Abstract
In recent years YAG laser is to be applied to welding of car body as light weight construction used thin plates. Lap joint is used generally on welding two thin plates as compared with butt joint. Because groove precision is necessary for butt joint. So, fillet weld has been adopted to lap joint by MAG welding that is conventional welding way. Narrow bead width and deep penetration shape are characteristics of laser welding. But, these characteristics are weak points in case of fillet weld by laser welding, because minute positioning becomes necessary. When it applies laser welding to lap joint, deep penetration shape that is a characteristic of laser welding is able to weld lapped two plates and it does not need positioning precision. In this studies, it picks up fatigue strength of lap joint of thin plates and it examined a rational joining measurement of laser welded joint by an experiment and numerical analysis. As a result, it got some knowledge about joint width of lap joint and it shows a major conclusion to the following. The radius of curvature on weld toe of YAG laser fillet welded joint is larger than that of MAG fillet welded joint and stress concentration on weld toe of YAG laser fillet welded joint is relaxed more than MAG fillet welded joint. So, fatigue strength of lap joint by YAG laser fillet weld is larger than that by MAG fillet weld in case of almost same leg length. Using a mode I stress intensity factor of nonpropergating crack, it was able to predict fatigue strength of lap joint, fillet welded joint by YAG laser and fillet welded joint by MAG in an error of approximately 23%. If it makes joint width of lap joint larger than plate thickness, a stress intensity factor becomes almost constant value. Accordingly, it needs to make joint width larger than plate thickness. Slit length of lap joint hardly cause influence to fatigue strength.
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