Carbon Fiber Preforms Research Articles

Continuous mapping of large surfaces with a quality inspection robot

This paper addresses the problem of mapping large surfaces with a moving sensor. In particular, it proposes image registration and mapping algorithms that enable to use in continuous motion sensors that need multiple shots to perform a measurement. These methods exploit the knowledge of the shape of the part to inspect in a both efficient and accurate fashion, thus allowing to obtain a measurement quality comparable to that of static measurements, while guaranteeing fast sensor motion and thus short scanning times. This work describes the application of these methods for the mapping of carbon fibre parts with an inspection robot equipped with a sensor estimating 3D carbon fibre orientation from multiple 2D images captured with different illumination. Experiments on carbon fibre preforms of complex 3D shape demonstrates that this system accurately reconstructs in real-time the 3D fibre orientations of the outer layer of carbon fibre parts. Accuracy assessments report small errors within the tolerances allowed by the automotive industry on flat and generic 3D surfaces. The inspection robot system presented in this paper has been demonstrated both as an in-line quality inspection robot for production of carbon fibre preforms and as a measurement device for improving the draping process in the prototyping of carbon fibre parts.

Ablation behaviour of Cf–ZrC-SiC with and without rare earth metal oxide dopants

Continuous carbon fibre/carbon composites are candidates for ultra-high temperature applications due to their ability to retain their strength at elevated temperatures, however they easily oxidize and ablate in high temperature oxygen-based environments, a fact that seriously limits their applications in the aerospace industry. The introduction of ultra-high temperature ceramics (UHTCs) as a matrix in carbon fibre preforms effectively improves their oxyablation resistance at ultra-high temperatures in air atmospheres. In the present study, zirconium carbide-based ultra-high temperature ceramic matrix composites (UHTCMCs) simultaneously doped with silicon carbide and rare earth (RE) metal oxides were prepared by a slurry impregnation and pyrolysis method using phenolic resin as the bonding agent. The combination of injection and vacuum impregnation achieved a maximum density of up to 60% of theoretical. These composites were subsequently evaluated in terms of their ablation properties using an oxyacetylene (OAT) torch at temperatures of ∼2500 °C for 60 s. No significant surface damage was observed on any of the ablated samples. When ceria was used as the RE metal oxide dopant, the evidence suggests that cerium silicate was formed by the ceria dissolving in the molten silica; though this didn't appear to offer very much additional oxyablative protection. In contrast, when yttria was used, it improved the performance via stabilization of the cubic zirconia that formed on oxidation; this provided the greatest protection of all the samples tested. The combination of both ceria and yttria yielded the combined mechanism.

Fabrication of carbon fibre preform with water-glass binder and infiltration of aluminium alloy melt by squeeze casting

ABSTRACT For reducing the forming cost of the PAN-based carbon fibre preforms, a water glass binder was used as a substitute for conventional silica binder. The preforms were infiltrated with an aluminium alloy melt by squeeze casting to fabricate the fibre-reinforced composites. The microstructure and properties of the composites were compared to the composites using the silica binder. In the composites, the water glass binder mainly remained in the vicinity of the fibre–aluminium interface and partially distributed in the matrix. The reaction near the interface between the alloy melt and binder was not recognised. The thermal expansion coefficient, thermal conductivity and the compressive strength of the composites using the water glass binder were approximately equivalent to those of the composite using the silica binder. Based on these results, the water glass can be used as an alternative binder to the silica sol.

