Investigation on Energy Director-less Ultrasonic Welding of Thermoplastic to Thermoset Composites

The exceptionally short heating times achieved with ultrasonic welding make this technique highly promising for joining thermoplastic (TPC) to thermoset (TSC) composites, since it can prevent thermal degradation of the thermoset adherend. A neat thermoplastic coupling layer is co-cured on the surface to be welded as typical procedure to make the TSC “weldable”. It is therefore of great interest to investigate whether that coupling layer by itself has the potential to promote heat generation during the ultrasonic welding process with no need for a separate energy director (ED). A possible drawback of this procedure could be that it is more challenging to prevent thermal degradation since the coupling layer is involved in heat generation rather than acting as a thermal barrier. In this research CF/epoxy coupons with a polyetherimide (PEI) coupling layer were welded to compatible CF/TP adherends. The usage of (1) a 0.25 mm thick flat PEI ED and the usage of (2) no ED at all were investigated. Mechanical testing (single lap shear) as well as microscopic analysis of as-welded and tested samples were carried out in this study. Preliminary successful results were obtained for the energy director-less welding process. This research is part of the EFFICOMP project, funded by Horizon2020