Fibre-reinforced composites (FRCs) are already well established in several industrial sectors such as aerospace, automotive, plant engineering, shipbuilding and construction. The technical advantages of FRCs over metallic materials are well researched and proven. The key factors for an even wider industrial application of FRCs are the maximisation of resource and cost efficiency in the production and processing of the textile reinforcement materials. Due to its technology, warp knitting is the most productive and therefore cost-effective textile manufacturing process. In order to produce resource-efficient textile structures with these technologies, a high degree of prefabrication is required. This reduces costs by reducing the number of ply stacks, and by reducing the number of extra operations through final path and geometric yarn orientation of the preforms. It also reduces waste in post-processing. Furthermore, a high degree of prefabrication through functionalisation offers the potential to extend the application range of textile structures as purely mechanical reinforcements by integrating additional functions. So far, there is a gap in terms of an overview of the current state-of-the-art of relevant textile processes and products, which this work aims to fill. The focus of this work is therefore to provide an overview of warp knitted 3D structures.

The possibility of direct preforming in the near net shape of final component structure with load- and shape-conforming fiber orientations is highly essential in composite production, not only to reduce costs but also to attain better mechanical properties and form stability. Based on the concept of varying the reinforcement yarn lengths during the feed-in (warp yarn delivery) and segmented doffing, synchronous working numerically controlled warp yarn delivery and doffing machine modules have been newly developed for multiaxial warp knitting machines to create a resource efficient textile process chain by a single-step, large-scale oriented production of load- and form-conforming warp knitted three-dimensional shell preforms with free-form geometrical surfaces. Such customized preforms in the near component net shape offer higher material utilization and increased lightweight potential.

In the wind energy sector, automotive and aviation industries, non-crimp fabrics have been established for many years. Non-crimp fabrics are also increasingly being sought in the construction sector. Due the connection to the concrete, the non-crimp fabrics with a grid-like open structure are used as textile reinforcements. This paper presents the development of alternative stitch-free bonding technologies for non-crimp fabrics based on multiple carbon fiber heavy tows for textile-reinforced concrete components. For this purpose, an initial analysis is carried out to find out the effect of impregnation on the number of roving layers. Further examinations to determine the process-related limits and mechanical process parameters for using this kind of rovings in textile machines are performed on the influence of multiple roving tension on changes width. Finally, the strength of the bonding points of the non-crimp fabrics produced in a laboratory scale is thoroughly investigated by varying the grid geometry, number of roving layers and bonding technology. The investigations show a good potential of the developed bonding technologies for the production of alternative bonded stitch-free non-crimp fabrics. Compared to grid-like open structures, which are connected by stitching threads, the strength of the bonding points can be increased up to 30%, by the developed stitch-free bonding technologies.

This study investigates a novel approach in modeling the system limits of a braked, high-speed yarn-laying process with in situ impregnation. Special attention is paid to the investigation of the yarn spool overrun after the robot has come to a standstill. This phenomenon occurs at low yarn tensions in combination with high traversing speed and/or acceleration. The modeling of the yarn spool overrun is carried out using physical equations, taking into account the travel speed, acceleration of the robot, and braking force of the spool brake. Previous research has confirmed various operating points of the yarn-laying process, but a comprehensive and complete analysis of the system limits at different operating points and speeds up to 2 m/s is missing. The result of the study is a novel model that describes the system boundaries of the direct-yarn-placement. Furthermore, models for robot braking time, carbon spool diameter, and spool mass are developed. The proposed models have an $R^2$ > 0.9674. Regarding the system stability boundaries, the calculations reveal that, as acceleration rises, the minimum tension requirement also increases. The same trend is found for system velocity. At $a=12.5$%, a minimum tension of 16 N suffices, compared to 23 N and 32 N at $a=25$% and 50%, respectively. The impact on tension of quadrupling the speed outweighs that of acceleration, with tension increasing by factors of up to 22.5 and 2, respectively.