Computation of the Permeability Tensor of Non-Periodic Anisotropic Porous Media from 3D Images

The direct proportionality between the flow rate and the pressure gradient of creeping flows was experimentally discovered by H. Darcy in the 19th century and theoretically justified a couple of decades ago using upscaling methods such as volume averaging or homogenization. X-ray computed micro-tomography (CMT) and pore-scale numerical simulations are increasingly used to estimate the permeability of porous media. However, the most general case of non-periodic anisotropic porous media still needs to be completely numerically defined. Pore-scale numerical methods can be split into two families. The first family is based on a direct resolution of the flow solving the Navier–Stokes equations under the assumption of creeping flow. The second one relies on the resolution of an indirect problem—such as the closure problem derived from the volume averaging theory. They are known to provide the same results in the case of periodic isotropic media or when dealing with representative element volumes. To address the most general case of non-periodic anisotropic porous media, we have identified four possible numerical approaches for the first family and two for the second. We have compared and analyzed them on three-dimensional generated geometries of increasing complexity, based on sphere and cylinder arrangements. Only one, belonging to the first family, has been proved to remain rigorously correct in the most general case. This has been successfully applied to a high-resolution 3D CMT of Carcarb, a carbon fiber preform used in the thermal protection systems of space vehicles. The study concludes with a detailed analysis of the flow behavior (streamlines and vorticity). A quantitative technique based on a vorticity criterion to determine the characteristic length of the material is proposed. Once the characterized length is known, the critical Reynolds number can be estimated and the physical limit of the creeping regime identified.

Fabrication and mechanical property of three-dimensional carbon fiber reinforced Mg-based bulk metallic glass matrix composite

Carbon fiber (CF) reinforced bulk metallic glass matrix composites (BMGMCs) have received widespread attention due to their light weight, but subsequent development is facing urgent challenges of uncontrollable interface reaction and poor plasticity. Here, we report a three-dimensional CF-reinforced Mg-based BMGMC, which significantly improves the microstructure and compressive plasticity by adjusting the pressure infiltration parameters. It has been found that the electroless copper plating improves the wettability of the CF and the melt without inducing the crystallization of the matrix, in spite of the partially dissolving and diffusing of the coating to the matrix. Under a similar infiltration pressure difference, high vacuum conditions are beneficial to reduce the capillary resistance of the porous CF preform, thereby improving the formability of BMGMC. Compression test results prove that the introduction of three-dimensional CF effectively improves the plasticity of the composite material and reduces its brittleness tendency. It can be attributed to the fact that the carbon fibers distributed in different directions effectively bridge the multi-directional cracks and prevent the early rapid shear band propagation. The present work provides meaningful enlightenment for the development of CF-reinforced BMGMC materials.

Structural properties of the fiber –matrix interface in carbon-fiber/carbon-matrix composites and interfaces between carbon layers and planar substrates

Abstract The structure of the fiber –matrix interface region of carbon-fiber/carbon-matrix (C/C)-composites, which is important for the mechanical properties of a composite, was studied by transmission electron microscopy. The pyrolytic carbon matrix was obtained by chemical vapor infiltration of carbon fiber preforms with different fiber architecture and fiber types. While the texture of the carbon matrix can be controlled by the infiltration conditions, the carbon texture at the fiber –matrix interface differs from the bulk matrix and cannot be determined by the infiltration parameters. We often observe a high-textured layer with a thickness up to 100 nm at the interface prior to the formation of the bulk matrix with a lower texture. The fiber –matrix interface properties of C/C-composites are compared with the interface of pyrolytic carbon layers deposited on planar Si-, BN- and cordierite-substrates. In contrast to BN-substrates, thin high-textured pyrolytic layers are observed at the interface of carbon on planar Si- and cordierite-substrates where strong bonding between pyrolytic carbon and the substrate is achieved by the formation of Si-C bonds. Stress-induced ordering is discussed as a mechanism for the formation of the high-textured interface layers.

