【作者】 姜莞；

【导师】 史文库；

【作者基本信息】 吉林大学 ， 车辆工程， 2011， 博士

【摘要】 橡胶悬置成本低,承载能力大,普遍用于中重型商用车的动力总成悬置系统,在动力总成和车架(车体)间起到衰减振动和限位的重要作用。由于中重型商用车的工作载荷大、路况环境恶劣,常发生橡胶悬置的过早失效,表现为橡胶的开裂和金属与橡胶层的脱落,严重影响到整车可靠性和耐久性,更影响到用户的经济利益。由于橡胶悬置的静动刚度和寿命影响因素较多,机理非常复杂,目前大多厂家对橡胶悬置的的设计通常是逆向设计,靠经验进行设计,缺少正向设计的理论和开发流程,迫切需要基于静动刚度特性和疲劳寿命的橡胶悬置的正向设计开发理论和方法。目前金属材料疲劳寿命预测方法及理论已经发展成熟,但是在橡胶悬置的设计方面,缺少成熟的理论和方法,尤其是在橡胶悬置疲劳寿命预测方面,更是少之又少。本文以某重型商用车所配道依茨(DEUTZ)动力总成前、后橡胶悬置研究对象,进行动力总成橡胶悬置系统的隔振性能模拟仿真和疲劳寿命的预测研究,具体内容分为七个部分：第一章归纳总结了国内外有关橡胶减振件有限元模拟及橡胶减振件疲劳寿命预测方面的研究现状,回顾了有限元方法作为现代设计方法最有效的手段,在橡胶减振件方面的应用和发展,重点对汽车动力总成橡胶悬置有限元建模、静动刚度特性模拟、疲劳寿命预测,特别对橡胶疲劳破坏分析所采用的各种研究方法等进行了归纳和总结。第二章建立了动力总成橡胶悬置的有限元模型,并进行有限元计算分析。将橡胶悬置的三维几何模型导入有限元前处理软件,进行网格划分,继而导入非线性有限元软件ABAQUS中,根据橡胶材料试样的应力——应变数据,构造了本橡胶悬置的本构关系,并采用马斯林效应和永久变形力学特性,模拟橡胶材料在循环载荷造成的累进破坏过程。对橡胶悬置的静、动刚度特性进行计算模拟,并与静、动刚度试验数据对比,吻合较好,验证了有限元模型的正确性,也为下一步对橡胶悬置的寿命预测奠定基础。第三章基于前面的理论模型,对动力总成橡胶悬置疲劳裂纹萌生寿命开展研究。以最大主应变为中间破坏变量,将动力总成橡胶悬置的寿命与标准3D哑铃状试件的寿命联系起来,预测元件的单轴载荷下疲劳寿命,并曲线拟合得到以载荷表示的单轴载荷疲劳寿命预测公式。动力总成橡胶悬置实际上不仅受到Z向载荷,而且还受到X向载荷和Y向载荷,因此以最大主应力为中间破坏变量,预测动力总成橡胶悬置多轴载荷下的疲劳寿命,并曲线拟合得到多轴载荷-疲劳寿命关系,其中前悬置载荷-寿命关系以双轴载荷-疲劳寿命曲面图来表示,后悬置载荷-寿命关系以X向、Y向、Z向载荷形成三维坐标轴系,以不同色彩区域表示寿命,制成三轴载荷-疲劳寿命云图来表示。双轴载荷-疲劳寿命曲面和三轴载荷-疲劳寿命云图的提出能够直观有效地揭示多轴载荷下动力总成橡胶悬置的载荷-疲劳寿命关系。第四章采用断裂力学方法分析动力总成橡胶悬置的疲劳裂纹扩展。道依茨动力总成前后悬置的失效形式为橡胶悬置疲劳裂纹发展及断裂。依据悬置实际破坏形式确定裂纹的位置和角度,划分会聚于裂纹线的网格,建立带有裂纹的常规有限元模型模拟动力总成悬置的橡胶体断裂的失效形式。为分析悬置橡胶-金属界面上的开裂,采用粘接单元模拟橡胶和金属材料间复杂的结合部界面层,模拟动力总成橡胶悬置的橡胶-金属硫化界面疲劳裂纹扩展。为满足预测裂纹出现的时机、位置及发展方向的需要,本文采用最新的扩展有限元技术,模拟了沿任意的路径自动产生和传播的裂纹。第五章对影响动力总成橡胶悬置性能的影响因子进行分析。橡胶悬置的刚度、疲劳寿命受很多因素的影响,针对分析的不同阶段,将正交设计、回归拟合、方差分析及相关分析等方法有机结合,形成了影响因子综合分析体系。本文重点考虑了预载、尺寸形状、硬度等因子对于动力总成橡胶悬置的静动刚度和疲劳寿命的综合影响,得出了一系列结论：硬度对于前、后悬置影响均较大,又可以方便调节,且对动刚度影响不显著,较适于抗疲劳破坏特性的设计；预载也有一定影响。前悬置的锥面角度影响较大,而底面中径影响不大；增加后悬置宽度尺寸会提高其疲劳寿命和Z向刚度。基于有限元方法对橡胶悬置的设计,目前尚处于初期发展阶段,第六章以道依茨动力总成橡胶悬置为本文的研究实例,提出道依茨动力总成橡胶悬置应该具备的静、动刚度和疲劳寿命。第七章对动力总成橡胶悬置进行试验研究。对动力总成橡胶悬置进行了静、动刚度试验、台架疲劳试验,进行了实车动力总成橡胶悬置的振动传递率测试,试验结果表明,本文建立的动力总成橡胶悬置有限元模型和分析方法的正确。第八章总结了本文的主要工作、研究成果和工作展望。更多还原

