Composite Preforms Research Articles

Directionally Oriented Reinforcements of Warp-Knitted Fabrics for Composite Preforms

This paper focuses on the development of a methodology for the directional structural modification of warp-knitted fabrics by sewing on carbon fiber tapes. Four-, five-, and six-axial geometric systems were designed to optimize the qualitative distribution of stresses on the surface of the tested product. Through a numerical experiment in the ANSYS environment, the impact of the change in the axiality of a textile structure on the mechanical properties of the modeled geometric configuration was assessed. This analysis was experimentally verified by measuring the multiaxial force distribution on the knitted surface, which demonstrated that Variant 7, with six axes 30° apart, was the most favorable.

Large deformation of variable thickness woven composite preforms considering interlayer difference. Application: Forming simulation of a blade preform

The main objective of this work was to investigate the interlayer difference of 3D orthogonal woven fabrics (3DOWFs) during deformation. Tensile, shear, and compression tests were performed on two types of 3DOWFs with different layer numbers. To determine the variations in the deformation behavior within the fabric, a layer decomposition method was developed. This process involved the decomposition of the fabric into two layers, the inner layer and the outer layer, depending on the difference in structural features of the yarn. Then the deformation characteristics of the inner layer and outer layer were derived based on their series or parallel relationship in the load path. The results indicate that there are noticeable variations in the deformation characteristics among the layers of 3DOWF, which are associated with the interwoven structure of the yarns. In particular, in compression deformation, the difference in yarn structure causes the initial stage (Compressive strain <0.2) of fabric compression deformation to be mostly attributed to the compression of the outer layer. Subsequently, the deformations of the inner layer and outer layer gradually tend to balance. Based on a simple anisotropic hyperelasticity model, the interlayer differences were considered in the blade preform simulation. The simulation result shows a good agreement with the preforming results. The results show that the interlayer difference has a significant impact on the deformation of the blade preform, particularly in the posterior edge region, which is not strongly compressed.

Improved densification of SiCf/SiC composites by microwave-assisted chemical vapor infiltration process based on multifrequency solid-state sources excitation

This paper addresses the possibility of improving and controlling the temperature profile of a Ceramic Matrix Composite preform in a multiport Microwave-assisted Chemical Vapor Infiltration (MW-CVI) pilot-scale plant, based on a multifrequency excitation of the reactor by three solid-state sources. The choice of the most suited excitation frequencies is guided by rigorous numerical modeling of the reactor loaded by the sample, solving the coupled electromagnetic and thermal problems in a self-consistent way. The resulting infiltration front and residual porosity have been evaluated by a pseudo1D model, along the sample thickness, according to the previously computed heating pattern. The practical implementation and validation of the proposed technique are illustrated with MW-CVI trials on 10×10×0.3 cm3 SiCf/(SiC/BN)3/SiC preforms manufactured by Filament Winding method. The obtained results confirm the inside-out densification pattern, expected from the sample volumetric heating, along with an extension of the densification region by a factor of 2–3.

A hyperelastic model considering the coupling of shear-compression for the forming simulation of 3D orthogonal composite preforms

The shear-compression coupling phenomenon is vital in the forming process of complex 3D woven composite components, but has not been effectively considered in existing macroscopic material models. A hyperelastic material model considering shear-compression coupling is developed here. Firstly, in-plane shear tests on pre-compressed specimens and compression tests on pre-sheared specimens were carried out, respectively. The results show that pre-compression can hinder and promote the in-plane shear deformation before and after shear locking occurs in the fabric, respectively. In-plane shear can contribute to compression. Then, a nonlinear hyperelastic constitutive model is presented and implemented in an Abaqus/Explicit user subroutine. Finally, a simulation study of the hemispherical forming of 3D orthogonal woven fabric was conducted using this model. The simulation results considering shear-compression coupling show more accurate in-plane shear angles and edge shapes compared to those without considering coupling. Moreover, since the shear-compression coupling is considered, the friction between the fabric and the tool needs to be reasonably discussed in the moulding simulation.

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.

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.

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.

