Improved fatigue strength of HSS tailored blanks

This project investigated HSS tailored blanks in order to improve fatigue behaviour using knowledge of material, material combinations, welding, pre-straining, strain restriction and defects. The results are presented in a database as fatigue strengths, S-N curves, Haigh-diagrams. It was found that longitudinal welds of homogeneous welds have a stabilising effect on the blanks, when no cyclic softening occurs. Heterogeneous welds are governed by the properties of the welded materials and show a rise in fatigue strength based on the strength of soft partners. Factors like pores, transversal weld seams or strain restriction reduce the fatigue strength. Pre-straining and a thickness difference in longitudinal welded blanks reveal an improvement of fatigue strength, but are related to a reduced capability to absorb compression stress. FEM calculations including the different welding zones show that the local notch concept generates too conservative results. Using a notch radius between 0.05 and 0.1 mm, the theoretical results confirm the experimental results.