Rapid evaluation of fatigue limit using infrared thermography: comparison between two methods for quantifying temperature evolution

The technique of rapid evaluation of fatigue limit using infrared thermography was developed and has been paid attention during the past 30 years. This technique is beneficial because it also makes possible to detect the location of fatigue damage in real products. In the thermographic technique, the fatigue limit is determined based on the temperature evolution with the load amplitude. In this research, two methods for quantifying the temperature evolution from measured temperature variation (mean temperature rise and second harmonic amplitude) as well as two types of infrared camera (quantum and thermal type) are compared with each other in order to assess the applicability of the thermographic technique. Experiments are conducted for double edge notched specimens of type 304 stainless steel. A data processing technique developed by the authors recently is employed in order to determine the fatigue limit appropriately. The results of fatigue limit evaluation are compared with true fatigue limit. In conclusion, it is found that the second harmonic amplitude is not affected by heat conduction and provides sufficiently accurate result. In contrast, the mean temperature rise is affected by heat conduction and should not be applied to objects with high stress concentration. It is also shown that the thermal type camera is not sensitive enough to measure the second harmonic amplitude