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Large-tow carbon fibers are increasingly utilized in the field of composite materials, owing to their unique cost advantages and superior performance. The spreading width is a critical factor influencing both the performance of the fiber bundle and its impregnation properties. In this study, four 12K small-tow bundles were combined using a filament-combining device to form 48K large-tow bundles with varying spreading widths. Tensile tests were conducted on the carbon fiber tow bundles to investigate their mechanical properties at different spreading widths. Additionally, a weighing method was employed to identify the optimal impregnation technique for the carbon fiber tow samples. The experimental results indicate that the tensile performance of the 48K carbon fiber large-tow bundle is enhanced when the spreading width is smaller. However, excessively small spreading widths may compromise the internal fiber alignment and resin impregnation efficiency. Thus, the mechanical properties of the 48K large-tow carbon fiber bundle are optimized when the spreading width is 14 mm after filament combining.

The interfacial strength between carbon fibers and epoxy resin is one of the key factors affecting the strength of carbon fibers and has been the focus of researchers’ attention. It is necessary to consider it systematically because the stresses borne by the carbon fiber will be shared by the cured epoxy resin. In this paper, by constructing simulation models and tensile tests, we verified the changes of carbon fiber stresses in the presence and absence of epoxy resin, as well as under a variety of temperature conditions, and proved that epoxy resin curing does affect the changes of the tensile properties of large tow of carbon fibers. The results show that with the increase of load, the carbon fiber stress tends to increase nonlinearly, and the error value increases and the results of simulation calculation and experimental verification are basically in agreement. As the temperature decreases, the error value decreases slightly. These research results have important practical significance for the enterprise to reduce the cost and also have a reference for the simulation software on how to set the interface layer parameters.

New concepts of lightweight components are conceived nowadays thanks to the advances in the manufacture of composite structures. For instance, mature technologies such as Automatic Fibre Placement (AFP) are employed in the fabrication of structural parts where fibres are steered along curvilinear paths, namely variable angle tow (VAT), which can enhance the mechanical performance and alleviate the structural weight. This is of utmost importance in the aerospace field, where weight savings are one of the main goals. For that reason, shell structures are commonly found in the aerospace industry because of their capabilities of supporting external loadings. Straight-fibre composite shell structures have been studied in recent decades and, now, spatially varying composite shells are attracting the attention of manufacturers. This work analyses the mechanical behaviour of VAT composite shells subjected to different external loadings and boundary conditions. The Carrera Unified Formulation (CUF) is employed to obtain the different structural models in a systematic and hierarchic manner. The outcomes of such numerical models are discussed and compared with commercial software Abaqus.

Accurate segmentation is essential for creating digital twins based on volumetric images for high fidelity composite material analysis. Conventional techniques typically require labor-intensive and time-consuming manual effort, restricting their practical use. This paper presents a deep learning model, MBL-TransUNet, to address challenges in accurate tow-tow boundary identification via a Boundary-guided Learning module. Fabrics exhibit periodic characteristics; therefore, a Multi-scale Feature Fusion module was integrated to capture both local details and global patterns, thereby enhancing feature fusion and facilitating the effective integration of information across multiple scales. Furthermore, BatchFormerV2 was used to improve generalization through cross-batch learning. Experimental results show that MBL-TransUNet outperforms TransUNet. MIoU improved by 2.38%. In the zero-shot experiment, MIoU increased by 4.23%. The model demonstrates higher accuracy and robustness compared to existing methods. Ablation studies confirm that integrating these modules achieves optimal segmentation performance.

