アルミニウム平板に生じた疲労き裂先端へのDry-LP処理およびLPwC処理の効果

抄録

Laser peening can generate compressive residual stress on the object surface. In this study, effects of the laser peening for fatigue crack propagation of friction stir welded butt joint were investigated. As a result of fatigue crack propagation investigating with laser peening treated specimen with a thickness of 3mm which have a surface fatigue cracks, the following was obtained. (1) When the laser peening without coating (LPwC) treatment with usual condition are applied to front and back surfaces of specimen, if the stress intensity factor at the surface fatigue crack tip of the specimen is larger than about 4.5MPam^1/2, crack propagation cannot be stopped. (2) If the LPwC is applied only to the pre-crack tip at the surface of specimen, the specimen is warped. As a result, the generated compressive residual stress is reduced and tensile residual stress is generated in the unworked part near the pre-crack, which accelerates the propagation rate of the pre-crack. (3) If the dry laser peening (Dry-LP) is applied only to the pre-crack tip, high level compressive residual stress is generated on top surface of the specimen. As a result, the propagation rate of the pre-crack is temporarily delayed.