3D-Analysis of surface damage in metallic materials under fatigue loading

这个跨学科的项目涉及金属材料在疲劳载荷下表面损伤累积的原位分析。在这里，研究的重点是在材料科学的基础上，以高分辨率白光干涉仪研究承受疲劳载荷的工业钢为目的。这两个，在表面形貌和振动补偿的广泛变化的调查，在第一个项目阶段开发的MEMS方法-应适应高分辨率Linnik白光干涉仪。用这种直接安装在伺服液压试验机上的干涉仪分析滑移带和晶粒塑性变形的局部损伤过程。所研究的双相钢晶粒尺寸小，对测量系统提出了很高的要求。由于测量的复杂性和加载周期之间的目标短中断，将渴望快速，高度并行化，计算时间优化和自动化的测量和评估过程。此外，从光学的角度来看，白光干涉仪在接近机器的应用将进行调查。从获得的测量结果，表面形貌的时间发展将与试样加载。此外，还将确定表征损害程度的参数。这些损伤参数的时间发展可以可靠地确定使用干涉表面分析在原位设置，因为没有安装和安装的标本所造成的干扰，因为一个比较大的区域可以很容易地进行分析。因此，将有一个一致的数据库，从中可以得出统计相关性。双相钢中的疲劳损伤以孤立的滑移线和塑性变形的晶粒区域（晶粒面积的约10%至100%）的形式发生。到目前为止，这种损伤过程在文献中几乎没有引起兴趣，但似乎是体心立方铁素体相的特征。它通常在含碳量低的相中起作用，并且似乎对裂纹萌生以及因此对整个损伤累积过程有显著贡献。用高分辨率扫描电子显微镜进行的进一步研究将阐明表面起伏变化与微观塑性变形之间的关系

This interdisciplinary project deals with the in-situ analysis of surface damage accumulation under fatigue loading in metallic materials. Here, the focus of the research is on metrological aspects as well as on materials science with the aim of investigating technical steels subjected to fatigue loading with a high-resolution white-light interferometer. Both, the metrological approaches for the investigation of extensive changes in surface topography and the vibration compensation - developed during the first project phase - should be adapted to a high-resolution Linnik white-light interferometer. Local damage processes in terms of slip bands as well as plastic deformation of grain areas will be analyzed with this interferome-ter set-up directly at the servo hydraulic testing machine. The small grain size of the investigated dual phase steel place high demands on the measurement system. Due to the complexity of measurements and the targeted short interrupts between the load cycles, a fast, highly parallelized, computing time optimized and automated measurement and evaluation process will be aspired. Furthermore, from the metrological perspective the use of white-light interferometers in close-to-machine applications will be inves-tigated. From the gained measurement results, the chronological development of the surface topography will be related to specimen loading. Moreover, parameters that characterize the extent of the damage will be defined. The time development of these damage parameters can be reliably determined using interferometric surface analysis in an in-situ set-up, because there are no disturbances caused by mounting and dismounting of specimens, and because a comparatively large area can be easily analyzed. Consequent-ly, a consistent database will be available from which statistical correlations can be derived. Fatigue damage in a dual phase steel occurs both in terms of isolated slip lines and as plastically deformed grain regions (ranging from about 10% to 100% of the grain area). This damage process has gained little interest in the literature up to now, but seems to be characteristic for the body-centered cubic ferrite phase. It typically plays a role in phases with low carbon content and seems to contribute significantly to crack initiation and hence to the damage accumulation process as a whole. Additional investigations with a high resolution scanning electron microscope will elucidate the relation between change in the surface relief and micro-plastic deformation