【作者】 魏勇强；

【导师】 王黎钦；

【作者基本信息】 哈尔滨工业大学 ， 机械设计及理论， 2010， 博士

【摘要】 高速、高温、低温、重载、高频振动环境和工况条件在航空、航天、国防领域及民品高端产品领域越来越频繁,在这种条件下,密封、轴承、齿轮和泵、阀中的磨损问题日益突出,严重制约着复杂装备的寿命、可靠性、极限性能及其稳定性。其中,有一类由于冲击滑动耦合作用产生的磨损,往往直接导致高速轴承及密封的快速、异常失效,最终导致型号等高速复杂机械系统的止转性失效。本文建立了冲击滑动磨损试验机及冲击滑动耦合作用下摩擦副的热-机耦合分析模型,通过模拟分析及试验研究,对该类磨损的机理进行了探索。首先基于密封和轴承中典型冲击滑动耦合作用的摩擦副实际工况,研制了冲击滑动磨损试验机。实现了所有物理参量的自动显示、存储和监控,主要技术参数调节灵活,冲击工作载荷稳定,持久工作能力强。模拟试验的有效性和重现性结果表明:在相同条件下的试验数据具有较好的重现性,能够用于材料在冲击滑动耦合作用下的磨损机理研究。为了研究冲击滑动作用下由于热-机耦合效应产生的微区特性变化,本文建立了冲击滑动耦合作用下的接触模型,利用虚拟接触载荷法离散载荷,简化了有限元模型中的接触搜索算法,提高了计算效率。结果表明:冲击滑动接触主要表现为反复的热冲击和剪切表面化,并伴随冲击和滑动加剧,材料的表面及亚表层存在温度梯度分布和剪切表面化加剧。热-机耦合作用下,热影响区很薄,仅存在于0.3mm以内的亚表层。热效应增加了沿深度方向分布的等效应力梯度,且最大等效应力更接近接触表层。设计了L16(45)四水平正交试验,研究了5种典型摩擦配副材料在冲击滑动耦合作用下的磨损特性及行为。通过因素对磨损影响的极差分析和多元线性回归分析得到:冲击滑动耦合作用下,冲击力及冲击频率对冲击试件的磨损体积影响最大。较硬的钛合金TC4和较软的铝青铜QA10-4-4配副时会出现异常磨损行为,即“软磨硬”现象。在20CrNiMo钢及硬铝与GCr15钢配副时,冲击试件的平均磨损量与冲击频率、冲击力幅值及滑动速度之间存在十分显著的三元线性回归关系,为建立配副定量设计准则提供了依据。为研究材料在冲击滑动耦合作用下的磨损机制,本文利用二维、三维轮廓测试、X射线衍射、EDS能谱分析及电子扫描显微镜对磨痕进行分析。结果表明,金属冲击试件在磨损后,磨痕表面分布着大量剥落坑,表明剥落是金属冲击试件磨损的主要原因,磨损机制适用剥层理论。其中当冲击试件屈服极限高时,在冲击滑动耦合作用下材料主要发生疲劳剥落,且冲击频率增加剥落趋向严重,随着摩擦系数增大,导致剥落的裂纹趋向表面化。当冲击试件屈服极限较低时,材料主要发生显微切削、磨粒磨损及粘着剥落,工况参数增加,磨损机制发生由显微切削、磨粒磨损向粘着剥落的转变过程。浸渍锑合金石墨在冲击滑动耦合作用下,接触区内材料颗粒不断剥落,在对偶件的推碾作用下部份被挤入冲击试件的空隙中,在一定程度上减少了接触区内材料的气孔及微裂纹等缺陷,提高了材料的耐磨性。在五组配副试验中,钛合金回转试件发生了严重的磨损。钛合金产生“软磨硬”的机制为,钛合金与铜等低熔点金属接触时,其断裂强度与塑性指标显著降低,会发生铜脆现象,导致钛合金发生剥落,并且表面温度大幅变化导致铜的扩散加速,铜脆倾向增大。其他配副中,尽管回转试件磨损轻微,但材料表面的原始形貌发生较大的变化,其中GCr15钢磨痕区内残余奥氏体含量增加,导致这一转变的主要原因为摩擦生热产生的接触区高温及接触区应变产生的再结晶温度降低。论文为高频工作环境下选配合理摩擦副材料提供了依据。更多还原

