Failure behaviour of extrusion welding seams made of thermoplastic plastics

With regard to the extrusion welding of plastics, the correct choice of the setting variables determines the mechanical properties and the morphology of the welding seam. The failure behaviour provides indications of the optimum welding parameters and component geometries. Therefore, the development of cracks in the creep-rupture tensile test was analyzed first of all. In this case, it was possible to observe three different types of failure: fractures at the joining level, in the base material and in the shrinkage cavity. It was shown that the type of fracture is influenced by the welding speed, the hot-gas temperature, the extrudate temperature, the specimen shape, the seam-preparation angle and the notch geometry on the seam coverage. Depending on the type of fracture, this resulted in different service lives. Furthermore, the stresses in the region of the welding seam were investigated using the finite-element method. Accordingly, the most critical point of an extrusion welding seam is located at the seam coverage in the base material.