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Spread‐tow woven fabrics (STW) have attracted considerable attention because of their ultrathin structure and low porosity, which benefit the design and application of STW composites. Little is known about how the thickness relationship between the middle and surface layers affect the mechanical properties of sandwich structures. Therefore, this study developed an anti‐sandwich stitched composite with STW in the center and a nonwoven felt/STW hybrid on both sides. The interlayer shear behavior and damage mode transformation of STW composites with different middle‐layer thicknesses were studied using short‐beam shear tests, digital image correlation (DIC) full‐field strain nephograms and micro‐computed tomography (micro‐CT). The results showed that the anti‐sandwich structure improved the shear strength, particularly when the middle layer thickness was four times that of the surface layer. As the middle layer thickness ratio decreased, the synergistic effect of the anti‐sandwich structure was weakened, and the damage mode changed from ductile to brittle. Furthermore, the hybrid ratio of the STW/nonwoven fabric in the surface layer had little effect on the performance because of the good interfacial adhesion between the STW and nonwoven fabric. The anti‐sandwich structure that can improve the properties and stability of STW composites provides a reference for the structural design of STW composites in engineering applications. Highlights: An anti‐sandwich composite was developed by spread tow woven fabrics.Nine types of anti‐sandwich composite were designed and fabricated.The thickness of the middle layer affected the synergistic mechanisms.The optimal anti‐sandwich structure has a 4.59% increase in shear strength.The specific shear strength is 14.86% higher over pure spread tow laminates. [ABSTRACT FROM AUTHOR]

In the manufacturing of fiber‐reinforced composite materials, the preforming stage of dry fiber fabric entails compaction operations carried out under constant pressure, a specific preforming temperature, and in‐plane tension. Throughout this process, permanent deformation and creep/recovery behavior are observed in the fabric, correlating with factors such as time, sustained pressure, temperature, and in‐plane tension. Effective control of fiber volume fraction and material composition necessitates a thorough comprehension of these phenomena as well as the capacity to predict them with accuracy. To solve this, a viscoelastic‐plastic model was put forth, which provides an account of the viscous effects on the fabric during its stages of compression and recovery. The proposed model incorporates changed Burgers units to manage time‐dependent deformations and plastic units to address permanent deformations. Through the application of a single set of parameters, the model precisely and comprehensively characterizes through‐thickness creep/recovery behavior of preformed dry fiber fabrics under varying conditions, including creep stress, temperature, and in‐plane tension. To enhance the practical utility of the model, an application has been developed and validated against experimental data conducted under diverse test conditions. The results demonstrate consistency between experimental curves and model‐predicted curves across various compression scenarios. Highlights: A viscoelastic‐plastic model was proposed with a single parameter set.Stress, temperature, and in‐plane tension all exacerbated creep/recovery.Model captures temp. and time‐related creep/recovery with in‐plane tension.The model has been transformed into a practical application tool. [ABSTRACT FROM AUTHOR]

The compaction of a fabric reinforcement in a Universal Testing Machine (UTM) allows to determine the achievable fiber volume fraction across a wide range of pressures, a valuable information for composite manufacturing. As seen in the first international compressibility benchmark, inaccuracies in the fabric stack thickness measurement, the approach to compliance correction and the non-parallelism between compaction plates resulted in highly inaccurate compression curves. In this paper, the different variability sources affecting indirect thickness methods, based on the machine displacement, and direct methods with laser sensors are presented and its impact on the accuracy is estimated. In conclusion, both thickness measurement methods produced similar results; however, the thickness measured by direct methods experienced more variability due to minor changes in the rig's displacement or the orientations between plates, combined with other sources of variability such as external interferences or vibrations from the compaction plate which led to variations in measurement precision throughout the tests. [ABSTRACT FROM AUTHOR]

Shear thickening fluid (STF), carbon nanotubes (CNTs) are both promising in body protection and anti-impact for the drastic viscosity change of STF and the extremely high tensile strength and elongation of CNTs. The excellent performance of the above two combined with traditional Kevlar fabrics can significantly improve the mechanical properties and reduce the number of layers used for body protection. This work reports a new method to prepare STF/CNTs/Kevlar with excellent tensile properties and anti-impact performance by spraying method with 1 wt% polyvinyl alcohol (PVA) solution as a binder for better integration between CNTs and Kevlar. Surface morphology changes in the preparation process indicate the combined structure of PVA binder, CNTs, and STF, presenting a uniform macroscopic and nonuniform microscopic surface of STF/CNTs/Kevlar composite. The tensile strength and anti-impact properties including punch residual velocity and energy absorbed were studied and results for STF/CNTs/Kevlar composite are 669.8 ± 18.1 MPa, 1.602 ± 0.045 m/s, and 21.683 ± 1.182 J in 12 ms, increased by 46.4%, 23.0%, and 240.2%, respectively, compared with neat Kevlar, owing to the improved tight bonding and friction between fabrics yarns caused by PVA adhesive and tangled CNTs, accompanied with the enhanced viscosity of STF under forces. Highlights • Composites were made by spraying PVA, CNTs, and STF onto Kevlar fabrics; • The tensile strength of the composite was 46.4% higher than Kevlar; • The energy absorbed in 12 ms in anti-impact tests was improved by 240.2%; • Tight bonding and friction between yarns are reasons to improve properties; • The raised viscosity of STF under forces is useful for mechanical properties. [ABSTRACT FROM AUTHOR]

The article presents the results of the study of Novgorod and Pskov birch-bark letters of the second third of the XIII – XV centuries, containing information about fabrics. The research includes an analysis of data on fabric length measures, textile dyeing and bleaching, range of fabrics and value of their certain types. Besides that, a special focus is given to the texts pointing out the local manufacturing of fabrics or their foreign origin. The most important data on fabrics mentioned in the birch-bark letters are compared with the pre-Mongol period. As a result of the analysis, it was found out that textiles common in Rus in the period from the second third of the XIII to the XV century were made of the same raw materials as in pre-Mongol times – wool, silk, flax and hemp; meanwhile the birch-bark letters indicate a variety of fabrics from the same raw material, and that was due to the differences in the quality of textile processing and its dyeing. At the same time information about the use of cotton fabrics appeared in the period under review, though such information was absent in the documents of the previous period. The study of birch-bark letters also showed that Rus fabrics were measured by cubits and by pieces of cloth, textiles were being dyed in different colors, and fabrics made from vegetable raw materials could be bleached. The fact of presence on the market of silk and cotton, which were imported fabrics, confirms the existence of economic relations of Rus with other countries. Besides, birch-bark texts demonstrate that fabrics were involved in internal trade, they could be used for tax payment instead of money, as well as means of paying debts and compensating losses.

