抄録
A study was made to determine the effects of specimen size, configuration and crack orientation to the weld axis on the fatigue crack growth rate of mild steel butt welded joints. Two types of welded specimens, the compact type (CT) specimens with three different sizes and the center-cracked-tension (CCT) specimens were used. Residual stress distributions in CT specimens were examined by means of the strain gauge method.
In the case of welded specimens, the fatigue crack growth rates of CT specimens having widths of 100 and 260mm were roughly the same regardless of crack orientations to the weld axis, while the crack growth rates in specimens with width less than 100mm were faster than those of the larger width specimens. In the case of base metal specimens, the specimen size had no appreciable effect on crack growth rates. The crack growth rates of welded CT specimens were markedly reduced as compared with those of CCT specimens. This discrepancy may be attributed to the difference in residual stress distribution between CT and CCT specimens. Therefore, if the test results of welded CT specimens were used to evaluate the life of a welded structure, it is on the unsafe side. The crack growth rates of specimens with welding residual stress were found to be governed by the magnitude of residual stress near the crack tip in the interior of a specimen. And the fatigue crack growth rates of base metal specimens and weld metal specimens were well correlated with ΔKeff estimated based on the crack closure experiments.
