Textile Preforms Research Articles

Free-Forming of Customised NFRP Profiles for Architecture Using Simplified Adaptive and Stay-In-Place Moulds

Design and production technology of natural fibre reinforced polymers not only aims to offer products with a lower environmental impact than conventional glass fibre composites but also caters for designers’ needs for the fabrication of lightweight free-formed architectural components. To combine both characteristics, the forming process itself, once scaled up, needs to be based on efficient material moulding strategies. Based on case studies of adaptive forming techniques derived from the composite industry and concrete casting, two approaches for the mass production of customised NFRP profiles are proposed. Both processes are based on foam from recycled PET, which is used as either a removable mould or a stay-in-place (SIP) core. Once the textile reinforcement is placed on a mould, either by helical winding of natural fibre prepregs or in the form of mass-produced textile preforms, its elastic properties allow for the free-forming of the composite profile before the resin is fully cured. This paper investigates the range of deformations that it is possible to achieve by each method and describes the realisation of a small structural demonstrator, in the form of a stool, through the helical winding of a flax prepreg on a SIP core.

Structure-property relationships of 3D woven fabric composites: A critical review through bibliometric and content analyses

3D fabric composites generally have significant thickness in a monolithic structure eliminating the need for multi-ply laminates. 3D fabric preforms have given significant boost to the composite industry by reducing one of the major failure modes, i.e., delamination. In the past few decades, an enormous amount of researches has been conducted in the domain of 3D woven fabric composites highlighting their structure-property relationships. There are 459 research articles related to 3D fabric composites in Scopus-indexed journals. The objective of this review is to summarise the extant literature, highlighting the current research trends, thematic research areas, structure-property relationships, and future research directions of 3D fabric composites. This review amalgamates bibliometric and content analyses to identify the dominant research themes within the 3D woven composite area. Content analysis of the research papers has revealed that the properties of 3D fabric composites depend on structural parameters such as weave design, binding step, binding depth, and stuffer-to-binder ratio. However, the results of these studies on the role of structural parameters are often divergent, implying that there is a need for more systematic research on the structure-property relationships of 3D fabric composites.

Generalized Background Vector Method for Tailored Three-Dimensional Nonperiodic Woven Composite Designs

In critical aerospace applications such as Ceramic Matrix Composite structures, novel three-dimensional nonperiodic textile composite preforms hold great promise for creating advanced composite structures with strategically aligned fiber tows. However, the inherently challenging nature of determining tow locations, a large-scale combinatorial problem, presents a significant obstacle in textile architecture design. This study generalizes the previously developed Background Vector Method (BVM) to address diverse design requirements and constraints, effectively circumventing combinatorial design complexities via a game theoretic approach. This approach allows for the creation of tunable designs for woven architectures with complex geometries, such as channels and tapering features, through simple control parameter adjustments. The method demonstrates exceptional computational efficiency, making it suitable for large-scale nonperiodic textile structures. Case studies including woven sandwich and airfoil structures highlight the generalized BVM’s versatility and effectiveness in addressing complex design challenges within the aerospace sector.

Tailored directional porosity in ceramic matrix composites (CMCs) for hypersonic applications

AbstractIn the field of hypersonic systems and their missions, the occurring flows impose extreme mechanical and thermal loads on the materials used. At the German Aerospace Center (DLR), extensive research is conducted in this area, ranging from design and specification to the development of suitable materials concluding with the proof of concept under realistic conditions in wind tunnels. In recent years, ceramic matrix composites (CMCs) have been investigated for specific aspects of hypersonics. These materials exhibit consistent mechanical behavior over a wide temperature range (up to 1600 °C), coupled with high damage tolerance and thermal shock resistance, distinguishing them from metals and superalloys. Particularly, special porous C/C–SiC ceramics (carbon-fiber-reinforced carbon with silicon carbide) enable innovative material applications for components in transpiration cooling, fuel injection, or boundary-layer transition control. The work presented focuses on the next generation of porous C/C–SiC ceramics currently in development. By deliberately modifying the textile preform, the resulting microstructure and pore morphology are influenced, allowing for control over both the total volume and the orientation of the pores. Relevant parameters influencing porosity have been determined based on the results, and an initial characterization has been conducted. It has been demonstrated that there is a preferred direction of porosity within the sample thickness (Z-axis), and in terms of hypersonic-relevant properties, an absorption coefficient of 0.58 for an acoustic wave at 500 kHz (static pressure of 15 kPa), as well as a length-specific flow resistance of 3.4 MPa s/m2 and an overall porosity of 12.25% were determined. Building upon these promising initial findings, the goal is to further expand the understanding of the parameters influencing porosity and to generate a tailored material for different application scenarios by correlating them with hypersonic properties.

