Bonded joints with composite adherends. Part I. Effect of specimen configuration, adhesive thickness, spew fillet and adherend stiffness on fracture

This paper deals with glass-fiber-reinforced vinylester composite laminates manufactured by resin infusion and bonded with an epoxy adhesive. The effect of joint configuration, adhesive layer thickness, defects, humidity, spew fillet, and adherend stiffness were investigated by means of tension tests. Four joint configurations were considered: two configurations representing real aeronautical applications namely, the joggle lap joints (JLJ) and the L-section joints (LSJ) and two configurations representing the most popular standard joints namely, the single lap joint (SLJ) and the double strap joints (DSJ). The SLJ and DSJ show higher ultimate loads and displacements to failure than the JLJ and LSJ. The failure load and displacement were found to decrease dramatically when the adhesive layer thickness was increased or when the joint was aged in a hot-humid environment. Intentionally unbonded area in the middle of the joined area did not seem to affect the joint resistance. The investigation of the spew fillet and adherend stiffness for the JLJ showed that the spew fillet effect depended on both the adherend stiffness and the adhesive ductility. The fracture mechanisms were found to change dramatically. Finally, the effect of adherend stiffness was investigated for the JLJ configuration with adherend laminates having stacking sequences of (±45)n and (0/90)n. Most of the joints made from (0/90)n laminates failed at the adherend joggle knee and all the joints made from (±45)n laminates failed at the interface at lower load.