氢化物诱致金属稳态裂纹扩展数学模型的应用

在温度和裂尖速度恒定、平面应变和小规模屈服、小规模氢化物沉淀条件下,应用有限元法研究氢化物诱致金属稳态裂纹扩展的信息.在考虑氢扩散、氢化物沉淀、非机械能量流和氢化物/固溶变形等多物理的耦合现象条件下,有限元结果和导出的分析表达式给出的结果都证实应力平稳平台的存在,且两种计算结果相当一致.分析关系式基于氢化学平衡并明确表明了温度、远端氢浓度和氢化物弹性性态效应.裂纹尖端场特性用于发展断裂准则和估计应力强度因子阈值.当归一化应力强度因子趋于零时,临近应力强度因子阈值的裂尖场产生,表现为氢化物沉淀区出现常静水应力.随着归一化应力强度因子值增加,裂纹扩展裂尖场从阶段I演化到阶段II,氢化物沉淀区域实际尺寸减小并偏离平台水平,裂尖场附近的力学响应基本和金属中不含有氢的工况一致,此时裂尖场强烈依赖于远离裂尖场的氢浓度.

Application of mathematical model to the analysis of hydride-introduced steady-state crack growth in metals

The present paper is inclined to present the authors' analysis and investigation over the hydride-induced steady-state crack propagation in metals under conditions of constant temperature,plane strain,small-scale yielding and small-scale hydride precipitation.While taking into full consideration the coupling of hydrogen diffusion,the hydride precipitation and the material deformation of the metal itself and the other factors concerned,it is necessary to confirm the development of the stress plateau,which is independent of the finite element study as well as the derivation of analytical relations,which should be based on the hydrogen chemical equilibrium and give explicit indication of the effects of temperature,remote hydrogen concentration and hydride elastic properties.In so doing,the analytical and numerical predictions on the level of the stress plateau are to be in perfect agreement.In addition,it is also necessary to use the characteristics of the near-tip field to develop a fracture criterion and estimate the threshold stress intensity factors.However,when the normalized stress intensity factor tends to be zero,the crack-tip field will be produced near the threshold stress intensity factor,which is characterized by a constant hydrostatic stress in the hydride precipitation zone.As the value of the normalized stress intensity factor increases,the near-tip field for crack propagation will be evolving from stage-I to stage-II.Then,while the actual size of the hydride precipitation zone becomes smaller,the hydrostatic stress will increase,deviating from the level of the plateau,with the near-tip field turning to be that of a hydrogen-free metal.Thus,it can be seen that the near-tip field has to depend strongly on the hydrogen concentration far from the crack tip.