Abstract
Low cycle fatigue tests at elevated temperatures under several types of saw-tooth wave strain cycling were carried out on two steels, a low carbon steel and an austenitic stainless steel, in order to investigate the effect of the difference in strain rate between tension going and compression going periods on the fatigue life. For both steels, the fatigue life was found to be longest under the strain cycling with equal tension going and compression going periods, and it became shorter as the difference between the two periods became larger. These results of fatigue life can be explained by the following damage concept.
The fatigue damage in one cycle Δφ, which is defined as the inverse of the cycle number to failure, is given by the equation: Δφ=(Δφ'+Δφ")/2+η(Δφ'-Δφ")/2, where Δφ' and Δφ" are the values calculated from the tension going and compression going strain rates by using the relation between strain rate and fatigue life under triangular wave strain cycling. The intensity parameter η in the second term depends only on the condition whether the tension going period was longer or shorter than the compression going period.
