Optimising a non-tubular adhesive bonded joint for uniform torsional strength

The paper analyses the problem of optimising the profile of a non–tubular adhesive bonded lap joint under torsion. The joint considered consists of two thin rectangular section beams bonded together along a side surface. The aim of the investigation is to make the joint uniformly resistant to torsion, without however weakening it in other stress situations: the result is a stronger and lighter structural element. The predominant stress field developed in the adhesive at the bond area between the two beams in single–lap and scarfjoints is determined. The stress field pattern is highly nonlinear along the longitudinal coordinate (joint axis) and is heavily dependent on joint geometry: maximum stresses are reached at the ends of the adhesive for the first type of joint, and along its centreline for the second type. An intermediate type of joint can be produced by modifying the joint profile, thus ensuring that the stress field is constant along the longitudinal coordinate and thereby optimising the joint for uniform torsional strength.