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。

微动疲劳造成的失效在工业领域广泛存在，是影响航空、航天、核电等行业产品结构可靠性的重要因素。工程实际中局部关键位置出现的复杂循环载荷作用下的微动疲劳失效问题制约着机械产品的结构可靠性。研究表明，在相同的交变循环外载荷作用下，试件表面的微动疲劳作用会使试件的疲劳寿命降低30%~50%。微动疲劳导致的事故对国民经济造成巨大经济损失，甚至造成人员伤亡。.本课题通过试验研究和数值模拟，获得了复合交变载荷作用下的微动疲劳裂纹的萌生和扩展规律，提出了能够用于紧固面微动疲劳分析与预测的工程计算与分析方法。具体研究工作包括以下几方面的内容：.（1）完成复合交变循环载荷特征参数与微动疲劳裂纹扩展规律之间关系的试验研究。利用谐振式微动疲劳实验系统进行不同特征复合循环交变载荷条件下的微动疲劳实验，获得了不同循环特征交变载荷条件下微动疲劳问题的循环内聚力模型参数。.（2）完成了复杂机械结构的紧固面接触分析方法及载荷传递方法研究，形成了基于有限元子模型方法的复杂机械结构紧固面接触应力及相对位移计算方法，完成了相关接口程序的建立，实现了试件及工装整体结构在动态载荷作用下的局部应力场及相对位移场的精确求解。.（3）完成了微动疲劳裂纹的数值计算方法与理论模型研究，确定了疲劳裂纹的萌生准则、扩展准则及裂纹扩展方向的判断准则，完成了ABAQUS用户子程序和Python后处理程序编写，实现了基于循环内聚力模型的扩展有限元计算。.（4）完成了复合交变循环载荷作用下的复杂机械结构的微动疲劳裂纹模拟和分析。提出了裂纹数值计算过程中通过边界驱动面上的节点位移驱动模拟复合交变循环载荷的方法，确定了基于试验结果的循环内聚力模型的内聚力参数及损伤参数，形成了复合交变循环载荷作用下微动疲劳裂纹模拟计算方法。.本课题研究成果对提高工程实际中紧固面结构疲劳强度具有重要意义。基于本课题研究结果能够提升高承载结构设计能力，提升机械产品寿命和可靠性。