Ultrasonic welding of <scp>CF</scp> /epoxy‐ <scp>CF</scp> / <scp>PEI</scp> joints with enhanced vibration transfer efficiency and optimized welding quality

Abstract This study investigated the impact of welding force on the ultrasonic welding quality of epoxy‐based to polyetherimide (PEI)‐based composite joints. PEI film layers were used on the carbon fiber/epoxy (CF/epoxy) composite surface through a co‐curing process, rendering it “weldable.” The ultrasonic welding for CF/epoxy and CF/PEI composite adherends were then performed, with varied welding force. The results showed critical effects of the welding force on the vibration transfer efficiency, morphology of welding lines and strength of welded joints. Lap‐shear strength (LSS) value of these joints initially increased and subsequently decreased with continuously increasing welding forces. Pore defects formed during the welding process were efficiently avoided while an optimal welding force was utilized, that resulted in the best quality welding line and the largest LSS of 39.4 MPa. In this case, CF/PEI and CF/epoxy composite adherends were cohesively failed, which was the main failure mechanism for the hybrid joints. Highlights Weldability of CF/epoxy composites was realized by co‐curing a PEI layer. Increasing welding force provided enhanced vibration transfer efficiency. Optimal welding force led to efficiently improved welding‐line quality. The largest LSS of 39.4 MPa was obtained with an optimal welding force.