Abstract
The fatigue crack propagation behavior was observed under two step variable stresses. In the first step, the stress was below the fatigue limit and the maximum stress was compressive. In the second step, the stress was above the fatigue limit. The testing was carried out on notch sheet specimens of SUS 410 (13% Cr) under repeated bending. The number of fatigue cycles at the first or second step systematically was changed. The results obtained are as follows ; (1) The fatigue life decreased by about 40% when the number of fatigue cycles at the second step (above the fatigue limit) was above 1×105 cycles. (2) The fatigue crack propagation rate decreased when the number of fatigue cycles at the second step was 2×104 cycles.
