Study On Damage And Fracture Mechanism Of PBM By Acoustic Emission

This thesis probed into the application of acoustic emission (AE) technique to study the mechanical properties and fracture mechanism of polymer-bonded explosive (PBX), basing on the experiments of mock and real PBX material and structure. Three-point-bending experiments for none-edge-notched and single- edge-notched specimen of mock PBX material had been done. The experiments had obtained plenty of AE signals, and the damage position of the specimen can be determined by these signals. It is proved that the AE technique can monitor the damage and failure process of this material. Based on the result of mock material, the experiments for real PBX material under different loading conditions had been finished, including three-point-bending, compression, tension, and several constant loads. According to the systematic analysis, computation, and discussion, the damage and fracture characteristics of PBX are studied, and some quantitative and qualitative results are gained. AE technique can monitor the whole process of damage evolution and crack propagation of PBX, distinguish the stages of damage initiation, evolution and coalescence, give the exact position of micro-damage starting point and macro-crack breaking point, and inspect the influence of pre-crack. By AE counts ?time curve, the critical fracture load can be determined easily. This critical load can be directly used to compute the fracture toughness K1. In this paper, the fracture toughness of mock and real PBX material under different loading rates was measured. The damage state and the load level can be described by the characteristic parameters of AE signal in different loading stages. Whether Felicity effect appears or not can reflect the inherent characters of material and the influence of experimental conditions, indicating that mock materialcan not really simulate real PBX in some aspects. The damage modes and fracture mechanism can be identified by AE characteristic parameters, which are confirmed by scan electrical microscope, metallurgical microscope and stereo microscope observation. Furthermore, the compression AE test for hemispherical shell of mock PBX material had been done. The experimental data were discussed in several aspects, such as Felicity ratio, loading AE, constant loading AE, and unloading AE. The AE characteristic parameters, especially counts, can be used to describe the damage state. AE parameters can also give warning messages about damage evolution under low stress level and structure failure under high stress level. This thesis has systematically demonstrated the possibility of AE technique to study the mechanical properties and fracture mechanism of PBX. AE signals can not only reflect the damage evolution of small specimen, but also monitor the fracture process of complicated structure. This research widens the application field of AE technique, and provides a efficient method for PBX.