High Fiber Volume Fraction Research Articles

Numerical simulation of fiber orientation kinetics and rheology of fiber-filled polymers in uniaxial extension

During processing of fiber composites, the fiber-induced stresses influence the local flow fields, which, in turn, influence the stress distribution and the fiber orientation. Therefore, it is crucial to be able to predict the rheology of fiber-filled polymer composites. In this study, we investigate the fiber orientation kinetics and rheological properties of fiber composites in uniaxial extensional flow by comparing direct numerical finite element simulations to experimental results from our previous study [Egelmeers et al., “In-situ experimental investigation of fiber orientation kinetics during uniaxial extensional flow of polymer composites,” J. Rheol. 68, 171–185 (2023)]. In the simulations, fiber–fiber interactions only occur hydrodynamically and lubrication stresses are fully resolved by using adaptive meshing. We employed a 7-mode and a 5-mode viscoelastic Giesekus material model to describe the behavior of, respectively, a strain hardening low-density polyethylene (LDPE) matrix and a non-strain hardening linear LDPE matrix, and investigated the influence of the Weissenberg number, strain hardening, and fiber volume fraction on the fiber orientation kinetics. We found that none of these parameters influence the fiber orientation kinetics, which agrees with our experimental data. The transient uniaxial extensional viscosity of a fiber-filled polymer suspension is investigated by comparing finite element simulations to a constitutive model proposed by Hinch and Leal [“Time-dependent shear flows of a suspension of particles with weak Brownian rotations,” J. Fluid Mech. 57(4), 753–767 (1973)] and to experimental results obtained in our previous study [Egelmeers et al., “In-situ experimental investigation of fiber orientation kinetics during uniaxial extensional flow of polymer composites,” J. Rheol. 68, 171–185 (2023)]. The simulations describe the experimental data well. Moreover, high agreement is found for the transient viscosity as a function of fiber orientation between the model and the simulations. At high strains for high fiber volume fractions, however, the simulations show additional strain hardening, which we attribute to local changes in microstructure.

Effective mechanisms responsible for increased strength and fracture strain of carbon fiber-reinforced plastic/steel hybrid laminates

The tensile properties of carbon fiber-reinforced plastic (CFRP)/steel laminates have been observed to exceed the expected values predicted by the rule of mixture. While the CFRP/steel laminate is expected to fail at the failure strain of the CFRP lamina, it was observed that hybridization with a steel lamina improves the failure strain. This study investigates numerically and analytically the roles of each influential mechanism responsible for this enhancement, including the thermal residual strain, bridging effect, effect of compressive transverse stress on CFRP layers, and effect of tensile transverse stress on steel layers. To assess these mechanisms, multiple finite-element and analytical models were developed. A mesoscale finite-element model was proposed, which uses novel random fiber distribution algorithm capable of reproducing random fibers with high fiber volume fractions exceeding 65%. Rather than the meso-scale model, macro finite-element models and analytical relationships were developed to assess each hybrid mechanism. Analysis showed 6% increase of the failure strain due to thermal effect and up to 11% increase of strength due to multiaxial stress in steel layer. The results of this study contribute to a deeper understanding of the role of each phenomenon that contributes to improved tensile properties in hybrid CFRP/metal laminates.

The effect of fibre misalignment in an impregnated fibre bundle on stress concentrations

This work investigates the stress redistribution around a broken fibre in a unidirectional impregnated fibre bundle accounting for misalignment of fibres. The study reveals, a statistically significant increase in stress concentration factor (SCF) within misaligned bundles. The effect of fibre misalignment is more pronounced for high fibre volume fraction (VF) and for the nearest neighbour fibres (NNFs) to the broken one. The peak of the SCF graphs shows a significant increase about 16 %, 33 %, and 55 % for VF30 %, VF50 %, and VF60 %, respectively. This implies that the influence of fibre misalignment is more localised, resulting in stronger SCF in the NNFs. Ineffective lengths at applied strain 2 % do not change in the case of fibre misalignment in comparison with the case of aligned fibres. This is linked to matrix yielding, as at applied strain 0.1 % the ineffective length increases for the misaligned case by 12–30 %, depending of fibre volume fraction.

