Studies On Elastic-plastic Effects To Ignition Of Granular HMX Under Impact

The ignition and explosion of explosive under low speed impact has brought a hazard to the explosives' component device. The conditions for ignition of the explosives are able to be determined, some preventive measures may be taken for avoiding the occurrence of the accident. During low impact behavior the impacting velocity is generally less than 20m/s. It usually occurs in the experiment called drop hammer test for the measurement of the impact sensitivity of explosives. In order to observe the deforming process of explosive particles that may arouse the formation of hot spot, simulation method has been taken to study such process in HMX particles from the quantitative perspective on the condition of low velocity impact by drop hammer.The impact process for drop hammer was simulated in 2D geometry by using ANSYS/AUTODYN software based on actual drop hammer apparatus. The temperature rise generated in particles was calculated from the heat conversion from the local plastic work. In the study, the explosive sample was particulate HMX. Particles were assumed to be of circular geometry with elastic-plastic deforming properties. Two configurations of explosive sample were considered: one was that all the particles were of the same dimension, being dubbed as regular arrangement, the other was called irregular arrangement by arranging the particles randomly. Both arrangements were composed of 5 layers, each layer consisting of 25 particles; The initial velocity of the drop hammer was calculated from the height of drop hammer using free-falling body formula. The temperature rises in the samples for the cases of(1) different heights of hammer,(2) different yield strength values of the HMX particle,(3) the chemical reaction of HMX particles,(4) the different shape of particles, were carried out respectively. It was found that the temperature rises in the samples were quite different in situations of the regular and irregular arrangements. In the case of regular arrangement the temperature rise is low, only being of 37.2 ?,however, in the irregular arrangement, it reaches the value of 142.9?, nearly approaching the critical ignition temperature obtained by experimental measurement elsewhere. Regarding the yield strength for HMX particle, two magnitudes with high and low values were considered for comparison. The case with smaller yield strength gives a low temperature rise(83.2 ?) in the particles. By the numerical simulation for different shape of HMX particles, the temperature rise from plastic work by particle shape is also altered. Finally, with regard to chemical reaction, the temperature rise is not obvious because of the slow chemical reaction rate. But after a period of time, the heat of chemical reaction accumulation can lead to the ignition of HMX particles.