The state consistency of polyacrylonitrile (PAN) precursor fibers significantly impacts the stability of carbon fiber performance. In this paper, the impacts of folding during boxed storage on the microstructure and mechanical properties of large-tow PAN fibers and pre-oxidation fibers (OXFs) were explored. It was found that folding can damage the surface of PAN fibers, giving rise to defects like cracks and extrusions. Moreover, it leads to the loosening of the internal microfibril arrangement, the enlargement of pore sizes, and the decrease of microcrystalline orientation within the fibers. These structural alterations are inherited by OXFs, which not only disadvantage the pre-oxidation process but also result in the deterioration of mechanical properties. This research offers valuable reference data for the selection and optimization of precursor fiber storage methods prior to entering the pre-oxidation oven in the industrial production of large-tow PAN-based carbon fibers.

Large-tow carbon fiber (LCF) meets the low-cost requirements of modern industry. However, due to the large and dense number of monofilaments, there are problems with uneven and insufficient infiltration during material preparation. The permeability of large-tow carbon fibers can be used as a two-scale expression of resin flow during infiltration, making it an important factor to consider. This paper provides support for the study of pore formation. A two-dimensional model of randomly bundled large-filament carbon fibers is generated based on scanning electron microscope (SEM) maps. Microstructure size parameters are obtained, and a semi-analytical model of the transverse permeability of large-filament-bundled carbon fibers is established. Permeability values are then obtained. The analysis shows that the monofilaments in the tow are arranged randomly, and their periodic arrangement cannot be used to calculate permeability. Additionally, the number of monofilaments in a carbon fiber tow of the same volume fraction affects the permeability of the tow. Therefore, the permeability model of large-tow carbon fibers is reliable.

Spread-tow woven fabrics (STWs) have attracted considerable attention owing to their thin-layered characteristics, high fiber strength utilization rate and superior designability, finding wide application in the aerospace field. To meet the application requirements for materials with high specific strength/specific modulus in the aerospace field, this study designed an anti-sandwich structured composite with high specific load-bearing capacity. Herein, the core layer was a load-bearing structure composed of STW, while the surface layers were hybrid lightweight structures made of STW and nonwoven (NW) felt. Repeated impact test results showed that increasing the thickness ratio of the core layer enhanced the impact resistant stiffness of the overall structure, whereas increasing the proportion of NW felt in the surface layers improved the energy absorption of the composites but reduced their load-bearing stiffness and strength. The composite exhibited superior repeated impact resistance, achieving a peak impact load of 17.43 kN when the thickness ratio of the core layer to the surface layers was 2:1 and the hybrid ratio of the surface layers was 3:1. No penetration occurred after 20 repeated impacts at the 50 J or 3 repeated impacts at 100 J. Meanwhile, both the maximum displacement and impact duration increased, whereas the bending stiffness declined as the number of impacts increased. The failure mode was mainly characterized by progressive interfacial cracking in the surface layers and fracture in the core layer.

As worldwide agricultural production rises, agro-industrial biomass becomes an abundant raw source for uses in energy and materials production. In Colombia fique plants ( Furcraea spp.) are traditionally used to extract hard cellulosic fibers using mechanical decortication. Juice, pulp and tow, the by-products of this process, represent almost 95% of the fique leaf weight and are produced in large quantities. Data on these materials is scarce and greatly needed to guide and fuel fique agro-industrial development in Colombia. In this contribution we study the physicochemical properties of fique fibers and by-products (tow and pulp), before and after alkaline hydrogen peroxide treatment (AHP), using spectroscopic and microscopic techniques. Raw/clean fique tow is similar in structure and composition to fique fibers with average cellulose, hemicellulose and lignin contents of 52.3, 23.8 and 23.9%; in this by-product cellulose exists as a highly ordered structure with crystallinity index of 57%. Raw/clean fique pulp, composed of cellulose filaments from secondary cell walls and leaf epidermis, has average cellulose, hemicellulose and lignin contents of 30.5, 29.7 and 9.6%, with cellulose exhibiting an amorphous structure with a crystallinity index of 35%. The AHP treatment of these by-products effectively removed non-cellulosic compounds such as hemicellulose and lignin. After AHP lignin content in fique tow decreases to 2.8% while cellulose crystallinity increases up to 73%, Likewise, fique pulp shows a reduction in lignin to 2.1% and an increase in cellulose crystallinity up to 47%. IR spectroscopic analysis, after AHP, show a decrease of signals attributed to hemicellulose and lignin and FESEM images show a disruption of the lamellar structure in the macro fiber by the removal of hemicellulose, lignin and ground tissue, leaving cellulose fibrils exposed. As the first in-depth report on fique by-products characterization, our results indicate that pulp and tow are interesting lignocellulosic materials due to their significant content of crystalline and amorphous cellulose.

