Determine the effect of residual stress on part performance in sheet metal parts after stamping

Materials are exposed to some stresses during and after their productions such as Shaping, Stamping and additional processes (welding, machining, heat treatment, etc.). These stresses affect the fatigue behavior of the material according to the regions where they are located. These stresses are called residual stress. Residual stress is the name given to the stress remaining in the material during production. Stresses on the material increase when external forces are applied. Applied stresses and residual stresses are evaluated together to determine the ultimate strength or performance of the material. For example, if the residual stresses are large, the material will not withstand high stresses. It is known that residual stresses have a significant impact on fatigue crack initiation, propagation and therefore fatigue life. Although these effects have often been quantified using an empirical approach, no true correlation has been established. In this thesis, experimental studies were carried out in two processes in order to see the effect of stamping operations. In the first study, the sheet metals most commonly used in automotive were obtained from different thicknesses and their tensions were examined as a result of stamping. In the second stage, samples were taken from all stages of a steel wheel production to observe how the residual stress changed, and then different stress relief processes were performed and their effects on fatigue were examined. In the study conducted on the plate, it was observed that as the shaping of the sheets increased, the tensions increased perpendicularly to the rolling direction, and there was no change in residual stress in the rolling direction. It has been determined that the tension increases as the forming increases, but the tension is not affected much as the type of sheet and thickness changes. In the second stage, the points identified in the samples taken from the steel wheel production steps were examined and results parallel to the first stage of the study were determined. Afterwards, the rims resulting from the metal shot peening operations performed on the final rim at different times were tested until they broke. It was concluded that the residual stress values and fatigue values were parallel to the results. With these studies, it has been understood that the stress can increase significantly during forming, regardless of the sheet type and thickness, that this is parallel to the actual part production, and that these stresses directly affect the life of the sheet metal.