Influences of loading direction and thickness ratio on fatigue properties of tailored welded blanks

Fatigue properties of tailored welded blanks with the same material and different thickness were investigated. Fatigue tests of specimens with angles of 0°, 70° and 90° to the laser weld line were performed in order to clarify the influence of loading direction and thickness ratio. The levels of stress range affected the crack initiation areas of the 0° and 90° specimens, and simple heterogeneous mechanical models roughly expressed the macroscopic fracture behavior. The fatigue strength of the 0° specimens was almost the same as that of the base metal. In the 90° specimens, fatigue strength showed a clear decrease under relatively low stress range. Insufficient grinding of the 70° specimen edge caused crack initiation at the weld toe and low fatigue strength. An increase of thickness ratio induced a decrease of fatigue strength of the 90° specimen, although that of the 0° specimens was independent of thickness ratio. Fatigue crack propagation analyses under cyclic stress distribution revealed a close correlation with the test results. These experimental and analytical results were less sensitive to thickness ratio than estimations by elastic stress concentration factors.