Solid resins (SR) are fully reactive resin systems that are solid at room temperature. Up to a critical temperature they can be quasi‐infinitely molten and solidified without any relevant curing reaction. This study deals with novel SR‐based prepregs where a dry textile is covered with a regular SR (uncured) pattern, allowing for storage and draping at room temperature. The manufacturing of SR prepregs with accurate pattern geometries and the processing of the same into laminates with a pore volume content <1% using a vacuum bag only process is demonstrated for four pattern types and two curing cycles. The study furthermore shows that the pattern design has an influence on the mandatory drying phases as well as on fiber undulations. With sufficiently long drying phases, equivalent pore volume contents and interlaminar shear strength could be obtained with different pattern types. Highlights: Manufacturing of carbon fiber (CF) solid epoxy prepregs with patterned resin distributionEpoxy powder processingOut‐of‐Autoclave manufacturing with vacuum‐bag‐only prepregsInterlaminar shear strength of carbon fiber reinforced plastics (CFRP) made of woven CFsAnalysis of pore volume content and fiber undulation [ABSTRACT FROM AUTHOR]

The production of high-performance composite parts with non-crimp fabrics (NCFs) requires a profound understanding of the material’s behavior during draping to prevent forming defects such as wrinkling and gapping. Simulation methods can be used to model the complex material behavior of NCFs and predict their deformation during the draping process. However, NCFs do not intrinsically deform under pure shear like most woven fabrics, but often under superimposed shear, transverse tension and in-plane roving compaction. Therefore, non-standard characterization methods have to be applied besides typical picture frame tests or bias-extension tests. Off-axis-tension tests (OATs) utilize a simple setup to characterize a fabric’s membrane behavior under different ratios of superimposed shear, transverse tension and in-plane compaction. OATs at three different bias angles (30 ∘ , 45 ∘ and 60 ∘ ) are conducted to investigate a unidirectional and a bidirectional NCF. A method is presented to measure the fiber curvatures in addition to the occurring strains. The investigations reveal a relatively symmetrical, shear-dominated behavior with limited roving slippage for the Biax-NCF. The behavior of the UD-NCF strongly depends on the stitching load during tests and is characterized by an asymmetric shear behavior as well as significant roving slippage. The off-axis-tension test results can be used as the basis for the development and validation of new simulation methods to model the complex membrane behavior of NCFs. [ABSTRACT FROM AUTHOR]

The friction between twisted yarns during the process of manufacturing textile reinforcements has been considered an important issue that can strongly influence the mechanical properties of the preform, which deteriorate the mechanical characteristics of fiber-reinforced composites if the friction is excessive. Based on Hertzian contact theory, a novel analytical model has been developed in this research to describe the friction behavior between the twisted yarns in orthogonal and non-orthogonal contact. The realistic contact area was modeled under micro/meso scales taking into account the contact angle between the yarns and the orientation of the fibers influenced by the twist. The efficacy of the developed model was confirmed by the experimental approach. Through the developed model, the yarn/yarn friction behaviors were characterized under different conditions considering the weaving process, such as orthogonal and non-orthogonal contact, same/different twist level, and same/different twist direction, which is essential for optimizing the textile preform forming process and enhancing the mechanical properties of the composites. [ABSTRACT FROM AUTHOR]

Significant fluid–structure interaction is present in fiber metal laminate forming with a low viscous matrix. A modular, process-inspired test setup is presented for one-dimensional saturated and unsaturated infiltration experiments for fiber metal laminates. Permeability measurements for different fabric orientations, fabric layers, and fiber volume contents show low scatter and good repeatability for fiber volume contents up to 65%. Fiber metal laminate specimens were formed by exchanging the mid-segment of the test setup with a punch and die. The stiffness differences between metal and fabric lead to remarkably high compactions in the bending radii, significantly reducing the flow during infiltration. Contrary to resin transfer molding processes, no formation of resin-rich zones along bending edges occurs due to the high normal pressures from metal forming. A numerical forming simulation was developed to predict the local fiber volume content. Comparing the experimental results with the numerical simulation shows that the high fiber volume content in the radii almost exclusively impacts the overall permeability. Implications for fiber metal laminate processing and modeling are outlined. [ABSTRACT FROM AUTHOR]

This paper studies the compressive failure behavior of pw-GFRP (plain-woven glass fiber reinforced polymer) sandwich composite L-joints for ships. Six L-joint specimens were subjected to ultimate compressive tests, which show that damage and stiffness degradation started much earlier than any visible signs. A modified fiber kinking criterion is developed for the compressive failure of pw-GFRP layup structure. Moreover, a hybrid stiffness degradation model is applied to simulate the damage progression. The criterion and the degradation model are implemented in simulation through Abaqus user coding. The simulation results are compared with other existing theories, and the proposed criterion is validated by the similar damage initiation time. The combination of the proposed criterion and hybrid degradation model demonstrates a clear advantage over conventional methods in predicting the compressive damage evolution and ultimate failure behavior of the L-joint structure. [ABSTRACT FROM AUTHOR]

Bamboo-fiber-reinforced polymers have gained popularity in numerous industries because of their mechanical properties, lightweight, and ecological benefits. In this study, to determine the effects of textile structure on the impact resistance performance of bamboo-textile-reinforced polymers (BTRPs), we evaluated three impact modes: simple support beam (SSB), drop weight, and Charpy impact. We then used 3D X-ray scanning to determine the effects of the textile structure and impact modes on the microscopic fracture and crack development. The results indicated that the woven structure allowed for energy transmission in all directions during the drop weight impact test. During the SSB impact test, the large quantity of bamboo tows parallel to the major axis of the specimen increased the absorbed energy. When additional layers were added in the loading direction, the deflection of the entire specimen decreased, thus leading to lower absorbed energy. According to 3D X-ray images and quasi-static bending fracture results, similar fracture patterns appeared on dynamic and static loaded specimens. Consequently, the energy required for internal fracture and the strain energy of deflection are the two significant reasons that enable the excellent impact resistance performance of BTRPs.

