【作者】 刘娟；

【导师】 杨翊仁； 沈火明；

【作者基本信息】 西南交通大学 ， 工程力学， 2013， 博士

【摘要】 扭动微动作为一种基本相对运动和变形方式,大量存在于实际工况中,如交通工具中大量存在的球窝配合件及旋转紧固件、轮轴配合、人体关节、及各种人工关节等。其产生的磨损损伤会引发机械零部件服役安全及人体生命健康问题。但扭动微动研究起步较晚,报道较少,解析解存在一定局限性。西南交通大学摩擦学研究所开展的系统试验研究,主要在二类微动图基础上,建立了扭动微动磨损的运行和损伤机理,但扭动微动的力学行为和机理却有待分析与研究。同时,减缓微动损伤措施的研究主要集中于切向微动,表面工程技术在抗扭动微动损伤中的应用研究极为少见。因此开展扭动微动磨损和防护的力学行为分析,不仅可以深化扭动微动磨损损伤机理、丰富微动摩擦学理论,而且对实际应用中抗扭动微动磨损失效具有重要的工程指导意义。本研究基于接触问题有限元方法对扭动微动开展数值分析,研究关键微动参数对接触表面及次表面的应力应变分布的影响。从力学角度分析扭动微动磨损损伤特性,并将力学行为和实验现象进行对比分析；并利用ABAQUS用户子程序Fric引入接触表面随时间和空间各项同性变化的摩擦系数,对扭动微动磨损进行数值模拟。在摩擦扭矩曲线和试验结果较好吻合基础上,进一步分析扭动微动力学行为；同时开展MoS2涂层扭动微动有限元分析,通过与基体力学行为的比较,探讨固体润滑涂层在抗扭动微动磨损中应用的可行性。获得的主要结论如下：(1)扭动微动有限元分析结果显示：不同运行区域扭矩曲线形状与试验结果较好吻合,说明有限元分析中接触表面的变形行为和摩擦行为与实际基本相符。在有限元分析中,需依据T-θ曲线形状结合接触状态转变特征分析来划分运行区域。椭圆型T-θ曲线,并且接触状态云图中粘着区随循环周次增加有减小趋势,表明微动运行于混合区。(2)数值模拟结果的三种微动运行区域下摩擦扭矩—角位移幅值曲线与试验结果无论在形状还是数值上均较好吻合,说明所采用摩擦系数模型能够模拟扭动微动接触界面摩擦系数演化及变形行为,在扭动微动磨损力学机理分析中考虑摩擦系数的动态变化非常有必要。在此基础上,扭动微动的力学行为分析和损伤机理揭示更加可靠。(3)表面塑性变形和摩擦剪力对表面磨损起主控作用。三种扭动微动运行区域塑性应变和摩擦剪应力的分布和演化不同,相应的磨损损伤程度和演化也不同。(4)结合SWT参数和关键平面方法,对混合滑移区接触副表面的裂纹萌生与扩展位置进行预测分析。结果表明：次表面应力应变分布状态决定了裂纹萌生与扩展,裂纹应在粘滑交界处和滑移区内接近接触边缘处萌生与扩展,预测结果与试验结果较好吻合。(5)与LZ50钢相比,MoS2涂层的运行区域没有混合区,其滑移区向小角位移幅值和高法向载荷方向移动,说明通过微动运行区域的改变消除了混合区的损伤；MoS2涂层表面呈现的低摩擦使其与基体相比极易进入滑移区,表面相对运动幅度较大,但摩擦扭矩值却处于较低水平,表面摩擦剪力始终较小,故由摩擦磨损产生的表面损伤比基体材料轻微。更多还原

【Abstract】 As a fundamental mode of relative motion and deformation, torsional fretting takes place in many practical engineering applications, such as ball socket matching parts and rotary fastener widely used in vehicles, wheel axle matching parts, the human joint and artificial joint, etc. Wear caused by torsional fretting can lead to problems about mechanical components service safety and human health. With recent beginning of torsional fretting research, few correlative reports exist. Analytic solution about torsional fretting is limited. At present, the systemically experimental study of torsional fretting is made by the Tribology Research Institute of Southwest Jiaotong University. The operation and damage mechanism of torsional fretting wear has been established basing on two kinds of fretting maps. But the mechanical behavior and mechanism of torsional fretting are required to be analyzed. At the meantime, the research of the measure to slow down the fretting damage mainly focuses on tangential fretting while there is little report on resisting torsional fretting damage by the technology of surface engineering. Thus, analyse on the mechanical behavior of torsional fretting wear and protection not only has a great scientific significance to deepen the torsional fretting damage mechanism and to enrich the fretting tribology theory, but also offers important engineering guidance for anti-failure of torsional fretting wear in practical application.Based on finite element method of contact problem, numerical simulation of torsional fretting has been developed. The effect of pivotal fretting parameters on surface and sub-surface stress and strain distribution is investigated. Damage characteristic of torsional fretting has been revealed by mechanical analyse, and comparation between mechanical behavior and experimental phenomenon has been made. The isotropic variable coefficient of friction (COF), which is expressed in space and time, is introduced and implemented in the finite element code ABAQUS by the user subroutine FRIC. Then numerical simulation of torsional fretting was carried out. With the good consistency between simulation results of friction torque curves and experimental results, mechanical behavior of torsional fretting was further analyzed. Torsional fretting finite element analyse of MoS2coating has been performed to discuss the feasibility of the solid lubricant coating in resisting torsional fretting wear application,comparing with the mechanical behavior of the substrate. The main obtained conclusions are listed as follows:(1) There was good consistency between finite element results and experimental results.That is, contact surface deformation behavior and friction behavior simulated by finite element analyse agree with the practice. In the finite element analyse, the running region was partitioned according to T-θ curves shape and contact state transformation. Elliptic loops and sticking zone minishing with cycles indicated fretting run in the mixed slip regime.(2) For friction torque-angular displacement amplitude curves, there was good consistency between the simulated results and the experimental results under three different fretting running regimes.It indicated that the COF model was able to simulate the COF evolution and deformation behavior during the torsional fretting. The numerical simulation considering dynamic change of COF was much more reliable.(3) Surface wear was mainly dominated by surface plastic deformation and friction shear stress. Accordingly, the different distribution and evolution of plastic strain and friction shear stress under three different torsional fretting running regimes leaded to different wear damage degree and damage evolution.(4) Combining the SWT parameter with the critical plane approach, prediction analysis of contact surface crack initiation and propagation position in the mixed slip regime was carried out. Results indicated that sub-surface stress and strain state decided crack initiation and propagation, and cracks were expected to initiate and propagate at the stick-slip interface or near contact edge within the slip region. Prediction results agreed well with the experimental phenomenon.(5) Compared with LZ50steel, no mixed slip in the coating existed in the running regime for MoS2. Its gross slip running region removed to small angular displacement amplitude and high normal load. As a result, damage in the mixed slip regime was eliminated by the transformation of the fretting running regime. Because of surface low friction, MoS2coating was much easier to entering slip regime than the substrate, and surface relative motion amplitude was larger. But, friction torque value was in lower level, and plastic strain and surface friction shear stress were smaller. Consequently, surface damage caused by friction and wear was slighter than the the substrate material.更多还原