Design optimization of a three-dimensional hexagonal braiding technique

The three-dimensional hexagonal braiding technique, utilizing an individually controllable horn gear mechanism, enables the automatic generation of a wide range of intricate fabric preforms for structural composites. However, the limited yarn-carrying capacity and the potential risk of collisions between horn gears hinder the development of this type of braiding machine. This study proposes an optimized hexagonal braiding technique to enhance the machinery and control system, aiming to improve the yarn-carrying capacity and prevent collisions. Specifically, the optimization includes modifying the switch device, developing a new algorithm for controlling each horn gear, and designing a control panel to facilitate human–computer interaction. Additionally, simulations of various fabric structures demonstrate improved braiding capability compared to traditional hexagonal braiders. Moreover, a prototype braider is assembled, capable of automatically braiding diverse fabrics using the control system, thereby demonstrating its potential to manufacture complex composite preforms.

A progressive optimization of axial compression performance of 3D angle-interlock tubular woven composites through textile structure and yarn configuration innovations

Lightweight tubular composite materials with excellent compression performance are important structural components for load-bearing or energy absorption. Generally, outstanding performance depends on the structural design. Herein, a progressive structural optimization of 3D angle-interlock tubular woven reinforced composites (3DATWCs) is performed. The structural factors under consideration involve proportion of warp lining yarn, layers of weft yarn, surface constraint yarn and weft density. The axial compression performance and failure process of 3DATWCs with different structures are investigated through experiments and finite element method. The results indicate that increasing proportion of warp lining yarn can significantly improve the axial compression performance of 3DATWC. However, simply increasing proportion of warp lining yarn may decrease the straightness of yarn and constraint on warp yarns, leading to the performance reduction. The problem of performance reduction can be solved by introducing surface constraint yarn or increasing weft density. Finally, an optimization strategy is unveiled. Compared to ordinary structure, the ultimate load, plateau average load, ultimate stress, elastic modulus, total energy absorption and specific energy absorption of optimized 3DATWC increase by 101.88 %, 96.12 %, 77.46 %, 142.55 %, 119.06 %, and 77.39 %, respectively. Additionally, the axial compression performance is seriously affected by the fiber waviness, yarn waviness and interfacial properties, and can be further improved through reducing the waviness during the preparation of fabric preform.

Efficient numerical analysis of in-plane compression-induced defects in thick multi-ply woven textile preforms during double diaphragm forming

To gain adoption in the composites manufacturing sector, forming process models must be assessed for their suitability in analysing representative preform architectures processed in industrial production environments. A computationally efficient, mutually constrained Shell-Membrane (S-M) finite element approach is developed to predict the anisotropic, non-linear deformation of a woven textile preform in a Double Diaphragm Forming (DDF) process. Formability of a thick, multi-ply aerostructures preform is numerically investigated and experimentally correlated using a high-volume, industrial forming process. The effects of fibre orientation, preform thickness, and inter-ply friction on defect formation are investigated. The process model identifies in-plane axial fibre compression as the primary mechanism leading to macroscopic buckling defects and infers the underlying defect morphology. Defect formation is shown to be weakly correlated with the state of the fabric shear strain field. The study concludes that buckling defects are mitigated by reducing tangential contact friction between preform plies.