In this paper, the effect of intra-yarn fibre hybridisation on the homogenised elastic properties and micro- and meso-scale matrix stress fields in 2D woven composite laminae (i.e. plain, 2/2 basket, 2/2 twill and 5-harness satin) is studied with a two-scale homogenisation scheme—employing a representative volume element model at micro-scale and a repeating unit cell model at meso-scale. The study is focused on S-glass/polypropylene/epoxy woven laminae with intra-yarn fibre hybridisation. A modified random sequential expansion algorithm generates microstructure for the micro-mechanical model, and a periodic meso-structure is used to generate the weave architecture for the meso-mechanical model. Both models are verified using analytical models. It is found that intra-yarn fibre hybridisation can significantly alter the homogenised properties as well as the micro- and meso-scale matrix stress fields—depending on the degree of hybridisation (i.e. the combination of S-glass and PP fibre volume fractions). Moreover, the homogenised lamina properties are found to be less sensitive to weave architecture and yarn thickness, but more so to the degree of intra-yarn fibre hybridisation, yarn width and yarn spacing. It is shown that the lamina properties can be tailored, and the micro- and meso-stress fields can be manipulated, by intra-yarn fibre hybridisation and weave architectures. [ABSTRACT FROM AUTHOR]

Experimental permeability measurements saw a considerable increase in accuracy when recommendations and guidelines were imposed upon the realization of two international benchmarks. Such requirements aid the design stage and experimental validation of a permeameter rig however, systematic errors in the measurements still compromise the comparability of measurements obtained by different radial permeameter rigs. Owing to hurdles and limitations in the data acquisition system, validation of the mold cavity and fluid injection system, optical errors in the visual tracking of a flow front, and uncertainties in the measurement of the fluid viscosity, the measurement’s accuracy is yet lower than the required for a standardized process. In this study, the detailed study and calibration of such parameters was able to identify and minimize error sources that would otherwise result in undetected systematic deviations from the expected results. In conclusion, the verification proposed by the radial benchmark does not guarantee the accuracy of the measurement, as the error in the instruments proposed for the verification is comparable to the requirements themselves. This creates a certain uncertainty in the verification that needs to be tackled with more detailed measurement protocols to ensure not only the compliance with the measurement requirements but also to set the limits of the attainable accuracy. The rig was validated by measuring the permeability of the fabric reinforcements used in the radial benchmark exercise. Due to the scattering in the results reported in the benchmark exercise, 13 out of the 19 reported values were excluded to obtain a good estimation of the expected permeability for each volume fraction. Although the rig complied with all recommendations currently in place, the obtained permeability showed a 20% deviation in the K1 direction, while the K2 was within the expected range for the average value. The observed deviation was later found to be caused by an optical distortion, which affected the measurement of the real-world flow front dimensions. A correction for this deviation needs further systematic investigation, also a possible revision of the future standard since a correction for optical distortions is yet not included in the measurement guidelines.

A novel preforming process was developed for non-crimp fabric (NCF) materials that generated in-plane tension through discontinuous blank boundary conditions. The method employed magnetic clamps and was designed to be both flexible and scalable, with clear routes to industrialisation. The capability of the process was explored in physical trials for a hemispherical and a cubic geometry. Characterisation of a biaxial veiled NCF showed the veil had a dominant effect on the bending mechanics. Subsequently a macroscale finite element model was developed to include an efficient bending idealisation and non-orthogonal in-plane material behaviour. Finally, global process optimisation of the preforming process was demonstrated. The optimisation approach used Gaussian process modelling with a periodic kernel to estimate the wrinkle size for untested clamping arrangements and then deployed Bayesian optimisation to find the optimal configuration. Results indicated that distributed magnetic clamping was effective and amenable to surrogate modelling. [ABSTRACT FROM AUTHOR]

This paper studies the compressive failure behavior of pw-GFRP (plain-woven glass fiber reinforced polymer) sandwich composite L-joints for ships. Six L-joint specimens were subjected to ultimate compressive tests, which show that damage and stiffness degradation started much earlier than any visible signs. A modified fiber kinking criterion is developed for the compressive failure of pw-GFRP layup structure. Moreover, a hybrid stiffness degradation model is applied to simulate the damage progression. The criterion and the degradation model are implemented in simulation through Abaqus user coding. The simulation results are compared with other existing theories, and the proposed criterion is validated by the similar damage initiation time. The combination of the proposed criterion and hybrid degradation model demonstrates a clear advantage over conventional methods in predicting the compressive damage evolution and ultimate failure behavior of the L-joint structure.

