Fatigue Characteristics and Crack Propagation Behaviour on Spot Welded Joints using High Strength Steel

摘要

In order to obtain the knowledge about fatigue characteristics of spot welded joints using the high strength steel, fatigue tests were conducted. Test results showed that spot welded joints used in this study had the low fatigue strength compared with the tensile strength of that. Additionally, specimens indicated the different fracture morphologies. Then, noticing the small fatigue crack in the spot welded joints, the three dimensional observation of the fatigue crack propagation was carried out sequentially on the each fracture morphology. As this result, it was clarified the fatigue crack propagation behaviour around the welded spot in each fracture morphology. Moreover, spot welded joints require many cycles over the whole life to initiate the fatigue crack. These facts imply that fatigue characteristics of the spot-welded joints are likely to produce a unified evaluation irrespective of the stress level.