Abstract
In order to investigate the effects of overload history on the behavior of crack growth threshold and the crack closure at the threshold, fatigue crack propagation tests under multi-overload and single overload of four different load patterns were carried out using 784MPa class high-tensile-strength steel bending specimens for the case of R=-1 and R=0.
The results obtained were as follows;
(1) For the multi-overload tests, the greater the overload stress intensity KOL was, the greater the threshold stress intensity Kthv was, both for the case of R=-1, and R=0.
(2) As the result of single overload tests, in the case of R=0, the effect of the overload pattern appeared remarkably and the effect of the tension overload pattern was similar to that of multi-overload. However, in the case of R=0, the effect mentioned above was little.
(3) The fatigue crack growth threshold was expressible only by the effective threshold stress intensity range ΔKeffth, independent of the load history tested in this investigation.
