Thermoplastic composite welding is a key-technology that can enable the aviation industry to be more sustainable. Furthermore, the technology can support cost-efficient high-volume production. In this work, thermoplastic composite conduction welded joints are characterized, tested and analysed. Fracture toughness characterization specimens are designed and welded by using a 0.5 meter long welding tool. The welds are representative for the joints of the stiffened structures of the next-generation thermoplastic composite fuselage as shown in Figure 1. In the specimen design, special attention is paid to the weldability of the laminates and a zero degree welded interface angle is used to promote stable crack propagation in the weld. The mode I and II fracture toughness is characterized by using the Double Cantilever Beam and End-Notched Flexure test, respectively. For validation of the analysis approach, experiments are performed by loading Single Lap-Shear specimens in both tension and three-point-bending. Finally, the cohesive zone modeling approach is used to demonstrate that the strength of the conduction welded joints can be reliably predicted. This study provides new insights into the influence of the manufacturing process on the material properties and quality of the welded joint. The measured fracture toughness is found to be significantly different in comparison to autoclave consolidated composites.