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The ring spinning technology is widely used in the textile industry to produce high‐quality yarn. One of the challenges for higher productivity is the limited spindle speed due to friction in its conventional ring/traveler twisting system. However, it was recently shown that a superconducting magnetic bearing twisting system might overcome this limitation due to significantly reduced friction, which allows the use of higher spindle speeds and thereby increases productivity. To analyze the impact of speed increments on the yarn formation, it is crucial to model the yarn balloon dynamics. This is of particular importance as new challenges arise for such high‐speed processes, including the increase in yarn tension due to higher centrifugal forces and increased air resistance of the yarn itself. Therefore, in this work, a model based on a chain of springs and masses as an alternative to traditional continuous models was developed. In the proposed model, each mass corresponds to a yarn segment, while the springs represent the interactions between adjacent segments. This discrete approach allows for a simplified simulation of the three‐dimensional yarn balloon dynamics, leading to a reduced computational load, which allows to analyze the yarn path more easily under different conditions. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Because of a growing demand and usage of carbon fiber, effective methods to re-use waste and recycled carbon fiber recoverable either from process scraps or from end-of-life components are attracting increased attention. The development of different hybrid yarn structures consisting of recycled carbon fiber and thermoplastic fibers (recycled carbon fiber content approx. 50% by weight) for thermoplastic composites have been reported earlier. Yarns with high recycled carbon fiber content (>90% by weight) required for thermoset composites are still not realizable due to high shortening in recycled carbon fiber length (≥70%) during different processing steps of spinning. The reason lies in low shear strength, smooth fiber surface and high brittleness of recycled carbon fiber. Second, a lack of crimp in recycled carbon fiber leads to drafting errors during the drawing and spinning process. In this paper, the spinning limit regarding the core to sheath ratio of noble yarns with a recycled carbon fiber content greater than 90% by weight based on friction spinning technology for thermoset composites is reported. Slivers of recycled carbon fiber solely required for the development of yarns are produced on carding and drawing machines optimized for the gentle processing of recycled carbon fiber. Furthermore, different spinning parameters such as spinning drum speed and suction air pressure are investigated and their effect on tensile properties of yarn is analyzed. The results show that yarns with high recycled carbon fiber content (>90% by weight) can be produced with reproducible quality on the DREF-3000 friction spinning machine. [ABSTRACT FROM AUTHOR]

This article reports the results of investigations carried out to produce yarns consisting of staple carbon fiber (CF) obtained from process waste for the manufacturing of composites suitable especially for thermoset applications. For this purpose, a comparative analysis is done on processability between 100% staple CF and 60 weight% staple CF mixed with 40 weight% PVA fibers in carding, drawing and spinning process. The hybrid yarns are produced by varying twist level. The PVA fibers of the hybrid yarn are then dissolved using hot water treatment. The mechanical properties of yarns consisting of 100% staple CF and hybrid yarns consisting of staple CF and PVA before and after hot water treatment are investigated. Furthermore, test specimen is also prepared by impregnating 100% staple CF yarn and the hybrid yarns (after the dissolving of PVA) with epoxy resin. The results of the tensile test of the yarns in consolidated state reveals that the hybrid yarn produced with 80 T/m after hot water treatment exhibits approximately 75% of the tensile strength of virgin filament tow, and it is expected that the hybrid yarns can be applied for the manufacturing of thermoset based composites for load bearing structures.

This paper aims to conduct theoretical modeling of tensile properties of thermoplastic composites developed from novel unidirectional recycled carbon fiber tapes. Unidirectional recycled carbon fiber tape structure is an innovative, sustainable and cost-efficient prepreg structure designed to develop carbon fiber reinforced plastics with the highest resource efficiency. In order to do modeling, existing theoretical models of tensile properties of unidirectional composites were reviewed in the first part of this paper. Subsequently, reviewed theoretical models were further modified by considering the tensile properties of fibers, fiber length, fiber orientation, fiber volume content and short fiber content to predict the tensile properties of composites based on novel tape structure. The results of this study reveal that the proposed theoretical models are in good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The implementation of a Superconducting Magnetic Bearing (SMB) system is a promising solution for the problem of friction exhibited in the twisting elements of the conventional ring‐spinning process. This research focuses on the development of a dynamical model with six degrees of freedom of the Permanent Magnet (PM) ring used in an SMB system for a high‐speed ring spinning process. The modeling takes into account the magnetic forces and torques that enable the magnetic levitation of the PM ring. Experimental tests allow the identification of unknown parameters of the model and the validation is done through simulations. [ABSTRACT FROM AUTHOR]

