Optimization of ultrasonic welding parameters for laminate PEEK-based composites with carbon fiber prepreg

Abstract

In this study, ranking of the key ultrasonic welding (USW) parameters for joining laminate composites was carried out using the Taguchi method. To understand the nature of the revealed effects, an analysis of the structure at the fusion zone interface was performed. In shear tests, fracture of the lap welded joints through the base material was associated not only with high shear stresses, but also with double macrobending of the samples because of the increased rigidity of their central parts, possessing twice thickness values. It was found that fracture of carbon fibers due to the prepreg melting was a negative factor. However, it could provide additional reinforcement of the material in the fusion zone upon the USW process, increasing shear strength. The porosity formation at the interface could be associated with melting of both Energy Director (ED) films and the prepreg, in addition to the joined plates from the PEEK-based composite. The prepreg melting inevitably resulted in fracture of reinforcing fibers. As a result of the study, the most rational mode was reported. Finally, it is proposed to use changes in thicknesses of the lap welded joints as one of the key parameters for controlling the USW process.