Effect of tapered natural fiber on elastic properties of sisal fiber-reinforced composite: An experimental and micromechanics approach

In the characterization of natural fiber-reinforced composites, it is crucial to consider the nonuniform cross-section of fibers extracted from plants or leaves, which results from the inherent variation in fiber diameter. This variation is a key aspect of the actual reinforcement behavior, and disregarding it by assuming a uniform cross-section can violate the physical understanding of the composite’s mechanics. This study focuses on characterizing the elastic properties of a natural tapered sisal fiber-reinforced epoxy composite, taking into account the variation in fiber diameter along its length. To achieve this, both experimental, analytical, and micromechanics methods are employed. The experimental approach involves conducting tests to measure the mechanical properties of the composite, while the micromechanics analysis provides a framework to understand the reinforcement behavior and predict the composite’s mechanical response. The study aims to identify and present various elastic properties of the composite, including the longitudinal modulus, transverse modulus, in-plane and out-of-plane shear modulus, and major and minor Poisson’s ratios. The fiber taper angle has a significant effect on longitudinal and transverse modulus and interfacial stresses. The longitudinal modulus experiences a reduction of 25.9% when increasing the taper angle from [Formula: see text] to [Formula: see text] at a higher fiber volume fraction (40%). However, at a lower volume fraction of the same fiber (10%), the reduction in modulus is limited to 5.74%. Similarly, the transverse modulus is also affected by the taper angle. At the higher fiber volume fraction, there is a decrease of 24.52%, whereas at the lower volume fraction and higher taper angle of the fiber, the decrement is 4.94%.

Unraveling the effects of preform structures on the microstructure, electromagnetic shielding properties, and thermal conductivity of 3D orthogonal C/C composites

To expand the application of C/C composites in the field of 5G satellite, this paper explores the influence of different preform structures on the mechanical properties, EMI shielding properties, and thermal conductivity of C/C composites. Three common 3D fabric preform structures with different weaving parameters are designed. The pore evolution process of different samples was analyzed by image recognition processing method and pore partition method. The findings indicate that the 3D Fine weave pierced structure leads to higher graphitization degree. 3D orthogonal woven structure results in a higher compression strength of up to 240 MPa. Furthermore, the molding method of 3D orthogonal woven structure exhibits superior EMI SE and thermal conductivity. The EMI shielding mode of C/C composites is the coexistence of absorption and reflection. And excellent texture and a high fiber volume fraction are beneficial to improve thermal conductivity. In conclusion, 3D orthogonal woven structure is more suitable for producing C/C composites with high strength, superior EMI shielding, and enhanced thermal conductivity compared to 3D Fine weave pierced structure. This study reveals a new control method of high-performance materials for 5G satellites.

Micromechanical characterization of Carbon/PEEK thermoplastic composite material in-situ consolidated by automated fiber placement: Stiffness prediction

Despite manufacturing challenges, Automated Fiber Placement (AFP) offers a viable alternative to conventional manufacturing methods, allowing for time and cost savings. Creating a Representative Volume Element (RVE) that realistically represents long-fiber-reinforced composites with high fiber volume fraction is a challenging task in modeling their response. The present research aims to predict effective stiffness properties of in-situ-consolidated Carbon/PEEK thermoplastic composite material by considering the effect of fiber volume fraction, void content, degree of crystallinity, and interlaminar resin pocket resulting from AFP in-situ consolidation manufacturing process. In this regard, two sets of samples were manufactured by AFP in-situ consolidation and autoclave re-consolidation methods. Both of them were evaluated by micrographic study and thermoanalytical Differential Scanning Calorimetry (DSC) technique to obtain inputs required for micromechanical analysis. The 2D RVEs on a micro-scale are developed to predict the transverse elastic modulus, out-of-plane Poisson's ratio and out-of-plane shear modulus of the composite material by applying Periodic Boundary Conditions (PBCs) and using Asymptotic Homogenization Theory (AHT). Results show that AFP in-situ consolidation may lead the transverse elastic and out-of-plane shear moduli of Carbon/PEEK thermoplastic composite material to be reduced by about 10 % and 20 %, respectively, compared to autoclave re-consolidation whereas the out-of-plane Poisson's ratio remains unchanged. The findings of the present work confirm that the mechanical performance of Carbon/PEEK thermoplastic composite material could be remarkably influenced by AFP in-situ consolidation manufacturing process, particularly in the transverse direction, which must be taken into account in finite element modeling, analyses, and design of AFP-manufactured composite laminates and structures.

