An accurate constitutive model is one of the basic aspects to ensure a precise simulation. This study presents an improved unified viscoplastic model to simulate the various behavior of P92 steel under low cycle fatigue (LCF) and creep fatigue interaction (CFI) loadings. In the proposed model, an accumulated inelastic strain dependent parameter is introduced into the nonlinear kinematic hardening rule to represent the evolutionary behavior of strain-stress hysteresis loops and the varied relaxation behavior during CFI loadings. The traditional isotropic hardening rule is modified as well to capture the accelerated cyclic softening phenomena observed in the prolonged hold time of CFI tests. To validate the accuracy and the predictive capability of the proposed model, LCF tests at various strain amplitudes and CFI tests at different hold time are conducted at elevated temperature of 650 °C. Good agreement between the experimental and simulated results verifies the robustness of the proposed model. In addition, the proposed model is distinguished from published models by few determined material parameters.

准确的本构模型是确保精确模拟的基本方面之一。这项研究提出了一种改进的统一粘塑性模型，以模拟P92钢在低周疲劳（LCF）和蠕变疲劳相互作用（CFI）载荷下的各种行为。在提出的模型中，将累积的非弹性应变相关参数引入到非线性运动硬化规则中，以表示应变-应力磁滞回线的演化行为以及CFI加载期间的变化松弛行为。还修改了传统的各向同性硬化规则，以捕获在延长的CFI测试保持时间内观察到的加速循环软化现象。为了验证所提出模型的准确性和预测能力，在650°C的高温下进行各种应变幅度的LCF测试和不同保持时间的CFI测试。实验结果和模拟结果之间的良好一致性验证了所提出模型的鲁棒性。此外，所提议的模型与已发布的模型的区别在于确定的材料参数很少。