氢致钢内部疲劳裂纹萌生和扩展的有限元分析

对氢致钢内部疲劳裂纹的萌生和扩展进行了数值模拟.首先用有限元法分析了氢在疲劳载荷作用下向钢中缺陷处扩散富集的过程,然后计算得到氢含量分布结果.根据夹杂理论将氢富集区视为在缺陷附近分布的弹性夹杂,用有限元法计算得到的氢含量场求出夹杂处的应力强度因子,进而建立疲劳裂纹萌生和扩展的判据.比较了在不同加载条件下氢致疲劳裂纹萌生和扩展的规律.用梯形法修正了Sofronis和McMeeking的瞬态扩散有限元公式,发现用梯形法可以缓解加载初期较高的浓度梯度和应力梯度引起的计算结果震荡的情况,这对于计算开裂判据是十分重要的.最后讨论了提高模拟精度和改进模型的方法.

Finite element analysis of hydrogen induced internal fatigue crack initiation and propagation in steel

Hydrogen induced internal fatigue crack initiation and propagation in steel was studied by numerical simulation. First, finite element analysis (FEM) was used to analyze the process of hydrogen diffusion and accumulation at a defect in steel under fatigue load, and then the concentration of hydrogen was computed. According to the inclusion theory, the area where hydrogen accumulated was regarded as an elastic inclusion in the vicinity of the defect, and the concentration result of FEM analysis was used to calculate the stress intensity factor induced by the elastic inclusion. Thus a criterion of crack initiation and propagation was established. Hydrogen-induced fatigue crack initiation and propagation rules were studied under different load conditions. The FEM formula of transient diffusion deduced by Sofronis and McMeeking was adjusted with the trapezoidal rule. The trapezoidal rule reduces oscillations due to steep concentration and stress gradients after initial loading, this is very important to calculate the criterion of crack initiation and propagation. At the last, some methods of improving the simulation precision and refining model were discussed.