Properties of High-Content Micro-Steel Fiber Self-Compacting Concrete Incorporating Fly Ash and Slag Powder Performance Study

The addition or substitution of various gel materials in cement-based composites has been proven to be an effective approach in enhancing the performance of concrete. Current research focuses mainly on enhancing the toughness of concrete, but lacks discussion on the performance of alternative gel materials. Therefore, this study aims to explore the effects of partially substituting cement with fly ash and slag powder as gel materials, while incorporating a high volume fraction of micro-steel fibers (6%), on the workability and mechanical properties of self-compacting concrete. By means of rigorous experimental investigation and meticulous analysis, we comprehensively assessed the workability characteristics of self-compacting concrete, encompassing critical aspects such as filling ability, cohesion, and permeability. Additionally, we conducted an extensive evaluation of the mechanical attributes of self-compacting concrete, encompassing vital parameters, such as compressive strength, axial compressive strength, splitting tensile strength, and flexural strength. Last but not least, through a holistic integration of workability and mechanical properties, we conducted a comprehensive performance evaluation of self-compacting concrete incorporating a synergistic blend of fly ash, slag powder, and micro steel fibers. The experimental results indicate that the composite addition of fly ash and slag powder in self-compacting concrete, while compatible with up to 6% micro-steel fibers, leads to a decrease in concrete workability and an increase in cohesiveness due to the addition of micro-steel fibers. Moreover, fly ash predominantly influences the tensile properties of concrete, while the addition of slag powder significantly affects the compressive and flexural properties of concrete. Additionally, the addition of micro-steel fibers significantly improves the overall mechanical properties of concrete.

3D flow and fibre orientation modelling of compression moulding of A-SMC: simulations and experimental validation in squeeze flow

Sheet Moulding Compound (SMC) based composites have a large potential in industrial contexts due to the possibility of achieving comparatively short manufacturing times. It is however necessary to be able to numerically predict both mechanical properties as well as manufacturability of parts.In this paper a fully 3D, semi-empirical model based on fluid mechanics for the compression moulding of SMC is described and discussed, in which the fibres and the resin are modelled as a single, inseparable fluid with a viscosity that depends on volume fraction of fibres, shear strain rate and temperature. This model is applied to an advanced carbon-fibre SMC with a high fibre volume fraction (35%). Simulations are run on a model of a squeeze test rig, allowing comparison to experimental results from such a rig. The flow data generated by this model is then used as input for an Advani-Tucker type of model for the evolution of the fibre orientation during the pressing process. Numerical results are also obtained from the software 3DTimon. The resulting fibre orientation distributions are then compared to experimental results that are obtained from microscopy. The experimental measurement of the orientation tensors is performed using the Method of Ellipses. A new, automated, accurate and fast method for the ellipse fitting is developed using machine learning. For the studied case, comparison between the experimental results and numerical methods indicate that 3D Timon better captures the random orientation at the outer edges of the circular disc, while 3D CFD show larger agreement in terms of the out-of-plane component. One of the advantages of the new image technique is that less work is required to obtain microscope images with a quality good enough for the analysis.

Characterization of the void content and laminate quality of fiber‐reinforced plastic composites manufactured using the resin spray and compaction method

AbstractVoid fraction and fiber volume fraction (FVF) are among the most important parameters determining the quality of fiber‐reinforced plastic products. Most of the voids in liquid composite molding–manufactured composites are directly related to the viscous matrix (resin) flow through the porous medium (fiber) during impregnation. In this investigation, a different method, resin spray rather than injection was used to reduce the resin's flow path, which resulted in low void content and higher FVF. The resin was sprayed on the surface of the preform, and compaction was applied to infiltrate the resin towards the thickness. Sample laminates were manufactured, and computer tomography scanning was applied to diagnose void content and laminae quality. The images collected from the scanner were analyzed using ImageJ software. Effects of compaction pressure and compaction speed were characterized. According to the investigation, compaction speed was the key factor in determining a laminate's void content. Only 1.5% void fraction was integrated with a compaction speed of 1 mm/min and a compaction pressure of 100 KPa. On the other hand, compaction speed has less of an impact on a laminate's FVF.Highlights The void fraction of a composite is reduced via the spray and compaction method. Fiber volume fraction is not much affected by compaction speed. Slow compaction speeds minimize void content. Spray compaction is a low‐cost manufacturing method.

