DAMAGE FAILURE AND SAFETY OF POLYMER BONDED EXPLOSIVE CHARGES UNDER IMPACT LOADING

Abstract

As energetic composite materials, polymer bonded explosives (PBX) are composed of highly filled explosive crystals and a small of polymer binder. Accidental explosion could occur under low velocity impact. The ignition mechanism has drawn great attention to scientists and engineers. Hotspot is considered to induce the occurrence of ignition. Our works focus on the relation between the microcrack evolution and hotspot formation. The deformation, damage and failure behavior of PBX was investigated by split Hopkinson pressure bar, gas gun impact and penetration. In these dynamic loading experiments, the microstructure of the recovered specimens was analyzed by scanning electron microscope. It reveals that the cracking along the interface between the explosive crystal and the polymer binder under the tension, while the intergranular fracture is the main mode under the compression. The numerical manifold method was developed to simulate the tension and compression behavior. The effect of the initial defect, the strain rate and temperature on the tension and compression behavior was analyzed. The fracture modes of the tension and compression match the dynamic experiments above well. The low impact ignition analysis was conducted by means of Steven impact test. The specimen size effect on the ignition was mainly focused. The ignition observation and ignition delay time were measured. Also, the ignition velocity and reaction level were discussed. In addition, based on Visco-SCRAM model, a mechanical-thermal-chemical coupling model was developed to understand the ignition behavior in Steven impact test. The effect of the impact velocity on the ignition was analyzed. The mechanism of the size effect on ignition was discussed. Different projectile shapes were designed to act on the specimen. The difference of the ignition among these projectiles was compared. Further, the model was applied to simulate the multi impact corresponding to the real application scenarios. Moreover, in order to refine the microcrack evolution, the tension-compression asymmetrical microcrack evolution was proposed. The stochastic distribution of the microcrack length and density produced the ignition uncertainty, and further based on the Monte Carlo method, the ignition probability was quantified. These simulations matched the experimental results well.