The influence of bond line thickness and peel arm thickness on adhesive fracture toughness of rubber toughened epoxy–aluminium alloy laminates

Abstract

The adhesive fracture toughness ( G A) of rubber toughened epoxy–aluminium alloy laminates is studied using two types of peel test, namely fixed arm peel and roller-assisted mandrel peel. In the fixed arm tests, the peel angle is varied in the range 45–135° and in the mandrel peel experiments, the mandrel roller size is selected in order to ensure conformance of the peel arm to the roller during fracture. The principal aims of the study are two-fold: (i) To investigate the influence of adhesive bond line thickness on G A. (ii) To investigate the influence of peel arm thickness on G A. The peel crack growth experiments were complemented with measurements of cohesive fracture toughness using tapered double cantilever beam geometry with a range of values for bond line thickness. Throughout the work, it is important to identify the mode of peel fracture and in particular to establish whether the peel cracks are cohesive (propagating in the adhesive) or interfacial (propagating at the interface between adhesive and substrate). To this effect, confocal laser scanning microscopy was used in order to study the peel arms after testing and to measure the thickness of adhesive coating on the peel arms. The experimental work was conducted on a wide range of laminates where two adhesives with a common substrate were employed.