An experimental study on filling of gaps and void pockets during vacuum-bag-only consolidation of fiber placed preforms

Gaps and void pockets are inevitably present in tailored thermoplastic composite preforms manufactured via automated fiber placement (AFP). Filling these gaps and voids can be challenging during the consolidation due to the high viscosity of thermoplastic composites, especially in the case of vacuum-bag-only (VBO) consolidation, where the applied pressure is limited. Therefore, the current work investigates whether one bar pressure is sufficient to fill the gaps and voids during VBO consolidation. For this purpose, two experiments are performed. First, a hot plate setup is built and used to capture the real-time gap-filling behavior during the VBO consolidation. Second, VBO consolidation of tailored preforms is performed to study the filling of ply-drop induced void pockets. Here, the tailored preform consists of plies of different orientations dropped at different locations to verify if one bar pressure available during the VBO process is sufficient to fill the void pockets. The results from both experiments answered the main question that one bar pressure is sufficient for filling the gaps and void pockets for the given material systems, and further, it was confirmed that the transverse squeeze flow was dominant in filling gaps. However, in the case of fillings of ply-drop induced void pockets, the orientation of the dropped ply and covering plies majorly dictated the filling behavior.

Preparation and characterization of high load‐bearing needled composite preform based on novel ordered short fiber network needling method

AbstractNeedled preform and its composite using felt and base cloth stacked needled have small fiber volume fraction and relatively weak mechanical properties, which are difficult to meet the service requirements of structural and functional integrated components of high‐speed aircraft. Responding to this issue, this paper proposed a new method for preparing high load‐bearing needled composite preform based on ordered short fiber network needling. The high load‐bearing needled preforms were prepared by designing different structural parameters of ordered short fiber network and forming process parameters, and then preform structure was characterized and mechanical properties were tested. The results showed that using ordered short fiber network as carrier of the short fibers, the formed needled fiber bundles were longer and denser, volume content of needled fiber bundles and mechanical properties of needled preform were greatly improved, and needled fiber bundles volume content of ordered short fiber network reinforced needled preform was 1.5 times and 46.3 times that of half‐cut cloth and felt respectively. Compared with traditional felt needled preform and half‐cut cloth needled preform, the interlaminar peeling strength of the ordered short fiber network reinforced needled preform increased by up to 246.4% and 49.2%, respectively. The tensile strength of ordered short fiber network reinforced needled preform was 12.9% higher than that of half‐cut cloth in X‐axis direction. In addition, the effects of ordered short fiber network structure, short fiber length, areal density and needling density on the needled preform structure and properties were also revealed.Highlights High load‐bearing needled composite preform was prepared based on novel ordered short fiber network needling method. The needled fiber bundles formed by using ordered short fiber network were longer and denser, and their volume content was 46.3 times that of felt needled preform. The interlaminar peeling strength of the ordered short fiber network reinforced needled preform increased by up to 246.4%. The tensile strength of ordered short fiber network reinforced needled preform was 12.9% greater than half‐cut cloth in the X‐axis direction.

Experimental study on mechanical responses of 3D needle‐punched composite preforms at different needling densities: Failure structures, tensile and interlayer peeling strengths

AbstractIn this study, needle‐punched quartz fiber felt / fabrics preforms (NQFFPs) with a wide needling densities (NDs) range from 70 to 280 punches/cm2 were manufactured, then the inner correlation among the NDs, mechanical properties and structural failure modes were studied and revealed. Firstly, the effects of NDs on mechanical strengths, which included tensile and interlayer peeling strengths of NQFFPs, were analyzed through experimental methods. Moreover, MATLAB software was applied to fit the NDs‐mechanical strength curves, then best fitting equations were defined to characterize the change rules between NDs and mechanical strengths. Additionally, with NDs increment, tensile strengths decreased from 0.727 to 0.0925 MPa, whereas interlayer peeling strengths increased from 83.46 to 135.04 N/m. Afterwards, the 3D image technology was utilized to capture failure morphologies of NQFFPs at different NDs from tensile and interlayer peeling experiments, which furtherly revealed the failure mechanisms of NQFFPs at different NDs. This work is significant for the engineering manufacturing and application of needle‐punched preforms and the composites.Highlights Failure structure characteristics of NQFFPs at different NDs were captured. Change rules between NDs and strengths were characterized by math equations. The correlation among NDs, fracture morphologies and strengths was revealed.

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.