Pultrusion of thermoplastic composites with mechanical properties comparable to industrial thermoset profiles

Pultruded thermoplastic composite profiles offer several advantages over their conventional thermoset counterparts, such as high impact toughness, recyclability, and smaller environmental footprint. However, thermoset profiles outperform thermoplastic composite profiles in terms of mechanical properties through high fiber volume fraction. The study is aimed at producing thermoplastic profiles with high content of reinforcing fibers, using preconsolidated tapes manufactured in-house from glass fiber/polypropylene commingled yarns with fiber content of 80 % by weight. The tapes were manufactured with the use of extrusion machine at speeds of 2, 5, and 8 m/min under the same temperature conditions. The strip profiles of 75 mm × 3.5 mm with fiber volume fraction of 50 % were produced of 76 tapes by thermoplastic pultrusion process at the pulling speed of 0.2 m/min. The results of mechanical tests show that flexural strength and modulus of obtained thermoplastic profiles exceed minimal requirements to industrial thermoset profiles, constituting at least 488 MPa and 37 GPa respectively. Thermoplastic profile pultrusion from tapes made of commingled yarns does not require the use of a preheating chamber, produces profiles with 1 % porosity, and more energy efficient pultrusion process than pultrusion from commingled yarns.

Optimizing the thermal properties of fiber reinforced phthalonitrile composites

AbstractThe development of lightweight composites with desirable thermo‐mechanical properties is progressively increasing. Phthalonitrile (PN) based composites have shown great potential in this regard. However, the basic thermal properties of PN composites required for engineering design are not yet fully understood. In this work, we investigated the thermal stability, thermal expansion behavior and thermal conductivity of PN composites reinforced with carbon fiber (CF) and high silicon fiberglass (HSF) via combined experimental studies and numerical simulations. The results indicated that CF/PN performs better in thermostability than HSF/PN at temperatures below 500°C. Moreover, the incorporation of CF and HSF lowered the coefficient of thermal expansion (CTE) and thermal insulation of PN. At room temperature, the in‐plane CTE of CF/PN and HSF/PN were 1.97E‐6 and 9.24E‐6°C−1, respectively, while the out‐plane thermal conductivities of CF/PN and HSF/PN were 0.65 and 0.34 W/(m K). It is worth noting that an excessively high fiber volume fraction would lead to poor thermal insulation and lightweight properties of the PN composites, while a low fiber volume fraction would result in poor stiffness and thermal dimensional stability. Determined via TOPSIS model, a fiber volume fraction range of 50%–60% was ideal for both composites with comprehensive optimal properties, respectively.

Degradation of Kapok Fiber-Reinforced Polyester Composites with Calcium Carbonate Filler in Seawater

This research investigates the development of polyester composites reinforced with kapok fiber and CaCO3 filler to reduce environmental impact. Natural fibers, valued for their lightweight, fire resistance, cost-effectiveness, and biodegradability, are commonly used in composites. However, synthetic fibers, despite their superior mechanical properties, raise environmental concerns. The study focuses on the composites' performance, stability, and endurance in harsh conditions. Kapok fibers were manually extracted, and CaCO3 powder was sieved to 80 mesh. Composite samples were created with varying volume fractions of CaCO3 powder and kapok fibers, using polyester as the matrix. Tensile and bending tests, according to ASTM D3039 and ASTM D790 standards, were conducted on these samples. Additionally, water absorption was assessed gravimetrically, and mechanical strength degradation was studied via immersion in artificial seawater at different temperatures. Results indicated that water absorption increased with higher fiber volume fractions in the composite, primarily due to the water-absorbing capabilities of natural fibers and CaCO3 particles, surpassing that of polyester resin. Increased immersion temperatures accelerated water diffusion, impacting interactions between water molecules, polymer chains, and natural fibers. Furthermore, an increase in the CaCO3 filler volume fraction negatively affected the mechanical strength of kapok polyester-fiber composites. This was attributed to the agglomeration of CaCO3 powder, disrupting the polyester resin's viscosity and damaging the bond between kapok fiber and the matrix. The composites exhibited their highest tensile strength with 10% CaCO3 filler before immersion, but this strength decreased following exposure to high temperatures.

