Finite Element Analysis of Metals Fatigue Damage, Based on Thermodynamic Entropy models

The amount of entropy generation during the fatigue loading is treated as an indicator of the damage accumulation in the material. Using the thermography technique and recognizing the temperature field distribution at a specimen surface under cyclic loading and calculating the dissipated energy and also considering the possibility of the specimen heat transfer with the environment, the net entropy production rate of the system can be computed.  This research has been conducted to feasibility study and applicability of the methodology through numerical modeling and analysis. In this thesis, using the finite element numerical method and in the framework of Abaqus software, simulations of fully reversed bending are carried out on the standard specimens of aluminum (Al6061-T6) whose experimental test results are available in the literature. Based on results of the mechanical and thermal analysis, calculating the entropy production rate, fatigue fracture entropy, damage variable and remaining life assessment based on this variable are performed. The results obtained from the numerical simulation are compared and validated with the results of experimental tests. Also, a numerical analysis is carried out to estimate the temperature enhancement and fatigue self-heating phenomenon due to the cyclic loading based on the strain-life curve characteristics and dissipated energy on the axial specimen made of (AISI 4340). The results obtained from the research indicate that the infrared thermography technique as a non-destructive evaluation method in the low cycle fatigue range, is a suitable tool for the temperature field evaluation and subsequently, the accumulated damage estimation in material.