Effect of residual stresses and inclusion size on fatigue resistance of parabollic steel springs

Abstract

The effect of inclusion size and residual stresses of spring steel grade 51CrV4 on fatigue lifetime in high cycle was investigated by experimental results obtained by fatigue testing. Since spring with obvious surface defects or inclusions at the surface are failed during pre-stress, the residual stress profile under surface becomes relevant for fatigue crack initiation and failure. Investigation shows that fatigue threshold for high cycle fatigue depends, besides residual stresses, on inclusion size and material hardness. In order to determine allowed size of inclusions in spring steel and the influence of residual stresses, the Murakami's and Chapetti's models and concepts have been used. The stress loading limit regarding inclusion size and applied stress has been determined for loading ratio R = −1 and 0.1 on specimens with and without residual stresses.