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

在实际应用中，受循环载荷作用的金属构件的使用寿命受到所用合金疲劳损伤的限制。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。特别是晶体和晶界的不利取向导致了额外的应力集中，因此即使在宏观弹性的变形中，局部塑性也可能表现出来。这里，包辛格效应具有特别重要的意义，因为它描述了与载荷方向相关的应变硬化。通过微压痕和微弯曲实验以及应用于各种热处理的拉伸-压缩实验，将通过显微组织分析(包括扫描电子显微镜)详细地确定变形机制。除了EBSD和FIB，以及透射电子显微镜)，拟议的项目将导致单晶和多晶材料模型的开发，从而允许在有限元方法中显式地实现包辛格效应。对双相钢和镍基高温合金718这两种重要技术合金的验证实验将显示所提出模型的潜力和局限性。

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.