Hongqi Guo1 Mark Gingerich1 Leon Headings1 Marcelo Dapino1

1, The Ohio State University, Columbus, Ohio, United States

Carbon fiber reinforced polymers (CFRPs) offer significant opportunities for lightweighting in structural applications. However, to integrate CFRPs in hybrid structures, it is necessary to design and construct robust CFRP-metal joints. Traditional joining methods, such as adhesive and mechanical fasteners, are not favorable for this application due to long curing time or damage to the CFRP. Researchers have been investigating CFRP-Al joints made by various welding methods including ultrasonic welding, induction spot welding and friction spot joining. However, the strength of the joints is at most 52 MPa based on the literature. Also, the CFRP-Al joints made by spot welding technologies are discrete, which limits their application. Ultrasonic additive manufacturing (UAM) is a solid-state welding technology that utilizes ultrasonic metal welding to additively join thin metal foils to create 3D parts. A method is presented here for using the UAM process to embed carbon fiber tows into aluminum, creating strong CFRP-Al hybrid joints by mechanical interlocking without fracturing any fibers. The carbon fiber tows are embedded into the aluminum matrix in a continuous looped geometry, which enables this joint to accommodate many arbitrary shape requirements. With this UAM CFRP-Al joint as a transition part, CFRPs can be easily connected to the metal structure by applying any traditional metal-metal weld between the Al portion and the metal structure. Tensile tests were performed on coupon-level UAM CFRP-Al joint samples which achieved a strength of 131.2 MPa. Two typical failure modes, CF tow failure and Al failure, have been analyzed with the aid of a Digital Image Correlation (DIC) system. The desired failure mode can be designed by adjusting the volume fraction of carbon fiber embedded in the Al matrix to achieve either maximum strength or maximum energy dissipation.