Predicting the tensile behaviour of adhesively bonded sheets using equivalent geometrical heterogeneities

In the present work, the formability of adhesively bonded sandwichsteel sheets is predicted during tensile tests, with the help of equivalent geometrical heterogeneities in the base sheets, without incorporating adhesive layer and properties during modelling simulations. This will help us mainly to overcome the difficulties while incorporating adhesion/adhesive properties during formability simulation and prediction. The limit strains during the tensile test are predicted and validated with experiments. The effect of hardener to resin (H/R) ratios of adhesive on the forming limit strains has been predicted with a set of thickness heterogeneity factor ‘f’ and size (w) of the defect, located in the base material. In other words, a relationship between defect morphology (f, w) and adhesive properties has been evaluated. For example, in the case of rectangular-infinite groove of width, w = 0.5 mm, the limit strains of DDQ steel evaluated during tensile tests at f = 0.912, f = 0.9137, f = 0.924, f = 0.927, and f = 0.95 are equivalent to the H/R ratios of 0.6:1, 0.7:1, 0.8:1, 0.9:1, and 1:1 of adhesive, respectively. The limit strains are predicted in the same manner with a square hole and finite square defect in the base material. It is suggested that the overall forming (tensile) behaviour of adhesively bonded blanks (ABB) can be predicted with the help of a thickness heterogeneity factor (or similar geometrical heterogeneities) that is equivalent to all the geometrical and structural heterogeneities in the whole bonded sheets.