A Prediction Of Low Cycle Fatigue Life Based On Energy Dissipation Theory In Copper T2

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.