旋转弯曲微动疲劳裂纹萌生及扩展机理和寿命预测方法研究

Rotary bending fretting fatigue refers to the failure phenomenon that the fretting damage occurs on the contact surfaces of rotating components under external cyclic torsion and bending loads, and promotes a relative early crack nucleation and propagation. So far, the failure mechanism of this phenomenon has not been studied systematically. This project mainly concentrates on the investigation of the nucleation and propagation mechanism as well as the life prediction method of rotary bending fretting fatigue cracks in the context of traction motor shaft and pinion shaft of locomotive. Firstly, by analyzing the actual working condition and failure process, the material property,geometrical parameter, external loads and so forth of the structure are extracted, and the dynamic government equation as well as the weak form of the traction motor shaft and pinion shaft system is established accordingly. Afterwards, combined with the partition of unity theory, an extended finite element method (XFEM) in consideration of dynamic loading effects is established to simulate the fretting fatigue crack nucleation and propagation process under rotary bending loads and a special program is developed based on FerContact/View simultaneously. After that, the stress states around the crack tip from the crack nucleation to the critical fracturing point are studied thoroughly with XFEM and the microscopic features of the fracture surface are observed by microanalysis. Then, the failure mechanism of rotary bending fretting fatigue is investigated by analysis of the changes of stresses near the crack tip and the physical process of fatigue crack growth. Further, a general failure criterion for the whole crack growth process as well as a prediction model of rotary bending fretting fatigue lives is established correspondingly. Finally, the test data of rotary bending fretting fatigue are used to validate the failure mechanism and the fatigue life prediction model. This project possesses the scientific value to further enrich the fundamental theories of fretting fatigue. Moreover, it owns much significance for practical applications, including the protection of fretting damage and accurate prediction of fretting fatigue lives of key components, such as the wheel shafts of locomotives, turbine shafts of aero engines, etc.

旋转弯曲微动疲劳是指相互接触的旋转构件在外加扭转和弯曲载荷下接触面间发生微动损伤，促使构件过早萌生裂纹并扩展失效的现象，至今其损伤机理研究尚不系统。本课题以机车电机轴/小齿轮轴为背景，研究旋转弯曲微动疲劳裂纹萌生及扩展机理和寿命预测方法。依据结构实际工况和失效分析，提取模型的材料、几何、外载等信息，建立系统的动态控制方程及弱形式；结合单位分解原理，建立模拟旋转弯曲微动疲劳问题的扩展有限元法；进而基于FerContact/View开发考虑动载效应的旋转弯曲微动疲劳裂纹萌生和扩展专用模拟程序。结合裂尖处应力等模拟结果和断面微观分析，揭示旋转弯曲微动疲劳失效机理，建立裂纹扩展准则和寿命预测模型。最后，结合旋转弯曲微动疲劳试验，验证失效机理和寿命预测模型的正确性。本研究具有深化微动疲劳体系的理论意义，且有重要的工程应用背景，对机车轮轴、航空发动机涡轮轴等部件的损伤防护和寿命预测具有重要应用价值。

旋转弯曲微动疲劳裂纹萌生及扩展机理探索对飞机、机车等大型结构关键部件的安全评估、损伤防护和寿命预测具有重要意义。已有研究多视此类部件为均质材料，较少考虑微观非均质性、夹杂及过渡层等影响，难以系统揭示结构内损伤和裂纹演化机制。此类因素不仅影响微动接触状态、材料参量等宏观信息，且决定着损伤萌生位置和裂纹扩展路径等微观特性。故本课题开展了3D裂纹面自动重构、过渡层/晶界理论等效、复杂微结构精确建模等研究，主要进展包括：.（1）3D微动裂纹前缘自动重构和应力强度因子自动求解：通过裂纹前缘局部模型重构、物理场分解和等效区域J积分计算，建立了任意3D裂纹前缘应力强度因子计算方法，并开发了自动求解程序；同时，该方法被拓展用于分析太阳能板开裂机理。.（2）结构内夹杂/基体间过渡层及晶界特性等效建模和XFEM模拟实现：通过引入简化假设和严格理论推导，建立了过渡层和晶界的等效界面模型及相应边值问题控制方程（强形式和弱形式）；采用XFEM实现了结构响应和材料模量的有效预测，为微动过程接触状态和裂纹萌生/扩展过程准确描述提供了工具。同时，等效模型和模拟方法已拓展应用于非均质材料响应及传热/耦合场模量预测等问题。.（3）结构内复杂非均质相数学描述方法和精确建模实现：采用水平集法建立了稀疏填充和高填充结构内复杂非均质相的数学描述；借助模型物理信息和离散数据，开发了复杂微结构自动建模策略；通过自编程序实现了复杂非均质模型自动重构。.（4）相场方法实现非均质钢结构内损伤演化、裂纹萌生及扩展模拟：通过自编软件实现了包含夹杂、过渡层、缺陷等特征的结构损伤演化和裂纹萌生及扩展的有效预测，为解决真实结构旋转弯曲微动损伤萌生、裂纹起始和寿命预测奠定了重要基础。.项目资助下，已发表SCI检索论文6篇， SCI源刊在投论文2篇；申请国家发明专利1项；申请实用新型专利2项，授权2项；申请软件著作权3项，授权2项；培养毕业硕士4人，合作培养毕业博士1人。