A Study on mechanisms of cleavage crack propagation of polycrystal metallic materials in crystal grain size level

点击翻译按钮获取中文摘要

We studied on mechanisms of cleavage crack propagation in steels from mesoscopic view by 2-D numerical simulations and investigated the effects of some factors on crack path and morphology of the fractured surface. Assumptions used in simulations are that a crack propagates through cleavage plane of each grains and fracture initiation is dominated by maximum tensile stress of that plane. Stress field solutions of crack by FEM and the kink-crack analysis of Cottrel & Rice were used in simulation. For small scale yielding crack in the multi-axial stress mode, the solutions by Shih was used, too. The results simulated were compared with Charpy test and other fracture tests. As for the crystal grain diameter, fracture surface for random size of grains was rougher than constant one, and elastic-plastic cracks than elastic. Irregularity of fractured surface of cristal textures was increased as compared to the case of random distributed grains. These correspond with the experimental results from the viewpoint of tendency. Although the pop-in phenomena have been considered to take place by non-homogenious toughness of materials, it was shown that a small ckack could stop by only crack kinks. As far as crack is small, the above things can be said. But, when initial crack size is large, crack path becomes almost constant despite of grain sizes and cristal textures.