Investigating the lap shear adhesion of coir and glass-fibre reinforced epoxy bonding to mild steel with varying volume fractions

Bonding synthetic fibres to metals to improve strength, durability, and corrosion resistance is a prevalent practise in the automotive, marine, and aerospace industries. Lap shear adhesion, a measurement of the bonding strength between composites and metallic substrates, is essential for structural integrity. The emergence of natural fibre composites as sustainable alternatives to synthetic composites makes it essential to investigate their lap shear behaviour and the effect of fibre volume fraction on composite properties. This research investigates the adhesion behaviour of coir and glass fibre epoxy composites to mild steel. Coir fibres, which are known for their resilience and tenacity, were treated with an alkaline solution to improve their adhesion to the resin. Samples of lap shear adhesion were prepared in accordance with ASTM specifications, and tests were conducted using a tensile machine. Increasing the volume fraction of coir or glass fibres decreased the bond strength, as demonstrated by the results. Due to the fibres’ greater tensile strength and rigidity, glass fibre composites exhibited superior strength. However, under tensile loading conditions, coir fibres exhibited superior adhesion to mild steel surfaces. SEM micrographs confirmed that coir composites exhibit shear failure while glass composites exhibit fibre pull-out behaviour. This study concludes by highlighting the engineering potential of coir fibres, considering their natural properties and cost-effectiveness. It is necessary to further optimise the fiber-matrix interface and comprehend the mechanical behaviour of coir composites in order to maximise their effectiveness. To assure the long-term durability of composite-metal joints, surface preparation, adhesive type, application procedure, and environmental conditions must also be considered. At a content percentage of 10%, glass fibres exhibited 100% higher shear strength compared to coir fibres in epoxy composites. Conversely, coir fibres at 10% content demonstrated approximately 75% greater shear strength than the values obtained with 40% glass fibres. The failure mechanisms observed are delamination or fibre fracture in the bonding area under tensile and shear loading. Increasing the fibre volume fraction reduces bond strength. Factors such as limited space for the matrix, tension concentrations, and the mechanical properties of the fibres contribute to weakened bonds. Glass fibres have better strength and rigidity than coir fibres, affecting load transfer and adhesion. Interfacial bonding is crucial, and maintaining it becomes more difficult with higher fibre volume fractions, resulting in weakened bonds.

Torsional performance of FRP bars reinforced seawater sea-sand engineered cementitious composites (SS-ECC) beams without stirrup: A numerical study

To alleviate the shortage of raw materials and tackle the challenge of steel corrosion, the authors used seawater and sea-sand to fabricate engineered cementitious composites (SS-ECC) beams and reinforced them only with fiber reinforced plastic (FRP) longitudinal bars. This article focused on the torsional behaviors of the SS-ECC beams through experimental and numerical studies. Finite element models (FEM) were established and well verified based on the torsional tests. The failure mechanism of the SS-ECC beams under pure torsion was carefully explored by analyzing the stress and strain distribution of SS-ECC at different positions. It is indicated that the SS-ECC beams with high fiber volume fraction tend to fail due to compressive damage. Furthermore, a parametric analysis was conducted to study the effects of various factors on the torsional performance. The strength grade of SS-ECC, rather than longitudinal reinforcement ratio and height/width ratio, makes the critical factor that determines the ultimate torque of the SS-ECC beams. This research lays the groundwork for understanding the torsional performance of the SS-ECC beams without stirrup.

Measuring the Mechanical Properties of Glass Fiber Reinforcement Polymer Composite Laminates Obtained by Different Fabrication Processes.

