role in debris peeling. It is also found that increasing the diameter of the spherical indenter results in more shear cracks and rougher scratch surfaces, without affecting the depth of tensile crack propagation. In addition, the normalized material removal volume and its depth sensitivity are greater for the spherical indenter than for the conical indenter. These findings provide valuable insights into the friction mechanisms of the energetic crystal HMX.