Phase-Specific Analysis and Simulation of Micro Deformation and Damage in Metal Matrix Composites

金属等延性材料的应变局部化和微损伤的形核具有很高的技术意义，因为这些微观组织过程影响着这类材料在加载、成形和加工过程中的力学行为。此外，一侧的应变升高区域与另一侧的细观损伤位置和宏观破坏模式之间存在一定的关系。为了控制这种微观结构过程，金属材料被强化，例如通过分散硬质颗粒。这类金属基复合材料(MMC)因其力学性能可以在很大范围内定制而受到越来越多的关注。本项目结合2D/3D实验分析和模拟技术，在考虑残余应力的情况下，以Co/WC金刚石系统为例，了解MMCs微观结构区域的微变形和损伤过程：由不同Co/WC金刚石MMCs制成的试件将被拉伸加载到不同的应变阶段。在这些阶段，用扫描电子显微镜和三维微层析成像(µCT)对试件的标准截面进行成像。利用将在项目中建造的、专用于µCT设置的试验台，将进行现场拉伸测试。将开发一种用于三维应变场的特定相位分析的相关算法，并将其应用于三维图像。这种迭代相关算法考虑了可以从层析图像中提取的显微组织中相的分布。基于实验得到的相分布，建立了Co/WC金刚石MMC相结构的三维有限元模型，模拟了Co/WC金刚石MMC的微观变形和损伤过程。在模型边界测量的位移矢量场将用作有限元模拟的边界条件。将模拟结果与基于应变场、残余应力和损伤过程的实验结果进行比较，将有助于验证模拟模型。有了这样一个经过验证的数值模型，就有可能通过对不同相排列和不同相体积分数的参数研究来更好地了解复合材料的变形和损伤行为。实验分析和模拟之间的密切合作被认为是实现这些目标的关键因素。

The localization of strain and the nucleation of micro damages in ductile materials like metals are of high technical significance since these microstructural processes affect the mechanical behavior during loading, forming and machining of such materials. Moreover, there is a relationship between the regions of elevated strain on one side and the sites of micro damages and the modes of macroscopic failure on the other side. In order to control such microstructural processes, metallic materials are reinforced for example by dispersing hard particles. Such metal matrix composites (MMCs) have become more and more attractive since their mechanical properties can be tailored to various applications over a wide range.Using a combination of 2D/3D experimental analysis and simulation techniques and under consideration of residual stresses, this project aims at the understanding of micro deformation and damage processes in microstructural regions of MMCs by the example of the system Co/WC diamond:Specimens made of various Co/WC diamond MMCs will be loaded in tension to different stages of strain. In these stages, the gauge sections of the specimens are imaged by SEM and 3D micro-tomography (µCT). With a test rig which will be constructed in the project and which is dedicated for the µCT setup in situ tensile tests will be carried out. A correlation algorithm for the phase-specific analyses of the 3D strain fields will be developed and applied to the 3D images. This iterative correlation algorithm takes into account the distributions of the phases in the microstructure which can be extracted from the tomographic images. Furthermore, the effect of residual stresses, microstructural parameters and the Co/diamond bonding on the initiation of strain and stress concentration sites and the beginning of damage at a microscopic scale will be investigated.Based on the experimentally obtained phase distributions a realistic 3D FE model of the phase geometry of the Co/WC diamond MMC will be built up to simulate the micro deformation and damage processes of the investigated MMC. Displacement vector fields measured at the model boundaries will be used as boundary conditions for the FE simulation. The comparison of the simulation results with the experimental findings on the basis of strain fields, residual stresses and damage processes will help to verify the simulation model. With such a verified numerical model, it will be possible to derive a better understanding of the deformation and damage behavior of the composite by performing parameter studies concerning different phase arrangements and different phase volume fractions. The close cooperation between the experimental analyses and simulations is considered to be a key element for achieving these aims.