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Experimental and FE analysis of Bonded Single-lap Joints Strengthened by Self-tapping Screws

Lap joints based on low-modulus polyurethane adhesives are being increasingly utilized in vehicles for automotive and railway mass transit. From the one hand, significant elasticity of such adhesives allows to fill relatively large gaps formed while gluing large-scale structure elements and ensures high production effectiveness of the structures. From the other hand, polyurethane sealants cannot provide the effective shear loads transfer, which is significantly important for automotive and railway vehicle’s frames with load-carrying skin made of composite sandwich panels, which predominately takes the shear loads of a metal frame. In this study the experimental and FEA analysis carried out for the strengthening method of bonded single-lap joints by means of small diameter self-tapped metal screws (diameter – 2.5 mm). The adherents made of GFRP, the sealant used as low modulus polyurethane adhesive. Strengthening improves the load transfer due to the shear of metal transversal elements and prevents the delamination usually caused by peel stress at the ends of a joint. In addition, the special method employed for the stiffening of joints with self-tapped screws under cyclic loads. The method involves a filling of gaps between screw and composite bearing face by room-hardened epoxy resin. The analysis of specimen’s cross-section and cyclic tension-compression tests show, that the healing results to stiffening of joint due to the enlargement of element-adherent interaction area and the reduction of residual damages of GFRP, which occurred after screwing.