Fracture Mechanics Based Simulation for Microstructural Control in Metal Matrix Composites

通过弹塑性有限元分析，分析了增强体周围的PFZ层、粗大的界面平衡析出物、溶质原子偏析等局部非均匀组织对复合材料变形和断裂特性的影响.由于PFZ层的延性，PFZ层内的集中塑性流动促进了整个基体中有效塑性应变的增加，从而降低了MMC的强度.另一方面，界面析出物有效地延缓了PFZ层内的集中塑性流动，从而抑制了由于PFZ的形成而导致的强度下降。空洞的起始率受析出物的形态和密度的影响很大。考虑到上述微观组织特征，我们构建了模拟裂纹通过非连续强化的模拟程序。模拟中考虑了微裂纹、裂纹偏转、主裂纹与微裂纹之间的相互作用以及裂纹尖端的稳态奇异性向非稳态奇异性的转变。研究了不同微观结构参数对裂纹扩展阻力的影响。这项研究中最有趣的信息是，钢筋的适当不均匀分布提高了裂纹扩展阻力。并用数值模拟的方法对存在钢筋偏析的复合材料的静强度进行了评估。通过模拟，提出了最佳的显微组织形态。

Effects of locally-inhomogeneous microstructures, such as PFZ layrs around reinforcements, coarse interfacial equilibrium precipitates, solute atom segregation, on deformation and fracture characteristics of the MMCs are analyzed by means of the elastic-plastic finite element analysis.Due to the ductile nature of the PFZ layrs, concentrated plastic flow within the PFZ layrs promotes increase of effective plastic strain in the whole matrix, thereby reducing stregth of the MMCs. On the other hand, the interfacial precipitates effectively retard the concentrated plastic flow within the PFZ layrs and consequently they suppress reduction of the strength due to the formation of the PFZ.The initiation rate of the void is remarkably affected by the morphologies and density of the precipitates.Taking above-mentioned microstructural features into account, we constructed a simulation program which simulates crack propagation through the discontinuously-reinforced. Micro-cracking, crack deflection, interaction between the main crack and the microcracks, and transition of stationary to non-stationary crack-tip singularities are taken into consideration in the simulation. Effects of the various microstructural parameters on the crack propagation resistance are evaluated. The most interesting information of this study is that the properly inhomogeneous distribution of the reinforcement improves the crack propagation resistance. We also evaluated static strength of such composites having reinforcement segregation by means of numerical simulation. The optimum microstructural configuration was proposed by the simulation.