Types Of Preforms Research Articles

Titanium powder production by preform reduction process (PRP)

To develop an effective process for titanium powder production, a new preform reduction process (PRP), based on the calciothermic reduction of preform containing titanium oxide (TiO 2), was investigated. The feed preform was fabricated from slurry, which was made by mixing TiO 2 powder, flux (e.g. CaCl 2) and binder. Various types of preforms in the form of plates, spheres, or tubes were prepared using a conventional technique, and the fabricated preform was sintered at 1073 K before reduction in order to remove the binder and water. The sintered solid preform containing TiO 2 was then placed in a stainless steel container, and reacted with calcium vapor at a constant temperature ranging between 1073 and 1273 K for 6 h. Titanium powder was recovered from the reduced preform by leaching it with acid. As a result, pure titanium powder with 99 mass% purity was obtained. This process was found to be suitable for producing a homogeneous fine powder when the composition of flux and the size of the preform are controlled.

Analysis of Transversal Permeability for Different Types of Glass Fiber Reinforcement

In some of the new processes to produce elements in composite materials, the innovation is due to the fact that the resin flow is perpendicular to the plane of the reinforcement during the impregnation. So a very important parameter is the transversal permeability of the reinforcing materials used in these processes. In fact for a high value of this parameter it is possible to increase the product quality and to reduce the process time. In this work, using Darcy's law and a particular permeameter, the transversal permeability of preforms constituted by fabric and mat layers of fiber glass has been valued for different injection pressures. In particular, the permeability of two types of preform, consisting respectively of only mat layers and of only fabric layers, have been determined by tests and calculated by Kozeny–Carman equation. The research has been also focalised on the evaluation of the permeability of preforms constituted by a mix of the two different types of reinforcement. Furthermore an analytical model has been studied to calculate the permeability of preforms consisting of layers of different reinforcement types, starting from the permeability data characterizing the single reinforcement type and determined by the tests or by Kozeny–Carman equation.

Failure behavior of three-axis woven carbon/carbon composites under compressive and transverse shear loads

This work examines the responses of three-dimensional carbon/carbon composites under axial compression and transverse shear. By using a 3D weaving technique, two types of preforms with different bundle sizes of the weaving yarns were prepared for assessing its influence on the failure behavior. Carbon yarns were arranged in a three-axis, orthogonal form with interlacing loops on outer surfaces. The carbon matrix was added by using a phenolic resin as the matrix precursor. Resin transfer molding was used for resin impregnation, followed by the curing and carbonization of the resin. The matrix filling was repeated up to five cycles, and the efficiency of the matrix filling was examined. Special fixtures were designed for applying the loads to the 3D composites. Microscopic observations on the induced damage were carried out. The axial yarns were found to undergo bending fracture in the compressive tests. The yarn imperfection, rather than the fiber misalignment, was the major failure-determining factor. The bending of the yarns is analyzed, and the critical value of imperfection that leads to bending fracture is given. The transverse shear resulted in complex but intriguing damage modes, which are closely related to the surface loops and through-thickness yarns. Some keys for preform design to best withstanding the shear are discussed.

Detection of Preformed Type A Botulinal Toxin in Hash Brown Potatoes by Using the Mouse Bioasssay and a Modified ELISA Test

A foodborne illness caused by type A toxin-producing Clostridium botulinum was investigated by using the standard mouse bioassay and a rapid invitro test for toxin detection. The patient, who consumed improperly stored hash brown potatoes that contained the preformed toxin, was diagnosed with type A botulism. C. botulinum type A toxin was detected in the hash brown potatoes as well as in the tryptone-peptone-glucose-yeast extract (TPGY) medium subcultures of this food using the mouse bioassay and an amplified ELISA technique. The mouse bioassay revealed preformed toxin at 10,000 minimum lethal dose (MLD)/g uncooked product and the amplified ELISA an equivalent 50,000 MLD/g. The cultural toxin from the uncooked product killed mice at the 10(6) dilution and a modification of the ELISA procedure was positive at the 10(3) dilution. Cooked food obtained from the consumer's waste can contained 100 MLD/g and the ELISA was also positive at the same dilution of the product. The culture of the cooked product obtained from the waste can was lethal for mice at the 10(7) dilution and positive using the modified ELISA at the 10(4) dilution. The unmodified amplified ELISA method indicated a toxin level of approximately 1 ng/mL (equivalent to 5 x 10(5) MLD/mL) in diluted culture fluid from the uncooked food and the culture of cooked food obtained from the waste can. The hash brown potatoes were negative for types B, E, and F preformed and cultural botulinal toxins using both assays.