Prediction of the in-plane permeability and air evacuation time of fiber-placed thermoplastic composite preforms with engineered intertape channels

The two main void removal mechanisms during vacuum-bag-only (VBO) consolidation of thermoplastic composites are through-thickness diffusion and in-plane air evacuation. The automated fiber placement (AFP) process allows for the creation of preforms with an engineered intertape channel network by deliberately introducing spacing between the tapes that can facilitate air evacuation during the VBO consolidation. However, it is unclear what dimensions of the intertape channels allow for effective in-plane air evacuation. The current research presents a predictive simulation tool to optimize the intertape channel dimensions for effective in-plane air evacuation. An analytical method is developed to calculate the in-plane permeability tensors of the composite preform with uniform intertape channel dimensions. In addition, a more elaborate mesoscale method is developed that estimates the in-plane permeability tensor of the engineered intertape channel network based on the distributions in intertape channel dimensions. Finally, a finite difference model is implemented to calculate the time required for air evacuation as a function of the in-plane permeability tensors of the preform and its in-plane dimensions. The results from the models indicated that in-plane air evacuation through the engineered intertape channel network is quick, and it takes only a few minutes to evacuate 99% of the air from large preforms like fuselage panels.

Predicting the topology of braided structures in arbitrarily composite preforms based on yarn interactions

The performance of braided fiber-reinforced composites is determined by the braided structure, so yarn spatial arrangement prediction is a crucial step in the manufacturing process of fiber-reinforced composites. This study aims to predict fabric on arbitrary mandrels based on the yarn interactions, especially for mandrels with flat surfaces. An interaction yarn deposition model is proposed to simulate the process of braiding arbitrary-shaped mandrels. A dynamic deposition model is established at the moment of deposition, and a quasi-static equilibrium equation is added to determine the spatial position of yarn interaction points. Post-processing of positional information is performed to obtain the yarn spatial arrangement on the mandrel’s surface. Experiments were conducted using Zhongfu Shenying 12K T700 carbon yarn and Yunlu Composite 176-carrier radial braiding equipment. The experimental results show that the actual fabric exhibits an S-shaped distribution on the flat surface of the mandrel, matching the predicted results of the model.

Horngear and carrier design for braiding tailorable composite preforms

Braids can be found in structural composite parts used in the car and the aerospace industries. The architecture of the braid has a direct impact on its mechanical properties. However, traditional braiding machines are limited to a single braid architecture. Few braiding machines, so called “3D braiding machines”, have been developed to enable variable carrier’s paths. This allows fabrication of several braid architectures using the same machine. These machines use a switching mechanism, which complexifies the machine and the braiding process. A new type of braiding machine was introduced in Assi et al. [1], which uses a “chain and sprocket” mechanism, allowing variable carrier’s paths without any switching mechanism. Nevertheless, the original chain and sprocket braiding machine cannot be used for vertical braiding. When placed in the vertical position, the carrier jam between the horngears due to the force of gravity. This limitation does not allow braiding over a mandrel or coupling the braiding machine with a pultrusion line. This paper presents design guidelines for enabling vertical braiding for the chain and sprocket braiding machine. A new carrier design is proposed as well as a new horngear design. Additionally, the carrier is fitted with a guiding foot and a track is machined into the braider’s bedplate. A functional prototype has been developed to validate the design. The design complexity has been assessed and compared to existing braiding machines. The design proposed in this paper remains 30% less complex compared to other vertical braiding machines enabling variable carrier’s paths.

The Method of Ply Generating in Composite Laminate in Fibersim

In Fibersim the digital design of the composite preforms laying process begins with the creation of laminates, which define the required preforms and its plies. The digital design of ply-based laying process, zone-based laying process, multi-ply-based laying process, and the methods of multi-ply and zone-based laying process are elaborated.

Optimization control of guide bar array deformation in flexible‐oriented 3D woven process

AbstractThe flexible‐oriented 3D woven process (FO3DWP) enables the production of high‐performance 3D composite preforms. However, the deformation of the Guide Bar Array (GBA) during the weaving process poses a major challenge and hinders the further advancement of FO3DWP. This study aimed to address this challenge by developing an optimization control method for automatic GBA correction during the manufacturing of 3D orthogonal preforms. The deformation state was predicted using a theoretical model and a control path was designed to reverse the GBA deformation. The height and fiber tension of the control paths were calculated using the particle swarm optimization (PSO) algorithm. A series of 3D woven experiments were conducted to evaluate the effectiveness of the proposed method. The results showed good agreement between the experimental and theoretical deformation eigenvalues (with a difference of less than 15%), and the control path significantly reduced the deformation eigenvalues. This method holds great potential for aerospace applications as it enables high‐quality production through automatic GBA correction by the weaving mechanism.Highlights A control path was designed to automatically correct the deformed GBA. The height and the fiber tension of the control path were calculated using the PSO algorithm. The experimental eigenvalues in the y‐direction were significantly reduced by the optimization control method.

