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Stainless steel sheet (18Cr-9Ni) was tested in fatigue under axial-load cycling in plain and notched conditions. Various stress ratios were used ranging from R = −1.0 to +0.91, and endurances (see Definitions) from 10 to 107 cycles were covered using testing frequencies of 5 to 15 cpm and 3000 cpm.
The effect of mean stress on notch fatigue strength could not be predicted empirically solely from unnotched material data; at least one notched fatigue curve would be required.
A fatigue strength reduction factor based on maximum stress for a particular mean stress and endurance provided the most reliable correlation between unnotched and notched data.
Low-cycle and high-cycle fatigue curves matched up only to a limited extent at the overlap, but there was generally strength reduction at low frequency. Under certain conditions of mean stress and stress ratio a cyclic creep or ratchetting mechanism leading to ductile rupture was obtained at low endurances.
Simple functions existed in the low-cycle region between stress range and plastic strain range and total energy and cycles to fracture, both of which were largely independent of stress ratio.
Bell, W. J.
Rexall Chemical Co., Odessa, Tex
Benham, P. P.
Lecturer in Applied Mechanics, Imperial College, London,