The effect of protrusion density on composite-metal joints with surfi-sculpt reinforcement

The effect of protrusion density on the static mechanical properties of composite-metal joints strengthened by surfi-sculpt protrusions has been experimentally studied with single lap joints. The CFRP composite adherends were constant thickness with a quasi-isotropic layup. The metallic adherends were Ti-6Al-4V alloy with a variable number of protrusions per unit area, manufactured by electron beam surfi-sculpt. Digital image correlation was used to measure the debonding on the overlap during the tests. Although the surfi-sculpt protrusions did not significantly affect the onset of debonding, they did resist the initial unstable failure mechanism and converted it into stable growth. The analysis indicated that the efficiency of the surface protrusions was different at the metal and composite ends of the overlap. This finding opens the possibility to vary the protrusion density across the overlap to meet specific damage tolerance criteria and optimise joint efficiency. Increasing the protrusion density significantly increased the ultimate failure load, joint extension and hence absorbed energy.