Friction and damage of carbon fiber in tow-metal friction during the formation of flexible-oriented three-dimensional composite preforms

As the main structure of fiber-reinforced composite, the preform affected the mechanical properties of the composite. The forming of preforms is associated with the damage of fiber due to tow-metal friction, which can compromise the properties of the composite component. This study simulated the frictional behavior of carbon fibers during flexible-oriented three-dimensional woven process to reveal the mechanism of damage and determine the process window, and the effects of processing-related parameters on friction and carbon fiber were discussed. The normal load and pre-tension played a dominant role in generation of hairiness and wear, while the weaving speed had a minimal effect. The different parameters affected the damage of tow by changing the contact area between filament and metal. According to the results, the process window of pre-tension on filament was set to [0.083 mN, 0.183 mN]. The normal load should be within the window of pre-tension, as normal load was determined by pre-tension. The process window of weaving speed was set to [1 Hz, 5 Hz]. The optimized process parameters could improve the tensile strength of woven carbon fiber by 25.7%.

Geometrical modeling and experimental validation of 3D woven honeycomb fabric for lightweight aircrew helmet liner manufacturing

This research focused on the development of a honeycomb fabric by predicting the areal density suitable for aircrew helmet liner. The aim was to fulfill the requirements for the lightweight and mechanical properties of composite liner. The model was based on the structural characteristics of the preform, including the weave design and geometric parameters. The predicted areal density, based on varying yarn linear density and the number of picks in the free and bonded wall, was compared to experimental results and showed good agreement. A geometric model was derived to predict the areal density of 3D woven honeycomb preforms for producing the composite liner of aircrew helmet. The model was validated using experimental data from a variety of 3D woven honeycomb preforms, showing that it accurately predicts the areal density and can be used as a tool to design 3D woven honeycomb preforms for advanced composites.

A compact yet flexible design space for large-scale nonperiodic 3D woven composites based on a weighted game for generating candidate tow architectures

Three-dimensional non-periodic woven composite preforms have sufficient design flexibility that tows can be aligned along principal loading paths even in shaped structural components with detailed local features. While this promises competitive performance, the feasible design space is combinatorially large, far beyond exhaustive search. Seeking a design space that is compact and easily searched yet can span the full potential of 3D weaving, we propose a method for generating candidate designs called the Background Vector Method (BVM) which treats weaving tows as agents in a game competing to match background vectors derived from different design requirements. The BVM generates candidate designs that adapt local architecture to global design goals by adjusting scalar weights. A manufacturing-based parameterization assures fabricability. The scope of possible designs and the speed of the BVM are illustrated by re-creating common periodic 3D weaving patterns and novel complex non-periodic architectures, with a route demonstrated to forming cavities, ducts, and other open volumes. How the BVM might be incorporated within an optimization algorithm is outlined and pathways are shown for systematically enlarging the design space as individual design problems may require.

Numerical analysis of composite preform structure based on flat cross-linked braiding

Composite materials are widely used in aerospace, automotive industry and medical equipment, where most of the structural parts are made of fiber laminates. Rotary braiding is one of the most important methods to prepare composite preforms. The ordinary rotary braided preforms have low porosity and dense yarns, but are single-layer structures after molding, which do not meet the needs of most applications. To solve the problem that traditional laminates are prone to delamination, this paper designs a flat cross-linked braiding process for the preparation of multilayer-interlocking composite panels. The carrier trajectory is analyzed, and the spatial coordinate system of the braided chassis is established by combining the effect of the end traction system on the morphology of the preform yarns. The numerical model of the preform is initially obtained by using cubic B-spline curve fitting, and an algorithm for gathering yarns towards the fabric center is proposed to optimize the numerical model. Experimental samples of flat cross-linked preforms are prepared according to the braiding process, and the reliability of the optimization algorithm is verified by comparing the yarn coordinates of the experimental samples with those of the optimized numerical model.