Gas–surface interactions in lightweight fibrous carbon materials

We investigate reactive and non-reactive scattering of hyperthermal beam of gas particles within highly porous carbon-fiber preform using particle-based numerical simulations. High-resolution X-ray tomography images of the microstructure is used to resolve its complex fiber network. The gas–surface interaction is studied at material temperatures up to 2000 K, typical of hypersonic aero-thermal environments. We extended a detailed surface chemistry model for oxidation of vitreous carbon to carbon-fiber materials. The model agrees well with experiments and predicts increasing oxidation product flux with larger porosities. Higher porosities lead to a larger fraction of thermalized argon atoms and greater mole fraction of CO for the oxygen beam due to greater penetration of the beam into the microstructure. It is found that a 6% porosity increase results in higher mole fractions of CO and lower amounts of O, with differences of around 10% of the total product flux. Furthermore, we construct an effective oxidation model with porosity-dependent rates that inherently accounts for the characteristics of the material microstructure and its varying porosity. Comparison of full microstructure simulation results and the effective model applied to a flat surface showed excellent agreement, thus suggesting that the model can be used directly in computational fluid dynamics codes.

Thermal Qualification of the UHTCMCs Produced Using RF-CVI Technique with VMK Facility at DLR

Ultra high-temperature ceramic matrix composites (UHTCMCs) based on carbon fibre (Cf) have been shown to offer excellent temperature stability exceeding 2000 °C in highly corrosive environments, which are prime requirements for various aerospace applications. In C3Harme, a recent European Union-funded Horizon 2020 project, an experimental campaign has been carried out to assess and screen a range of UHTCMC materials for near-zero ablation rocket nozzle and thermal protection systems. Samples with ZrB2-impregnated pyrolytic carbon matrices and 2.5D woven continuous carbon fibre preforms, produced by slurry impregnation and radio frequency aided chemical vapour infiltration (RF-CVI), were tested using the vertical free jet facility at DLR, Cologne using solid propellants. When compared to standard CVI, RFCVI accelerates pyrolytic carbon densification, resulting in a much shorter manufacturing time. The samples survived the initial thermal shock and subsequent surface temperatures of >2000 °C with a minimal ablation rate. Post-test characterisation revealed a correlation between surface temperature and an accelerated catalytic activity, which lead to an understanding of the crucial role of preserving the bulk of the sample.

Effect of preparation method on the mechanism for oxidation of C/C-BN composites

C/C-BN composites and C f /BN/PyC composites exhibiting different structures for pyrolytic carbon (PyC) and boron nitride (BN) were studied comparatively to determine their oxidation behavior. This study used five types of samples. Porous C/C composites were modified with silane coupling agents (APS) and then fully impregnated in water-based slurry of hexagonal boron nitride (h-BN); the resulting C/C-BN preforms were densified by depositing PyC by chemical vapor infiltration (CVI), resulting in three types of C/C-BN composites. The other two C f /BN/PyC composites were obtained by depositing a BN interphase and PyC in carbon fiber preforms by CVI; one was treated with heat, and the other was not. This study was focused on determining how the PyC deposition mechanism, morphology and pore structure were affected by the method of BN introduction. In the 600–900 °C temperature range, the C f /BN/PyC composites and C/C composites underwent oxidation via a mixed diffusion/reaction mode. The C/C-BN composites had a different pore structure due to the formation of nodules comprising h-BN particles; both interfacial debonding and cracking were reduced, resulting in higher resistance to gas diffusion, lower oxidation rate and larger activation energy (Ea) in the temperature range 600–800 °C. In addition, the mechanism for oxidation of C/C-BN composites gradually exhibited diffusion control at 800–900 °C because the formation of h-BN oxidation products healed the defects. The oxidation mechanism was more dependent on pore structure than on BN structure or content.

