Investigation on failure modes and mechanical properties of CFRP-Ti6Al4V hybrid joints with different interface patterns using digital image correlation

An advanced hybrid joining technology for joining metal and composite is introduced. Protrusions formed on the surface of the metal by electron beam are embedded into carbon fibre reinforced polymer layers and thus forms an integrated joint. The performance of a joint produced using such method was found to be better than traditional joints. In this paper, the properties of two different patterns of protrusions, including a linear pattern and a cylindrical pattern were studied by uniaxial tensile testing of double lap composite structures using digital image correlation. The distributions of strains in the composites tested varied and were found to be influenced by the shape of the protrusions which also resulted in different failure modes. The joints with a linear pattern failed between laminate layers, whereas the joints with a cylindrical pattern fractured at the interface of metal and composite. Furthermore, the tensile properties such as the ultimate tensile strength and elongation to failure of the joint with the linear pattern were around twice the value of the joint with the cylindrical pattern. Consequently, the performance of hybrid joints can be improved significantly by optimising the protrusion pattern. [Display omitted] •Significant stress concentrations at the Ti-6Al-4V-CFRP interface were observed for both linear and cylindrical patterns.•Cylindrical protrusions displayed more homogenous distribution of stresses compared to that for linear protrusions.•No damage in the pins was observed since they were sufficiently strong for both linear and cylindrical patterns.•Digital Image correlation was used to characterise the strain field evolution and the failure mechanism in hybrid joints.