Influence of the engagement ratio on the shear strength of an epoxy adhesive by push-out tests on pin-and-collar joints: Part I: Campaign at room temperature

This paper focuses on an epoxy adhesive (LOCTITE 9466), which is particularly suitable for applications involving different materials and where a clearance is present between the adherents. The investigated subject is concerned with the effect of the Engagement Ratio (ER, coupling length over coupling diameter) on the shear strength of LOCTITE 9466 at room temperature. Motivations arise from the increasing interest in epoxy-adhesive joints in lightweight structures and from the consequent need for design data. Decoupling tests have been performed on pin-and-collar samples manufactured according to current Standards. The height has been adjusted in order to explore a sufficiently wide ER range at four different levels. The results have been processed by the tools of the Analysis of Variance and of the Fisher test to investigate the significance or the not significance of ER on the joint shear strength. The final outcome was that ER significantly affects resistance at a very high confidence level. This result has then been refined by the tool of orthogonality, in order to allocate the differences among the four levels of ER. This further analysis has shown that the joint strength is significantly enhanced, when ER exceeds 1 and assumes values around 1.3 or higher.