Numerical and experimental study on anisotropic heat transfer behaviors of quartz fabric composite preforms: Multiple micro‐scale models method

AbstractThis paper presents a comprehensive study on anisotropic heat transmission behaviors in quartz fiber fabrics. Considering the random distribution characteristic of fibers within the yarn, an innovative two‐scale finite element method (tFEM) is introduced, incorporating multiple micro‐scale fiber models (MMFM) based on scanning electron microscope (SEM) observations. MMFM are divided into 8 distinct models to capture intricate fiber arrangements. The macro‐scale fabric model is constructed based on the geometric structure analysis by Micro‐CT technology. Both micro‐ and macro‐scale models are assembled with the air matrix to form the two‐phase composite model. The Hot‐Disk thermal analysis instrument is applied to measure the anisotropic thermal conductivity (ATC). Numerical results from MMFM shows more excellent agreements with the experimental ones at 3D orthogonal directions of fabrics, i.e., the error rates of the thermal conductivity in the warp, weft and thickness directions between numerical and experimental methods are all less than 3%, which indicates the tFEM including MMFM in this paper is more accurate than the tFEM including OSMFM. In addition, the temperature distribution and heat transmission differences due to fiber arrangements are simulated and illustrated through the MMFM. Afterwards, temperature drop and isothermal characteristics are demonstrated in this study.Highlights Effects of fiber arrangements on steady heat transfer behaviors at micro‐scale are illustrated. Isothermal and temperature‐drop characteristics at micro‐ and macro‐scale are simulated and studied. The transverse isotropy of thermal conductivity at micro‐scale and the anisotropy of that at macro‐scale are revealed.

Thermophysical Characterization of Materials for Energy-Efficient Double Diaphragm Preforming

The Double Diaphragm Preforming (DDPF) process uses vacuum pressure and heat to pre-shape dry carbon fabric reinforcements between flexible diaphragms in liquid composite molding (LCM). Accurate modeling of heat transfer within DDPF requires knowledge of the thermophysical properties of the constituent materials under processing conditions. This study investigates the thermal conductivity of silicone diaphragms and carbon fabrics with embedded thermoplastic binder webs, utilizing transient plane source (TPS) and modified transient plane source (MTPS) methods, respectively. Additionally, the specific heat of silicone, carbon fibers (both chopped and powdered), and binder were measured using differential scanning calorimetry (DSC). Mixed samples comprising chopped fibers with 1.8 wt% binder and powdered fibers with 3.6 wt% binder was also analyzed with DSC. This study also examined the influence of reheating cycles on the specific heat of carbon fiber—3.6 wt% binder samples—and the effect of compaction and vacuum on the thermal conductivity of carbon fabrics with an embedded binder. While silicone exhibited linear-specific heat behavior, the thermoplastic binder showed non-linearity due to phase change. The combined carbon fiber-binder samples demonstrated slight non-linear specific heat variations depending on reheating cycles. The thermal conductivity of the fabric preforms decreased with the addition of thermoplastic binder and under vacuum-compaction conditions. The established temperature-dependent specific heat relationships and thermal conductivity provide valuable data for optimizing DDPF preforming parameters and enhancing energy efficiency in composite manufacturing.

A multicriteria approach to quantify contaminant shives in industrial batches of flax fibres

Residual shives have a major impact on the quality and performance of flax textile and composite preforms. Quantifying the content of shives in batches of scutched flax fibres is a time-consuming and operator-dependent process. Although the shive content can be estimated from the chemical composition, our aim here is to explore a series of effective, reliable and complementary approaches to quantifying shives. Various methods are presented: microscopic observations, analytical biochemistry (monosaccharides, lignins), indirect methods (infrared spectroscopy) and dynamic morphological analysis (QICPIC). A reference standard was first analysed and then compared with batches of flax tow fibre of unknown shive content from current industrial production. This approach shows that calibration curves can be established by applying each selected method to batches with known fibre and shive content. In addition, a database was generated to determine the shive content of industrial batches using partial least squares (PLS) regression. Finally, a detailed study of shives in industrial batches is presented, comparing the different analytical methods.

