基于应变能的复杂应力场低周疲劳分析

塑性应变能使材料微观组织结构发生不可逆变化，从而引起等效宏观应力，该应力随循环加载而增大．假定材料疲劳源处破坏是由最大拉应力引起的，最大等效宏观应力与外加应力叠加达到材料本征断裂应力时形成微裂纹．微裂纹引起上述两部分应力变化，继续加载直至宏观裂纹出现，从而得到材料的疲劳寿命．本文所建立的多轴疲劳寿命公式包含材料参数、拉应力以及塑性应变能等，以上数据可通过单轴疲劳数据和有限元方法获得．通过对SM45C材料的计算验证，表明该模型对多轴随机应变加载低周疲劳寿命，具有良好的预测结果．

Complex Stress Field Low Cycle Fatigue Life Prediction Model Based on Plastic Energy

Due to the plastic potential energy, the microscopic structure of material is irreversibly changed such that the equivalent macroscopic stress arises. The stress increases under the cyclic loading. Assumed that the material damage in fatigue source is caused by the maximum tensile stress, and the micro-crack emerges when the superposition of the maximum equivalent macroscopic stress and the applied loading stress reaches the material’s intrinsic fracture stress. The macro stress and applied loading stresses can be changed by the micro-crack until the macrocrack appears under constant loading. The fatigue life is subsequently determined. The material parameters, tensile stress and plastic potential energy were incorporated in the established multiaxial fatigue life prediction formula, and they can be determined from the uniaxial fatigue test data and the finite element method. Computational validation of material SM45C indicates that the model is able to well predict the low cycle fatigue life under multiaxial random strain loading.