The traditional wet hand lay-up process (WL) has been widely applied in the manufacturing of fiber composite laminates. However, due insufficiency in the forming pressure, the mass fraction of fiber is reduced and lots of air bubbles are trapped inside, resulting in low-quality laminates (low stiffness and strength). The wet hand lay-up/vacuum bag (WLVB) process for the fabrication of composite laminates is based on the traditional wet hand lay-up process, using a vacuum bag to remove air bubbles and provide pressure, and then carrying out the heating and curing process. Compared with the traditional hand lay-up process, laminates manufactured by the WLVB process show superior mechanical properties, including better strength and stiffness, higher fiber volume fraction, and lower void volume fraction, which are all benefits for composite laminates. This process is completely manual, and it is greatly influenced by the skills of the preparation personnel. Therefore, the products are prone to defects such as voids and uneven thickness, leading to unstable qualities and mechanical properties of the laminate. Hence, it is necessary to finely describe the WLVB process, finely control steps, and quantify material ratios, in order to ensure the mechanical properties of laminates. This paper describes the meticulous process of the WLVB process for preparing woven plain patterned glass fiber reinforcement composite laminates (GFRPs). The fiber volume content of laminates was calculated using the formula method, and the calculated results showed that the fiber volume content of WL laminates was 42.04%, while that of WLVB laminates was 57.82%, increasing by 15.78%. The mechanical properties of the laminates were characterized using tensile and impact tests. The experimental results revealed that with the WLVB process, the strength and modulus of the laminates were enhanced by 17.4% and 16.35%, respectively, and the specific absorbed energy was increased by 19.48%.

A new method for generating the random fiber arrangement of representative volume element for unidirectional fiber reinforced composites

This study presents a new method to generate random fiber arrangements in a representative volume element model, which remains applicable at high fiber volume fractions. First of all, the fibers are arranged regularly to ensure accurate fiber volume fraction. Afterwards, disturbances are applied to all fibers to generate random arrangements. The image recognition technique and statistical analysis are used to quantitatively evaluate the randomness of the disturbed fiber arrangement. Eventually, the high efficiency of the method is verified by analyzing the consumption time of modeling, and its validity is also confirmed by comparing the calculated results with the tested results.

An asymptotic homogenization model for evaluating the mechanical properties of random fiber reinforced composites with high volume fraction

In this study, we propose an asymptotic homogenization strategy based on local-global RVEs to predict the elastic properties of random fiber reinforced composites (RFCs) with high fiber volume fraction (HFVF). During the calculation, RFCs were divided into a set of local pseudo units with various material properties determined by its spatial orientation of the short fibers. The macroscopic mechanical properties of the RFCs with HFVF were asymptotically determined by integrating transformation matrices, periodic boundary conditions, and numerical homogenization method. The results show that the proposed models were in good agreement with the experimental tests of short fiber reinforced magnesium matrix (Cfs/Mg) composites. When the length ratio of the RVE to the local pseudo L/Ls was >10, the overall orientation of the fibers tended to be completely random, and the results gradually converged. With an increase in the fiber volume fraction, the effective elastic properties of the Cfs/Mg composites grew linearly. Additionally, the proposed asymptotic homogenization framework can also be extended to evaluate other macroscopic physical properties of RFCs such as thermal and electric conductivities.

Design and fabrication of high-performance 3D printed continuous flax fibre/PLA composites

The mechanical properties of 3D-printed continuous plant fibre-reinforced poly(lactic) acid (PLA) composites are insufficient due to the low fibre volume fraction (∼30 %). Further increase of fibre volume fraction of composites by reducing the line width may result in a composite with low fibre impregnation degree or the clogging of printer nozzle because of the twisted nature and uneven diameter of plant yarns, which also degrades the mechanical properties. This study proposed a method to obtain 3D printed continuous flax fibre reinforced composites (CFFRCs) with a high fibre volume fraction and excellent mechanical performance by statistical analysis of the dimensions of flax fibre yarns as well as surface modification. The CFFRCs were printed by a fibre prepreg-based 3D printing method, and an in-situ impregnation method was also used to prepare CFFRCs for comparison. The results showed that the CFFRCs by the fibre prepreg method had a fibre volume fraction of 44.1 % and a void content of ∼1.9 % due to the high impregnation degree. Correspondingly, the tensile modulus and strength of the CFFRCs were the highest among the existing reported values of the composites made by 3D printing and even greater than those of the CFFRCs with a fibre volume fraction of ∼51.4 % prepared by the in-situ impregnation method.

