一种考虑非比例附加损伤的多轴低周疲劳模型

在实际工作环境中,机械结构往往承受着多轴非比例循环载荷.相比多轴比例循环加载,多轴非比例循环加载由于产生了附加强化现象,造成机械结构疲劳寿命下降.通过分析薄壁圆筒管件在非比例加载工况下应力应变变化规律和发生破坏位置,本文基于临界面法提出一种考虑多轴非比例附加损伤的疲劳模型.该模型将最大剪切应变幅平面作为临界面,提出一个新的附加强化因子,结合临界面上切应变幅和正应变幅组成新的多轴疲劳损伤参量.此参量不仅考虑了非比例加载下临界面上正应变幅和切应变幅对材料造成的疲劳损伤,还考虑到应变路径的变化和材料非比例加载敏感特性对材料疲劳寿命的影响.考虑到实际情况下模型所需材料附加强化系数有时难以获得的情况,给出了材料附加强化系数的有关近似计算公式.只需要材料基本力学参数便可得到材料附加强化系数,方便工程实际应用.采用8种材料的多轴疲劳寿命数据对提出的新模型进行检验,结果表明所提出的新模型与传统多轴疲劳模型相比预测寿命精度更高. 

A MULTIAXIAL LOW-CYCLE FATIGUE MODEL CONSIDERING NON-PROPORTIONAL ADDITIONAL DAMAGE1)

In the actual working environment, the mechanical structure is often subjected to multi-axial non-proportional cyclic load. Compared with the multiaxial proportional cyclic load, the multiaxial non-proportional cyclic load has an additional strengthening phenomenon, resulting in a decrease in the fatigue life of the mechanical structure. With the analysis of the stress and strain variation and the failure location of thin-walled cylindrical specimen under non-proportional loading conditions, a new low cycle multiaxial fatigue life prediction model considering multiaxial non-proportional additional damage is proposed based on the critical plane approach. The new low cycle multiaxial fatigue life prediction model takes the maximum shear strain plane as the critical plane, and proposes a new additional strengthening factor, which combines the shear strain amplitude and the normal strain amplitude on the critical surface to form a new low cycle multiaxial fatigue damage parameter. This new low cycle multiaxial fatigue damage parameter not only considers the fatigue damage caused by the positive strain amplitude and the shear strain amplitude on the critical surface under non-proportional loading, but also considers the influence of the strain path change and the non-proportional loading sensitivity of the material on the fatigue life of the material. Considering the fact that the additional strengthening coefficient of the material required by the model is sometimes difficult to obtain, the approximate calculation formulas of the additional strengthing coefficient of the material is given. Only the basic mechanical parameters of the material can be used to obtain additional strengthening coefficient of the material, which is convenient for practical application of the project. The fatigue life data of eight materials were used to test the new low cycle multiaxial fatigue life prediction model. The results show that the new low cycle multiaxial fatigue life prediction model has higher life prediction accuracy than the traditional multiaxial fatigue life prediction model.