Note: The Optimum Profile for a Lap Joint.

IN LAP JOINTS, stress concentrations in the adhesive layer can arise from differences in elastic moduli and abrupt variations in thickness of the adherends and the adhesive layer1. Various attempts have been made to design joints in which these stress concentrations are minimised. Mylonas and de Bruyne2 suggested that the stress concentrations could be reduced by tapering the ends of the adherends, so that a more even distribution of strain along the joint could be obtained. Hennig3 suggested that the same objective would be attained by using a high modulus adhesive in the centre of the joint and a lower modulus adhesive at the ends of the joint; he reported that an increase in joint strength of 20% could be obtained by this method. Segerlind4 discussed the variation of the magnitude of the stress concentrations in a lap joint with the dimensions of the joint and showed that since the increase in joint strength with increase in overlap effectively fell to zero above a given length of the overlap (dependent upon the geometry of the joint and the physical properties of adhesive and adherend), then it was possible to specify an optimum overlap for the joint.