Fatigue Characteristic of Designed T-Type Specimen under Two-Step Repeating Variable Amplitude Load with Low-Amplitude Load below the Fatigue Limit

In order to investigate the non-linear fatigue cumulative damage of joints in ocean structural parts, one type low carbon steel Q345D was employed prepare designed T-type specimens, and a series experiments were carried out on specimens under two-step repeating variable amplitude loading condition. The chosen high cyclic loads larger than constant limit (CAFL) below CAFL. Firstly, S-N curve specimen obtained via different tests. Then, load with aim calculating load. discussions about interaction effect between loadings life out, some meaningful conclusions according results show that calculated based Miner’s rule ranges from 0.513 1.756. Under same cycle ratio, increases increase stress, at stress linearly ratio. Based evaluation method, it is found exhibits or strengthening effects change ratio