Application of Sheet-like Energy Directors for Ultrasonic Welding of Carbon Fiber-Reinforced Thermoplastics

Abstract

A highly efficient joining method using ultrasonic welding is required for the manufacturing and processing of thermoplastic carbon fiber-reinforced plastic (CFRP) structures. Herein, the application of resin mesh as a sheet-like energy director is proposed, and its feasibility is assessed. The relationship between the welding conditions and the tensile shear strength was investigated using single lap joint specimens prepared by ultrasonic welding. The fracture surface observations indicated that resin mesh melting occurred from the end of the specimen, whereas the unmelted zone remained at the center of the welding surface. It was necessary to supply a sufficient amount of resin to the welding surface and select a resin mesh suitable for the welding conditions to minimize variations in the bonding strength. Under the welding conditions used herein, the specimens with the coarsest resin mesh showed an average tensile shear strength of 34 MPa and a coefficient of variation of 0.1. From these results, it was concluded that the application of a sheet-like energy director for the ultrasonic welding of thermoplastic CFRP is a promising method to achieve a practical level of bonding strength.