Bulk Tungsten Fiber-Reinforced Tungsten (Wf/W) Composites Using Yarn-Based Textile Preforms

The use of tungsten fiber-reinforced tungsten composites (Wf/W) has been demonstrated to significantly enhance the mechanical properties of tungsten (W) by incorporating W-fibers into the W-matrix. However, prior research has been restricted by the usage of single fiber-based textile fabrics, consisting of 150 µm warp and 50 µm weft filaments, with limited homogeneity, reproducibility, and mechanical properties in bulk structures due to the rigidity of the 150 µm W-fibers. To overcome this limitation, two novel textile preforms were developed utilizing radial braided W-yarns with 7 core and 16 sleeve filaments (R.B. 16 + 7), with a diameter of 25 µm each, as the warp material. In this study, bulk composites of two different fabric types were produced via a layer-by-layer CVD process, utilizing single 50 µm filaments (type 1) and R.B. 16 + 7 yarns (type 2) as weft materials. The produced composites were sectioned into KLST-type specimens based on DIN EN ISO 179-1:2000 using electrical discharge machining (EDM) and subjected to three-point bending tests. Both composites demonstrated enhanced mechanical properties with pseudo-ductile behavior at room temperature and withstood over 10,000 load cycles between 50–90% of their respective maximum load without sample fracture in three-point cyclic loading tests. Furthermore, a novel approach to predict the fatigue behavior of the material under cyclic loading was developed based on the high reproducibility of the composites produced, especially for the composite based on type 1. This approach provides a new benchmark for upscaling endeavors and may enable a better prediction of the service life of the produced components made of Wf/W in the future. In comparison, the composite based on fabric type 1 demonstrated superior results in manufacturing performance and mechanical properties. With a high relative average density (>97%), a high fiber volume fraction (14–17%), and a very homogeneous fiber distribution in the CVD-W matrix, type 1 shows a promising option to be further tested in high heat flux tests and to be potentially used as an alternative to currently used materials for the most stressed components of nuclear fusion reactors or other potential application fields such as concentrated solar power (CSP), aircraft turbines, the steel industry, quantum computing, or welding tools. Type 2 composites have a higher layer spacing compared to type 1, resulting in gaps within the matrix and less homogeneous material properties. While type 2 composites have demonstrated a notable enhancement over 150 µm fiber-based composites, they are not viable for industrial scale-up unlike type 1 composites.

Method of Manufacturing Structural, Optically Transparent Glass Fiber-Reinforced Polymers (tGFRP) Using Infusion Techniques with Epoxy Resin Systems and E-Glass Fabrics.

Recently, fiber-reinforced, epoxy-based, optically transparent composites were successfully produced using resin transfer molding (RTM) techniques. Generally, the production of structural, optically transparent composites is challenging since it requires the combination of a very smooth mold surface with a sufficient control of resin flow that leads to no visible voids. Furthermore, it requires a minimum deviation of the refractive indices (RIs) of the matrix polymer and the reinforcement fibers. Here, a new mold design is described and three plates of optically transparent glass fiber-reinforced polymers (tGFRP) with reproducible properties as well as high fiber volume fractions were produced using the RTM process and in situ polymerization of an epoxy resin system enclosing E-glass fiber textiles. Their mechanical (flexural), microstructural (fiber volume fraction, surface roughness, etc.), thermal (DSC, TGA, etc.), and optical (dispersion curves of glass fibers and polymer as well as transmission over visible spectra curves of the tGFRP at varying tempering states) properties were evaluated. The research showed improved surface quality and good transmission data for samples manufactured by a new Optical-RTM setup compared to a standard RTM mold. The maximum transmission was reported to be ≈74%. In addition, no detectable voids were found in these samples. Furthermore, a flexural modulus of 23.49 ± 0.64 GPa was achieved for the Optical-RTM samples having a fiber volume fraction of ≈42%.