抄録
Laser peening without coating (LPwC : LP) is used practically as a preventing method for stress corrosion cracking (SCC) of nuclear reactor structure. Therefore it is known that the LP treatment improve the fatigue properties of cast aluminum alloy. However, there is no report about the retardation of fatigue crack growth on casting aluminum alloy by the LP treatment. In the present study, to evaluate the effects of the LP treatment for fatigue crack propagation behaviors on AC4CH cast aluminum alloy, some pre-crack specimens which had a surface fatigue crack length as about 2.5mm at center part of cylindrical test specimen were prepared and rotating bending fatigue tests were conducted on those specimens. As the results, fatigue crack propagation was prevented by LP treatment and the results obtained are summarized as the followings, (1) If a maximum stress intensity factor of fatigue crack tip at surface of specimen is lower than about 5 MPam^<1/2>, the fatigue crack growth can be stopped by the LP treatment. (2) Apparent maximum stress intensity factor of fatigue crack tip at surface on LP treatment specimen was nearly equivalent to about 4 times of threshold stress intensity factor of long fatigue crack at AC4CH when the surface crack began propagation. It was clear that the cause of this threshold stress intensity factor increasing was effect of compressive residual stress with LP treatment by calculation of the stress intensity factor.
