Experimental and Numerical Analysis of Work Hardening Effects in Single- and Polycrystals during Cyclic Loading (Bauschinger Effect)

在实践中，循环加载金属部件的使用寿命受到所用合金的疲劳损伤的限制。循环塑性变形的部分不可逆性导致应变局部化、裂纹萌生和扩展，最终导致断裂。特别是，晶粒和晶界的不利晶体学取向导致额外的应力集中，因此，即使在宏观弹性的变形下，也可能表现出局部塑性。在这里，包辛格效应是特别重要的，因为它描述了负载方向相关的应变硬化。通过微压痕和微弯曲实验以及适用于各种热处理的拉伸-压缩测试，其中变形机制将通过微观结构分析（使用扫描电子显微镜，包括EBSD和FIB，和透射电子显微镜），拟议的项目将导致单晶和多晶材料模型的发展，允许在有限元法中明确实施包辛格效应。两个技术上的重要合金，双相钢和镍基高温合金718的验证实验，将显示所提出的模型的潜力和限制。

In practice, the service life of cyclically loaded metallic components is limited by fatigue damage of the alloys applied. Partly irreversibility of the cyclic plastic deformation leads to strain localization, crack initiation and propagation and eventually, to fracture. Especially, unfavorable crystallographic orientations of grains and grain boundaries cause additional stress concentration, and therefore, local plasticity may exhibit even at deformations that are macroscopically elastic. Here, the Bauschinger effect is of particular significance, since it describes load-orientation-dependent strain hardening. By means of micro-indentation and micro-bending experiments as well as tension-compression tests applied to a variety of heat treatments, where the deformation mechanisms will be identified in detail by microstructural analysis (using scanning electron microscopy, incl. EBSD and FIB, and transmission electron microscopy), the proposed project will lead to the development of single crystal and poly crystal material models, that allow for explicit implementation of the Bauschinger effect in the Finite Element method. Verification experiments on two technical important alloys, the duplex steel and Ni-based superalloy 718, will show the potentials and the limits of the proposed models.