New Approaches to 3D Non-Crimp Fabric Manufacturing

Textile reinforcements have outstanding load-bearing capabilities due to the excellent tensile properties of high performance multifilament yarns (e.g. carbon fibers). However, in order to take full advantage of their high potential, it is necessary to ensure that the filaments run in a straight line. In order to guarantee this straight filament course, the highly efficient multiaxial warp knitting process is used for the production of 2D non-crimp fabrics (NCF) as textile preforms. In various industrial applications, most structures have complex 3D geometries. Therefore, the 2D textile needs to be shaped for reinforcement, which often results in a rearrangement of the filament orientation. Consequently, the 3D shaping process has to be taken into account during the textile production or in the shaping process itself in order to guarantee the highest mechanical properties. Using the example of lattice girders for concrete reinforcement, a new approach for the fabrication of 3D textile lattice girders in a continous shaping process is presented. The results of the production tests of the developed technology approach show no apparent filament damage and exact roving orientation with no inadvertent deflection, compression or bulging, indicating a precise and gentle shaping process. The developed technology contributes to the future reduction of the production costs of 3D textile reinforcements.

Experimental Global Warming Potential-Weighted Specific Stiffness Comparison among Different Natural and Synthetic Fibers in a Composite Component Manufactured by Tailored Fiber Placement.

This work aims to evaluate experimentally different fibers and resins in a topologically optimized composite component. The selected ones are made of carbon, glass, basalt, flax, hemp, and jute fibers. Tailored Fiber Placement (TFP) was used to manufacture the textile preforms, which were infused with two different epoxy resins: a partly biogenic and a fully petro-based one. The main objective is to evaluate and compare the absolute and specific mechanical performance of synthetic and natural fibers within a component framework as a base for improving assessments of sustainable endless-fiber reinforced composite material. Furthermore, manufacturing aspects regarding the different fibers are also considered in this work. In assessing the efficiency of the fiber-matrix systems, both the specific stiffness and the specific stiffness relative to carbon dioxide equivalents (CO2eq.) as measures for the global warming potential (GWP) are taken into account for comparison. The primary findings indicate that basalt and flax fibers outperform carbon fibers notably in terms of specific stiffness weighted by CO2eq.. Additionally, the selection of epoxy resin significantly influences the assessment of sustainable fiber-plastic composites.

Use of a commingling process for innovative flax fibre reinforced unidirectional composites

Optimisation of textile preforms play a crucial role in the development of high-performance biobased composites materials. In this context, the main ambition of this work is to quantify and assess the mechanical properties and behaviour of biocomposite materials made from unidirectional commingled preforms based on flax and poly-(propylene) fibres. To the best of our knowledge, there is no literature examining the effect of the commingling process on the ultrastructure and the mechanical properties of flax fibres. At the scale of the elementary fibre, fibre mechanical properties are observed to be stable after commingling. However, repeated drawing in the commingling process leads to increased cellulose crystallinity and a larger fraction of elementary fibres exhibiting quasi-linear tensile behaviour. The composite materials produced with these commingled flax/poly-(propylene) preforms contain few cortical residues and show a remarkable degree of fibre individualisation. Moreover, they exhibit high Young's modulus and a stress at break of 24 GPa and 194 MPa, respectively, for a fibre volume fraction of 36 %. A substantial drop in properties is however noted at high fibre fractions due increased heterogeneity of the materials. Remarkably, the biocomposites achieved unprecedented transverse modulus and stress at break of 2.3 GPa and 16.5 MPa, respectively. Our results validate the potential and interest in commingling processes for designing a new family of plant fibre composite materials.

LCM of thermoset-based fiber reinforced composites for large-scale applications: are process kinetics and structural properties antagonistic?

