Fracture toughness of spot-welded steel joints

Fracture toughness is one of the parameters, which are used to estimate the fatigue life of spot-welded joints. The spot-welded pair is affected by the welding zone shear stress, when it is subjected to tensile load. Repetitive loads reduce the fatigue life of the spot-welded pair, and the material splits at the spot-welded region. In this study the fracture toughness of spot welded joints has been investigated. The commercially available AISI 1010, 1030, 1040, 1050 and 50CrV4 steel sheets of 3 mm thickness were used as the test specimen for welding. Welds were performed to sheet pairs arranged as AISI 1010-50CrV4, 1030-50CrV4, 1040-50CrV4, 1050-50CrV4. The dependence of the estimated values, i.e. fracture toughness (K-IIC), crack lengths (a(IIC)), and J-integral (J) to the Vickers hardness of the spot weld zone has been investigated. The fracture toughness parameter (KIIC) for spot-welded steel sheets is calculated by using the formulae given in the literature. The results show that the fracture toughness, K-IIC, and J-integral decrease as the hardness, H, increases. The fracture toughness of the spot weld is not only dependent on the nugget diameter D, but it also depends on sheet thickness t, tensile rupture force and the hardness H.