The deformation of textile composite reinforcement is influenced by its fibrous composition. In-plane bending behaviour is an inherent aspect of textile reinforcement, yet it is frequently overlooked. The paper elucidates the significant influence of in-plane bending behaviour on fibre orientation during forming process and emphasizes the necessity of accounting for in-plane bending virtual work to prevent non-physical deformation mode. To this purpose in-plane bending calculation is implemented into a fibrous shell finite element by using the neighbouring elements method. Numerical spurious mode involving in-plane shear is avoided due to the new approach. Finally, the model is validated by comparing with composite reinforcement draping experiments: fibre orientations and distributions of shear angles are simulated in good agreement with experiments and give better results than the simulations neglecting the in-plane bending behaviour. [Display omitted] • Neglecting in-plane bending energy in fibrous reinforcements forming simulations often lead to spurious modes. • In-plane bending contribution is highlighted through dedicated patch tests and forming simulations tests. • Enhanced fibrous shell considering the in-plane bending behaviour is proposed. • Forming simulations accounting for in-plane bending energy led to better results. [ABSTRACT FROM AUTHOR]

Impact experiments of thick fabric carbon/epoxy laminate specimens, with small thickness ratio, are conducted at distinct energy levels and thicknesses to characterise the damage process. These specimens and loading conditions are representative of a new generation of critical structural components in aviation, such as wing spars, landing gear beams and fittings, that are increasingly being made entirely from composites. The tests address the need to better understand the damage process for specimens with a small thickness ratio since existing experimental impact data for large thickness ratio (thin laminates) may not be directly applicable. Two energy levels, two different fabric layups and two impact methods (drop-weight and gas-cannon) were used. Data from high-speed cameras were processed in a novel way, providing the force during impact. C-scans and micrographs were used to characterise damage. The results show that specimens with a thickness ratio of 5 (20 mm thick) experience more bending compared to specimens with a ratio 2.5 (40 mm thick). For gas-cannon impacts, this results in a higher delaminated area. The drop-weight impacts show almost no differences in damage size for the thickness range analysed. The influence of layup on the global impact response is negligible, but locally it can result in significant variations in dent depth. The dent depth scales linearly with the impact energy and the delaminated area linearly with the impact velocity. There is no clear correlation between the compression-after-impact failure mechanisms and the residual strength. Impact damage, at the current energy levels, showed a minimal reduction of residual strength. [ABSTRACT FROM AUTHOR]

In this study, four representative finite element (FE) based modelling techniques and an analytical solution for the prediction of 2D woven fabrics’ deformation during forming are compared back-to-back. Ordered from high to low fidelity they are: 1/a Multi-Filament (MF) method that sits between micro- and meso-scale that uses multiple beam element chains to represent each fibre yarn; 2/a meso-scale 3D representation (3D-Shell method) that uses 2D structural shell elements to model each fibre yarn; 3/a 2D continuum element approach that uses coincident membrane and shell elements with user defined material properties to capture the deformation response of textiles in an homogenised sense at the macro-scale; 4/pin-jointed net (PJN) models where the reinforcement directions are represented by extendable 1D elements, pin-jointed at the elements’ crossover points. These modelling approaches are systematically compared for identical forming processes with identical process and material parameters such as boundary conditions, weave architecture and tooling geometries. For completeness and to highlight the importance of considering inter-yarn and preform-to-tool interactions, a kinematic drape algorithm (based on geometrical mapping) is also considered. An attempt is made to visualise the overall modelling performance and computational cost of all representative modelling approaches by simplified metrics.

Current wind turbine rotor blades have a significant impact on the cost of the turbine, which is mainly a consequence of the manual process steps involved in blade production. The manual, labour-intensive production process leads to high tolerances and requires high safety and reliability factors. Especially in the case of offshore turbines with current and upcoming blade dimensions, automation will make the blades cost effective, quicker to produce and guarantees a higher quality. Here, we analyse the current blade structure and production processes and present a technical review of the existing automation approaches for the textile build-up process in industry and academia. Thereby we classify these approaches according to the different techniques based on the rotor blade structure parts.

For the application of composite materials to become more widespread and replace traditional materials their manufacturing processes and final products will need to be competitive and be e.g. lighter, stronger or stiffer and quicker, easier or more cost-efficient to produce than traditional materials. The state of the art for pick-and-place operations for the manufacturing of composite parts focuses on handling single lab-sized layers at undisclosed speeds. The process could however be more competitive by being able to handle more and larger layers in a faster manner than currently presented in research. The aim of the paper is to evaluate the existing pick-and-place strategies on their suitability for the swift automated handling of multiple large-sized layers of reinforcement. The review shows that many of the existing techniques could be suitable for different scenario’s and discusses which factors are to be taken into account when dealing with large layers, more than one layer or rapid handling.

Exposure to prolonged or excessive noise has been shown to cause a range of health problems. In this study, flexible sandwich composites (FSCs) with excellent sound absorption and mechanical properties were designed and fabricated by a one-step foaming process. The compound fabric as composite panel and fabric sequence contacted with PU foam has been designed and optimized for excellent cushioning and sound absorption properties. In comparisons of three processing methods for fabricating compound fabrics as reinforced panels of FSCs, punching/hot pressing was found to be the most effective method. Through experiments, the L (low-melting polyethylene terephthalate nonwoven fabric, LPNF) -W (warp-knitted spacer fabric, WKSF) -F (flexible polyurethane foam, FPF) composites had the best performance, reaching the sound absorption coefficient of 0.997 (1000 Hz), 107.77 KPa in compression modulus, 6541 N in maximum impact contact force and 44.68% in impact energy absorption. Morphological study revealed that the transition region formed by FPF and WKSF played a vital role in the L-W-F structure. In that region, small cavities and complex porous paths were observed that effectively improved the sound absorption and cushioning properties by dissipating the stress wave and sound wave level-to-level. [ABSTRACT FROM AUTHOR]

The reconstruction quality of a three-dimensional (3D) model of woven composites and the mechanical performance of minicomposites have an important influence on the accuracy of finite element (FE) analysis. Through edge detection and morphological operations, the cross-sectional area of a SiC/SiC minicomposite and the volume content of each component were calculated. This method can also be used to obtain the pore distribution. For the SiC/SiC two-dimensional (2D) woven composite, the structure tensor was used to initially classify the weft and warp in the top view of the X-ray computed tomography (XCT) image, and then, the front view was derived to readily correct the misclassification regions. The edge equivalent is proposed because watershed segmentation cannot compute the edge at the overlapping regions. Then, multiple morphological operations were applied to achieve accurate individual warp recognition. Finally, comparing the modulus predicted by the reconstructed FE model with the experimental results, the prediction was found to be in good agreement with the experiment. [ABSTRACT FROM AUTHOR]

