抄録
Fatigue tests were conducted at a frequency of 20Hz or 5Hz under push-pull or reversed torsion or combination of these two loading modes. Temperature of specimen rose by heat generation during cyclic stressing at 20Hz but was kept at room temperature by air-cooling throughout the testing at 5Hz. The variations of fatigue strength and strain range resulted from heat generation were studied in each loading mode.
The heat generation became greater in the order, torsional, combined, push-pull loading, which resulted in shortening of the fatigue life at higher stress amplitude. The fatigue strength under combined loading was able to be evaluated by using S-N diagrams derived on the basis of Gough's ellipse quadrant theory except that the slope in the finite fatigue life region varied depending on temperature rise.
Mises' equivalent plastic strain range (Δεp)eq increased rapidly at an early stage of fatigue life and decreased during subsequent stress cycles. In the case of heat generation, the change of (Δεp)eq was amplified and its average in fatigue process was lowered.
The relationship between the maximum of (Δεp)eq and fatigue life was expressed by a straight line with a narrow scatter band on a log-log diagram, irrespective of the heat generation.