Design and manufacture of automotive components in thermoplastic composite (Part II)

The thermoplastic RTM process (T-RTM) is currently one of the most demanded process for R&D in the automotive sector. This sector tries to lighten the weight of the vehicle with highly resistant non-metallic components and with efficient manufacturing in cycle-time and cost. In the framework of the BIHARKONP project, EDERTEK-TECNALIA proposes the migration of a suspension arm, currently manufactured by means of metal stamping, to high mechanical requirements composite materials, obtaining a weight reduction of 30%. For the manufacture of this component it was proposed to redesign the component in carbon fiber (CF) and polyamide 6 matrix (APA6). The redesign (Part I) consisted in a mechanical calculation of the loads that the component had to support. The geometry has been changed with the aim of fulfilling the part specification and the peculiarities of the T-RTM process. For the manufacture of the component, a CF/APA6 composite laminate was defined and characterized and a specific CF for thermoplastics was selected. Subsequently, a T-RTM mold was designed and manufactured with inserts for fiber compaction and eight thermal control zones. The geometry of the control arm involves the manufacture of CF preforms by means of a thermal forming process with thermoplastic veils. Caprocast technology has been used to manufacture the prototype by caprolactam injection and its polymerization inside the heated mold. The prototype was subjected to bearing test, bushing insertion-extraction test and bushing strength test. The component was validated.

Implementation of a viscoelastic material model to predict the compaction response of dry carbon fiber preforms

Determining the compaction behavior of fibrous material is essential for fiber reinforced composites manufacturing processes. The compression state directly influences both fiber volume content and tooling forces in closed mold processes. In this work, we present a viscoelastic material model which describes the compaction stress response. In its incremental formulation, the model is implemented into a finite element code, which makes it possible to calculate the thickness of force-controlled setups. We derived model parameters from compaction experiments with woven and non-crimp fabric carbon fiber preforms. The predicted compaction stress for both materials was in good agreement with the experimental data. Moreover, the model is capable of predicting creep and spring back behavior for force-controlled experiments. We proved that the developed model can be used to eliminate peak stresses during compaction and is also capable of predicting the time-dependent thickness response by means of a single set of formulas.

Epitaxial Grown Carbon Nanotubes Reinforced Pyrocarbon Matrix in C/C Composites with Improved Mechanical Properties.

In order to achieve the highly efficient preparation of high-performance carbon/carbon (C/C) composites, epitaxial grown carbon nanotubes (CNTs) and a pyrocarbon matrix were simultaneously synthesized to fabricate CNT-reinforced C/C composites (CC/C composites). With precise control of the temperature gradient, CNTs and the pyrocarbon matrix could grow synchronously within a 2D needle-punched carbon fiber preform. Surprisingly, the CNTs remained intact within the pyrocarbon matrix at the nano-level, and the CNT-reinforced nano-pyrocarbon matrix was compact, with virtually no gaps and pores, which were tightly connected with the carbon fibers without cracks. Based on the results of Raman analysis, there is less residual stress in the CNT-reinforced pyrocarbon matrix and carbon fibers, and less of a mismatch between the coefficient and thermal expansion. Additionally, CC/C composites fabricated by this method could achieve a low density, open porosity with a large size, and improved mechanical properties. More importantly, our work provides a rational design strategy for the highly efficient preparation and structural design of high-performance CNT-einforced C/C composites.

Investigation of penetration forces during tufting of stacked carbon-fibre preforms

This study investigates the penetration forces during tufting of stacked dry carbon non-crimp fabrics (NCF). The stacked material with a thickness between 20 to 60 mm is made of several quadriaxial [0°/+45°/90°/-45°] NCF layers that are tufted at frequencies up to 2.3 Hz. Furthermore, the effects of the preforming process, the frequency of tufting and the thickness of specimen on the needle penetration force are investigated. Lastly, digital image correlation (DIC) is applied to study the displacement of the fabric during the unthreaded tufting of material. Future work will involve the integration of the experimental results into the simulation of the tufting process.