Experimental and theoretical studies of fabric compaction behavior in resin transfer molding

Experimental and theoretical studies have been conducted on the compaction behavior of fabric preforms in the resin transfer molding process. Compaction experiments were carried out for three types of preforms, i.e. continuous strand mats, plain woven fabrics, and unidirectional knitted materials. The major factors contributing to the preform compaction behavior were identified. Then, in-situ contact pressure between adjacent fabric layers during compaction was measured using a TekScan system. The results of the pressure measurement motivated the improvement in the existing compaction model. Thus, the theoretical part of this paper focuses on modeling the compaction behavior of woven-fabric preforms with uniform, linear, and sinusoidal inter-layer contact pressure distributions. Analytical expressions for the relations among the fiber volume fraction, the applied compressive force, and the preform thickness reduction, have been established. Finally, the improved model is applied to predict the geometry of the resin channels of the preform under compaction. This knowledge can be readily used for evaluating the resin permeability as a function of applied pressure in the resin transfer molding process.

Permeability Estimation with the Method of Cells

The Method of Cells (MC) is used to predict the permeability of preforms regardless of their architecture, and to study the effect of disturbances during preform manufacturing on the permeability of the preform. Preforms are made up of bundles of fibers called fiber tows. Different types of preforms can be produced from the same fiber tow. In the MC, a repetitive unit cell is subdivided into subcells in such a way that there is only fiber tow or air in a subcell. The pressure field in each subcell is modeled as a second order polynomial of local coordinates. The coefficients of the polynomial are estimated using a set of equations that include governing equations, boundary conditions, continuity conditions and constitutive equations. Subsequently, the flow field in the subcell is determined. The pressure is averaged at the faces of the unit cell and the pressure gradient is calculated assuming a linear pressure profile across the unit cell in all three dimensions. The velocity is averaged over the unit cell volume. Finally, overall permeability values are estimated using Darcy’s Law. The geometry of the preform varies to some extent due to several effects during production or processing; or there might be some imperfections in the preform, such as improper stitches. The permeability is influenced by both of these disturbances. By varying the properties of the subcells in the model, the effect of these disturbances on the permeability can be evaluated.

Synthesis and characterization of stiffness-critical materials using interconnected wires as reinforcement

Magnesium based composites reinforced with two types of galvanized iron wire preforms equivalent to about 5 vol% reinforcement were fabricated using conventional casting technique followed by hot extrusion. Microstructural characterization of the extruded composite samples showed minimal porosity and good interfacial integrity between the reinforcement wire and the matrix material. The mechanical characterization of the composites revealed that the Rule-of-Mixtures (ROM) stiffness was realized in both the composite materials. The yield strength of the composites and the monolithic material were the same within the standard deviations. An attempt is made to rationalize the microstructure and tensile behavior, especially the stiffness of the composite material, with the presence of interconnected wires in the form of preform and the type of preform in the magnesium matrix.

Drapability of dry textile fabrics for stampable thermoplastic preforms

Sandwiches based on stampable foam core and face sheets offer potential for cost-effective applications. Since the formability of such sandwich structures mainly depends on the drapability of the face sheets, the deformation behaviour of several types of textile preforms was evaluated. Glass fibre fabric preforms in the form of plain weave, twill, crowfoot and eight-harness satin as well as warp and weft-knitted architectures were studied. The tensile properties of the dry fabrics at various orientations and the locking angle of woven fabrics in the bias direction were determined. An analytical model is proposed to relate the fabric parameters to the locking angle. Drapability tests were performed on several woven and knitted fabrics in order to relate the forming energy to the preform architecture. Due to their high drapability and low forming energy, warp-knitted structures were selected as textile reinforcement for the sandwich face sheets.

A study of the deformation of weft-knit preforms for advanced composite structures Part 2: The resultant composite

This paper investigates the formability (i.e. the ability of a textile preform to conform to a 3-D shape) of weft-knit reinforced composites via the use of a composite case study (helicopter door track pocket), including the cutting plan methodology used for composite fabrication in the RTM process. The difficulties encountered during composite fabrication with specific preform types are discussed and expanded on the findings of the dry preform simulated formability results reported in part 1. The formability in the composite part was investigated through the deformation patterns of the various preform structures. The formability is specifically expressed as distributions of the preform deformation. The results of the composite case study showed that formability is influenced by the extensibility of the preform, the quality of the subsequent composite in terms of the degree of faults, and the distribution of the preform elongation in the composite.

