【作者】 丛广佩；

【导师】 童小燕；

【作者基本信息】 东北大学 ， 机械设计及理论， 2008， 硕士

【摘要】 目前的疲劳能量耗散理论还存在诸多问题,尤其缺乏对它进行全面研究。以往限于实验手段及理论知识,研究人员只能根据各自感兴趣的问题从不同的角度开展研究,但是随着科技的发展,各种高精度仪器的相继出现,实现这种全面研究已有可能。作者在前人的基础上,对疲劳耗散过程本身和疲劳耗散能量的计算给出了个人的观点。作者分析了纯铜疲劳过程中的能量耗散过程,发现材料形变过程中消耗的机械功以多种能量形式耗散。其中绝大部分是以热耗散的形式散失于环境中和以显微结构畸变的形式贮存于材料中。通过分析热耗散及储能的变化规律,发现热耗散的不均匀分布使材料单元间产生热传导、材料与环境间产生热交换,并在材料中形成局域温度场；储能的变化引起材料微观结构的变化,甚至表面微观形貌的变化,这是与材料的损伤状态是直接相关的。大量研究表明,温度的变化与热耗散的变化具有自相似性,且能够反映材料疲劳变化的不同过程；表面微观形貌的变化与储能的变化是一致的,它反映了材料疲劳变化的不同状态。本文介绍了疲劳过程中机械能耗的测试方法和结果。采用高精度的红外热像仪和远距高倍显微镜同步测量了光滑纯铜试样与缺口纯铜试样在疲劳过程中的温度变化与表面微观形貌变化。实验过程中发现温度与储能(表面微观形貌)在能量的基础上存在一定的联系。试样在变形的过程中,其表面温度变化与表面微观形貌变化存在明显的相关性。作者根据试验分析,发现循环滞回能在循环初期变化很大,随后逐渐减小趋于稳定,在疲劳破坏发生前的最后阶段又迅速衰减。并且根据热传导的傅立叶定律、对流换热微分方程及能量耗散控制方程,推导出温度与疲劳寿命之间的关系。限于时间及试验手段,作者并没有得出温度与储能的关系。为此,作者希望通过下一步的深入研究,进一步解决目前存在的问题,完善疲劳能量耗散理论。更多还原

【Abstract】 It is found that the existing energy dissipation-based fatigue theory has many deficiencies, especially an integrated study is lacked. The former researchers only studied the energy dissipation during fatigue from their most interested subjects due to lack of experimental condition and theory, however, with the appearance of advanced experiment apparatus, it is conceivable to achieve the integrated research. On the groundwork of former, the author hopes to give the fatigue’s dissipation process itself a new explanation and a new governing equation of the energy dissipation group.With the analysis of energy dissipation process during fatigue, the author finds that the mechanical energy is dissipated in various forms of energy. The energy mainly are the heat energy dissipated in the environment and the stored energy consumed by the deformation of the microstructures, which mainly is heat energy. Through analyzing thermal dissipation and stored energy during the fatigue damage, it is found that the thermal dissipation elevates the temperature of the specimen above that of the environment; thermal conduction takes place between the material volume units and thermal exchange between the specimen and the environment,which bring on local temperature field on the specimen. The energy stored in materials during fatigue changes the energy state of the materials, and the energy state reflects the change of the surface microstructures, which is directly related to the damage state. Many studies show that the change of temperature, which can reflect the dissimilar course of the fatigue behaviors of materials during low cycle fatigue, is self-similar with the change of thermal dissipation. The change of surface micrograph, which can reflect the dissimilar state of the fatigue behavior of materials, is coincident with the change of the stored energy.In this paper, the test method and test result of the mechanical energy dissipation during fatigue are introduced. The temperature response and the micrograph change of copper under low cycle fatigue are studied by use of infrared photography instrument and remote high power objective microscopy. The temperature has one relation on the basis of energy with the surface The results showed that there exits obvious relationships between the measured temperature and the microscopic shape. The temperature and the microscopic occur to dissimilar change with the difference of loading mode and specimen shape.Through analyzing the fatigue date, the author found that:The cyclic hysteretic energy is very high at its earlier cycle, and gradually it rises steadily at the steady cycle, but it decreases quickly before ruptures. According to the Fourier’s Law of the thermal conduction, convectional equation, the governing equation of the energy dissipation, the author derived that the equation with temperature and fatigue life. The predicted lives were found to be in good agreement with the experimental results. The determinate relation between temperature and stored energy isn’t obtained due to the lack of the experiment instruments and time. Therefore, the author hopes to solve this problem and perfect the energy dissipation-based fatigue theory through farther studies.更多还原