Initiation Mechanics of Fatigue Crack at Weld Joint of High Strength Bridge Steel

The dislocation shape alteration at weld joint of high strength bridge steel was studied at different fatigue cycle index. The results show that the dislocation changed as follows with the increase of cycle index, dislocation tangle→dislocation wall formed→dislocation cell formed→subgrain formed. Then the crack developes when the subgrain boundary split.