Fabric structure and mold curvature effects on preform permeability and mold filling in the RTM process. Part II. Predictions and comparisons with experiments

Abstract In Part I, an experimental study was completed in a series of five molds, each having corners of different radii (from 0.06 to 8.0 in.). The primary goal of this work has been to determine whether corners in LCM molds significantly affect the filling process, by altering the structure of the preform locally in such regions. Consistent trends were found for each series of experiments completed in the mold, for which the same preform type, and number of layers were used. For constant flow rate injection, the required injection pressures to fill the two molds with tighter radii was significantly increased as compared to the other molds. Composite parts were manufactured in these molds, measurements made on these parts revealing design flaws, the cavity thicknesses not being equal in all sections of the molds. Several numerical simulations are presented in this paper, the goal being to separate any effects due to the varying thicknesses from effects due to the corners present. Careful simulations have been completed, taking into account the actual thicknesses in each mold, and the resulting preform volume fraction. Experimentally measured permeability data was employed, and the predicted injection pressures match very well for all four molds studied, seeming to indicate that the corners present have not affected the filling. A simple model for preform compression in corners has been developed, which predicts local permeability modifications due to in-plane compression of the fabric layers. These predictions have been employed in conjunction with an existing tool to analytically predict the permeability components of a preform in a flat cavity. This code requires from the user a geometrical model of a preform unit cell, this data being measured from samples cut from the parts manufactured. The resulting predictions for injection pressure are good for an entirely predictive approach, underpredicting experimental values by only 30–60%. Sensitivity analyses have demonstrated the strong relationship between permeability and the details of the preform cell. Two numerical studies were completed to determine how sensitive the injection pressure curves are to reduced permeabilities in the corner regions. For the two injection schemes having two different gate locations, pressures were not significantly affected, while the permeabilities in this region were reduced up to 100 times. Though the molds used were not ideal for isolating effects on mold filling due to corner radii, the evidence presented does not show the existence of any strong behavior related to mold radii.

Studies on Mechanical Behaviour of Knitted Glass-Epoxy Composites

Resin Transfer Molded (RTM) laminates from weft rib knit glass preforms with added reinforcements were developed using closed mould vacuum resin suction technique. In all, six types of preforms (with additional reinforcements in the course direction) were obtained using a flat bed hand-knitting machine. The laminate fibre weight fractions ranged from 0.37 to 0.67 and their tensile and flexural properties were evaluated. Test results indicated that strengths higher than those of the woven fabric composites could be achieved in the course direction with unique failure modes occurring differently from those of the latter.

Characterization and modeling of race-tracking in liquidcomposite molding processes

Liquid composite molding (LCM) processes require the impregnation of a polymeric resin through a porous preform, usually composed of glass, carbon, or Kevlar fibers. Numerical mold-filling simulations are currently being developed to predict the flow through LCM mold cavities and are a powerful design tool. The accuracy of such simulations are very sensitive to the permeability components, input provided by the user to represent the resistance to flow provided by the porous preform. Air channels can be present within a mold cavity, either unintentionally formed, or intentionally placed to enhance the mold filling process. Such channels provide paths of relatively low flow resistance, and can drastically alter flow front advancement and injection pressures, this effect being commonly referred to as ‘race-tracking'. Race-tracking must be considered in numerical mold-filling simulations, one common approach being the application of ‘equivalent permeabilities' to finite elements within a model that physically represent the air channels present. A planar rectangular mold cavity is studied here, having a single air cavity of known dimensions running along one side of the mold. This geometry provides the simplest flow configuration, all Darcy velocity components being in-plane. In this paper, the equivalent permeability magnitudes are based upon steady-state, fully developed flow through a rectangular duct. Detailed flow visualization experiments have been completed, recording flow-front advancement and injection-pressure histories, for two different preform types, and a variety of mold cavity thicknesses, preform volume fractions air-channel widths. Significant effort was made to provide exact comparisons of both flow front advancement and injection pressure, between the experiments and simulations based on the equivalent permeability approach. The comparisons are very good, the magnitude of the deviations being close to what should be expected from natural permeability variations from preform to preform. Sources for experimental error have been examined, the major limitation of these experiments being caused by the complex interaction of the acrylic mold, and stiffening bars used. The equivalent permeability approach has been shown to model flow front advancement and injection pressures very well within a Darcy's law based mold filling simulation, for the volume fractions studied (0.50 to 0.16). This study has been limited to low volume fractions, and care should be taken when extending the equivalent permeability approach to woven and stitched preform styles. An alternative numerical method was investigated, modeling flow in the preform by using Darcy's law, and one-dimensional Stokes flow in the air channel, with a variable source term to model the transverse flow into the preform. The results from the two simulations are in excellent agreement, demonstrating that the equivalent permeability approach employing Darcy's law over the entire domain, models the transverse flow into the preform from the air channel accurately.

