A Novel Quality Factor for Thermoplastic Composites Welding

Fibre-reinforced thermoplastics are increasingly replacing metal alloys in aerospace due to their low weight, high specific strength and possibility to be welded. However, traditional development processes for joining technologies are experimentally based hence resource-intensive. This work introduces a novel thermally based quality factor, the Sanger factor, to predict the mechanical joint strength of resistance-welded thermoplastic composites using simulated temperature data. The approach leverages a meso-scale model, the newly modified mosaic model (M³) to capture heterogeneous heating patterns and integrates four temperature characteristics: degree of melting, degradation, homogeneity, and crystallisation potential. The model was validated experimentally using single lap shear tests and evaluated across various process configurations. Results demonstrate a strong correlation between thermal and mechanical properties, with prediction accuracies exceeding 90% for a ±10% error margin and 75% for the ±2σ confidence interval. Thereby, the Sanger factor offers a digital, resource-efficient method to optimise thermoplastic joining processes and reduce experimental effort.