Abstract
In the general area of fatigue crack growth in the presence of residual stress, it is noted that the correction of stress intensity factor (K) to account for residual stress is important for the determination of both range and ratio (R) of K during a loading cycle. The superposition technique can be applied generally for the determination of K. For compact specimens, however, redistribution of residual stress occurs during crack growth and its effect is not negligible. In this study, experiments were done for the compact (CT) specimens which had such an orientation that the crack grew along the weld line in the weld metal of a butt weld joint of carbon steel. Fatigue crack growth characteristics of the weld joint were examined in comparison with that of the base metal and discussions for the evaluation of residual stress were made. The results obtained are as follows;
(1) For the CT specimen, it is possible to predict the crack growth characteristics by using the initial residual stress distribution.
(2) When the crack grows first through the compressive portion of a residual stress field, the effect is actually a result of the ratio (R) of K, although apparent high values of the crack opening stress intensity factor Kop were obtained experimentally.
(3) The residual stress distribution through the thickness has no important effect on the average through-thickness crack growth rate, although it has some effect on the crack curvature.
(4) Near the threshold region, the crack growth rate of the weld joint is higher than that of the base metal beyond the consideration of the residual stress effect.
