基于内聚力模型的白点萌生机理研究

基于内聚力理论、氢压理论和应力作用下氢富集理论，在以往孔洞锻合研究的基础上，建立了白点萌生扩展的有限元分析模型。研究了初始氢浓度、裂纹长度以及多裂纹耦合作用等多种因素对白点萌生的影响，确定了不同条件下白点萌生的临界氢浓度及其变化趋势。结果表明，氢对白点萌生具有重要的影响，在白点萌生过程中，高浓度的氢聚集在裂纹端部，极大地降低了钢的内聚力强度；对于单裂纹，随着裂纹长度的增加，白点萌生的临界氢浓度逐渐减小并趋于稳定值；当多个密集小裂纹同时存在时，裂纹间的耦合效应会导致小裂纹有贯穿形成大裂纹的趋势，而远端裂纹的耦合效应则相对较小；对于多裂纹，白点萌生临界氢浓度具有随裂纹个数的增加而线性递减的趋势。

Study on mechanism of flake initiation based on the cohesion method

Based on the previous experimental studies,a finite element model of flake initiation was established.The theories of cohesive strength,hydrogen pressure and stress induced hydrogen diffusion were coupled in this model.The effects of hydrogen content,crack length and multi-crack coupling on flake formation were studied.Meanwhile,the critical hydrogen concentration and its changing trends for flake formation under different conditions were determined.The results show that hydrogen is of important effect on the initiation of flakes.During the process of flake formation,a high concentration of hydrogen was accumulated at the crack tip,which is greatly reduces the cohesive strength of steel.As for a single crack,the critical hydrogen concentration of the flake initiation gradually decreases and tends to a steady value with the crack length increasing.When a plurality of dense small cracks are present at the same time,the small cracks tend to form large cracks because of the effect of stress coupling,while the distal cracks has less influence on the flake initiation.For multiple cracks,the critical hydrogen concentration at the flake initiation tends to decrease linearly with the increase of the number of cracks.