This article reviews the main methods to manufacture large-scale composite parts, with a focus on Liquid Composite Molding techniques of thermoset-based fiber reinforced structural parts. As this process relies on the impregnation of a dry textile stack, this manufacturing step is crucial in terms of part production rate, and part quality. To increase the process kinetics, a large effort has been devoted to increase the permeability of the textile preforms, while keeping a similar fiber content. An increase of almost two orders of magnitude can be attained if the textile shows a strong separation of scales between densely packed tows and large intra-two spaces. This however leads to a potential degradation in the resulting structural properties, particularly in dynamic mode due to the presence of the resin rich pockets. Alternative solutions emerge, which may help reach a cost-effective compromise.

Development of Flexible Tooling for Deformation Sensing Applied to Composite Materials Fabrication Process

Among the existing techniques for composite materials manufacturing, Vacuum Assisted Resin Infusion (VARI) is a liquid composite molding (LCM) process where resin flows through a dry fiber preform to fully impregnate it. This method uses flexible film sealed onto a rigid mold to form the infusion cavity containing the fibers. As the fabric preform is impregnated, its thickness varies due to the changes in the applied compaction pressure. This thickness variation affects the resin flow and the final fiber volume fraction of the manufactured part. This study focuses on the initial steps of developing an integrated acquisition system for thickness variation monitoring during VARI. The conventional flexible tooling is to be replaced by a flexible membrane equipped with optical fiber Bragg grating (FBG) sensors. A prototype was developed by embedding FBG sensors in a silicon rubber material and initial measurements of a cylindrical profile curvature were performed. Preliminary results show satisfactory precision of the device, which opens a gap for a more precise and accurate thickness monitoring process during real part manufacturing.

Development of a highly various warp yarn manipulation system for the fabrication of 2D net-shape non-crimp-fabrics for highly material efficient concrete reinforcements

Textile reinforcements have revolutionized many industries, most of all aerospace, automotive and building. Due to its high performance and the significant increased lightweight potential, they have established themselves as an efficient and sustainable alternative to conventional materials. However, in view of the increasing demand of an ever growing population in contrast to a scarcity of resources and urge of material efficiency in the face of climate change, novel technologies for highly material efficient products in large-scale productions are required. In this regard, a major research field involves the multiaxial warp-knitting technique for the production of high performance textile preforms. In several steps, this technology has been further developed to enable the production of application-specific and bionic-inspired textile preforms, which are characterized by a force compliant and multi-material design. Yet the structural possibilities are still limited. This article presents a novel developed warp yarn manipulation system for multiaxial warp-knitting machines. The system enables the fabrication of 2D net-shape non-crimp-fabrics (NCF) made of up to 16 single warp yarns that specify by an alternating diagonally offset and overlapping edge-strand. This structure is suitable for the use as textile lattice girder for reinforcing concrete slab structures Hereby the developed warp yarn manipulation system allows highly various structural parameters of the 2D net-shape NCF for highest material efficiency and product variety. The technological development is discussed in means of the constructive and electronic control design as well as a specific application example for new net-shape reinforcement structures.

Effect of angle interlocking/plain weave compound fabric system on mechanical properties of aramid epoxy resin composites

Preform is one of the important factors affecting the mechanical properties of textile composites. To further reflect the influence of the preform structure on the mechanical properties of composite materials, the angle interlocking and plain weave structures are configured in a certain proportion to form a composite fabric with both structures. The results show that the compound fabric preform has a positive effect on the improvement of the mechanical properties of AERC. An increase in the proportion of angle interlocking organization configuration in the compound fabric system is beneficial to the increase in tensile strength of AERC. In this experiment, when the ratio of angle interlocking structure and plain weave structure in the compound fabric system is 3:1, the tensile strength of AERC increases significantly, which is 80.98% higher than that of AERC with angle interlocking preformed structure. When the preform is made of compound fabric, the bending properties of AERC are greatly improved, and the bending strength is also increased 1.20 times compared to the AERC with angle interlock structure as the preform. When the ratio of angle interlock weave and plain weave in the compound fabric system is 1:3, the bending strength of AERC increases 1.81 times the maximum. The proportion of two fabric structures in the compound fabric system has a significant impact on the impact properties of AERC. The increase in the proportion of plain weave in the compound fabric system is not conducive to the increase in impact strength of AERC, and the large proportion of corner interlock configuration is conducive to the increase in bending strength of AERC. When the ratio of angle interlocking structure to plain weave structure is 2:1, the AERC has the maximum impact strength of 33.14 KJ/m2, which is increased by 26.28%.