Reactive and inelastic scattering dynamics of hyperthermal O and O2 from a carbon fiber network

Pulsed beams containing O and O2 with incident velocities of ∼7900 m s−1 were directed at a carbon fiber preform network (FiberForm) at temperatures in the range, 1023–1823 K, and the products that scattered from the network were detected with a rotatable mass spectrometer as a function of their velocities and scattering angles. A beam containing pure Ar atoms was also directed at the network, allowing multiple-bounce effects in the absence of reaction to be characterized. Scattered O, O2, and Ar exhibited the dynamical characteristics of impulsive (non-thermal) scattering and thermal desorption (TD). On the other hand, CO and CO2 exhibited only TD dynamics. The fluxes of all products were quantified as a function of sample temperature and, for two focus temperatures, as a function of scattering angle. CO was the dominant reactive product. A temperature dependent hysteresis in the CO flux was quantified, and a comparison was made between the hysteresis on the carbon fiber network and on a planar vitreous carbon surface. The new results may be used to increase the fidelity of oxygen-carbon ablation models for hypersonic flight.

Failure mechanism and tensile constitutive model of the unidirectional-laminated Cf/SiC–Al composites

The unidirectional-laminated Cf/SiC–Al composites were prepared by using precursor infiltration and pyrolysis (PIP) and vacuum pressure infiltration processes. Bulk density and open porosity of as-prepared Cf/SiC–Al composites were characterized which showed a large number of pores in the unidirectional-laminated carbon fiber preform were filled with SiC and Aluminum alloy matrix. The uniaxial tensile tests were conducted to study the mechanical properties. The fracture surface and cross-section of tensile specimens were characterized to clarify the failure mechanism. The results showed that under the action of load, the propagation of microcracks in matrix led to interface debonding, fiber fracture and pull-out. According to the stress-displacement behavior and analysis of damage process, the prediction formulas of the linear proportional limit stress value and the tensile strength value were proposed. A bilinear constitutive model was established based on the assumption of the damage process which well characterized constitutive response of the composites.

Preparation and mechanical characteristics of fine‐woven cloth and punctured felt preform Cf/C‐SiC‐ZrC composite

AbstractA 3D architecture carbon fiber preform, specifically fine‐woven cloth and punctured felt preform, is used to manufacture a novel advanced Cf/C‐SiC‐ZrC composite. The composite matrix is produced by chemical vapor infiltration (CVI) plus precursor infiltration and pyrolysis (PIP) process and finalized by using a chemical vapor deposition (CVD) of SiC coating to make the final density of the material reach 1.95 g/cm3. The organic precursors of SiC and ZrC have a weight ratio of 4:1 in a xylene solute. The composite mechanical properties, such as tensile, compression, bending, shear, and Z‐direction load bearing, are introduced under analysis to find possible applications for the composite. What is more, scanning electron microscope (SEM) images are employed to illustrate the failure behavior of the ceramic composite. The results showed that the punctured filament tows will be beneficial, not only for the composite to withstand compression force up to 308.6 MPa and shear strength to 18.14 MPa but also for the alternatively stacked weave piles and short fiber layers to support the punctured bundles, as well as to hold the composite structure under mechanical forces from different orientations, which is believed to reinforce the ceramic matrix for some high pressure and severe ablation applications.

Vacuum infiltration molding and mechanical property of short carbon fiber reinforced Ti-based metallic glass matrix composite

• New vacuum infiltration method using Cu-mold-prepared CF preform is developed. • Electroless-Cu-plated layer dissolves to improve the wettability during infiltration. • Interface microstructure control is achieved by Cu-layer and short-term infiltration. • Ti-based CFRMGMC has obviously improved plasticity together with high-strength. • Randomly and uniformly distributed short CF leads to brittle-ductile transition. The molding process is the key technology for the development of carbon fiber reinforced metallic glass matrix composites (CFRMGMCs), which not only needs to tackle the challenge of the mixing uniformity of carbon fibers, but also should take into account the rapid cooling technology to obtain a fully glassy matrix. Herein, a new vacuum pressure infiltration molding method is developed to fabricate a Ti-based CFRMGMC, in which a copper mold is performed as the container for carbon fiber preforms in addition to being used as a rapid cooling device. In order to prevent the interface reaction between carbon fiber and metal liquid, an electroless copper layer is plated on the surface of carbon fiber. It is found that the thin copper layer is dissolved in the glassy matrix and no crystalline phase is formed on the interface between the fiber and the matrix, showing a good effect on the control of interface microstructure. Meanwhile, electroless copper layer also effectively improves the wettability between the carbon fiber and the titanium alloy melt, thereby improving the infiltration forming ability of the composite material and reducing the tendency to form macroscopic defects. The as-prepared Ti-based CFRMGMC shows a significantly improved plasticity of ∼5 % and a high yield strength of 1880 MPa. The toughening mechanism can be attributed to the random distribution of short carbon fibers in different directions, which originates from the preparing process of carbon fiber preforms. This multi-directional posture is frozen in the glassy matrix and stimulates the multiple shear band behavior of the CFRMGMC. This work sheds lights on the use of carbon fiber in bulk metallic glasses, and is of great significance to the lightweight development and the interface reaction control of CFRMGMCs.

