Investigation of the Bonding Mechanism between Overlapping Textile Layers for FRP Repair Based on Dry Textile Patches.

Lots of damaged fiber-reinforced plastic (FRP) components are replaced by new components instead of repairing. Furthermore, only very labor-intensive repair methods are available on the market to fully restore the integrity of the structure. This requires a high level of experience or, alternatively, very cost-intensive technology, such as the use of computer tomography and robotics. The high costs and CO2 emissions caused by the manufacture of FRP components then bear no relation to their service life. The research project IGF-21985 BR "FRP-Repair" aims to solve the named challenges. Using semiconductor oxide catalysts, the matrix can be locally depolymerized by ultraviolet (UV) radiation, and thus removed from the damaged area of the FRP component. Subsequently, the damaged fibers in this area can be detached. By using customized textile repair patches and local thermoset reinfiltration, the repair area is restored. With this process, the fiber structure can be repaired locally with new fibers on the textile level. The repair is similar to the original production of a fiber composite in an infusion process. No additional adhesive material is used. As a result, repaired FRP structures with restored mechanics and a near-original surface can be realized. This article provides an insight into the actual steps of the development of the FRP component repair process using dry textile patches. The empirical investigation of overlapped rovings and UD material showed the expected results. Residual fracture forces of up to 86% could be achieved. The most interesting approach on the roving level was splicing the overlapping fibers. The free ends of the fibers of the patch and part are mechanically bonded. This bond at the textile level is further strengthened by infusion with matrix.

Recycling of Carbon Fibres and Subsequent Upcycling for the Production of 3D-CFRP Parts.

Carbon fibres (CF) are used in CF reinforced plastic (CFRP) components. However, waste from CF yarn trim, CFRP and the end of life (EOL) CFRP structures will cause a recycling challenge in the next decades because of strict environmental regulations. Currently, recycling is carried out almost entirely by the use of pyrolysis to regain CF as a valuable resource. This high temperature process is energy consuming, and the resulting fibres are brittle. Hence, they are not suitable for processing of textiles into yarns or new reinforcement structures. To enable grave to cradle processing, a new approach based on a solvolysis recovery of CF and subsequent yarn spinning to obtain hybrid yarns suitable for textile processing, especially by weft knitting, was the focus of the international research project IGF/CORNET 256EBR. For the first time, it was possible to process hybrid yarns made of rCF on a weft knitting machine to produce biaxial reinforced structures to form CFRP from recycled carbon fibres. Therefore, various modifications were done on the textile machinery. In this way, it was possible to process the rCF and to get out a reproducible textile structure for the production of 3D recycled CFRP (rCFRP) parts.

Novel Repair Procedure for CFRP Components Instead of EOL.

Today, numerous carbon fiber (CF) reinforced plastic (CFRP) components are in continuous usage under harsh environmental conditions. New components often replace damaged structural parts in safety-critical applications. In addition to this, there is also no effective repair method to initially restore the mechanics of these structures using dry fiber material. The high costs of CFRP components are not in proportion to their lifetime. The research project IGF-19946 BR "CFRP-Repair" addresses this specific challenge. By using an oxide semiconductor that is activated by ultraviolet (UV) irradiation, the thermoset matrix can be depolymerized and thus locally removed from the damaged CFRP component. Afterward, the harmed fibers can be physically removed from the laminate in this certain area. A load-adjusted tailored fiber reinforcement patch is subsequently applied and consolidated by local thermoset re-infiltrating. Using this procedure, the structure can be locally repaired with new CF. As a result, repaired CFRP structures can be obtained with reduced mechanics and an approximately original surface. This article gives an insight into the developed repair procedure of CFRP components in an innovative and more efficient way than the state-of-the-art.