Application of ultrasonic welding to repair adhesively bonded short carbon fiber reinforced Nylon 6 composites

Abstract A method of applying ultrasonic welding to repair adhesive-bonded 2.3 mm thick injection molded short carbon fiber reinforced Nylon 6 (Cf/PA6) composite with 30 wt% fiber was developed. The method included positioning the ultrasonic horn and anvil proximate the region on the workpieces having the partially adhesive-bonds and applying an ultrasonic oscillation at the workpieces where insufficient adhesive was dispensed at the faying surfaces. The effects of horn force, oscillation time, and inadequate adhesive on the quasi-static strengths of the nominal, partially adhesive-bonded and repaired joints were investigated. It was found out that the strengths of the partially adhesive-bonded joints with 0%, 25%,50% and 75% adhesive coverages were restored and achieved over 90% of the nominal joint strength (i.e., full adhesive coverage). Microstructure analyses of the repaired joints demonstrated that the second ultrasonic pulse produced viscoelastic heating and frictional heating, and consequently fused carbon fiber composites at the faying surfaces of the workpieces. The strengths of the repaired (i.e., weld-bonded) lap-shear joints were primarily from the combined contribution of adhesive-bond and ultrasonic weld at the faying surfaces, which were virtually unchanged regardless the amount of adhesive missing. Therefore, for the substrate and joint configuration and dimensions studied here, application of ultrasonic welding virtually restored the quasi-static strengths of partially adhesive-bonded lap-shear Cf/PA6 composites with 30 wt% fiber. Consequently, by the application of this repair method the scrap of the component assembly would be reduced.