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

本文建立了一个弹塑性有限元程序，分析了拉扭复合载荷作用下缺口根部的应力应变。通过与试验结果的比较，验证了该方法的适用性。在载荷控制条件下，进行了轴向-扭转同相载荷下的疲劳试验。试验材料为纯铜和中碳钢。通过使用塑性复制技术观察开裂行为。结果表明，疲劳寿命和裂纹形态与材料的微观结构和应力多轴性有关，本文提出了两种分析方法，其中一种是基于损伤力学的分析方法。用该方法得到的分析结果与裂纹分布随应力多轴性的变化规律有很好的对应关系。另一个过程是基于裂纹萌生和扩展过程的建模，同时。从模拟结果中发现，所提出的程序是有效的描述疲劳寿命和裂纹形态取决于微观组织和多轴应力状态。

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.