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

晶粒级多晶金属材料解理裂纹扩展机理研究

• 批准号: 13450407
• 负责人: YOSHINARI Hitoshi
• 金额: $ 7.1万
• 依托单位: The University of Tokyo
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (B)
• 财政年份: 2001
• 资助国家: 日本
• 起止时间: 2001 至 2002
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-13450407/
• 关键词: 2-D numerical simulation; cleavage crack; grain size; crack path; Charpy test; fractured surface; crystal texture; pop-in phenomena; 亀裂伝搬経路; ポップイン挙動; へい開破壊; 結晶粒; シャルピー試験片; 伝播シミュレーション

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.

我们通过二维数值模拟从细观角度研究了钢中解理裂纹扩展的机制，并研究了一些因素对裂纹路径和断口形貌的影响。模拟中使用的假设是裂纹通过每个晶粒的解理面传播，并且断裂萌生由该平面的最大拉应力主导。模拟中使用了有限元法的裂纹应力场解和 Cottrel & Rice 的扭结裂纹分析。对于多轴应力模式下的小规模屈服裂纹，也采用了Shih的解决方案。模拟结果与夏比试验和其他断裂试验进行了比较。晶粒直径方面，随机晶粒断裂面比恒定晶粒断裂面粗糙，弹塑性裂纹比弹塑性裂纹。与随机分布晶粒的情况相比，晶体织构的断裂面的不规则性增加。从趋势的角度来看，这些与实验结果是一致的。虽然弹出现象被认为是由材料的非均匀韧性引起的，但事实证明，小裂纹只能通过裂纹扭结来阻止。只要裂纹很小，就可以说上述的事情。但是，当初始裂纹尺寸很大时，无论晶粒尺寸和晶体结构如何，裂纹路径几乎变得恒定。