Performance Prediction for Ultrasonic Spot Welds of Short Carbon Fiber-Reinforced Composites Under Shear Loading

Abstract

Ultrasonic welding is a well-known technique for joining thermoplastics and has recently been introduced to joining carbon fiber-reinforced composites (CFRC). However, suitable models for predicting joint performance have not yet been established. At present, most failure models for bonded composites are built based on uniform adhesive joints, which assume constant joint properties. Nevertheless, the joint properties of ultrasonic spot welds for CFRC are variable, which depend on the input welding parameters. In this paper, the effect of welding energy, which is the most important welding parameter, on the joint properties is investigated. Then, a surface-based cohesive performance model based on mode-II (in-plane) shear loading is developed to predict the joint performance, wherein the critical fracture parameters in the model are described via the functions of welding energy. After comparing the simulated results with experiments, the model is proven feasible in predicting the joint properties of the ultrasonic spot welds under shear loading condition, and hence, a mix-mode cohesive-zone model is practical to predict the joint performance under any loading conditions with the predicted fracture parameters.