Microstructures of 3‐D carbon/carbon composites using solid rods as reinforcements

AbstractThis paper examines microstructures of 3‐D woven carbon/carbon composites. Unidirectional carbon/phenolic rods, with 1 mm in diameter, were made by the pultrusion technique and then combined into 3‐D preforms in the axial direction. The preforms were of three‐axis orthogonal structures based on 3‐D weaving. A special weaving setup to incorporate the rods has been developed, and three types of preforms with varying the weaving yarn sizes have been made. Another conventional type composed of carbon yarns in all axes was also made for purpose of comparison. The geometrical aspects of both types of preforms have been studied. Using the rods was found to effectively eliminate fiber crimp in the axial direction. The fabrication of the carbon/carbon composites has been carried out based on multiple impregnation and carbonization of the phenolic resin. Open and close pores of the materials have been measured after each densification process. The variations in open and close pores differ greatly in response to the densification process. The induced matrix cracks due to pyrolysis shrinkage have been examined based on microscopic observations. Dictated by the preform types, matrix cracks were regularly developed in the weaving yarns. While a dominant transverse crack was formed in each of the yarns, small pores were extensively created in the rods. Separation of bundle interfaces was also observed. Formation of these cracks in relation to processing and microstructures is discussed in detail.

Finite Element Assisted Modelling of the Microscopic Impregnation Process in Thermoplastic Preforms

Fibre reinforced composite materials incorporating thermoplastic matrices are gaining increasing popularity in many industrial applications. One of the potential preforms for the manufacture of technical components is commingled yarn composed of reinforcement and matrix in fibre form. These are often employed in the pultrusion process. Another innovative preform consists of polymer powder preimpregnated sheath surrounding fibre bundles. To achieve adequate mechanical properties of the final product it is essential, when producing laminates by a process such as pultrusion with both types of preform, that sufficient matrix impregnation is achieved. The prevention of voids and dry-spots in the laminate requires a theoretical understanding of the mechanisms involved. On a microscopic scale, several finite element (FE) models can be used to simulate the progress of the matrix flow into the interstitial spaces between the single reinforcement fibres. In the present simulations, a hexagonal and a square arrangement account for two of the various fibre packings occurring in a laminate. It permits an estimation of the impregnation performance of commingled and powder impregnated yarns. For each preform the shear rate, to which the polymer matrix is subjected during the impregnation and consolidation process, can be predicted.

Reconstruction of Peritoneal-like Structure in Three-Dimensional Collagen Gel Matrix Culture

The peritoneum is a serous membrane consisting of different kinds of cells and extracellular matrix components (ECM). The aim of the present study was to develop a three-dimensional (3D)in vitroculture system for possible investigation of pathological conditions of the peritoneum. Human omental mesothelial cells (MC) and endothelial cells from the umbilical vein (EC) were cultivated eitheron(MC) orin(EC) a preformed type I collagen matrix. In 3D culture mesothelial cells showed their phenotypicalin vivocharacteristics and the synthesis of a new basal membrane (BM). Endothelial cells developed vessel-like structures, produce a BM and express E-selectin after TNF-α stimulation. This 3D culture system presents extended possibilities for analyzing mesothelial and endothelial cell behavior as well as the cell–cell and cell–matrix interactions involved in several pathological processes in the peritoneum.

