Impact and lap shear properties of ultrasonically spot welded composite lap joints

Abstract

Ultrasonic spot welding (USSW) is a widely used technique for joining thermoplastics where high frequency, low amplitude vibrations are applied through an ultrasonic horn resting on the polymer surface to create frictional heat, producing a solid state joint between polymer sheets. Advantages such as short weld cycle time, fewer moving components and reproducibility make this technique attractive for automation and industrial use. The goal of this work was to evaluate the feasibility and analyze the lap shear and impact strength of a composite material joint created using ultrasonic spot welding. The base material used for the joints was a composite consisting of a polycarbonate matrix with chopped glass fibers. The strength of the lap joints was determined through experimental lap shear and impact testing. A finite element analysis was conducted for more thorough insight into the stress patterns in the lap joints. Experiments showed that the ultrasonically spot welded joints tested in tensile lap shear loading carried a load 2.3 times higher than adhesive joints and the impact tested joints had an impact strength 3.5 times higher than adhesive joints. The results of this work suggest ultrasonic spot welding as a viable joining method for thermoplastic composite materials.