Carbon fiber–reinforced plastics (CFRP) is a kind of advanced composite material with resin as the matrix and carbon fiber as the reinforcing phase. Due to differences in material orientation, laser cutting of CFRP exhibits anisotropic characteristics. In order to study the influence of material anisotropy on energy conduction in laser cutting CFRP, taking single-layer CFRP as the research object, based on the heat conduction theory and the mixing rate of composite materials, the three-dimensional finite element models of single fiber arrangement with tow-to-spot (fiber tow to laser spot) diameter ratio of 1:1, 1:2, 1:5, and 1:10 are established by using the commercial software ANSYS. Through the numerical simulation of the same-direction laser cutting process, the material temperature field and cross-section temperature gradient are analyzed. The results show that with the increase of fiber arrangement density (tow-to-spot diameter ratio approaching 1:10), the width of the heat-affected zone decreases, but the maximum temperature increases, which means that the temperature gradient increases. Therefore, it is speculated that when a larger laser spot is used (tow-to-spot diameter ratio is much smaller than 1:10), CFRP can be treated as a homogeneous composite. In order to verify the effectiveness of the model, a slit aperture is used to control the tow-to-spot diameter ratio at about 1:7, and a CO2 continuous laser is used for cutting experiments. By fitting the experimental measurements with the width of the carbon fiber ablation area and heat-affected zone in the numerical simulation results, it is found that there is a logarithmic correlation between both the width and the tow-to-spot diameter ratio. There are 3.37% and 1.92% deviations between the experimental result and the theoretical value, respectively. The agreement is relatively good, which can prove the effectiveness of the model. In conclusion, the establishment of a tow-to-spot diameter ratio model reveals the response characteristics of anisotropic materials to energy input and conduction in the process of laser cutting, especially the difference of radial and axial conduction efficiency. The influence mechanism of fiber arrangement mode (mainly density in this work) on temperature field and cutting effect is clarified, which provides important theoretical support and experimental basis for the laser precision cutting method of CFRP materials.

Expansive soils, prone to significant volume changes with moisture fluctuations, challenge engineering infrastructure due to their swelling and shrinking. Traditional stabilization methods, including mechanical and chemical treatments, often have high material and environmental costs. This study explores fibrous by-products of flax processing, a sustainable alternative, for reinforcing expansive clay soil. Derived from the Linum usitatissimum plant, flax fibers offer favorable mechanical properties and environmental benefits. The research evaluates the impact of flax tow (FT) reinforcement on enhancing soil strength and reducing cracking. The results reveal that incorporating up to 0.6% randomly distributed FTs, consisting of technical flax fibers and shives, significantly improves soil properties. The unconfined compressive strength (UCS) increased by 29%, with 0.6% FT content, reaching 525 kPa, compared to unreinforced soil and further flax tow additions, which led to a decrease in UCS. This reduction is attributed to diminished soil–fiber interactions and increased fiber clustering. Additionally, flax tows effectively reduce soil cracking. The crack length density (CLD) decreased by 6% with 0.4% FTs, and higher concentrations led to increased cracking. The crack index factor (CIF) decreased by 71% with 0.4% flax tows but increased with higher FT concentrations. Flax tows enhance soil strength and reduce cracking while maintaining economic and environmental efficiency, offering a viable solution for stabilizing expansive clays in geotechnical applications.