Advancing in the process of extending the use of composites for structural parts applications, it is inevitable to work on complex shapes. That is the main reason why understanding the complex forming mechanisms and the factors put into play during the process of composite materials is a major interest for both pre-impregnated forming and dry fabric preforming. Thus, the appearance of defects is a major concern and predicting their appearance for optimal product quality is the priority. A great number of authors showed that defects degrade the overall performance of the composite by creating local heterogeneities. Many factors can initiate these defects. This article is an assembly of the development of the literature on this subject. It is an attempt to provide a description for each defect and a classification order following the scale, the behavior mechanisms, the appearance plan. This will help to converge toward an identification of the defects manifesting during the composite forming. [ABSTRACT FROM AUTHOR]

In this work, a new full-field and non-destructive methodology for measuring process-induced fiber waviness in composites are presented, benchmarked, and successfully applied to predict long fiber-reinforced stiffness composite laminates. The proposed method, named the ''Full Field Nodal Method'' (FFNM), computes the misalignment angle by interpolating the displacement measured on a discrete set of sampling points. Sampling points have been traced on the prepreg surface before curing, and bilinear Lagrangian interpolating functions have been adopted and compared. Several samples, made with compression molded prepreg, have been used to test the new method capabilities in this work. A first benchmark was done measuring the fiber waviness on samples through the new method and by another one recently presented in the literature. Average fiber angles predicted by the FFNM, with bilinear interpolating functions, were in high agreement with experimental results. Fiber angle misalignment measured by FFNM was used to orientate the reference system of elements of the FEA model. Numerical results in terms of stiffness and strain field were compared to those detected by the Digital Image Correlation technique (DIC) during the tensile tests. Comparison of numerical and experimental results showed an excellent prediction of material stiffness and the strain field with an error of 15%.

This study addresses the experimental investigation of the influence of the thread count of carbon fiber (CF) twill textile-reinforced polyamide 66 laminates on their inductive heating behavior. By means of stationary heating experiments of laminates, different twill 2/2 fabrics have been investigated. The used twill 2/2 fabrics differ only in thread count and consequently in their area weight. Due to the different area weight, the manufactured laminates differ in the number of plies to guarantee an equal fiber volume content in each plate. In order to evaluate the heating behavior of the different specimens, the heating rates of both surfaces of the specimens were measured and compared. Thus, it was found that a lower thread count promotes a faster inductive heating of CF twill 2/2-reinforced polymer composites. Further investigations based on microsection analysis and measurements of rovings cross-section shape revealed that the increase of heating rates at lower thread counts relies more on the number of fabric layers. Through a higher number of fabric layers, the total contact area will be higher due to more interply and intraply contact interfaces which occur in the laminate. [ABSTRACT FROM AUTHOR]

Electrical contact conduction between carbon fiber yarns is one of the important current conduction paths inside carbon fiber composites and is easily affected with fabric reinforcement structure and manufacturing process. Here we proposed a micro contact model to predict the contact resistance and to reveal the current conduction behavior between carbon fiber yarns. The model takes into account tunneling effect and yarn geometric structure. The fiber contact probability between yarns was determined based on the statistical characteristic of the fiber height on the yarn surface. The relationship between the yarn contact resistance in plain weave fabric and out-of-plane force was measured and the experimental results agree well with the model. We found that the current conduction between yarns depends on contact conduction between fibers and the contribution of tunneling conduction is negligible. The proposed micro contact model provides insight into the current conduction behavior between carbon fiber yarns and is meaningful for the electrical conductivity design of carbon fiber composites. [Display omitted] • A micro contact model combining tunneling effect was proposed to predict contact resistance between carbon fiber yarns. • Current conduction behavior between carbon fiber yarns was revealed. • The relationship between yarn contact resistance and force was found. • Influences of fiber properties and yarn structural parameters on yarn contact resistance were systematically analyzed. [ABSTRACT FROM AUTHOR]

The automotive and aerospace industries are in continuous struggle towards the development of lightweight components to improve fuel efficiency. Thermoplastic matrix composites offer distinct advantages in terms of weight reduction, recyclability, specific strength, corrosion resistance, cost-efficiency, and design versatility. Natural fibres owing to their biodegradability, abundance in nature, and low cost not only expand the scope of these materials but also curtail the dependency on petroleum-based products. This review presents a comprehensive state of the art in natural fibres properties; mainly plant fibres, and their use as composite reinforcement followed by the textile technologies used to fabricate the engineered architectures. The review also covers the properties of commonly available thermoplastic matrices and the composite fabrication techniques to enable the selection of the precise material and process for any specific product development. Finally, the mechanical properties of natural fibre reinforced thermoplastic composites are reviewed and the key challenges that need to be dealt with are highlighted.

Developing smart fabric materials that can withstand stress, strain, and bending is a key factor to successful integration into smart clothing. The aims of this study were (1) development and characterization of multiwall carbon nanotube (MWCNT)- based electroconductive materials for sensing applications, (2) optimization of experimental fabrication parameters to sensor response, (3) optimization of experimental fabrication parameters for mechanical properties. Nylon-6/MWCNT nanocomposites have enhanced mechanical and electrical properties which make them an ideal candidate for integration into smart clothing. Nylon-6/MWCNT nanocomposites were fabricated by functionalizing an electrospun Nylon-6 scaffold for selective sodium detection. Selective sodium detection is realized using a calixarene functionalization of the MWCNT and the MWCNT is only responsible for increased charge transfer of the nanocomposite. Initially, three factors were considered for optimization of nylon-6/MWCNT nanocomposite fabrication: nanotube type, nanotube concentration, and the weight percent of nylon in the electrospinning solution. The sensing nanocomposite materials were characterized for the electrical and mechanical properties. The sensitivity of the sensor to changing sodium ion concentration (µA/mM) was optimized for 20wt% nylon-6 nanofiber base functionalized in a solution of 0.5 mg/mL of CNT. The optimized sensor has a nanotube length less than 0.2 µm and fiber diameter ranging between 0.25–0.32 µm. The target-controlled coat weight is 20 GSM (g/m2) for electrospun nylon nanofibers. Secondly, the impact of electrospinning conditions, particularly flow rate, on sensor response was considered. Sensor materials produced at an electrospinning flow rate of 1.0 mL/min had an enhanced stress at break, compared to neat nylon-6, without sacrificing elasticity. Additionally, sensors produced at electrospinning flow rates of 1.0 mL/h maintain their sensor response for approximately 20 stretches with no statistical difference between sensor response of the stretched and unstretched sensors.