Fabrication and high-temperature strength of 2.5D SiO2f /SiO2 composites prepared by a combined vacuum impregnation and sol-gel method

A combined vacuum impregnation and sol-gel method was used to prepare 2.5D SiO2f/SiO2 ceramic composites with good mechanical properties in both warp and weft direction in this study. Phase change and weight gain during forming process of the ceramic composites were measured to explain the forming process. The mechanical properties of materials along different direction at room temperature and high temperature were systematically analyzed, and the fracture mechanism in different service environments was elucidated. Results indicated that dense SiO2f/SiO2 ceramic composites could be prepared by impregnating the 2.5D woven fabric preforms in silica sol and sintering them at 800 °C for > 5 cycles. Flexural strength of the composite was directly affected by the arrangement density and straightening degree of the fibers in warp/weft direction. The composite prepared in this study showed a higher flexural strength (∼91.21 MPa) in the weft direction. With the increase of temperature, the quartz fibers inside the composites became brittle due to crystallization, resulting in the failure mechanism of the ceramic composite material changing from ductile fracture to brittle fracture.

Inferring material properties from FRP processes via sim-to-real learning

Fiber reinforced polymers (FRP) provide favorable properties such as weight-specific strength and stiffness that are central for certain industries, such as aerospace or automotive manufacturing. Liquid composite molding (LCM) is a family of often employed, inexpensive, out-of-autoclave manufacturing techniques. Among them, resin transfer molding (RTM), offers a high degree of automation. Herein, textile preforms are saturated by a fluid polymer matrix in a closed mold.Both impregnation quality and level of fiber volume content are of crucial importance for the final part quality. We propose to simultaneously learn three major textile properties (fiber volume content and permeability in X and Y direction) presented as a three-dimensional map based on a sequence of camera images acquired in flow experiments and compare CNNs, ConvLSTMs, and Transformers. Moreover, we show how simulation-to-real transfer learning can improve a digital twin in FRP manufacturing, compared to simulation-only models and models based on sparse real data. The overall best metrics are: IOU 0.5031 and Accuracy 95.929 %, obtained by pretrained transformer models.

Analysis of the transverse compressive behavior of cotton yarns and fabrics

The inherent complexity of textile preforms and a high degree of consistency in dry fabrics and yarns present a number of modeling challenges, including uncertainty in geometrical characteristics under external loads, non-elastic deformations of fibrous media, and multiple deformation modes at the fiber and yarn scales. The prediction of the compaction reaction for different preforms is still possible thanks to the direct measurements of yarn compaction. The data are checked against compression stress-thickness curves that were produced by compacting yarns and preforms. The yarn and fabric compaction model given in this article demonstrates the final characteristics of woven preforms. The yarn compaction curve exhibits asymptotic hardening with a restricted compaction state attained at high compression stress and as the limit deformations are being approached. The yarn count, yarn fiber volume ratio, and the spinning method all affected the compression modulus. The transverse compression behaviour of yarns and fabrics was studied both analytically and experimentally. Mechanisms of fabric compressibility have been found to be reliant on both fabric and yarn specifications of warp and weft Young’s modulus. Investigations were made into the fabric’s fiber volume fraction under compression stress. When producing composite with low fiber volume fraction preforms, it may be more efficient to use more compression, according to research on the link between compressive stress and fabric volume fraction. The relationship between the compressive stress and fabric volume fraction was investigated, as well as the value of maximum compression stress.