Introduction of AVK workgroup „continuous fiber reinforced thermoplastics (cFRTP)”
Continuous fiber reinforced plastics with a thermoplastic matrix material (cFRTP) offer numerous advantages compared to material systems with a thermoset matrix: among others, short process cycle times, meltability, weldability and the possibility of material recycling shall be named. These features facilitate the development of sustainable components. Furthermore, cFRTP feature a high specific stiffness (in terms of density) and strength as well as a high energy absorption capacity. Therefore, cFRTP are very suitable for use in structural components. From a historical point of view, fiber reinforced plastics with a thermoset matrix have been used in numerous applications – especially in aviation – and hence have a quite high technical maturity. Since cFRTP are a comparably young technology, their full potential has not been exploited yet in serial production.
Standardized test methods
The standardized characterization of fiber reinforced plastics also concentrates primarily on material systems with a thermoset matrix material. Since its foundation in June 2015, the AVK work group „continuous fiber reinforced thermoplastics” (figure 1; www.avk-tv.de/expertsworkinggroups.php) has been working on a standardization strategy for cFRTP (organic sheets and tapes) headed by Leibniz Institut für Verbundwerkstoffe (IVW). By now, a novel tapered specimen geometry for determining the tensile material properties (already standardized as ISO 527-4: 2021 type 4, figure 2) as well as a complete test schedule have been developed. The derived test schedule defines standardized test methods and conditions required for determining the full set of material parameters. Furthermore, detailed analyses on newly developed test methods (e.g. regarding compressive and bending load conditions) as well as round robin tests are conducted to evaluate their potential use for deriving material parameters or in quality assurance.
Based on the developed test schedule, cFRTP have also been introduced into the CAMPUS database. Since October 2019, uniform material properties and curve data are accessible publicly. In figure 3, an exemplary comparison of material data accessed from this database is shown. For more than 30 years, the CAMPUS database has been used by the world’s leading plastic manufacturers and their customers. Until now, only material data for thermoplastics for use in injection molding was available. Therefore, the introduction of cFRTP into CAMPUS marks a milestone regarding the future application and digitalization of this highly innovative material class.
Development of new test methods
Within the research project „Chara-TPC” (funded by the European Regional Development Fund (ERDF) and the state Rhineland-Palatinate; www.ivw.uni-kl.de/de/projekte/chara-tpc) new test methods for complex load conditions are developed at IVW. The research is focused on methods that are non-existent or have not been standardized yet and hence complements the established test schedule of the AVK work group. The work considers creep tests, short-term dynamic tests at high strain rates, testing under multiaxial loading conditions using tubular specimens (figure 4) as well as testing of joints in hybrid materials. The derived methods are an essential base for further standardization in the future as well as determining material cards of cFRTP for finite element analysis.
Dr.-Ing. Sebastian Schmeer I Phone: +49 631 2017-322
Dipl.-Ing. Florian Mischo I Phone: +49 631 2017-407