Representativity of thermal stresses in designing composite joints based on singular stress states at multimaterial corners

Using adhesives curing at temperature in bonded joints between dissimilar materials (composites and metals) gives rise to residual stresses due to the difference in the value of the thermal expansion coefficients of the adherents. The presence of multimaterial corners in these adhesive joints originates critical points where failure is likely to occur. Numerical results of several double-lap joints of aluminium to different carbon fibre laminates including the thermal stresses during curing are presented. The uniform temperature variation (from curing to room temperature) has been shown, numerically, to have a significant influence on the local stress field in the neighbourhood of these corners. Due to the fact that high stress gradients are developed at these corners in the curing process and stress relaxation effects may occur due to the viscoelastic behaviour of the polymeric adhesive at room temperature, experimental tests have also been carried out to study the influence of uniform temperature fields on the strength of these joints based on the parameters which define the singular stress state at these multimaterial corners. The experiments show that the thermal stresses during curing do not significantly alter the behaviour, type and load failures of the joint.