Experimental investigation of thermoplastic welded single-lap shear joints with a recycled core

Thermoplastic welded single-lap shear joints made from sandwich-like adherends with a recycled core and virgin face sheets are tested to measure their load-carrying capacity and to quantify damage growth. The results are compared with single-lap shear joints entirely made from laminates consisting of virgin materials. The adherend constituents are T300/polyphenylene sulfide (T300/PPS) and T700/low-melt polyaryletherketone (T700/LM-PAEK), joined via induction and conduction welding, respectively. Test bench data, digital image correlation, a high-speed camera, and microscopy are used to evaluate the structural response of the specimens. Damage initiation and propagation are heavily influenced by the actually welded interface regions. While the virgin joints only experience damage growth along the welded interface, adherend failure can also occur in the recycled core joints. The recycled core joints show a reduced lap shear strength compared to their virgin counterparts, limited to less than 14% for the induction welded T300/PPS specimens and around 40% for the conduction welded T700/LM-PAEK specimens. Despite the reduction in load-carrying capacity, recycled core joints may be considered as a suitable alternative in scenarios where the requirements for mechanical properties are less dominant and environmental considerations are more relevant.