Influence of Layer Thickness on Cohesive Properties of an Epoxy-Based AdhesiveAn Experimental Study

Cohesive laws are determined for different layer thicknesses of an engineering adhesive. The shape of the cohesive law depends on the adhesive layer thickness. Of the two parameters of the cohesive lawthe fracture energy and the strengththe fracture energy is more sensitive to thickness variation than the strength. The fracture energy in peel mode (Mode I) increases monotonically as the thickness is increased from 0.1 to about 1.0mm. At an adhesive thickness of 1.5mm, the fracture energy is slightly lower than for a 1.0mm adhesive thickness, indicating a maximum between 1.0 and 1.5mm. In shear mode (Mode II), the thickness dependence is not as strong, but an increasing trend in fracture energy with increasing adhesive thickness is evident. A slight decrease in strength with increasing adhesive thickness is found in both loading modes.