Abstract
This paper describes the effects of stress ratio on the ΔK_<th> improved by overload. High-tension steel (HT540) and aluminum alloy (A7075) were prepared as test materials. Tensile overload was applied to compact tension specimen, subsequently fatigue tests were carried out at stress ratio S=0.1 or 0.5. The main conclusions are as follows; (1) The value of ΔK_<th> increased with increasing of the tensile overload. (2) The effect of overload on ΔK_<th> did not differ between HT540 and A7075. (3) The improvement ratio of ΔK_<th> S=0.1 was larger than that at S=0.5.
