Characterization of spot weld strength is a key industrial issue, particularly in the case of Advanced High Strength Steels. Today, the most widely used mechanical test evaluating this strength is the Cross Tensile Test. However, investigating the role of the different zones of one spot weld based on this test is difficult.A wedge test has been developed in order to characterize interfacial failures of spot welds. A cross section of one spot weld is observed while a wedge is inserted in between the two welded sheets. A CCD camera records the observation of the propagating crack. The limited sheet bending occurring during crack propagation allows the spot weld classification based on the total energy dissipated per unit fractured area to be efficient.Furthermore, the stable crack propagation is characterized by the in situ measurement of the crack opening angle. Finite element simulations of the test are carried out to estimate a relation between these measurements and the material resistance, approached by a cohesive zone model.Interfacial failures of spot welds of DP and TRIP steels have been investigated. The experimental measurements allow to estimate parameters of a cohesive zone model representative of the molten material failure, providing reliable and appropriate data for simulations of the mechanical behavior of the complete spot weld.
