温度変動に基づく疲労限度推定法に関する研究

（温度の第二高調波の発生原因）

抄録

The technique of rapid evaluation of fatigue limit using infrared thermography 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 structures. In this technique, the second harmonic temperature variation during cyclic loading is often used as a measure of the temperature evolution. Source of the second harmonic above the fatigue limit has been already investigated quantitatively. However, below the fatigue limit, it has been investigated only qualitatively. In this research, three factors (second harmonic caused by internal friction, load signal and photoelectric current of infrared sensor) were examined quantitatively to examine the source of the second harmonic temperature variation below the fatigue limit. Experiments were conducted for double edge notched specimens of type 304 stainless steel. As a result, it was found that the second harmonic temperature variation below the fatigue limit is mainly caused by loading equipment. In conclusion, it is suggested that the fatigue limit should be evaluated by fitting curves considering the second harmonic proportional to the square of the load amplitude.