The manufacturing of large-scale structural components is still dominated by manual labor in many sectors of the modern composite industry. Efforts are being made to establish an automated layup technology for complex structural elements. Processing dry non-crimp fiber fabrics (NCF) offers great cost opportunities and high deposition rates, compared to prepreg-based technologies like automated fiber placement (AFP). Here, the fabric architecture is considered during the draping of the plane textile on curved surfaces. In this paper, the development of a draping unit for balancing fabric tension and consolidating continuously across the layup width is presented. We introduce a geometrical process model to achieve a fabric-friendly draping of the used unidirectional NCF. The shape of the resulting draping front depends on the surface geometry, the shearing of the previously laid-up textile, and the positioning of the material feed. To consolidate the fabric at the altering draping front in an automated layup process, the shape of the continuous consolidation element can be controlled by the elongation of serial soft actuators, manipulated by parallel robot kinematics. The shape replication ability of the draping unit is promising for the implementation of a continuous, fabric-friendly draping process for complex surface geometries. [ABSTRACT FROM AUTHOR]

Different approaches for the simulation of wrinkling during forming of textile reinforcements are presented. It is shown that 3D finite element modeling requires the consideration of an additional bending stiffness of the fibers. In shell-type modeling, the bending stiffness is important because it conditions the size of the wrinkles. Different methods to take into account the bending stiffness independently of the tensile stiffness are presented. The onset and development of wrinkles during forming is a global problem that concerns all deformation modes. It is shown in examples that the shear locking angle is not sufficient to conclude about the development of wrinkles. This article highlights the two points common to the different cases of wrinkling of continuous fiber textile reinforcements: the quasi-inextensibility of the fibers and the possible slippage between the fibers. It presents and compares different approaches to consider these two aspects. The simulation of the simultaneous forming of multilayered textile reinforcements makes it possible to see the influence of the orientation of different plies which is an important factor with regard to wrinkling. [ABSTRACT FROM AUTHOR]

Current wind turbine rotor blades have a significant impact on the cost of the turbine, which is mainly a consequence of the manual process steps involved in blade production. The manual, labour-intensive production process leads to high tolerances and requires high safety and reliability factors. Especially in the case of offshore turbines with current and upcoming blade dimensions, automation will make the blades cost effective, quicker to produce and guarantees a higher quality. Here, we analyse the current blade structure and production processes and present a technical review of the existing automation approaches for the textile build-up process in industry and academia. Thereby we classify these approaches according to the different techniques based on the rotor blade structure parts. [ABSTRACT FROM AUTHOR]

Woven fabric composites with thermoplastic matrices enable superior mechanical properties with low weight for applications in the field of sports, electronics, aviation, and automotive. In this study, the matrix rich areas of glass fabrics which provide an interlaminar free spacing were modified via in situ melt impregnation of Polyamide 6 (PA6) with varying contents of short glass fibers (sGF). The aim is to effectively use the interlaminar free spacing in a fabric to increase stiffness by filling the matrix rich free spacing with short glass fibers of tailored length distribution. It is shown that 2.6 vol% sGF located in the undulations of the fabric are able to increase the tensile modulus in orientation of the short fibers (sF) by 9% and create an even more pronounced anisotropic enhancement of 14% in compression modulus for both 4.1 and 5.7 vol% sGF and 40% in shear modulus for 2.6 vol% sGF. [ABSTRACT FROM AUTHOR]

Fibrous textiles are subjected to dry through-thickness compaction during most of the composites manufacturing processes. Usual tow models implemented in textile numerical simulations do not reproduce the tow widening occurring during the compaction. Nonetheless, this widening (that can reach 10%) would influence the internal microstructure of the considered fabric and its mechanical behavior. This paper proposes a simple mechanical approach to reproduce the width and thickness evolutions experimentally measured during through-thickness compaction of E-glass and carbon tows. Once the material parameters identified on laterally free tows, the tow cross-section model is employed to study the influence of the tow lateral confinement on the transverse mechanical behavior of its corresponding quasi-unidirectional fabric. It is observed that the lateral confinement depends on the quasi-unidirectional stitch tension. This confinement induces a densification of the tows leading to a stiffening of the quasi-unidirectional transverse behavior. This stiffening is well predicted by the proposed modeling approach. [ABSTRACT FROM AUTHOR]

For the application of composite materials to become more widespread and replace traditional materials their manufacturing processes and final products will need to be competitive and be e.g. lighter, stronger or stiffer and quicker, easier or more cost-efficient to produce than traditional materials. The state of the art for pick-and-place operations for the manufacturing of composite parts focuses on handling single lab-sized layers at undisclosed speeds. The process could however be more competitive by being able to handle more and larger layers in a faster manner than currently presented in research. The aim of the paper is to evaluate the existing pick-and-place strategies on their suitability for the swift automated handling of multiple large-sized layers of reinforcement. The review shows that many of the existing techniques could be suitable for different scenario's and discusses which factors are to be taken into account when dealing with large layers, more than one layer or rapid handling. [ABSTRACT FROM AUTHOR]

In this article, a theoretical model of resistive network for woven conductive fabric is proposed to compute the resistance in warp and weft direction respectively. In order to enhance the accuracy of predicting the contact resistance and the length-related resistance, two cross-sectional entities, i.e. racetrack shape and elliptical shape are employed according to the density relationship between warp and weft directions. The comparison between the theoretical predictions of the resistance and the experimental results indicate that the proposed model has better accuracy, with standard deviations of 0.046 Ω in warp direction and 0.0059 Ω in weft direction. A further comparison with previous work has revealed an average improvement around 138.72%. It is believed this work has provided a solid theoretical basis for the precise resistance evaluation on the development of electronic textile based on woven structure. [ABSTRACT FROM AUTHOR]

