Formability of adhesive-bonded steel sheets with artificial finite adhesive defects

In this investigation, the influence of artificial finite adhesive defects with different shapes and sizes, characterized by (1) aspect ratios, a/b = 0.5, 1 and 1.5 (where a is transverse axis length of defect; b is longitudinal axis length of defect), (2) number of defects and (3) different locations, in the epoxy adhesive layer on the formability of adhesive-bonded blanks, is analysed. The deep drawing quality cold-rolled steel and stainless steel (SS 316L) sheets were used as base materials. The increase in aspect ratio of adhesive defect reduces the ductility of adhesive layer and thereby decreases the formability of adhesive-bonded blanks. This is due to the early failure of adhesive layer at the location of defect where strain is locally concentrated. The strain hardening exponent (n) of adhesive-bonded blanks has decreased with increase in aspect ratio of adhesive defect in all the regions of deformation. The limit strain of deep drawing quality and SS 316L sheets constituting adhesive-bonded blanks shows decrement with increase in aspect ratio of adhesive defect. It is postulated that the aspect ratio of the finite adhesive defect influences significantly the formability of adhesive-bonded blanks, but not shape of the finite adhesive defects. There is no considerable effect of number of adhesive defects and different locations of adhesive defects on the formability of adhesive-bonded blanks.