Synchronized Survey On The Thermal Dissipation And The Microscopic Structure During Fatigue Damage

Fatigue damage is the energy dissipation process. According to thermodynamic viewpoint, the thermal dissipation can reflect the dissimilar course of the fatigue behaviors of materials during low cycle fatigue and the micrograph change can reflect the dissimilar state of the fatigue behavior of materials. Consequently, the author think it integrated and scientific to measure synchronously temperature response and the micrograph change of pure copper during low cycle fatigue.The thermal dissipation of fatigue damage generates the change of the surface temperature and the change of the surface microstructures is directly related to the change themicrostructures. So on-line monitor the change of surface temperature and microscopic structure during fatigue can provide experiment support for analysis the correlation and the synergism relationship of the thermal dissipation and the change of the microstructures. Using the infrared camera and long-distance video microscope, a test system was set up to on-line monitor the change of surface temperature and microscopic structure during fatigue. The temperature evolution measured by infrared camera indicated three stages: (1) the initial rapid increase, (2) the stabilization, and (3) abrupt increase before failure. The results showed that the temperature increase, resulting from plastic deformation, depended on the applied stress and frequency.During the initial phase, heat quantity that creates by the change of the microstructures almost apply to increase the temperature ,so the temperature increase rapid; with the increasing of cycle life, the temperature and the change of the microstructures vary gradually in the stabilization; before failure, the surface temperature increase abrupt for the quick energy delivery, and the microstructures vary quickly for the storage plastic strain energy raising. In this phase, test sample occurs necking phenomenon, and the surface is more rough in the adjacent fracture.Many studies show: Temperature change, 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. Consequently, in order to study the energy dissipation-based fatigue theory, the author think it integrated and scientific to measure synchronously temperature response and the micrograph change of pure copper during low cycle fatigue. Combining the infrared thermographic picture with the surface microstructure pictures, the author analysis the temperature change. It is found that the temperature change quickly in the designated field and the rough surface. This field is also the concentrated deformation field.According to the test, the author found in this paper: (1) there exits consistency between the surface temperature field and the damage, so it can use the surface temperature to detect the occurrence of the start and the evolution of damage. (2)there exits obvious relationships between the measured temperature and the microscopic shape, and it can be the basis of the damage measuring .(3) it is need to quantitative...