Weave Geometry Research Articles

Field emission of zinc oxide nanowires grown on carbon cloth

An extremely low operating electric field has been achieved on zinc oxide (ZnO) nanowire field emitters grown on carbon cloth. Thermal vaporization and condensation was used to grow the nanowires from a mixture source of ZnO and graphite powders in a tube furnace. An emission current density of 1mA∕cm2 was obtained at an operating electric field of 0.7V∕μm. Such low field results from an extremely high field enhancement factor of 4.11×104 due to a combined effect of the high intrinsic aspect ratio of ZnO nanowires and the woven geometry of carbon cloth.

Three-dimensional viscoelastic simulation of woven composite substrates for multilayer circuit boards

Viscoelastic properties of woven composite substrates are essential to design dimensionally stable multilayer printed circuit boards. Unlike most existing numerical work which rely on simplified constitutive (elastic) and geometrical models, this study involves a fully three-dimensional viscoelastic model of a plain weave composite with accurate characterization of the woven geometry. Comparisons between numerical predictions and experimental data clearly indicate that the creep compliance of the composite depends not only on the relaxation of the matrix, but also on the time-dependent flexural deformations of the woven fabric bundles. Predictions of the inhomogeneous deformation fields over the repeating cell agree with experimental observations.

An energy based model for the flattening of woven fabrics

Applications such as garment manufacture and composite structure fabrication require a two dimensional (2D) woven material to assume a three dimensional (3D) shape. The specification of the process is usually initiated by defining the 3D surface. Hence, the problem arises of determining the best 2D pattern. The problem is made more complex by the anistropic nature of woven fabrics which are often used as raw material. Such materials display a variation in mechanical properties with respect to the woven structure. This paper presents a model for determining the optimum 2D pattern for a specified 3D surface where optimality is determined in terms of minimising the energy distribution required to force the 2D pattern to assume the 3D shape.The 3D surface specification is assumed to consist of a polygonal mesh. The model allows affine transformations to be applied to the weave structure which can be unique for each polygon in the mesh. Important considerations in the modelling process include the following:1.The degree to which the specified 3D surface departs from a developable surface.2.The energy components used to model the woven structure and their sensitivity to weave direction. Essentially, these stem from tensile strain in each direction of the weave and shear strain.3.The prediction of weave geometry as it reacts to the energy distribution being applied.The model is demonstrated by applying it to a relatively simple pyramidal 3D shape. Energy values are optimised to produce a pattern that requires the minimum overall energy to be applied to the 2D pattern in order for it to assume the 3D shape. This 2D pattern is sensitive to the orientation of the woven structure with predictions being made of how the woven structure will behave in 3D.

Influence of Different Woven Geometry and Ply Effect in Woven Thermoplastic Composite Behaviour-Part 2

Works on woven composite both thermoset and thermoplastic are numerous, however in most instances they involve the use of preimpregnated fabric. It is apparent that woven thermoplastic system has significant potential due to the combined properties such as better damage tolerence, recyclability, easy processing, storage, etc. Here work on woven thermoplastic composites based on Continuous Fiber Impregnated towpreg (COFIT) tape rather than conventional approach is reported. The influences of different woven geometry and ply effect were investigated. Correlations between different woven geometry and weave characteristics were also noted. In general, the woven composite properties are influenced by many process variables such as type of towpreg, woven geometry, number of plies etc.

The effect of thermoplastic coating on the mechanical properties of woven fabric carbon/epoxy composites

The effect of a polyetherimide (PEI) coating on the mechanical properties of woven fabric carbon/epoxy composites was investigated by thermal mechanical analysis, fractographical analysis and mechanical properties measurements. PEI coating enhanced the mechanical properties of carbon/epoxy composites mainly through the improvement of matrix properties. This was because most of the PEI coated on the carbon fiber diffused into the bulk of epoxy matrix due to its good miscibility with epoxy resin. As for mechanical properties of woven fabric carbon/epoxy composites, the extent of improvement by PEI coating highly depended on the applied stress state. Among the mechanical properties, mode II delamination resistance of carbon/epoxy composites showed the highest increment because matrix shear property played an important role in delamination resistance of woven fabric carbon/epoxy composite. Because of the woven geometry of carbon fiber, the improvement in impact property of carbon/epoxy composite was trivial except the large amount of PEI coated case.

Evaluation of Various Approximate Analyses for Plain Weave Composites

The literature contains a variety of analyses for analyzing plain weave composites. These differ in both geometric approximation and assumptions about stress and strain distribution. Herein the weave geometry for a wide range of waviness was described using three-dimensional finite element meshes. These meshes were used with various stress and strain assumptions to determine how these assumptions affect predicted in-plane extensional stiffness. Assumptions about stress and strain can be tied to whether an analysis is equivalent to a virtual work, complementary virtual work, or hybrid formulation. Since these variational principles have well understood convergence behavior, it is easy to explain the observed effects of the various assumptions. The results indicate that sometimes accurate predictions for particular cases result from cancellation of errors, rather than sound formulation.

