Effect of the Engagement Ratio and of Temperature on the Shear Strength of Epoxy Adhesive Bonded Aluminum Alloy Pin-and-Collar Joints

Epoxy adhesives are widely used in industrial applications, as they are particularly suitable to bond many types of materials. Conversely, possible drawbacks may arise from the use under high temperature, which is likely to imply a drop of mechanical properties. Previous research indicated that the Engagement Ratio (ER), namely, the ratio between the joint length and its coupling diameter, has an effect on the shear strength of an epoxy adhesive applied to steel adherents. Moreover, the shear strength decreases for increasing temperature, with loss of any ER effect beyond the glass transition temperature. The present research is focused on EN AW 7075-T6 alloy adherents that are widely applied in lightweight constructions. The study has involved LOCTITE 9466 with experimental tests on Pin-And-Collar samples with ER varying from 0.4 to 1.7 over four levels (10 replications). The effect of temperature has also been assessed, by campaigns at room temperature and at 40°C, 60°C and 80°C. The results, also interpreted by an analytical model, indicate that keeping ER around 0.9–1 is advisable to optimise strength. Temperature leads to a shear strength drop, to a loss of ER effectivity and to higher scattering, when exceeding the glass transition temperature of the adhesive.