Fatigue impact of residual stresses from manufacturing processes

Abstract

This study was done to investigate how residual stress from different manufacturing processes could be simulated and what effect they would have on predicted fatigue life of the components. The two manufacturing processes investigated were forming and welding. The forming process was simulated through a two-simulation process, an explicit forming simulation and an implicit springback simulation were used to evaluate the residual stress formation. There were results from the forming simulation that need further investigations to ensure trustworthy results. The welding process featured a simplified simulation divided into two parts, a heat transfer simulation and an implicit static simulation. Results from the forming simulation gave similar stress levels as the measured values. The welding simulation did not give as good results as the forming simulation. A different method should be investigated to get more accurate results. Residual stresses impact on the predicted fatigue life was examined by comparing a component safety factor to fatigue with and without residual stress added to the simulation. The result showed that the safety factor decreased moderately when accounting for the residual stresses due to the elevated mean stress. This master thesis was done on behalf of Azelio in collaboration with Uniso Technologies. Azelio develops a thermal energy storage called TES.POD that uses stored thermal energy to provide energy through a Stirling engine. The system has a storage capacity of 13 hours that could work as an off-grid solar system storage.