A Constitutive Model for the Non‐shock Ignition and Mechanical Response of PBX Under Low Velocity Impact

ABSTRACT A physical framework is constructed to characterize the viscoelastic‐plastic response, crack damage, and ignition characteristics of polymer‐bonded explosives (PBXs) under low‐velocity impact conditions. This approach enhances the existing viscoelastic statistical crack mechanics model (Visco‐SCRAM) through multiple key advancements. Damage progression is determined using the generalized Griffith criterion for instability, focusing on the most critical (i.e., maximally unstable) crack size instead of an orientation‐averaged crack dimension. The collective effect of numerous microcracks on the dynamic mechanical response of microcrack‐containing materials is captured in a statistical sense through a dominant microcrack represented as an internal variable. A confined Steven test simulation is conducted to validate the model and to investigate the mechanical and thermal responses of PBXs. The analysis reveals that although the radius has a minimal effect on the temperature rise of the specimen, the thickness plays a significant role in determining the velocity threshold, the location of the hot spot, and the extent of temperature increase. The simulation results show that the critical impact velocities are 45 m/s for the oval projectile, 95 m/s for the flat projectile, and 24 m/s for the pin projectile. A comprehensive analysis is provided regarding the differences in temperature rise among the three types of projectiles. Moreover, the study demonstrates that frictional work is the dominant ignition mechanism during low‐velocity impacts. This research presents a new perspective for understanding and predicting the ignition behavior of PBX under such impact conditions.