An experimental and theoretical analysis of low carbon steel 1018 subjected to multiaxial loading is presented. Different loading conditions, including tension–compression, torsion, in-phase, and out-of-phase, are applied to investigate the effect of loading type on fatigue life. The fracture fatigue entropy (FFE) framework is then used to predict life using both hysteresis loops and thermography. The results show that the out-of-phase loading leads to the minimum fatigue life, while the torsion exhibit the maximum life at a similar equivalent strain. The FFE predictions using thermography successfully captured the specimens' fatigue life subjected to the multiaxial fatigue loading independent of the loading condition. Furthermore, the results show that the strain energy obtained from the hysteresis loop is a good measure of dissipation energy in the cases of tension–compression, torsion, and in-phase loading conditions. Accordingly, the predicted life using the hysteresis loop agrees well with the thermographic and experimental results. However, in the case of out-of-phase loadings, the plastic strain energy obtained from the hysteresis loop deviates from the dissipation energy because the stored energy originated from the internal state variable variation. Accordingly, the predicted life using the thermography is more accurate than the hysteresis loop, which agrees well with the experimental results.

提出了低碳钢1018承受多轴载荷的实验和理论分析。研究了不同的载荷条件，包括拉伸-压缩，扭转，同相和异相，以研究载荷类型对疲劳寿命的影响。然后，使用磁滞回线和热成像技术，将断裂疲劳熵（FFE）框架用于预测寿命。结果表明，异相载荷导致最小的疲劳寿命，而扭力在相似的等效应变下表现出最大的寿命。使用热成像的FFE预测成功地捕获了样品在多轴疲劳载荷下的疲劳寿命，而与载荷条件无关。此外，结果表明，在拉伸，压缩，扭转和同相加载条件下，从磁滞回线获得的应变能是耗散能的良好度量。因此，使用磁滞回线的预测寿命与热成像和实验结果非常吻合。但是，在异相负载的情况下，从磁滞回线获得的塑性应变能会偏离耗散能，因为所存储的能量源自内部状态变量的变化。因此，使用热像仪的预测寿命比磁滞回线更准确，这与实验结果非常吻合。使用磁滞回线的预测寿命与热成像和实验结果非常吻合。但是，在异相负载的情况下，从磁滞回线获得的塑性应变能会偏离耗散能，因为所存储的能量源自内部状态变量的变化。因此，使用热像仪的预测寿命比磁滞回线更准确，这与实验结果非常吻合。使用磁滞回线的预测寿命与热成像和实验结果非常吻合。但是，在异相负载的情况下，从磁滞回线获得的塑性应变能会偏离耗散能，因为所存储的能量源自内部状态变量的变化。因此，使用热像仪的预测寿命比磁滞回线更准确，这与实验结果非常吻合。