内燃机特征载荷作用下的紧固面微动疲劳损伤机理研究

As the developing of diesel engine, failures of highly-intensified diesel engine cylinder block caused by fretting fatigue have been reported in several bench tests. Fretting fatigue was considered as a synergistic competition among wear, corrosive and fatigue phenomena driven by both the micro-slip at the contact surface and cycle fretting contact stress. It is induced by combined localized cyclic sliding micro-motion and external bulk fatigue loadings, which result in premature dramatic failure of the contacting components. .Fretting fatigue was usually divided to two stages: fretting crack nucleation and fretting crack propagation. Previous studies have concluded that fretting induces the micro-crack nucleation and early age of crack propagation. It is considered that normal pressure, coefficient of fiction, and the minute relative slip between two surfaces were main factors to the initial of fretting crack. For most fretting tests, fretting fatigue conditions are simplified, i.e. metal-to-metal contact, cylinder on flat geometry, and fixed normal pressure. For an engineering problem, three of the factors may be vibrational in a loading period. It is necessary to combine the method from previous study with real loading conditions to analysis the fretting behavior..The intention of our current research is to analysis the failure of 6V150 diesel engine caused by the fretting fatigue and to study the fretting behavior of the contact surface between engine cylinder block and main bearing cap. The result can be used for avoiding same failure in later research and development of highly-intensified diesel engine.

内燃机特征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。而现阶段针对具有内燃机机体载荷特点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该载荷特征作用下微动疲劳失效的损伤模型和试验方法。本课题通过理论研究和实验研究相结合的方式对内燃机机体和主轴承盖典型接触面微动损伤问题进行研究。实验方面，利用谐振式内燃机微动疲劳实验台对机体隔板和主轴承盖结构及相应材料进行微动疲劳实验，通过实验获得内燃机主要性能参数和结构参数对微动疲劳损伤寿命的影响；理论方面，使用结合内聚力模型的扩展有限元方法对内燃机微动疲劳损伤规律进行研究，建立考虑初始刚度和剪切应力的内聚力模型，用于微动状态下材料的损伤演化过程的研究，在实验数据的支持下通过对模型的修正，获得能够用于描述具有柴油机载荷特点的典型接触面微动损伤数学模型，从而形成能够用于内燃机典型接触面的微动疲劳机理分析及实验研究方法。

微动疲劳普遍存在于机械行业领域，是造成机械失效的主要原因之一。目前随着内燃机强化程度不断提高，以微动失效为主的事故逐年增加，因此本研究以工程实际中内燃机机体隔板的微动失效事故为切入点，应用结合内聚力模型的扩展有限元法对内燃机典型载荷作用下的微动疲劳损伤问题进行研究。主要内容包括机体隔板与主轴承盖载荷特征分析、内燃机特征载荷作用下的微动疲劳实验、内燃机特征载荷作用下紧固面微动疲劳损伤机理研究、残余应力对机体隔板微动疲劳性能影响规律的研究。通过上述研究工作基础揭示了内燃机典型载荷下紧固面微动疲劳损伤机制，获得了内燃机性能参数与局部微动疲劳裂纹萌生和扩展之间的关系，同时探讨了机械加工导致的残余应力对机体隔板微动疲劳性能的影响规律，发现了残余压应力能够提高机体隔板抗疲劳性能，并进行了定量化研究。本研究对内燃机结构强度设计、抗疲劳设计等具有重要意义。