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Some challenging aspects of ductile materials

机译：延性材料的一些挑战性方面

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Crack tip blunting due to tension loads and re-sharpening of the tip in the course of unloading are two fundamental fatigue crack propagation processes in yielding metals. Using an elastic perfectly plastic material simulation, crack propagation analysis was performed up to several hundreds of complete cycles by means of remeshing at some phases of plastic deformation, including computations of the influence of overloads and compressive underloads. For the first several cycles, seaming was indicated, mainly when the crack surface was compressed, resulting in something that seems to suggest striations. Plastic cycling naturally renders a fair amount of crack growth per cycle, crack closure at the tip is predicted in each cycle next to an initial transient phase, and an overload ends in a reduced increase in crack growth. After introducing a single overload, tests on fatigue crack growth were performed with specimens of austenitic steel. The variables are K_(max) of the overload and the thickness of the specimen. The latter factor is of crucial importance when considering plane strain/plane stress. For this investigation, the following methodologies were employed: (i) fractographic observations, (ii) deformation analysis, and (iii) crack growth records. For modelling ductile fractures in structural materials, applying mechanism- based conceptions, two numerical methods can be used for simulating the material failure process. Firstly, voids are unambiguously regarded and simulated applying refined finite elements. Secondly, the material comprising the voids is regarded as a homogenized continuum described by porous plasticity simulations.
机译：由于张力负载和尖端在卸载过程中的裂缝尖端钝化是产生金属的两个基本疲劳裂纹繁殖过程。使用弹性完美的塑料材料模拟，通过在塑性变形的一些阶段进行倒闭，包括裂纹传播分析，通过倒置，包括过载和压缩欠压的影响计算。对于前几个循环，表示接缝，主要是当裂缝表面被压缩时，导致似乎表明条纹的东西。塑料循环自然地使每个循环的裂缝增长的相当数量，在初始瞬态阶段旁边的每个循环中预测尖端的裂纹闭合，并且越载成降低裂纹增长的增加。在引入单个过载后，用奥氏体钢标本进行疲劳裂纹生长的测试。变量是过载的k_（max）和样本的厚度。当考虑平面应变/平面应力时，后一因素至关重要。对于该研究，采用以下方法：（i）Fretography观察，（ii）变形分析和（iii）裂纹生长记录。用于在结构材料中建模延性骨折，应用基于机制的概念，两个数值方法可用于模拟材料故障过程。首先，空隙是明确的，并模拟应用精制的有限元。其次，包含空隙的材料被认为是多孔塑性模拟描述的均质连续体。

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