抄録
Temperature is one of the most important factors which affect the fatigue strength, and many researches have hitherto been conducted on the fatigue strength at various temperatures, but little is known about the fatigue strength under fluctuating stress amplitude at high temperature. In this research, notched and unnotched specimens made of aluminum alloy 7075-T6 were tested at room temperature, 200°C and 300°C. Constant stress fatigue test and Low-High and High-Low type two-stress fluctuating fatigue tests were conducted for each test condition. Discussion was made on the cumulative cycle ratio at high temperature. It has been claryfied that the cumulative cycle ratio is less than 1.0 in the High-Low test and it is greater than 1.0 in the Low-High test at room temperature and 200°C. But, at 300°C, the cumulative cycle ratio is greater than 1.0 in the High-Low test and it is less than 1.0 in the Low-High test. The test result can be explained by the variation of the metallurgical structure of the used material caused during the experiment. An additional experiment was conducted to show the appropriateness of the explanation.
