Study On Damage,Fracture And Constitutive Relation Of PBX

PBX is the abbreviation of polymer bonded explosive, it is a kind of condensed explosives composed of explosive granules and polymer. PBX is the main charge of weapon and its mechanical behavior is crucial to the weapon. In the first chapter of this dissertation the material and explosive characters of PBX were discussed. The author concluded that PBX and its mock material are belongs to the class of particulates-fihled polymer composites. After that, the character of PBX抯 mechanical behavior and its research development were discussed. Then, the dissertation, based on PBX with determined formulation and other formulation PBXs and mock materials, investigated the mechanical behavior of PBX from the aspects of damage mechanics, fracture mechanics, fracture dynamics, dynamic properties and constitutive relations. (1) The investigation of fracture surface of mock material through SEM indicates that the failure modes of mock material are consistent with the PBX. Due to the difference of failure modes of PBX (and mock material) under tension and compression, the mechanical behaviors of PBX are different under the two loading condition. (2) The damage evolution of PBX excites fruitful acoustic emission signals, from which the damage evolution and failure modes can be recognized and the crack propagation path for the cracked structure can be studied. The research indicates that the acoustic emission technique can be applied to the recognition of damage of PBX structure under loading. (3) According to the characters of microstructure and failure modes of PBX under tension, the damage parameter of PBX is defined as the microcrack density of unit area of the cross section of the specimen. The damage parameter is measured by the elastic modulus variation method and the damage evolution equation related to strain is derived (4) The research of the fracture of PBX and mock material indicates that the fracture toughness of these materials can be measured by the single-edged specimen with the non-dimensional crack length between 0.2 iii ,-~1 and 0.3. The fracture toughness of J0B9003 and its mock material are 1/2 1/2 measured as 0.2 MPam and 0.23 MPam respectively. Therefore, the mock material can also mock the fracture property of PBX. The characters of acoustic emission of the PBX and mock material cracked specimens indicate that the crack propagates along the interface of particulates and polymer. From acoustic emission the fracturing point of the specimen can be recognized, then the critical load at fracturing can be determined. (5) The dynamic stress intensity factor (DSIF) of the single-edged cracked specimen of PBX was computed by FEM, the results indicate that the DSIF is determined by the material elastic wave propagation velocity. If the elastic wave velocities of two materials are approximate, the results of DSIF are of little difference. The line-spring model can be used to approximately analyze the DSIF of the single-edged cracked specimen, the result of DSIF is consistent with that by FEM. According to the dynamic response of PBX specimen and the research on the measurement of the dynamic initiation toughness of metal, the method and experimental technique to measure the dynami...