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Growth of an initially sharp crack by grain boundary cavitation

机译:晶界空化使最初尖锐的裂纹扩展

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A new computational model is presented to analyze intergranular creep crack growth in a polycrystalline aggregate in a discrete manner and based directly on the underlying physical micromechanisms. A crack tip process zone is introduced in which grains and their grain boundaries are represented discretely, while the surrounding undamaged material is described as a continuum. Special-purpose finite elements are used to represent individual grains and grain boundary facets. The constitutive description of the grain boundary elements accounts for the relevant physical fracture mechanisms, i.e. viscous grain boundary sliding, the nucleation of grain boundary cavities, their growth by grain boundary diffusion and local creep, until coalescence of cavities leads to microcracks. Discrete propagation of the main crack occurs by linking up of neighboring facet microcracks. Assuming small-scale damage conditions, the model is used to simulate the initial stages of growth of an initially sharp crack under C~* controlled, mode I loading conditions. Material parameters are varied so as to lead to either ductile or brittle fracture, thus elucidating creep constrained cavitation near cracks. The role of the stress state dependence of cavity nucleation on the crack growth direction is emphasized.
机译:提出了一种新的计算模型,以离散方式并直接基于底层物理微观机制分析了多晶聚集体中的晶间蠕变裂纹扩展。引入了一个裂纹尖端加工区,其中晶粒和它们的晶界被离散表示,而周围未损坏的材料被描述为连续体。专用有限元用于表示单个晶粒和晶粒边界面。晶界元素的本构描述考虑了相关的物理断裂机制,即粘性晶界滑动,晶界腔的成核,它们通过晶界扩散和局部蠕变而生长,直到空腔的聚结导致微裂纹。主裂纹的离散传播是通过相邻小平面微裂纹的连接而发生的。假设破坏条件是小规模的,则该模型用于模拟在C〜*控制的I型载荷条件下初始尖锐裂纹的扩展初期。材料参数会发生变化,从而导致韧性断裂或脆性断裂,从而阐明裂纹附近的蠕变约束空化。强调了空核形变对应力状态的依赖性在裂纹扩展方向上的作用。

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