Prediction of fatigue crack growth rate in residual stress field. Application of superposition technique.

Abstract
In the general area of fatigue crack growth in the presence of residual stresses, it is noted that the correction of stress intensity factor (K) to account for residual stresses is important for the determination of both the 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, a redistribution of residual stresses occurs during crack growth and its effect is noticeable. In this study, experiments and analyses were done for compact specimens which had two orientations such that the crack grew through the weld metal of a butt weld joint of carbon steel parallel to or perpendicular to the weld line. The results obtained are as follows : (1) For the compact specimen, it is possible to predict the crack growth rates by using the superposition technique. (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.

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