Effects of micrometer-scale cavities on the shock-to-detonation transition in a heterogeneous LX-17 energetic material

Cavities and other fracture structures within energetic materials may have significant impact on their performance. The mechanism on how hot spots induced by cavity collapse affect the detonation initiation process is still not fully understood. In this work, two-dimensional simulations are conducted for heterogeneous LX-17 energetic material containing array-distributed cavities to investigate the detonation initiation process induced by the impaction of the incident shock wave (ISW), and the impacts of cavity size and volume fraction on the shock-to-detonation transition (SDT) are also evaluated. First, we fix the cavity radius to be 40 mu m and the cavity volume fraction to be 12.57%, and compare the detonation initiation processes for neat and heterogeneous LX-17 energetic materials. The results indicate that cavities within LX-17 can accelerate the detonation initiation, i.e., shortening the initiation distance and time. Then, the flow characteristics and incident shock wave evolutions during the cavity collapse process are analyzed. The results show that the interaction between the cavity and the incident shock wave results in the local hot spots and causes LX-17 reactant to auto-ignite, so as to accelerate the shock-to-detonation transition. Finally, the influence of the cavity size and volume fraction on the detonation initiation process is assessed. It is found that as the cavity volume fraction increases, the detonation initiation distance and time increase and even become larger than the results predicted of the neat case, i.e., the acceleration effect of cavities on the detonation initiation weakens and the cavities even inhibits the shock-to-detonation transition. When the cavity volume fraction is fixed, it is found cases of small-size cavity predict longer initiation distance and time than cases of large-size cavity. The analysis indicates that increasing cavity volume fraction corresponds to smaller density of LX-17 reactant, and the hot spot duration time is shorter for cases of small-size cavity than cases of large-size cavity. Therefore, the detonation initiation distance and time increase as the cavity volume fraction increases and the cavity size decreases.