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

Abstract Previous research led to the conclusion that the Engagement Ratio (i.e. the coupling length over the coupling diameter, ER) does not significantly affect the shear strength of an anaerobic adhesive (LOCTITE 648). Conversely, ER is effective on the response of an epoxy adhesive (LOCTITE 9466), with a beneficial effect for ER>1. The aforementioned campaigns have been performed at room temperature, whereas, the effect of ER combined to that of temperature is still unexplored. The subject of this paper consists in the experimental investigation of the impact of ER on the strength of LOCTITE 9466 at higher temperatures. Decoupling tests have been performed, considering three levels of temperature (40 °C, 60 °C and 80 °C). Pin-and-Collar samples have been prepared, considering four levels of ER. A fixture device has been designed, to prevent misalignments and to reduce heat dissipation during the pushing-out phase. The statistical processing of the data led to the conclusion that ER retains its effectiveness up to the temperature of 40 °C with strength enhancement for ER beyond 1. Conversely, at the highest levels of temperature, a strength drop to approximately 44% occurs, and the effect of ER is no longer significant to compensate this decrease. Moreover, a highly significant negative interaction was detected between ER and temperature.