• The creep in compaction was correlated with the recovery in the relaxation phase. • A unified viscoelastic-plastic model with one set of parameters was proposed. • The creep resistance decreased as the temperature rose for the considered fabrics. • The model could capture temperature- and time-dependent creep and recovery. The preforming process of dry fiber fabric usually involves compaction under constant pressure and specific temperature during fiber-reinforced composite manufacturing. The fabric exhibits time- and temperature-dependent considerable permanent deformation and creep/recovery behavior in compaction. A better understanding of these phenomena, combined with the ability to predict the behavior, will contribute to better control of fiber volume fraction and material composition. This study presented a universal viscoelastic-plastic model to represent the fabric's visco-effect in compression and recovery stages. The proposed model consisted of a modified Burges element for time-dependent deformation and a plastic element for permanent deformation that occurs in all cases. It used only one set of equations and one set of parameters to characterize the cyclic loading/unloading and the compaction and relaxation phases. It could consider the material densification effect observed experimentally. The model was validated against experimental data for unidirectional (UD), plain woven, and twill woven fabrics. A reasonable match between experiments and prediction was achieved under different compression scenarios. [ABSTRACT FROM AUTHOR]

Binder-stabilised preforms are being used increasingly in the production of large composite structures, such as wind turbine blades, to increase the throughput. The transverse shear behaviour of the preform is one of the driving factors in the development of wrinkling during manufacturing but has not previously been characterised in the literature. In this paper, the combined intra- and inter-ply deformations during transverse shearing of a binder-stabilised preforms for wind turbine blade manufacturing are characterised by a new test methodology. The results from two experimental campaigns are presented. In the first campaign, preform specimens are subjected to monotonic loading to a nominal transverse shear angle of 18.0° with three different deformation rates. The results show an increase in maximum load levels with greater deformation rates. In the second campaign, preform specimens are subjected to deformation-controlled cyclic loading with two different deformation amplitudes corresponding to a nominal transverse shear angle of 1.5° and 12.2°, respectively. During cyclic loading, permanent deformation is observed in all preform specimens and the maximum load at the 19th cycle is reduced to 48% of the maximum load at the first cycle for the tests with deformation amplitudes of 12.2°. The data generated in this study is freely available at https://doi.org/10.17632/9m78sg3zwn.1. [ABSTRACT FROM AUTHOR]

The manufacturing of large-scale structural components is still dominated by manual labor in many sectors of the modern composite industry. Efforts are being made to establish an automated layup technology for complex structural elements. Processing dry non-crimp fiber fabrics (NCF) offers great cost opportunities and high deposition rates, compared to prepreg-based technologies like automated fiber placement (AFP). Here, the fabric architecture is considered during the draping of the plane textile on curved surfaces. In this paper, the development of a draping unit for balancing fabric tension and consolidating continuously across the layup width is presented. We introduce a geometrical process model to achieve a fabric-friendly draping of the used unidirectional NCF. The shape of the resulting draping front depends on the surface geometry, the shearing of the previously laid-up textile, and the positioning of the material feed. To consolidate the fabric at the altering draping front in an automated layup process, the shape of the continuous consolidation element can be controlled by the elongation of serial soft actuators, manipulated by parallel robot kinematics. The shape replication ability of the draping unit is promising for the implementation of a continuous, fabric-friendly draping process for complex surface geometries.

Different approaches for the simulation of wrinkling during forming of textile reinforcements are presented. It is shown that 3D finite element modeling requires the consideration of an additional bending stiffness of the fibers. In shell-type modeling, the bending stiffness is important because it conditions the size of the wrinkles. Different methods to take into account the bending stiffness independently of the tensile stiffness are presented. The onset and development of wrinkles during forming is a global problem that concerns all deformation modes. It is shown in examples that the shear locking angle is not sufficient to conclude about the development of wrinkles. This article highlights the two points common to the different cases of wrinkling of continuous fiber textile reinforcements: the quasi-inextensibility of the fibers and the possible slippage between the fibers. It presents and compares different approaches to consider these two aspects. The simulation of the simultaneous forming of multilayered textile reinforcements makes it possible to see the influence of the orientation of different plies which is an important factor with regard to wrinkling.

• Tensile tests were performed on textile reinforced mortar (TRM) coupons. • Diagonal compression tests were performed on TRM strengthened masonry panels. • The role of textile and mortar matrix on TRM and TRM strengthened wall was investigated. • A design criterion of TRM was proposed base on the experimental and analytical results. Composite materials that are constructed of textiles with high mechanical strength and embedded in a mortar matrix (also known as textile reinforced mortars (TRMs)) have received significant attention as they are a promising material for strengthening historical masonry structures because of their superior sustainability and physical compatibility with masonry substrates. In this paper, three types of TRMs, which include steel, carbon and basalt textiles embedded in cement mortar matrices used as shear reinforcement of masonry panels, are experimentally investigated. The experimental component consists of the mechanical characterization of TRMs by testing 16 TRM coupons under tensile loading, and evaluation of their strengthening effect on the shear behaviour of an unreinforced masonry wall by testing 2 unreinforced and 5 strengthened masonry panels under diagonal compression loading. Finally, the contribution of TRM in strengthened panel is evaluated by analytical methodologies and a criterion to design the TRM for strengthening masonry wall is proposed. [ABSTRACT FROM AUTHOR]

This study focuses on the characterization of the in-plane shear response of a novel powder-impregnated, non-consolidated PA66/glass semipreg to evaluate its forming behaviour. The effects of temperature and rate on the behaviour of the semipreg and the preconsolidated material were investigated using bias-extension tests. Results obtained show an increase in shear stress with decreasing temperature and increasing rate, with the semipreg exhibiting a lower sensitivity to the test speed. An increase of the flow distance to impregnate the yarns, due to intra-ply sliding mechanisms specific to the powder-impregnated semipreg, is observed. A model based on a hypoelastic approach with temperature and rate dependence is proposed to represent the material behaviour. Isothermal simulations of the bias-extension test are conducted. Results show a good agreement between the model and experimental data in terms of force and shear angle prediction. [ABSTRACT FROM AUTHOR]

