アルミニウム合金板材の面外曲げ疲労強度に及ぼす曲げ加工の影響

抄録

Fatigue tests were performed on 90° V-shape bending-worked aluminum alloy specimens with various radii of curvature under deflection-controlled fully-reversed out-of-plane bending to clarify the effect of bending-work on fatigue strength of plates. Fatigue strength of the bent specimens was entirely lower than that of smooth flat one and decreased with reduction in radius of curvature. In order to investigate the cause of the reduction in fatigue strength of bent specimens, stress state in the vicinity of the bending-worked portion was analyzed employing a finite element method. Besides, crack initiation and growth behavior was observed and compared with those of smooth flat specimen. The crack initiation tends to be earlier with decreasing the radius of curvature because of the higher stress concentration around the center of inner surface of the bent portion. In addition, the crack growth rate in bent specimens was higher than that in flat specimen, especially in an early stage of short crack growth regime and increased with decreasing the radius of curvature. Since cyclic bending stress decreased with crack growth and accumulation of residual strains, the crack growth rate gradually lowered in latter stage of the life. Consequently, the reduction of fatigue strength in bending worked plate results from the earlier crack initiation and the acceleration of crack growth rate in early stage due to the stress concentration around the bent portion.