Damage and Void Shape Evolution during Destructive Testing of Resistance Spot Welded Joints

Ductile plug failure of resistance spot welded test specimens is studied, using the recent extensions to the Gurson model accounting for non-spherical void growth or damage development during low triaxiality shearing. A comparison of the predicted mechanical response is presented when using either i) the Gurson-Tvergaard-Needleman (GTN) model [1, 2], ii) the shear extension to the GTN-model by Nahshon and Hutchinson [3] or iii) the Gologanu-Leblond- Devaux (GLD) model [4]. All models are here based on an elastic-viscoplastic constitutive relation and account for void nucleation, void growth and coalescence. Hence, the only damage parameter is the void volume fraction, f, while a void shape parameter, W = R₁/R₂, denoting the void aspect ratio, exists in the GLD-model. Here, R₁ and R₂ are the length of the first and second axes of the spheroidal voids, respectively. Thus, W > 1 corresponds to a prolate void, while W < 1 is an oblate void. The work to be presented is based on the studies in [5, 6, 7]. In [5], the GTN-model was used to reproduce experimental observations for the plug failure mode during shear-lab testing, while the change from plug failure to interfacial shear failure was modelled using a shear modified GTN-model in [6]. A study of the void shape evolution is presented in [7] together with a comparison of the above models.