Substrate stress concentrations in bonded lap joints

A method based on the successive boundary stress correction approach is presented for the determination of the stress concentration in substrates of adhesively bonded joints with square edges or spew fillets at the ends of the overlap. The emphasis is given to developing an estimate of the stress elevation at the end of a bonded joint while the issue of corner singularity at the substrate-adhesive interface is not addressed in detail. It is shown that the adhesive shear stress which acts on the substrates is the main cause of the stress concentration; the adhesive peel stress has little effect. To circumvent the deficiencies of existing bonded joint theories which generally predict a maximum adhesive shear stress at the ends of the adhesive layer, an eigenfunction solution has been derived for the shear stress distribution near the ends of the overlap. Based on the improved adhesive shear stress solution presented here, the stress concentration determined from the present theory is found to be in good agreement with finite element results.