【作者】 李建军；

【导师】 陈旭；

【作者基本信息】 天津大学 ， 化工过程机械， 2016， 硕士

【摘要】 微动疲劳是指两个紧密配合的构件在循环载荷的作用下接触表面上发生微小幅度的、反复的相对滑动,从而造成构件表面产生疲劳裂纹,导致构件过早失效的现象。微动疲劳现象广泛存在于航空、核电、交通、汽车、化工和电力等工业领域中,被称为工业界的“癌症”。微动疲劳过程十分复杂、其变化参量众多,且相互影响。接触载荷是微动疲劳过程中最重要的影响参量之一,目前针对恒定接触载荷对微动疲劳损伤机理的影响已有大量研究,而尚未见到关于交变接触载荷条件下微动疲劳的研究报道。事实上,构件在实际的工程应用中承受的接触载荷是复杂变化的。因此,本文基于常规的疲劳试验机自行设计了一套接触载荷实时可控的微动疲劳试验系统。6061铝合金由于比强度高、良好的可成形性和可焊性等优点而被广泛应用于飞机和汽车零部件的材料。本文中将以6061铝合金为研究对象,对其分别进行恒定和交变接触载荷条件下微动疲劳试验。研究平均接触载荷、接触载荷幅值和最大接触载荷对其微动疲劳寿命的影响。研究结果表明:(1)6061铝合金试样在接触表面的粘着区和滑移区交界处存在剪应力集中,促使表面疲劳裂纹的萌生,其微动疲劳寿命明显低于纯疲劳寿命。(2)在恒定接触载荷条件下,6061铝合金微动疲劳寿命随接触载荷的增加呈现出先减小后增大的变化行为,在临界接触载荷2.0 kN处微动疲劳寿命最低。(3)在交变接触载荷条件下,随着平均接触载荷的增加,微动疲劳寿命的变化行为与接触载荷幅值大小有关。当接触载荷幅值较小时,微动疲劳寿命呈现出先减小后增加的变化行为;而当接触载荷幅值较大时,微动疲劳寿命呈现出逐渐递增的变化行为。此外,试样在交变接触载荷条件下也存在临界平均接触载荷,且其小于恒定接触载荷条件下的临界接触载荷。(4)在相同平均接触载荷作用下,当平均接触载荷小于2.0 kN时,试样在交变接触载荷条件下的微动疲劳寿命低于恒定接触载荷条件下的微动疲劳寿命;然而,当平均接触载荷大于2.0 kN时,试样在交变接触载荷条件下的微动疲劳寿命接近或高于恒定接触载荷条件下的微动疲劳寿命。此外,如果把最大接触载荷作为微动疲劳寿命的相关参数时,平均接触载荷的影响就可以忽略。(5)综合微动疲劳试验和有限元分析结果揭示了在低接触载荷作用下接触载荷的增大使得最大剪应力增加,有弊于材料的微动疲劳寿命,而在高接触载荷作用下接触表面两边出现粘着接触区,且接触载荷的增加使其宽度增加,从而有利于材料的微动疲劳寿命。更多还原

【Abstract】 The phenomenon known as fretting fatigue occurs at the contact surfaces of two close-contacting components that have an oscillatory relative slip of small amplitude,and the relative slip is the consequence of cyclic loading of one or both of the components.The relative motion between contact surfaces could accelerate the forming and expanding of surface cracks and eventually induces that the components failure earlier than that under the condition of plain fatigue.This phenomenon occurs widely in industrial fields,such as,aeronautical industry,nuclear industry,railway transport,motor industry,chemical industry,electric power and so on,thus it is called the “cancer”.The process of fretting fatigue is very complex and contains a large number of parameters,most of which affect each other.Contact pressure is considered as one of the most parameters and large studies have been done in terms of the effect of contact pressure on fretting fatigue behavior under the condition of constant contact pressure.In fact,the contact pressure of the process of fretting fatigue in the industrial scene is constantly changing.At present,however,the study on effect of changing contact pressure on fretting fatigue behavior has not been reported.Thus,a new fretting fatigue test system based on the general fatigue testing machine is developed in this study,the contact pressure of which could be controlled in real time.Furthermore,6061 Aluminum alloy has high strength,low density,good formability and weld-ability and other advantages and is widely used in the manufacture of the aircraft body and auto parts.In this study,a series of fretting fatigue tests of 6061 aluminum alloy under constant and cyclic contact pressure were investigated.In addition,the effects of mean contact pressure,contact pressure amplitude and maximum contact pressure on fretting fatigue behavior of 6061 aluminum alloy are also discussed.Major experimental results are as follows:(1)Shear stress concentration at the junctions of stick region and slip region on contact surfaces of 6061 aluminum alloy specimens induces initiation of fretting fatigue cracks and fretting fatigue life is significantly lower than plain fatigue life at the same axial cyclic stress.(2)Under the conditions of constant contact pressure,fretting fatigue life of 6061 aluminum alloy reduces rapidly first with increasing of the contact pressure,then increases slowly and reaches a minimum at the contact pressure of 2.0 kN which is considered as the critical contact pressure.(3)Under the condition of cyclic contact pressure,the variable behavior of fretting fatigue life of 6061 aluminum alloy with increasing of the mean contact pressure is determined by the cyclic contact pressure amplitude.When cyclic contact pressure amplitude is low,the fretting fatigue life reduces rapidly first and then increases slowly with increasing of the mean contact pressure.While cyclic contact pressure amplitude is high,the fretting fatigue life constantly increases with increasing of the mean contact pressure.In addition,the critical mean contact pressure under the condition of cyclic contact pressure also exists and is lower than the critical contact pressure under the condition of constant contact pressure.(4)When the mean contact pressure is lower 2.0 kN,the fretting fatigue life under the condition of cyclic contact pressure is significantly lower than that under the condition of constant contact pressure at the same mean contact pressure.while the mean contact pressure is higher 2.0 kN,the fretting fatigue life under the condition of cyclic contact pressure is not lower than that under the condition of constant contact pressure.Furthermore,mean contact pressure effect is not significant when maximum contact pressure is used as correlated parameter.(5)Over consideration of the fretting fatigue test and the finite element analysis result,it can be concluded that the increasing of contact pressure is detrimental to fretting fatigue life due to the increasing of maximum shear stress under the conditions of low contact pressures,while the increasing of contact pressure to fretting fatigue life due to the increasing of the width of stick regions on both sides of contact surfaces under the conditions of low contact pressures.更多还原