Non-proportional multiaxial low-cycle fatigue (MLCF) tests were performed on CP-Ti at different multiaxial strain ratios. The optical microscopy observations and life prediction models verified that the critical plane of CP-Ti was the maximum principal strain plane and that it was effective under non-proportional loading. A non-proportional life coefficient and strain energy density coefficient are proposed. Typical MLCF life prediction models, such as the ESN, FS, KBM, and KBM-P models, are discussed under non-proportional loading. Finally, by associating the newly defined non-proportional life coefficient with the non-proportional hardening factor, two comprehensive non-proportional MLCF life prediction models are established, which have higher accuracies than those of previous models.

在不同的多轴应变比下对 CP-Ti 进行了非比例多轴低周疲劳 (MLCF) 试验。光学显微镜观察和寿命预测模型验证了CP-Ti的临界面是最大主应变面，在非比例载荷下是有效的。提出了非比例寿命系数和应变能密度系数。在非比例载荷下讨论了典型的 MLCF 寿命预测模型，例如 ESN、FS、KBM 和 KBM-P 模型。最后，通过将新定义的非比例寿命系数与非比例硬化因子相关联，建立了两个综合的非比例MLCF寿命预测模型，其精度高于以往模型。