In-plane plane strain formability of adhesive-bonded steel sheets: influence of adhesive properties

In the present work, the influence of adhesive properties on the formability of adhesive-bonded sheets (deep drawing quality (DDQ) steel and SS 316L) has been studied through in-plane plane strain (IPPS) formability tests. The adhesive properties were modified by different hardener to resin ratios and by having epoxy and acrylic adhesives. The formability is quantified by load–extension behaviour, limit strains and strain hardening exponent of adhesive-bonded sheets. It is observed from the work done that with increase in hardener to resin ratio, the elongation of adhesives is found to improve during tensile tests. This forms the basis for the actual formability change of adhesive-bonded sheets at different hardener/resin (H/R) ratios. During IPPS formability tests of adhesive-bonded steel sheets, the total elongation is found to improve with increase in hardener/resin ratio. Likewise, limit strains also improve with increase in hardener/resin ratios. The improvement in elongation and limit strains is due to the conversion of a resin-rich formulation to a hardener-rich formulation, making the sample more ductile. Both the acrylic and epoxy adhesive-bonded sheets show an equal amount of improvement in limit strain. The strain hardening exponent (n) of adhesive-bonded blanks has improved with increase in hardener/resin ratio in all the three regions of deformation. The adhesive-bonded blanks have larger strain hardening exponent values as compared to double sheet in the corresponding regions of deformation, indicating formability improvement as compared to double sheet.