The application of the iosipescu shear test to structural adhesives

Abstract

SYNOPSISThe Iosipescu shear test method, adapted for adhesives, was used to evaluate shear stressstrain properties of five epoxy-based film adhesives. The shear strength of some adhesives, determined by this technique, was found to differ greatly from that determined by either lap shear and/or thick adherend tests. Accurate measurements of the adhesive bond-line deformation enabled evaluation of the adhesive elastic and plastic properties as well as the calculation of shear modulus. A high-speed video camera was employed to augment observation on the joint deformation.

Quasi‐Static Constitutive and Strength Tests

“…Test results reported by Grabovac and Morris [17] showed that the shear strengths of brittle adhesives achieved using the Iosipescu specimen were greater than the strengths found from lap shear joint specimens, suggesting that the Iosipescu specimen has lower stress concentrations. The strengths obtained for tougher adhesives that experience shear yielding were comparable with those obtained by the other methods.…”

“…Typically, a bulk specimen for a rigid adhesive, such as an epoxy, would be a minimum of 4 mm wide, and the effects of exothermic heating during cure need to be considered when preparing very thick specimens. Joint specimens can be wider; 20 mm wide adherends are used often [17,18], since exothermic heating is less of an issue with metallic adherends and thin bondlines.…”

“…However, a higher number of tests (15)(16)(17)(18)(19)(20) allows appropriate statistical analysis. Mechanical tests in which a high amount of variables can influence the final result reduce researchers' confidence.…”

“…The method can be applied to adhesives (both bulk and joint samples) [17]. Many of the issues discussed in the Section 2.5 are applicable to the Iosipescu method.…”