炭素鋼同種摩擦圧接継手接合部の疲労き裂進展抵抗について

Abstract

In order to evaluate the resistance to growth of fatigue cracks propagating along the weld interface of friction welded butt joints composed of carbon steel/carbon steel, a series of fatigue crack growth tests were carried out on S25C/S25C and S45C/S45C joints under three different cyclic load conditions. To investigate the effect of residual stress distribution in the specimen introduced in friction welding process on the crack growth behavior, two types of CCT plate specimens with a thickness of 2mm were prepared for respective carbon steel joints; one was the specimen as welded and another was the residual stress relief treated specimen. And the results of these joint specimens were discussed in comparison with those of the annealed CCT base metal plate specimens. First of all, whole crack growth behavior was investigated under increasing ΔK condition, and then the dependence of crack growth rate on the weld interface location was studied under a constant ΔK condition, and finally the ductility of the weld interface was evaluated indirectly through the observation of crack growth retardation behavior induced by the application of single static over-load during crack growth under constant ΔK. The results indicate that the residual stress does not play an important role on the fatigue crack growth of the joints, and metallurgical feature of the weld interface governs the fatigue crack growth behavior of the joints. And, the decrease in crack growth rate of the joint specimens by the application of the over-load is less than that of respective base metals, which indicates that the ductility of the weld interface of both joints is less than that of respective base metals.