A study on composite adhesive lap joint

In this study, a novel design of adhesive single-lap joint was proposed and investigated. In this new design, load eccentricity as well as singular peel stresses in the joint interface were avoided. In fact, numerical calculations show that, in the new design, the interfacial normal stress becomes compressive in the joint end region, and the shear load is more evenly transferred over the length of the joint. Experimental results using cross-ply carbon/epoxy composites as adherends show that the strength of the new joint is significantly higher than that of the conventional single lap joint. Efforts were made to investigate effects of the four most relevant design parameters of the wavy joint on the critical interfacial stress distributions. By careful selecting the design parameters, interfacial stresses can further be optimized. Test results with unidirectional composite adherends confirm that joint strength can further be improved through careful design. In order to fully demonstrate advantage of the new wavy-lap joint over the conventional single-lap joint, fatigue tests were carried out to determine durability performance of the wavy-lap joint. Fatigue tests show that under the same loading conditions, i.e. same maximum load levels or same load percentage levels, fatigue performance of the wavy-lap joint is much better than that of the conventional single-lap joint. Further study shows that fatigue life of adhesive joint, either flat or wavy, is strongly dependent on loading frequency. This is due to the fact that FM73 adhesive is a viscoelastic material. With the increase of frequency, fatigue lives of both joints also increase. However, the wavy joint still outperforms the flat joint at all loading frequencies