Fatigue behavior characterization of laser-welded cold rolled sheet metal (SPCEN)

For the present work, the fatigue behavior of laser-welded cold-rolled sheet metal (SPCEN) was studied. Also, the thickness heterogeneity effect of weldment on the fatigue strength and crack growth behavior was studied. The sheet metals of same thickness (0.9 mm) were laser-welded (Case A), and the sheet metal of 0.9 mm thickness was laser-welded to the sheet metal of 2.0 mm thickness (Case B). For both cases, fatigue tests were conducted applying the load perpendicular or parallel to the welding line. Finite element analysis was performed to determine the form of stress intensity factor as a function of crack length for both cases. The results showed that the fatigue strength of Case A was 8.5% higher than that of Case B when the loading direction was parallel to the welding line. However, the fatigue strength of Case A was similar to that of Case B for the perpendicular fatigue loading to the welding line. At the same crack length, the stress intensity factor of Case A was greater than that of Case B. It was also found that for both cases, the crack propagation rate decreased noticeably in the front of weld bead but increased rapidly in the weld bead. The retardation of crack propagation was due to the increased hardness in the front of weld bead, and the increased crack propagation rate was due to the reduced fracture toughness in the weld bead.