弯曲扭转耦合作用下轴类零件疲劳累积损伤建模及机理研究

The fatigue damage of the shaft components subjected to coupled effect of bending and torsion will accumulate gradually in service, which will eventually lead to fatigue failure. This project studies fatigue damage of shaft components with bending-torsion coupling and reveal the mechanism of crack initiation. Based on the further study of the micro-mechanism of crack initiation, a new theoretical method to determine the crack initiation location and direction of shaft components with bending-torsion coupling is proposed. Considering physical meaning of crack initiation and propagation, and redefining failure criteria of Miner linear damage accumulation theory, a equivalent Miner damage cumulative model applied to bending-torsion coupling loading is put forward, which integrated Miner damage accumulation theory and the critical plane method. The fatigue test is used to demonstrate the validity of the theoretical method and equivalent Miner damage cumulative model. At the same time, the effect of loading ratio, loading amplitude and loading sequence on fatigue damage and crack initiation is investigated through fatigue test under the symmetric/asymmetric constant amplitude loading, variable amplitude loading and random loading. The micro-mechanism of the fatigue accumulation damage is studied by analysising fatigue fracture morphology under different loading conditions. This project provides a theoretical basis for the investigation on the fatigue cumulative damage of shaft components with bending-torsion coupling and interprets the course of the fatigue accumulation damage, which aims to estimate the remaining useful life effectively and offer reference suggests for preventive maintenance. Therefore, this research has important scientific meaning and potential engineering application prospects.

轴类零件在服役过程中受到交变弯扭耦合载荷的作用，其疲劳损伤逐渐累积，最终导致疲劳失效。本项目重点研究轴类零件在弯扭耦合载荷作用下的疲劳累积损伤，揭示在此过程中裂纹萌生机理，提出一种确定弯扭耦合加载下裂纹萌生位置及方向的理论新方法；考虑裂纹萌生和扩展的物理意义，重新对Miner理论的破坏准则进行定义，结合Miner线性累积损伤理论与临界面法，拟创建一种能够适用于弯扭耦合加载的等效Miner累积损伤模型；采用实验验证理论方法及模型的正确性。通过不同幅值下对称/非对称恒幅、三级变幅及随机弯扭耦合疲劳试验研究载荷比、载荷幅值及载荷顺序与疲劳损伤及裂纹萌生的内在联系。观察分析不同加载条件下的疲劳断口，研究疲劳累积损伤的微观机理。本项目将为弯扭耦合加载下疲劳累积损伤的研究提供理论基础，重点阐释疲劳累积损伤的过程，有效预估构件剩余寿命，为预防性维修提供理论依据，具有重要科学意义和潜在工程应用前景。

项目以飞机起落架为研究对象，研究了飞机起落架在随机载荷作用下疲劳损伤，揭示了在此过程中裂纹萌生机理，提出了一种确定弯扭耦合加载下裂纹萌生位向的数值模拟方法，解决了需通过疲劳实验确定裂纹萌生位向的难题，从而避免代价较高的多轴疲劳实验。将单轴Miner线性累积损伤理论推广应用到弯扭耦合加载情况，结合临界面法建立了一种适用于弯扭耦合加载的等效Miner累积损伤模型，阐释了轴类零件在实际服役过程中疲劳损伤的累积过程，该模型不需弯扭耦合加载的材料参数及载荷参数，只需单轴加载的相关参数，为预防性维修提供理论依据。本项目的研究始终按计划进行，受本项目资助：2019年成功承办了第六届材料与结构强度青年工作论坛，在国内外专业学术期刊发表10篇论文，SCI数据库收录3篇，EI数据库收录4篇，CSCD数据库收录2篇，北大核心期刊收录1篇，获得1项国家发明专利，培养硕士研究生6名。