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An Araldite epoxy adhesive system from Huntsman Advanced Materials has been used in an experiment conducted by a research group, under the direction of Dr Trevor Young of the Irish Centre for Composites Research at the University of Limerick, in which the bondline stress concentrations and the influence of adhesive ductility on composite single lap joints were investigated.
For the purposes of testing, the centre used and compared two epoxy paste adhesives, with the Araldite system (Araldite AW 4858 / HW 4858) offering relatively low tensile strength and high ductility and the other providing high tensile strength and low ductility.Quasi-static tensile tests were conducted on single lap joints to failure at room temperature and local strain gradients in the adhesive fillet regions were analysed with high magnification two-dimensional digital image correlation. The fracture surfaces were also examined using scanning electron microscopy to identify plastic deformations and to understand the influence of adhesive ductility on joint failure.Due to its relatively low tensile strength and high ductility, results showed that the Araldite adhesive provided higher joint strength offering better stress distribution with lower adhesive stiffness prior to crack initiation and considerable local adhesive yielding with stress redistribution prior to joint failure.Araldite AW 4858 / HW 4858 is a room temperature curing black epoxy adhesive paste of high strength and toughness. It is suitable for bonding a wide variety of metals and is especially designed for bonding composites.The centre’s article on the ‘Experimental Analysis of the Bondline Stress Concentrations to Characterise the Influence of Adhesive Ductility on the Composite Single Lap Joint Strength’ has also been published in The Journal of Adhesion.More information:www.huntsman.com