【Abstract】 The wear problem of sealing, bearing, gear, pump and valve, caused by severe service conditions, including high temperature, high sliding velocity, extreme low temperature, high load and high frequency vibration, between wear parts, becomes increasingly serious, especially in the application of aviation, aerospace, national defense and high end civilian industry. The life, reliability, extreme performance and stablility of equipments are restricted by these problems. A kind of wear caused by impact-sliding motion between wear parts can induce severe abrasion, which leads to the sudden and abnormal failure of components, and failure of high speed mechanical system. An impact-sliding wear rig was designed and the fully coupled thermal-stress analysis model was constructed for this purpose. The research of mechanics of impact-sliding wear was implemented, using experiment and finite element analysis methods.First, an impact-sliding wear rig was designed and constructed, based on the working conditions of impact-sliding wear in sealing and bearing. This wear rig can display and store the physical parameters. The operation of the testing rig is flexible, the impact load is steady and it can endure long time operation. The results of repeatable tests exhibit good repeatability under the same test conditions. The testing rig meets the demands of the impact-sliding wear researches.To research the distribution of temperature and stress, caused by thermal-stress effect under impact-sliding motion, contact model was established. To increase the efficiency of calculation, a new contact tracking approach was adopted, using virtual contact loading method. The results show that impact-sliding contact causes transient heating and surfacial-tendency of shear stress. The gradient of temperature and surfacial-tendency of shear stress become intensively with the increasing of impact and sliding. The thermal influence area is thin, and the effect of thermal can take effects less than 0.3mm depth only. The thermal effects increase the gradient of mises distribution along depth direction, and the maximum mises stress is closer to contact surface.A four levels orthogonal table-L16(45) was adopted to design the experiments. The impact-sliding wear tests, including 5 sets of typical counterparts, were conducted, using the impact-sliding wear testing rig. The results, processed through multiple element linear regression and range analysis, show that impact motion, including impact frequency and impact load, has greater influence than sliding velocity on wear mass loss of impact specimens. The results of wear volume show clearly that although the titanium alloy TC4 has greater hardness than aluminum bronze, the wear volume of titanium alloy has much greater value compared with aluminum bronze yet. That is the phenomenon of the“the hard worn by the soft”. The relationship between average wear loss and experimental factors, including impact frequency, impact load and sliding velocity, is of ternary linear regression, when 20CrNiMo steel and duraluminium alloy wear against GCr15 steel. The quantitative design of wear counterparts can be established, using this conclusion.To research the wear mechanism of materials under impact-sliding interaction, some non-destructive examinations have been performed on worn specimens, including 2D and 3D profilometry, scanning electron microscopy, XRD and EDS technology. The results show that after abrasion, the surface profile of metal specimens changes greatly with large numbers of flaking on worn track. It indicates that material flaking is the main cause of wear of metal impact specimens, under impact-sliding contact, and the wear mechanism of metal impact specimens is delamination wear. When the yield limit of material is high, fatigue flaking is in dominant position, and the flaking becomes serious with the increase of impact frequency. The cracks are of surfacial tendency with the increasing of friction coefficient. When the yield limit of material is low, the wear of impact specimens is caused by mechanical removal and adhesion mainly, and with the increase of experimental factors, the wear mechanism of impact specimens changes from mechanical removal to adhesion. When material is brittle, the particles flake off impact specimen constantly. A portion of these particles fill the interspaces of impact specimen. As a result, the number of micro-crack and porosity is decreased and the wear resistance is improved.Among 5 sets of experiments, the rotational specimen, made of titanium alloy TC4, wears more severely than impact specimen, made of aluminum bronze. This phenomenon can be explained by the behavior of copper-induced embrittlement of titanium alloy. The fracture strength and plastic property of titanium alloy decrease greatly as contacted with certain kinds of metal with low melting point, such as Cu and etc. With the increase of temperature, the diffusion of Cu is accelerated, and copper-induced embrittlement becomes severely. In other experiments of countparts, the wear loss of rotational specimen is not detectable, but the profile and micro-structure changed obviously yet. It can be found that the content of residual austenite increases. This phenomenon can be explained by the decrease of recrystallization temperature, caused by high friction-induced temperature and strain of contact area. This thesis provides the guide line to select wear counterparts properly under high frequency work condition.更多还原