多轴疲劳载荷作用下的微动疲劳裂纹扩展规律研究

Fretting fatigue caused by multi-axis cycle loads, is a typical failure phenomenon. It is a challenge to find proper experimental methods and theoretical models to describe the fretting fatigue process under multi-axis. Here，in order to obtain a systematic method, about kinds of experimental methods and numerical methods are reviewed to discuss the fretting fatigue process. The frame of this dissertation is given as: A new experimental model based on the study of the characters of multi-axis cycle loads and the analysis of the dynamic stresses distribution of contact surface is used to simulate the failure process of the specimen under multi-axis cycle loads. Then relevant experiments are designed to certify the feasibility and demarcate the experiment parameters. Finally, under certain experiment loads the relationship between the number of cycle and crack length has been obtained through fretting fatigue experiments. The finite element method is used to study the stresses distribution of the contact region between specimen and punch under multi-axis cycle loads. The results with different FE solutions are discussed to obtain an FE solution which conduct more accurate results, sub-model technique is used to achieve detail results of fretting fatigue region, and the displacements of the nodes in the node based driving surface are used as a cycle displacement boundary condition for 2D local FE model. The cycle cohesive zone model (CCZM) and extended finite element method (XFEM) are used to describe the fretting behaviors. The fretting fatigue damage is described with damage evolution equation. Both extended finite element method as well as the cohesive zone models has been implemented into the commercial FEM software ABAQUS, via the user interfaces UEL and UMAT. The CCZM parameters are obtained from material fatigue test result and fretting fatigue experiment

多轴疲劳载荷作用下的紧固面微动疲劳失效是典型的微动失效现象。现阶段，针对多轴疲劳载荷作用下的微动疲劳损伤的相关研究还不充分，尚缺乏能够有效分析多轴疲劳载荷作用下微动疲劳失效的损伤模型和数值计算方法。本课题拟通过理论研究与试验研究相结合的方法对该失效机理进行研究并提出相应的理论模型。在试验研究方面，利用谐振式微动疲劳试验台对不同载荷特征下的多轴疲劳载荷进行微动疲劳试验，获得载荷特征参数与微动疲劳裂纹萌生及扩展速率之间的规律；在理论研究方面，使用结合循环内聚力模型的扩展有限元方法对多轴疲劳载荷作用下的微动疲劳裂纹萌生及扩展规律进行研究，建立包含裂纹萌生准则的循环内聚力模型，利用试验所得裂纹萌生与扩展规律，确定多轴疲劳载荷与内聚力模型参数之间的关系，建立能够描述多轴疲劳载荷作用下的紧固面微动疲劳裂纹萌生及扩展模型，从而形成能够应用于工程实际中紧固面微动疲劳问题的理论模型。