Research On Dynamic Response Characteristic Of PBXCD-2

Safety of the heterogeneous solid explosives becomes an important research field of detonation physics, which has received increasing attention from academic and industrial circles. Currently, the Hot-spot theory of the explosives detonation can only explain the phenomenon of PBX’s explosives under certain stimulation. But, the mechanism of Hot-spot generation is very complicated. There are two ways to study the mechanism of Hot-spot generation, no only the multiple scale method but also the research on dynamic response characteristic、constitutive relation and damage model of explosives, which can provide data and physical models for the research on chemical reaction model and safety assessment of explosion.PBXCD-2 is a kind of explosive which can be used in penetrating weapons. But in mission profile, it will suffer certain overload, which yields local deformation and friction, hence deformation、local damage and temperature increasing. Currentlly, there is not a unified model on both damage and temperature. This thesis is focused on the research of the temperature and damage effect in the dynamic response chracteristic of PBXCD-2. First, the internal damage of PBXCD-2 sample is observed and measured by Scaning Electron Microscopic, which is suffered from quasi-static progressive cyclic loading. Then, based on the stress-strain curves obtained from SHPB experiments with different temperature, finally a constitutive relation involving the strain-rate、the meso-damage evolution and temperature is proposed.There are four parts in the thesis.First, we studied the damage evolution of PBXCD-2 under quasi-static loading. The quasi-static progressive cyclic loading experiment of PBXCD-2 was made by Material Testing System. A series of stress-strain curves of different damage states were obtained in a fixed strain-rate 10-3 s-1. Using meso-scale crack density as a characteristic parameter to describe damage states, after theoretical analysis of damage model, the material damage states under different compressive loading level was achieved from the stress-strain curves. At the same time, the recovered samples were analyzed by SEM. The cracks of recovered samples were counted and measured; therefore the damage information was able to be directly achieved. The difference between the directly and indirectly damage measurements was tiny. This validated our measurements. Using strain as a characteristic parameter to describe compressive loading level, the damage model is finally built. Together with the coefficient of friction that was measured at the second part, several different strain-stress curves were fited. Based on this, we get a better undetstanding about damage effects, and verify the rationality of the damage model.Then we started preliminary frictional experiments of PBXCD-2. Experiments were performed on the Split Hopkinson Pressure Shear Bar system. The friction response between PBXCD-2 and LY12(aluminum alloy)、PBXCD-2 and rubber PBXCD-2 and itself were measured. The analysis of experimental data shows that dynamic friction coefficient of aluminum alloy is about 0.166～0.176, and would not change with the change of impact pressure. But the dynamic friction coefficient of rubber or PBXCD-2 that have viscous effects, increase with the increase of impact pressure. Also, the damage evolution of PBXCD-2 affects the dynamic friction coefficient. Therefore, it is important to form an appropriate temperature-related damage model for understanding of PBXCD-2 frictional response.The third part is about SHPB measurements under different temperatures. PBXCD-2 is a typical casting explosive. Owing to its low impedance and soft texture, cannot obtain valid constitutive data by conventional SHPB tests for its inability to attain uniformity requirement. A modified SHPB method was proposed to get reliable dynamic response data of casting explosive. The piezoelectricity quartz gauges have been used to measure dynamic stress processing of specimen directly and the measured data is used to calculate the stress-strain curve. This modified data processing method has been adopted which can eliminate the effect caused by stress nonuniformness. By using the modified data processing, the signal failure problem caused by long incident pulse can be resolved also. With the modified SHPB method, satisfactory results have been obtained in processing casting explosive SHPB tests under different temperatures.Because of the same damage pattern of dynamic loading and quasi-static loading, it is reasonable to use same damage model to build a damage-related constitutive model. This model was used to describe the other material PBXC-129 SHPB results, and the applicability of this constitutive relation is confirmed. Therefore, we applied this model to analyze SHPB data under different temperatures. Using real strain-rate history curve instead of average strain-rate constant, we get a more accurate result about the temperature effect on the PBXCD-2 dynamic response characteristics. The result shows that the damage and the modulus are changed slowly when the temperature is high or low, but in the middle region around 270K, they are changed dramatically with temperature. According to this characteristic a temperature model is formed, which is capable to describe the temperature effect on the material modulus and damage evolution.Therefore, we propose a constitutive relation concerning the strain-rate、the meso-damage evolution and temperature. Computing results show that this constitutive relation can describes the dynamic response charactristics of PBXCD-2 under different temperatue appropriately.