Development of the Low-Density Phenolic-Based Fibrous Ablator ZURAM-K

ZURAM is an ablative carbon–phenolic thermal protection material, developed by the DLR, German Aerospace Center (DLR) in cooperation with the Institute of Space Systems, University of Stuttgart. In addition to building up a basic competence in the sector of ablative thermal protection materials, an objective of the development was to provide a nonclassified ablative material for university research. ZURAM is comparable to similar low-density ablative thermal protection materials with respect to the material density and general ablative performance. It is based on a rigid, highly porous carbon fiber preform, which is filled with a nano-porous matrix derived from a phenolic resin. In the context of the ongoing material development, possibilities to improve the material were investigated with the aim to lower its thermal conductivity and to enhance the adaptability to varying mission profiles. Preliminary results indicate that by substituting the carbon preform with a phenolic fiber preform, a significant reduction of the thermal conductivity can be achieved while recession rates are comparable to the ones of standard ZURAM. The scope of the present work is the development of ZURAM-K based on phenolic Kynol fibers. Furthermore, results from tests in the arc-heated DLR facilities L2K and L3K, as well as data on the thermal conductivity and heat capacity, will be presented.

Carbon Paper as a Promising Free Standing Anode for Sodium Ion Batteries

Porous conducting carbon fiber composite papers have been developed by a two-step process. This involves fabrication of carbon fiber preform followed by composite formation. Different composite papers have been developed by varying the final heat treatment temperature of the composite, viz. 800 °C, 1100 °C, 1400 °C, 1800 °C and 2300 °C. The study gives an insight as to how the structure, porosity, morphology, electrical and mechanical properties of the carbon/carbon composites vary with temperature; and further the effect of these variations on the performance of the composites as anode material for Na-ion batteries. The sample heat-treated to 800 °C showed high reversible capacity of 278 mAh g−1 at a current density of 37 mA g−1. Additionally, high columbic efficiency (>99%) and 72% retention of the initial capacity has been demonstrated for 1000 cycles. This exceptional performance is attributed to the small crystallite size, large d-spacing and disordered structure of the sample which favors the insertion/de-insertion of sodium ion into the composite anode. Hence, it seems as a promising anode material for sodium-ion batteries.

Investigation of Gas-Phase Processes of Obtaining Fiber-Reinforced Organomorphic Ceramic Composites with SiC-Matrix

The isothermal process of chemical vapor deposition for the densification with a SiC-matrix of organomorphic carbon-fiber preforms obtained by carbonization of compressed fibers of oxidized polyacrylonitrile is investigated. Such preforms are characterized by a high (up to 70%) porosity and uniform pore size (the reduced pore diameter ranges from several micrometers to tens of micrometers). Technological parameters of the process of obtaining ceramic-matrix composites (CMC) were optimized by a combination of experimental studies and numerical simulations. Experimental samples of CMC were obtained using a non-halogen precursor, methylsilane CH3SiH3, and their residual porosity was determined. For the numerical study of the gas-phase process of densification of preforms, a 1D model was used. The simulation results were compared with experimental observations.