Textile reinforcements have established themselves as a convincing alternative to conventional steel reinforcements in the building industry. In contrast to ribbed steel bars that ensure a stable mechanical interlock with concrete (form fit), the bonding force of smooth carbon rovings has so far been transmitted primarily by an adhesive bonding with the concrete matrix (material fit). However, this material fit does not enable the efficient use of the mechanical load capacity of the textile reinforcement. Solutions involving surface-profiled rods promise significant improvements in the bonding behavior by creating an additional mechanical interlock with the concrete matrix. An initial analysis was carried out to determine the effect of a braided rod geometry on the bonding behavior. For this purpose, novel braided rods with defined surface profiling consisting of several carbon filament yarns were developed and characterized in their tensile and bond properties. Further fundamental examinations to determine the influence of the impregnation as well as the application of a pre-tension during its consolidation in order to minimize the rod elongation under load were carried out. The investigations showed a high potential of the impregnated surface-profiled braided rods for a highly efficient application in concrete reinforcements. Hereby, a complete impregnation of the rod with a stiff polymer improved the tensile and bonding properties significantly. Compared to unprofiled reinforcement structures, the specific bonding stress could be increased up to 500% due to the strong form-fit effect of the braided rods while maintaining the high tensile properties.

With the increased use of fiber-reinforced composites (FRPs), the design of a new generation of composite structures with high stiffness and a ductile material behavior is required to cope with complex load scenarios and high damage tolerances. This can be achieved, in particular, by a combination of conventional FRPs, which possess high stiffness and strength, with metallic materials characterized by their high ductility and associated higher energy absorption capacity. Currently, there are no solutions for the hybridization of high-performance filament yarns, metal filament yarns or thermoplastic filament yarns at the micro level. Therefore, the aim of this paper is the hybridization of multi-fiber components intermixed at the micro scale. For this purpose, three hybridization processes were investigated. They are conventional air-jet technology, air-jet technology based on a modified air nozzle and an additional pre-spreading device and a process based on a newly developed multi-level-intermixing device. The effect of different processing parameters, such as air pressure, air nozzle and type of manufacturing, on the tensile properties, appearance and damage of multi-material hybrid yarn was analyzed. The results show that the developed multi-material hybrid yarns have high potential for use in composites with high requirements for crash and impact properties.

With the increased use of fibre reinforced composites (FRP), the design of new generation of composite structures with high stiffness and a ductile material behaviour is required to cope with complex load scenarios and high damage tolerances. This can be achieved, in particular, by a combination of conventional fibre-reinforced composites (FRP), which possess high stiffness and strength with metallic materials characterized by their high ductility and associated higher energy absorption capacity. Currently, there are no solutions for hybridisation of high performance filament yarns, metal filament yarns and thermoplastic filament yarns on micro level. Therefore, the main objective of this study is to develop a fibre hybrid composite based on hybrid yarn consisting of glass, steel and polypropylene filament yarns and to compare its tensile and impact properties with those of the composite reinforced only with glass filament yarn. The tensile and impact properties of the unidirectional hybrid composites produced from the developed multi-material hybrid yarn consisting of steel, glass and polypropylene filament yarns are compared with those of a non-hybrid composite reinforced exclusively with glass filament yarn. The results show that by hybridising with steel fibres a characteristic post-failure behaviour can be achieved, so that the developed multi-material hybrid yarns have a high potential for use in composites with high crash and impact performance requirements, where safety demands are essential.

Yarns from recycled carbon fibre (rCF) and thermoplastic fibres have shown potential in achieving high mechanical properties in thermoplastic composites. As the thermoplastic fibre component of the yarn melted during the composite manufacturing to form the matrix of the composite, the rCF content of the yarn is equivalent to the rCF content of thermoplastic composites (typically 45–55% by volume). However, in order to use such yarns for thermoset composites from rCF, the yarn must be impregnated with a liquid thermoset resin. To ensure good mechanical properties in thermoset composites, the rCF content in the yarns must be as high as possible. Due to the smooth surface and lack of fibre-to-fibre cohesion, producing yarn or slivers from rCF alone through carding and drawing is highly challenging. As a result, the use of rCF yarns in thermoset composites remains underexplored. This research addresses the knowledge gap by examining the influence of rCF yarn structures on tensile and impact properties of composites. Two yarns were developed using friction and wrap spinning techniques, where a core of rCF is wrapped with thermoplastic filaments or fibres (90 wt%. The developed yarns were impregnated with epoxy resin using the resin transfer moulding technique to produce unidirectional composites. The investigations show that while the compactness, hairiness and processability of the yarn are significantly affected by differences in yarn structure, the tensile and impact properties of the composites remain comparable.

The aim of this research is to improve the impact strength of thermoplastic composites manufactured from recycled carbon fiber (rCF). For this purpose, the development of a novel multi-material, micro-scale hybridized and low-cost hybrid yarn by blending aramid fibers with rCF and polyamide 6 (PA 6) fibers through the processing route of carding, drawing and flyer spinning is reported in this paper. In addition, two other hybrid yarns were produced from rCF/PA 6 and aramid/PA 6 for comparison with the multi-material rCF/aramid/PA 6 hybrid yarn. Finally, the tensile, flexural and impact properties of composites based on the developed rCF/aramid/PA 6 multi-material hybrid yarn were compared with those of composites reinforced only with rCF and aramid fiber. The results of the Charpy impact test showed that the inclusion of 24 volume percentage aramid fiber increased the impact strength by 70% compared to the composite reinforced with rCF alone. The multi-material hybrid yarn consisting of rCF/aramid/PA 6 fibers shows good potential for designing a hybrid composite with tailored tensile, flexural and impact resistant properties.

This paper reports a comparison of tensile and impact properties between carbon/aramid and carbon/glass fibres reinforced unidirectional thermoplastic hybrid composites. For this purpose, different hybrid composites were produced using commingled hybrid yarns of carbon/aramid/polyamide 6 filament yarns and carbon/glass/polyamide 6 filament yarns with a defined mixing ratio based on air texturing technology. The results show that the density and specific Youngs’ modulus of the composites changes linearly with the proportion of carbon/glass and carbon/aramid fibre in hybrid composites. The specific Young’s modulus decreases linearly with decreasing carbon fibre content in the hybrid composites. On the other hand, the specific tensile strength does not change linearly according to the rule of mixture and a negative hybridization effect can be observerd for both types of hybrid composites. Furthermore, the combination of carbon/aramid and carbon/glass fibres can increase the impact strength by approximately 204% and 218%, respectively, compared to the composite reinforced by CF only. Although the specific tensile strength and specific impact strength of carbon/aramid reinforced hybrid composites are higher than those of CF/GF hybrid composites due to the lower density of carbon/glass hybrid composites, the potential impact strength achievable in hybrid composites is higher with the carbon/glass combination than with the carbon/aramid combination.