The Study Of High Polymer Bonded Explosives By Measuring The Plane Strain Fracture Toughness

The method for measuring the plane strain fracture toughness Klc has been introduce to high polymer bonded explosives (PBX) by systematically studying technologies concerning the shape of specimen, the depth and its machining of crack, the loading rate, the measurement of critical fracture load, and the computation of KlC, etc.The method has been used to test and study Klc of three typical high polymer bonded explosives which are J2, Jl, J3 respectively both at normal temperature and unmoral temperature. The results at normal temperature have shown that KlC of high polymer bonded explosive are very low comparing to metals and some high polymer materials, thus the ability of PBXs to resist crack expanding is very poor, and once some cracks occur inner a structural part of PBXs, the structure will fail very soon and easily. So in the process of machining and production, cracks should be avoided carefully in PBXs parts.Some important laws about KlC of the three typical PBXs above changes with temperature have been obtained as follows: a. with temperature increases, KlC of the three typical PBXs all decreases; b. when temperature higher than 45 ?, KlC of J2 decreases soonest, and when temperature up to 60 ?, KlC of J2 becomes very poor even lower than J1; c. KlC of J3 is higher than J2 and J1 at different temperatures, and this shows the stronger ability of J3 to resist crack expanding.Two probations have been tried to explore the reasons concerning the results above, one of which is by analyzing the compositions of the three PBXs above andshows that the stronger ability of J3 to resist crack expanding is probably mainly due to the use of bonder B2, and another is by using scanning electronic microscope SEM to observe the fracture face morphologies of the specimens at different temperatures. The quantitative observations strongly support the laws of Klc of PBXs changes with temperature is revealed as follows: a. the fracture mode of J3 at different temperature is mainly breaking between crystal mode; b. when temperature lower than 30?, the fracture mode of J2 and J1 is mainly breaking of crystal mode, and at temperature of 45 ?, both breaking between crystal mode and breaking of crystal mode exist at the same time, and at temperature of 60 ?, breaking between crystal mode has played dominate role.