Thermal methods for fatigue characterization of components

In recent years, the thermographic technique has been regarded as a key tool to investigate the fatigue behavior of materials instead of time and cost consuming traditional methods. One way to assess the fatigue as an irreversible process is studying the temperature signature due to the heat dissipation during the cyclic loading. Numerous studies have suggested that the shift from anelastic to inelastic strains results in a significant level of intrinsic dissipation, indicating the presence of the fatigue damage. The primary objective of this study is to explore heat dissipation in fatigue tests through a combination of experimental methods and numerical models by utilizing the fundamental temperature component related to dissipation, the second amplitude harmonic (SAH) of the temperature. The proposed hybrid approach integrates experiments with a numerical model to pinpoint the specific volume generating heat during the fatigue test. The investigation also delves into the impact of loading frequency on the fundamental temperature component associated with dissipation. In experimental part of the study, a comprehensive campaign was carried out to capture the material's response under both static and cyclic loading conditions. The experimental data are employed for comparing the accuracy of different thermal indices in fatigue limit estimation and establishing the numerical model, act as reference data for comparison. In the numerical part of the study, models are established in COMSOL Multiphysics 5.6 to simulate the temperature distribution on the surface of the specimen. After the verification with analytical solution of 1-D heat equation, a model is proposed for heat source identification. One of the main controversial issues in fatigue characterization is addressed in this study, whether the entire gauge volume dissipates or not. Additionally, the effect of loading frequency on SAH of temperature reveals its limitation in thermographic measurement and fatigue assessment.