功能梯度材料二维热弹性接触失稳分析

发布时间：2018-09-07 19:47

【摘要】：当两个弹性体之间有热流流过和/或相对滑动时,接触面上的接触热阻/摩擦热会引起温度场和接触压力的非均匀分布,进而导致接触面的非均匀热弹性变形;同时,非均匀热弹性变形又将加剧温度场和接触压力的非均匀分布。当热流和滑动速度达到一定值以后,系统在任意微小的扰动下将出现温度和压力分布的剧烈波动变化,这种波动变化会使系统丧失稳定性而发生自激震荡式的失稳,称之为热弹性接触失稳。通常热弹性接触失稳问题可以分为两类,一类是接触热阻导致的静态热弹性失稳,另一类是摩擦滑动所导致的摩擦热弹性失稳。而多数情况下,这两类失稳问题同时存在且相互耦合,称之为耦合热弹性接触失稳。热弹性接触失稳问题容易发生在高速列车、汽车和飞机的制动系统中,表现为摩擦副上热斑的形成,最终导致制动系统失效。大量的理论与实验研究表明将功能梯度材料用于表面涂层可提高结构构件抵抗由压痕、侵入、摩擦滑动、滚动、微动疲劳及相关的磨损过程中引起的接触损伤和摩擦损伤的能力。本文针对功能梯度材料的二维热弹性接触失稳问题开展理论研究,探讨利用功能梯度材料改善静态/滑动系统热弹性接触稳定性的可行性。主要内容和结论包括:(1)利用摄动法研究了沿厚度方向以指数形式变化的功能梯度层和均匀层之间的二维静态热弹性接触失稳问题,建立了静态热弹性接触失稳准则。研究结果表明,通过调整梯度层的梯度指数和厚度可以有效地改善系统的静态热弹性接触稳定性。(2)假设梯度涂层的物性参数沿厚度方向以任意函数形式连续变化,利用层合板模型、摄动法和矩阵传递法,求解了功能梯度涂层半平面反平面滑动系统的二维耦合热弹性接触失稳问题。研究结果表明,选择适当的梯度变化类型可以有效地调节反平面滑动系统的耦合热弹性接触稳定性;并且发现热扩散系数的梯度变化对系统热弹性接触稳定性的影响通常不可忽略。(3)进一步研究了功能梯度材料面内滑动系统的二维热弹性接触失稳问题。分别假设功能梯度材料的物性参数沿厚度方向以指数形式变化和任意函数形式变化,研究了梯度半平面的摩擦热弹性接触失稳和耦合热弹性接触失稳问题。研究结果表明,滑动系统的热弹性接触稳定性对热参数的梯度指数变化非常敏感,但对弹性参数的梯度指数变化不敏感;梯度变化对滑动系统的耦合热弹性接触临界失稳状态的影响与接触面热流流向相关。通过开展相关的理论研究,不仅完善了功能梯度材料热弹性接触问题的理论研究,而且对以改善热弹性接触稳定性为目标的功能梯度材料的优化设计与工程应用具有重要意义,为高速列车制动系统的设计制造提供了重要的理论基础和技术储备。
[Abstract]:When there is heat flow and / or relative sliding between two elastomers, the contact thermal resistance / friction heat on the contact surface will cause the non-uniform distribution of the temperature field and contact pressure, which will lead to the non-uniform thermoelastic deformation of the contact surface. The non-uniform thermoelastic deformation will aggravate the non-uniform distribution of temperature field and contact pressure. When the heat flux and sliding velocity reach a certain value, the temperature and pressure distribution of the system will fluctuate violently under any small disturbance, which will make the system lose its stability and cause the self-excited oscillation instability. It is called thermoelastic contact instability. Generally, thermoelastic contact instability can be divided into two categories, one is static thermoelastic instability caused by thermal contact resistance, and the other is friction thermoelastic instability caused by friction sliding. In most cases, these two kinds of instability exist simultaneously and are coupled to each other, which is called coupled thermoelastic contact instability. The thermoelastic contact instability is easy to occur in the braking system of high speed train, automobile and aircraft, which is represented by the formation of heat spot on the friction pair, which eventually leads to the failure of the braking system. A large number of theoretical and experimental studies have shown that the application of functionally graded materials to surface coating can improve the resistance of structural members to indentation, invasion, friction, sliding and rolling. The ability of fretting fatigue and associated wear processes to cause contact and friction damage. In this paper, the two-dimensional thermoelastic contact instability of functionally graded materials is studied theoretically, and the feasibility of using functionally graded materials to improve the thermoelastic contact stability of static / sliding systems is discussed. The main contents and conclusions are as follows: (1) the two-dimensional static thermoelastic contact instability problem between the functional gradient layer and the uniform layer varying exponentially along the thickness direction is studied by using the perturbation method, and the static thermoelastic contact instability criterion is established. The results show that the static thermoelastic contact stability of the system can be effectively improved by adjusting the gradient index and thickness of the gradient layer. (2) it is assumed that the physical parameters of the gradient coating vary continuously in the form of arbitrary function along the thickness direction. By using laminated plate model, perturbation method and matrix transfer method, the two-dimensional coupled thermoelastic contact instability problem of half-plane anti-plane sliding system with functionally gradient coating is solved. The results show that the coupling thermoelastic contact stability of anti-plane sliding system can be effectively adjusted by choosing the appropriate gradient variation type. It is also found that the influence of the gradient of thermal diffusion coefficient on the thermoelastic contact stability of the system can not be ignored. (3) the two-dimensional thermoelastic contact instability of the functionally graded material in-plane sliding system is further studied. The friction thermoelastic contact instability and coupled thermoelastic contact instability of functionally graded materials are studied by assuming that the physical parameters of functionally graded materials vary in exponential form and arbitrary function along the thickness direction respectively. The results show that the thermal elastic contact stability of the sliding system is sensitive to the gradient exponent of the thermal parameters, but not to the gradient exponents of the elastic parameters. The influence of gradient on the critical instability state of coupled thermoelastic contact is related to the flow direction of the contact surface. Through the relevant theoretical research, not only the theoretical study of thermal elastic contact problem of functionally graded materials is perfected, but also the optimization design and engineering application of functionally graded materials aiming at improving the thermoelastic contact stability are greatly improved. It provides an important theoretical basis and technical reserve for the design and manufacture of high speed train braking system.
【学位授予单位】：北京交通大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TB34

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