Assessment of mixed adhesive in single lap and peel joint with composite substrate

This study investigates the effect of mixed adhesive having different modulus on single lap joint and also under peel test. The study compares these joints with that of corresponding joint containing single adhesive under two loading rate of 5 and 100 mm/min and three temperature range of room, 100°C and 200°C. Five types of adhesives were used in this assessment namely: silicon, epoxy, mixed epoxy-silicon, epoxy toughened with liquid rubber (CTBN), mixed epoxy toughened with liquid rubber (CTBN) –epoxy. Result indicated better shear strength performance by mixed epoxy-silicon adhesive joint in the single lap shear at both loading speed followed by epoxy and liquid rubber modified epoxy joints . Similar assessment under the three temperature range also revealed better retention of shear strength for the mixed epoxy-silicon adhesive joint in particular at 200°C. This result revealed about 65 percent reduction in strength for epoxy adhesive as against 31 percent reduction for the mixed epoxy-silicon adhesive. Peel tests showed unstable peeling behavior in all joints except joint with rubber modified epoxy toughened adhesive joint. Further assessment of peel test results showed both mixed adhesives i.e. mixed epoxy-silicon, epoxy toughened with liquid rubber (CTBN), mixed epoxy toughened with liquid rubber (CTBN)-epoxy had higher peel strength compared to the other adhesive joint tested.