【Abstract】 Rubber mounts are widely used in medium and heavy commercial vehicles’ powertrain mount systems for their low cost and high load capacity, playing the important role of anti-vibration and position-limiter between the powertrain and chassis (body). For the work environment of medium and heavy commercial vehicle is poor, and their load are very big, premature failure of of rubber mounts often occure. The performances are cracking of rubber and rubber shedding from metal. Those seriously affect the reliability and durability of the vehicle, as well as the economic interests of users.The static and dynamic stiffness performance and life of rubber mount affected by many factors, whose mechanism is very complex, and now most of the rubber mount manufacturers adopt reversal design, that is design depend on experience. The design and development processes of top-down design are lack. The top-down design and development processes based on the static and dynamic stiffness characteristics and fatigue life of rubber mount are urgent needed. Although metal fatigue life prediction methods and theories have been developed maturely. While in terms of rubber damper design, mature method and theory are lack. Especially with respect to the fatigue life prediction of rubber damper. This dissertation take the front and rear DEUTZ powertrain mount of a heavy commercial vehicle as research object, studying the simulation of powertrain mount system vibration isolation performance and its fatigue life prediction. The content consists of seven parts:Chapter I summarizes current research status on finite element simulation and fatigue life prediction of rubber vibration isolator in domestic and overseas. Review The application and development of finite element method in the area of rubber vibration isolator as the most effective means of modern design are reviewed. The summary focused on the finite element modeling of vehicle powertrain rubber mount, static and dynamic stiffness simulation, fatigue life prediction, especially the different research methods adopted in the rubber fatigue and damage analyses.ChapterⅡestablishes the finite element models of powertrain rubber mounts and carries through the compute. Three-dimensional geometric models is builted in CAD software. Then they are imported into finite element pre-processing software for meshing. The FE models are imported into nonlinear finite element software ABAQUS. Constitutive behavior of the rubber mount obtained by fitting test data into stain potential energy. The decreasing load capacity of rubber material due to the progressive destruction under cyclic loading is simulated by the mechanical property of mullins effect and permanent set. The static and dynamic finite element analysis of rubber mount are conducted respectively. Through comparing with the static and dynamic stiffness test data of powertrain mounts, the finite element models are verified accurate, laying a foundation for the fatigue life prediction of rubber mounts.ChapterⅢstudies the fatigue crack initiation life of engine mounts. Taking maximum principal strain as a medium, the life of powertrain mounting components are linked to that of the standard 3D dumbbell specimen. Then the components’ fatigue life under uniaxial loading are predicted. And fatigue life prediction formulae are curve fitted being indicated by load. In fact there are not only uniaxial load on the engine mounts, but impacts and vibrations in all directions. Therefore the maximum principal stress is used for the medium destruction variable of powertrain mounts’ multi-axle fatigue life. The powertrain mounts’ fatigue life under multiaxial loading are predicted and curve fitted expressed by the multi-axis load-fatigue life relationships. For the front mount, three-dimensional load-life fatigue diagram is made, taking the vertical and radial load as x and y value, the mount life as the z value. While for the rear mount, multi-dimensional load-life fatigue diagram is made:loads in x, y and z directions are presented by value on x, y and z axles, value of fatigue life is presented by regions of different colors. Three-dimensional fatigue life surface and the multi-dimensional cloud chart proposed here can make it effective to reveal relationships between multi-axis load and fatigue life.of powertrain mounts.Chapter IV analyzes fatigue crack growth of powertrain mounts with fracture mechanics. The failure form of front and rear DEUTZ powertrain mounts is fatigue crack growth till fracture. According to the actual failure phenomena the location and angle of cracks on mounts is determined, and the conventional fracture FE model is established with meshes converging at the crack line to simulate the failure form of mount. To analyze the mount’s cracking near rubber-metal interface, the cohesive elements are made use of to simulate the complex junction layer of the rubber-metal interface, simulating the fatigue crack growth near the rubber-metal sulfide interface of engine mounts. The latest extended finite element technology is adopted to simulate the initiation and propagation of a discrete crack along an arbitrary, solution-dependent path without the requirement of remeshing in the bulk materials, meeting the needs of forecasting the appearance occasion, location and direction of cracks.Chapter V carries out the analysis with the factors that influence the performances of powertrain mounts. The stiffness and fatigue performances of rubber mounts are effected by various of complex factors. Contraposing different stages of analysis, the methods such as orthogonal design, regression curve fitting, analysis of variance and correlation analysis are combined organically to form a comprehensive analysis system of factors. Composite effects to the static and dynamic stiffness and fatigue life of engine mount costed by factors such as preload, configuration, hardness and other factors are analyzed, and a series of conclusions are obtained:hardness is of great impact for both front and rear mount, which can be adjusted easily, while its impact on the dynamic stiffness is not significant, suitable for the design of anti-fatigue performence; preload is also vnaanlbzon; the cone angle of front mount is of bigger impact, while the bottom diameter shows a lack of sensitivity; increasing the lateral size of rear mount would enhance its fatigue life and increase its vertical stiffness.The rubber vibration isolator design based on finite element simulation is still in the early stage of development, Chapter VI takes the DEUTZ powertrain rubber mounts as an research example, proposes the static and dynamic stiffness and fatigue life that DEUTZ powertrain rubber mounts should possess.ChapterⅦconducts experiment research on the powertrain mounts. The static and dynamic stiffness experiments, as well as fatigue bench test of powertrain mount is carried out. And the vibration transmissibility test of real vehicle powertrain rubber mounts are carried out. The experimental results demonstrate that the finite element model of engine mounts established and the analysis methods of this dissertation are veracity.ChapterⅧis a summary of the main work and achievements, as well as the prospects of future research.更多还原