Composites based on e.g. randomly oriented nonwovens and injection moulded structures from discontinuous carbon fibre (CF), which are processed industrially exhibit low tensile strengths of 200–300 MPa and 400 MPa, respectively. In contrast, composites based on twisted hybrid yarns from discontinuous CF and thermoplastic fibre show higher tensile strengths such as 1150 MPa. Reasons are improved fibre orientation and higher fibre volume content. However, tensile strength is still lower than that of uni-directional carbon fibre reinforced composites (CFRP) based on continuous filament yarn, which is around 1560 MPa. The reason is a low fibre orientation due to yarn twisting and high fibre shortening, which occurs throughout the yarn manufacturing process. As mechanical properties of composites largely depend on fibre orientation and length, there is a high potential to achieve higher mechanical properties in CFRP by ensuring gentle processing of CF and reducing yarn twist. However, due to brittleness and smooth surface of CF, spinning of yarns with low twist (<60 T/m (twist per meter)) is challenging. In order to exhaust the potential of hybrid yarns, a semi-industrial process chain to produce hybrid yarns while ensuring gentle processing of discontinuous CF (fibre length 100 mm) and polyamide 6 fibres (fibre length 80 mm) at significantly low level of twist 20 T/m is reported in this paper. Carbon fibre reinforced composite manufactured from these hybrid yarns show high tensile strength (1453 ± 27 MPa), Young's modulus (94 ± 6 GPa), flexural strength (1090 ± 41 MPa) and flexural modulus (98 ± 5 GPa). [ABSTRACT FROM AUTHOR]

The processing of recycled carbon fibres (rCFs) into hybrid yarn constructions is a promising recycling option, converting rCF into products with added value. Along with fibre length and strength, the sizing of rCF crucially affects their processing behaviour and subsequent composite properties. This article reports on the influence of sizing on the processing properties of rCF by mixing with polyamide (PA) 6 fibres to form a hybrid yarn construction. Moreover, resulting composite properties were studied as well. Thus, commercially available CF with thermoplastic and thermoset matrix compatible sizing in addition to pyrolyzed rCF without sizing was used for the investigations presented in this article. Results revealed that different sizing strongly influence the processing of rCF and PA 6 into hybrid yarn constructions. The opening and bending behaviour of rCF bundles with different sizing varied during the carding process so that various degrees of fibre shortening occurred. As expected, the sizing developed for thermoplastic matrix enabled the highest tensile and flexural strengths in thermoplastic composites. These findings greatly contribute to the understanding of rCF processing from different or unknown sources on industrial scale. [ABSTRACT FROM AUTHOR]

Due to the increasing application of carbon fibre–reinforced plastics, the use of recycled carbon fibres can help reduce the tremendous amount of carbon fibre waste growing worldwide. In this context, the processing of longer recycled carbon fibres (>40 mm mean length) into hybrid yarn constructions offers a promising solution. The characterisation of recycled carbon fibre length is essential for textile processes. However, to suit the atypical fibre characteristics of recycled carbon fibres compared to standard natural or man-made-fibres, the development of an adequate measuring technique is required. Investigations on the state of the art suggest that an adapted fibrograph method might pose an appropriate measuring system. Therefore, new test equipment and an alternative image analysing method based on pixel greyscale values were developed. To enable a calibration process, different samples with cut carbon fibre from carded and drafted slivers were intensively tested and compared. In addition, an adapted reference method was investigated by combining single fibre measurement and image processing techniques. In a final step, recycled carbon fibres samples with unknown fibre length were tested. Results proved that the presented measuring system is adequate for the testing of longer recycled carbon fibres in webs or slivers. All measured values were close to the measured reference length values (deviation ±4%). [ABSTRACT FROM AUTHOR]