Study of the effect of load frequency on infrared measurements using thermoelastic FE analysis method

The infrared thermoelastic method is considered a promising technology for the non-contact measurement of the stress distribution and fatigue limit of structures. In this method, the stress distribution can be detected based on the temperature variation caused by loading the structure, and the fatigue strength can be estimated from the dissipated energy. Additionally, the minute temperature variations of the structures under cyclic load conditions are evaluated. However, there is a concern that appropriate measurement results cannot be obtained using low-frequency cyclic loads owing to the large influence of heat diffusion. Therefore, the effect of the load frequency was investigated using a thermoelastic finite element (FE) analysis on a gusset welded joint specimen commonly used in welded structures. Furthermore, to simulate the thermoelastic effect, a stress field-temperature field thermoelastic FE analysis technique that calculates the heat transfer of the generated heat and heat absorption generated by decreasing and increasing tensile stress was developed. The calculated stress distribution showed consistency with the thermoelastic stress distribution measured using the infrared ray method, implying that the proposed technique is effective in reproducing the thermoelastic effect. A small gradient of temperature distribution was observed in the case employing a load frequency of 1 Hz; therefore, it is important to consider the influence of the load frequency when applying the thermoelastic method to the stress concentration field.