Experimental estimation of the mechanical and fracture properties of a new epoxy adhesive

Abstract

The automotive industry is currently increasing its use of high performance structural adhesives in order to reduce vehicle weight and increase the crash resistance of automotive structures. To achieve these goals, the high performance adhesives employed in the automotive industry must not only have high mechanical strength but also large ductility, enabling them to sustain severe dynamic loads. Due to this complex behaviour, the design process necessary to engineering structures with these materials requires a complete knowledge of their mechanical properties. In this work, the mechanical properties of a structural epoxy, Sikapower® 4720, were determined. Tensile tests were performed to determine the Young’s modulus (E) and tensile strength (σ f). Shear tests were performed to determine the shear modulus (G) and the shear strength (τ f). Tests were also performed to assess the toughness of the adhesive. For mode I toughness determination (G Ic), the double-cantilever beam (DCB) test was employed. For determination of toughness under mode II (G IIc), the end-notched flexure (ENF) test was performed. The data obtained from the DCB and ENF tests was analysed with the compliance calibration method (CCM), corrected beam theory (CBT) and compliance-based beam method (CBBM) techniques. The test results were able to fully mechanically characterize the adhesive and demonstrate that the adhesive has not only high mechanical strength but combines this with a high degree of ductility, which makes it adequate for use in the automotive industry.