Analyses on Damage and Deformation in Notched Component under Multiaxial Low Cycle Fatigue

建立了弹塑性有限元程序，分析了拉扭复合载荷作用下试件缺口根部的应力应变。通过与试验观测结果的比较，验证了所开发方法的适用性。在载荷控制条件下，进行了同相轴向扭转载荷下的疲劳试验。试验材料为纯铜和中碳钢。使用塑料复制技术观察了裂纹行为。结果表明，疲劳寿命和裂纹形态取决于材料的微观组织和/或应力多轴度。研究了两种分析方法来解释上述寿命和裂纹的差异，其中一种方法是基于损伤力学的方法。分析结果表明，裂纹分布与应力多轴度有很好的一致性。另一种方法是同时模拟裂纹的萌生和扩展过程。模拟结果表明，该方法能有效地描述疲劳寿命和裂纹形态与组织和多轴应力状态的关系。

An elastic-plastic finite element procedure was developed to analyze stress/strain at notch root of specimen subjceted to combined tension and torsion loadings. The applicability of the developed procedure was examined in the comparison with experimental observation.Fatigue tests were conducted under in-phase axial-torsional loadings in load-controlled condition. Tested materials were pure copper and medium-carbon steel. Cracking behavior was observed by using a plastic replication technique. The results indicated that the fatigue life and cracking morphology was dependent on the material microstructure and/or stress multiaxiality.Two analytical procedures were investigated to explain the difference in life and cracking mentioned above, One of the procedures was based on a damage mechanics approach. The analytical result obtained using the procedure showed a good correspondence with the crack distribution depending on the stress multiaxiality. The other procedure was based on modeling of both processes of crack initiation and propagation, simultaneously. It was found from the simulated results that the proposed procedure was effective for describing the fatigue life and cracking morphology depending on the microstructure and multiaxial stress state.