FATIGUE PERFORMANCE UNDER VARIABLE AMPLITUDE LOADING OF WELDED JOINTS BY INTRODUCING COMPRESSIVE RESIDUAL STRESS

Abstract

 The improvement effect on fatigue strength by introducing compressive residual stress under the variable amplitude loading has been investigated. Peening treatment and an additional welding with low temperature transformation welding material were used as the improvement methods. In addition, the change in residual stress distribution near the surface during fatigue life under variable amplitude loading was measured by the incremental hole drilling method. The results showed that a part of compressive residual stress introduced by peening treatment was released by the maximum load in the variable amplitude loading. Since the improvement effect under variable amplitude loading reduced compared with that under constant amplitude loading due to the relaxation of compressive residual stress, the damage accumulation based on the modified Miner's rule was about 0.2. The fatigue life of welded joints improved by introducing compressive residual stress can be estimated conservatively based on the results of fatigue test with constant maximum stress, which is same as the maximum stress in the variable amplitude stress.