Abstract This paper presents an experimental study carried out on the structural performance of shear-critical reinforced concrete (RC) deep beams internally reinforced with two different stirrups configurations; i.e. aligned and unaligned with the fabric-reinforced cementitious matrix (FRCM) strips. The test matrix involved two unstrengthened (reference) beams and twelve strengthened deep beams tested under three-point bending. Three test variables were investigated: (a) the configuration of the internal transverse reinforcement (ITR), (b) the type of FRCM fabric (carbon, glass, and polyparaphenylene benzobisoxazole, PBO), and (c) the strengthening technique (externally bonded, EB, and near-surface embedded, NSE). Experimental results demonstrated an effective application of the FRCM in improving the load capacities (P max) of deep beams; however, its performance depends on the test variables. The NSE-FRCM provided an inherent anchorage that prevented the premature debonding of the FRCM composite, which was a standard failure mode in the externally bonded FRCM strengthened beams. Finally, a simple strut and tie model (STM) is used to predict the load capacities of the deep beams strengthened with different FRCM systems and resulted in a satisfactory prediction with an average P th /P ex ratio of 1.11 and a standard deviation of 5.7%. [ABSTRACT FROM AUTHOR]

Abstract The manufacturing processes of composite materials modify the internal structure and therefore the mechanical properties of cured composite parts. In particular, draping of woven prepregs leads to angle changes between warp and weft yarns when the geometry of the part is double curved. We here propose to take the fiber reorientation caused by forming into account in the structural analysis of a cured composite. For this purpose, the simulation for the forming of prepregs was based on a rate constitutive equation. Then, a simple orthotropic elastic model of the cured composite was developed to take into account the angle change created by the forming. An experimental validation of this approach was performed in the case of traction on a cured test specimen after a bias extension test. Structural analyses of 3D composite parts obtained by draping also showed that it was necessary to take into account the reorientation of the fibers. [ABSTRACT FROM AUTHOR]

Abstract This paper presents the fundamental mechanical properties that characterise constitutive behaviours of GCCM for large-strain problems in unidirectional tensile and axi-symmetry puncture tests. The 2D nonlinear FEA was conducted to simulate the GCCM behaviour. The optimised stiffness parameters can simulate the elastic behaviour of GCCM. The post-cracking governed by inelasticity of woven geotextile is modelled by bilinear stress-strain relationship. The interface between woven geotextile and cement layer is explained by the existing bond-slip model. The analytical results are presented in terms of load-displacement curves as well as the crack patterns, which are similar to the experimental results. [ABSTRACT FROM AUTHOR]

Abstract The aim of this study is to estimate the mechanical behavior of cured draped fabric structures that have experienced macro and microscopic deformations. The effect of crimp angle variation of tows on compressive properties was considered to evaluate the exact failure behavior of the draped composite structures. Empirical formula for tow modulus degradation was suggested in terms of shear angle (or crimp angle) of the fabric composite. By using the suggested modulus degradation algorithm, the local mechanical properties of the draped fabric hemisphere were predicted, and the corresponding failure mode under compression was successfully estimated. [ABSTRACT FROM AUTHOR]

Abstract The aim of this study is to evaluate the performance of smart grid fabrics (SGF) comprising carbon dry fabric and a number of polyvinylidene fluoride ribbons with piezoelectric characteristics. Smart grid fabrics embedding composite structures can perform real-time structural integrity diagnoses under service conditions. Sensitivity checks of SGF sensors embedded in carbon/epoxy composite laminates under a drop-weight impact loading were performed. Finally, frequency analysis techniques, such as short-time Fourier transform and discrete wavelet transform, were used to correlate the frequency components of the output signals with the corresponding material failure modes of the composite laminate. Based on the results from a series of experimental tests, the feasibility of constructing smart composite structures using SGFs was verified. [ABSTRACT FROM AUTHOR]

Abstract The thermo-mechanical and impact behavior of bio-based polymers reinforced with a multilayer cotton fabric were determined and assessed for the potential use in building, furniture or automotive applications. The measured properties were compared to other composites with similar natural fabric content or to international standard requirements. Flexural properties of PLA composites fully satisfied the requirements for heavy duty load-bearing boards in humid condition (EN 312 standard), while the PHB copolymer composites still satisfied the conditions for load-bearing boards. The HDT evaluation through the dynamic mechanical thermal analysis revealed the great increase (+53 °C) in the temperature for PHB composites that reached 123 °C, potentially extending their application fields to automotive applications. For this focus, the Charpy impact strengths were also investigated. One of the highest values reported in the literature (54.5 kJ/m2) was reached with PHB, superior to what is commercially used for the interior part of the cars. Furthermore, an epoxy functional additive was employed and was found to reduce the void content and increase the flexural properties and the impact strength. [ABSTRACT FROM AUTHOR]

Abstract This paper presents the tensile behavior and the bonding between fabric and matrix of cement-based composites that had been reinforced with carbon fabric coated with hybrid fillers combining epoxy and active micro-silica particles (vs carbon fabric impregnated with epoxy or silica alone). The hybrid coating of the carbon fabric significantly improved the mechanical performance of the composites by virtue of a pozzolanic reaction at the fabric–matrix interface. The ways in which the hybrid fillers were mixed and applied to the fabric were found to impact the tensile behavior of the composites, namely, enhanced strength, ductility and toughness were obtained when the epoxy and silica particles were applied separately (giving epoxy inside the fabric bundles and silica at the bundle periphery), but greater stiffness was obtained when the epoxy and silica were first mixed together and then applied to the fabric (giving an epoxy–silica combination both inside and around the bundles). [ABSTRACT FROM AUTHOR]