These past decades, the ability of thermoplastic composites to be welded has been of great interest, with numerous studies investigating the process and mechanical strength of joints for quasi-static loadings. The present study aims to determine the loading speed influence on the behaviour of these structures, as crashworthiness is of tremendous interest in the transport industry for safety issues. The polyamide-based composite used in this work is sensitive to strain rate, which may influence the interface and the entire structure's behaviour. Tensile tests were performed on single lap joint specimens for loading speeds from 1.2 mm min−1 to 7 m s−1, considering several substrate orientations. Loading speed influences the lap shear strength for the different configurations: increasing loading speed induces a performance enhancement of 11.2%–22.9%. This phenomenon is caused by the matrix strain rate sensitivity, which stiffens and strengthens the substrate shear behaviour and the welded joint behaviour. Finally, the fractography analysis confirms that fracture mechanisms observed are similar for each loading speed tested with primarily fibre/matrix debonding. Therefore, improvement in the welded structures' performance is due to the mechanical performance of its constituents and their influence on the interfacial strength. •Single lap shear tests conducted up to 7 m s−1 for three cross-ply configurations.•Lap shear strength enhances with the increase in loading speed.•Stiffening of 0/45S/454 and 454/454 with the increase in loading speed.•Cohesive fracture leads to high performances of ultrasonically welded joints.