Binding of SPAAT, the 44-residue C-terminal peptide of α1-antitrypsin, to proteins of the extracellular matrix

SPAAT (short piece of alpha 1-antitrypsin [AAT]), the 44-residue C-terminal peptide of AAT, was originally isolated from human placenta [Niemann et al. (1992): Matrix 12:233-241]. It was shown to be a competitive inhibitor of serine proteases [Niemann et al. (in press): Biochem Biophys Acta]. The binding of SPAAT to one or more proteins of the extracellular matrix (ECM) was initially suggested on the basis of its recovery from tissue residues following a series of extractions designed to remove easily solubilized proteins [Niemann et al. (1992): Matrix 12:233-241]. Our binding studies with the model ECMs, Matrigel and Amgel, suggested that SPAAT might be bound by a specific collagen type as well as one or more non-collagenous ECM proteins. Individual ECM components were screened for their ability to bind SPAAT. When the four commonly occurring fiber-forming collagens (types I, II, III, and V) were evaluated, type III was found to be preferred. In addition, although SPAAT bound to preformed type III collagen fibers in a concentration dependent fashion, it did not bind to type III collagen molecules undergoing fibril formation. This is consistent with a physiological mode of interaction between SPAAT and type III collagen in vivo. Of the non-collagenous ECM macromolecules (laminin-1, fibronectin, entactin, and heparan sulfate) tested, laminin-1 was preferred. The binding of radiolabelled SPAAT to type III collagen and laminin-1 was competitively inhibited by unlabelled SPAAT as well as an unrelated protein, human serum albumin (HSA), to establish binding specificity. The kinetics of the release of the bound radiolabelled SPAAT were also examined to substantiate the non-covalent and reversible nature of this association. These results support the view that susceptible proteins of the ECM may actually be coated with SPAAT in vivo, possibly affording protection against inappropriate protease digestion.

Fiber Reinforced Metal Matrix Composite by a High Deformation Consolidation Process

Reinforcement geometry affects strengthening significantly for metal matrix composites. Using rule of mixtures, which assumes perfect stress transfer from matrix to reinforcement, as well as a differential CTE mechanism, which assumes a dislocation generation effect to strengthen the matrix, it can be shown that particulate reinforcement types are inherently inefficient for strengthening. As an alternative, a Ni pre-form fiber system has been used in this work as the reinforcement. The preform type eliminates the mixing problems inherent for a particulate system, but itself also introduces an additional binder burn-off step. Subsequent compaction was done using a cold isostatic press up to 3000 bars (−300 MPa), with the consolidation achieved by means of a hot extrusion / hot pressing method.

Progressive Crush Response of Hybrid Felt/Fabric Composite Structures

The energy absorption response and damage characteristics of composite structures are of increasing interest to both automotive and aerospace areas, as a means of achieving superior crash impact performance and energy absorption as compared to metals. Previous research has concentrated almost entirely on axisymmetric cylindrical tubes, hour-glass shapes and conical frustra. In this paper a multicelled geometry connected by flanges is considered and characteristics of progressive crush as a result of the use of needle-felts in addition to conventional fabrics in the preform are investigated. It is shown that the presence of the needle-felt layer can drastically modify crush response and can serve as a means of energy absorption through hybridization. The results of ten preform types are discussed and compared on the basis of a number of metrics in order to assess viability of both structural response and crash worthiness.

The processing and characterization of sintered metal-reinforced aluminium matrix composites

The current investigation involves the fabrication and characterization of an aluminium metal matrix composite reinforced with sintered metal preforms. Two types of metallic preforms were used (steel and stainless steel) and a variety of squeeze casting conditions were investigated using systematic design-of-experiments techniques to determine the effect of casting conditions on the composite microstructure and mechanical properties. It was observed that a detrimental reaction phase containing iron, aluminium and silicon formed around the metallic preform particles, with a lower volume fraction of reaction phase forming at the lower melt casting temperature. This reaction phase appears to promote premature fracture by facilitating crack initiation and propagation. The stainless steel-reinforced composites had a smaller volume fraction of reaction phase and exhibited superior properties compared to the steel-reinforced composites.

Experimental and theoretical studies of the elastic behavior of knitted-fabric composites

This paper presents experimental and theoretical studies of the elastic behavior of knitted-fabric composites. In the experimental studies, two types of weft-knit preforms based upon plain-stitch and rib-stitch fabrics were first fabricated and fabric composites were consolidated by using a hand lay-up process. Tensile and rail shear tests were performed, and Young's moduli along the warp and weft directions and shear modulus determined. In order to correlate the preform microstructure with composite elastic properties, geometric models for plain-stitch and rib-stitch fabric composites were developed. Modeling of the elastic behavior was conducted by using an averaging method. The predicted elastic constants are in reasonably good agreement with experimental values. Finally, the limitation and potential of knitted-fabric composites are discussed.