The research project aimed to standardise the welding, inspection and design of seams in expanded tetra‑fluoro‑ethylene (ETFE) films for architectural membrane structures. The overarching goal was to produce draft DIN standards that would later be incorporated into European technical specifications and Eurocode provisions for membrane structures. Five draft standards (DIN 18229‑1 to 5) were developed; four were finalised during the project, while the fifth was only conceptually outlined. The standards cover welding inspection, personnel qualification, welding process verification, welding procedure specification, and design guidance for ETFE seams.
Experimentally, the team performed mono‑axial and bi‑axial tensile tests on welded ETFE films supplied by three manufacturers and produced in two thicknesses (100 µm and 250 µm) and two welding processes (hand‑rigid and hand‑high‑intensity). Five specimens per configuration were tested at room temperature (23 °C ± 2 K) and at elevated temperatures. The 5 % fractile values of all tested seams exceeded the 30 MPa characteristic strength recommended by CEN/TS 19102, and the coefficient of variation never surpassed 8 %. The mean strengths ranged from 32 MPa to 53 MPa, with the highest values observed for the 250 µm films from manufacturers A and C. Only one specimen from manufacturer B’s 300 µm film fell below the 30 MPa threshold, indicating a potential outlier rather than a systematic trend. No significant reduction in strength was observed with increasing film thickness, suggesting that seam quality is largely independent of thickness within the tested range.
Temperature‑dependent tests revealed that welding parameters exert a stronger influence on ultimate strength than the base material. The variation in strength with temperature was more pronounced for seams produced with the high‑intensity process, underscoring the need for process‑specific qualification. The data therefore support the inclusion of welding‑process criteria in the forthcoming standards and highlight the necessity of individual material‑charge qualification for each project.
The project was organised into five work packages. Work package 1 focused on standardising the inspection method, including material procurement, specimen optimisation, and numerical modelling. Work package 2 addressed welding‑process verification, developing a welding plan and qualifying both the process and personnel. Work package 3 produced a DIN specification, while work package 4 carried out the mechanical testing and established minimum strength requirements. Work package 5 produced the final report and publications. The consortium comprised the University of Duisburg‑Essen (UDE) as the lead partner, DEKRA Automotive GmbH, VF, TE, SC, and formTL. UDE’s Institute for Metal and Lightweight Construction provided the experimental facilities and technical leadership; DEKRA supplied independent testing and quality assurance; VF, TE, SC, and formTL contributed expertise in welding technology, material science, and industry application. The project commenced on 1 January 2021, originally scheduled for two years, but was extended cost‑neutrally to 30 June 2023 due to material supply delays. Funding was provided by German research agencies, with UDE recognised as a national testing and certification authority under the German Building Code.
In summary, the project delivered a robust experimental database confirming that ETFE seams can reliably exceed the 30 MPa minimum strength at ambient temperature, with acceptable variability. It established a comprehensive set of draft standards that will guide welding practice, inspection, and design for ETFE membrane structures across Europe, thereby facilitating the integration of these materials into future architectural projects.