Measuring Crack Growth and Rise in Temperature around a Cylindrical Defect in Explosive Simulants under Low‐Pressure and Long‐Pulse Loadings

Low‐pressure and long‐pulse loadings are critical loading modes in research on non‐shock ignition. Under such loadings, viscoplastic deformation, fracture, and a local rise in temperature may occur around inherent defects in condensed explosives to cause non‐shock ignition. In this study, transparent poly(methyl methacrylate) was chosen as an explosive simulant to elucidate the processes of crack growth, pore collapse, and rise in temperature at a cylindrical defect by using a set of modified split Hopkinson pressure bars. A recently developed optical temperature‐sensing technique that uses the multiphonon‐assisted anti‐Stokes‐to‐Stokes fluorescence intensity ratio was used to monitor the rise in temperature in the cracks. By combining the work here with our previous research, two significant conclusions are arrived at: 1) Around the cylindrical defect, the opening‐mode crack initiated earlier than the shearing‐mode crack did but its rate of propagation was considerably lower. Moreover, the smaller the cylindrical defect was, the lower was the rate of propagation of the cracks. 2) The rise in temperature in shearing‐mode cracks was higher than that of the opening‐mode cracks. It can be inferred that the local rise in temperature caused by shearing was the major factor leading to the non‐shock ignition of condensed explosives