A Semi-Analytical Method for the Calculation of the Elastic Micro-Fields in Plain Weave Fabric Composites Subjected to In-Plane Loading

In this paper, a computationally efficient semi-analytical method is developed for the calculation of the elastic micro-fields dominating plain weave composites under remote in-plane loading. The framework needed to obtain analytical displacement estimates is derived using the Rayleigh-Ritz method for a composite plate with spatially varying laminate stiffnesses. The method is developed with the aid of a symmetric woven unit-cell geometry. Three separate boundary value problems, corresponding to remotely applied biaxial and uniaxial displacement, and simple shear boundary conditions are formulated. Unit-cell geometry and material characteristics for both polymer and ceramic matrix composites are incorporated in the formulation of the above boundary value problems. Extensive solution convergence studies are presented. As expected, convergence is shown to depend on the number of terms used in the Ritz series solution and the number of integration stations used to integrate the spatially laminate stiffnesses within the woven unit-cell geometry. Convergence results for the optimal selection of both of the above parameters are presented. The implications of the method's potential to yield accurate elastic microfields on the evolution of stress induced microdamage in woven systems is discussed.

Fractographical analysis on the mode II delamination in woven carbon fiber reinforced epoxy composites

Mode II delamination phenomena of woven fabric carbon/epoxy composites were investigated by scanning electron microscopy. End notch flexural (ENF) test was used to examine the mode II delamination. Woven fabric composites showed two peculiar crack propagation patterns due to the complexity of woven geometry. In warp yarn region, crack propagated with forming a shear band and breaking the fiber/matrix interface. In fill yarn region, however, no shear band was observed. Considering these crack patterns, matrix shear property and fiber/matrix interfacial strength played an important role in enhancing the delamination properties of woven fabric carbon/epoxy composites. Due to the woven geometry, matrix rich positions, which are interstitial and undulated region, were formed in woven carbon/epoxy composite. In these regions, matrix fracture and complex crack path were mainly observed.

Elastic Response of Porous Matrix Plain Weave Fabric Composites: Part II—Results

In this second of a two-part series of papers, the analytical and three-dimensional finite element models developed in Part I are implemented to predict the effective elastic response of both Stiff-porous ceramic and Soft-dense polymer matrix plain weave fabric composites. Analytical results obtained using a Modified Lamination Theory (MLT) model and which are based on four methods of unit-cell property averaging are presented. Effective elastic in-plane properties predicted via the finite element method for a single woven ply and for a laminate comprised of symmetrically arranged woven plies are also reported. Comparisons between the analytical estimates and the numerical predictions suggest that the Parallel (P-MLT) property averaging scheme yields, in an overall sense, good unit-cell effective property estimates. Thus, the P-MLT model was employed to conduct extensive parameter studies aiming at assessing the effects of the woven geometry and the overall microstructure on the effective elastic properties of Soft- and Stiff-matrix woven composites. Soft-matrix systems were shown to exhibit higher sensitivity to the unit-cell woven morphology and fiber/matrix elastic mismatch when compared to their Stiff-matrix counterparts. On the other hand, the effective elastic properties of Stiff-matrix systems were shown to be substantially reduced with increasing interbundle matrix porosity, and were also shown to be rather sensitive to the elastic properties of the thin fiber and bundle coatings. Surface contour data obtained from 3-D finite element analysis provide strong evidence of local micro-bending and stress concentrations within the unit cell. In both Soft- and Stiff-matrix systems, the out-of-plane normal and shear stresses along the bundle/matrix interface surfaces were shown to be at least an order of magnitude smaller than the predicted normal bundle stress along the fiber direction. This work presents detailed analytical and numerical parameter studies, and explores for the first time the relations between the microstructure and macromechanical woven composite response.

An experimental and theoretical study of creep of a graphite/epoxy woven composite

AbstractThe creep behavior of woven fiber polymer composites has been investigated through both an experimental study and analytical modeling. In the modeling, the matrix is assumed to be a 4‐parameter model (a Maxwell‐Voigt combination) and the fibers to be elastic. The fiber undulation model developed by Ishikawa and Chou for elastic behavior of woven fiber composites has been extended to the viscoelastic system by the correspondence principle. This considers the longitudinal and transverse fibers separately. The weave geometry and dimensions are accounted for, thus bringing the model closer to the actual composite. While this model has been used previously to predict the composites elastic behavior, this is the first time it is considered as a viscoelastic solid, which helps determine its time dependent behavior. The resultant model takes into account the different parameters associated with the weave (the density of the fibers in the weave, the radius of the fibers and the profile of the fill and warp fibers), volume concentration of the fiber and matrix in the composite, and the elastic moduli of the fill and warp fibers and the viscoelastic properties of the polymer matrix. We have conducted creep tests on graphite fiber/epoxy composites to evaluate our model. Experiments have been conducted from room temperature (22°C) to 200°F (93°C). The results from experiments have been analyzed and an inverse simulation has been performed to obtain the unknown parameters of the matrix and fibers in the composite. The model is then used to predict the creep behavior of the woven fiber composite under other loading conditions and temperature levels, showing satisfactory agreement with the data.

Edge and interlaminar stresses of glass-cloth-reinforced epoxy laminates under uniform axial extension at cryogenic temperatures

We considered the free-edge and interlaminar stress states of G-10CR woven glass-epoxy laminates under uniform axial extension with temperature-dependent properties. The damage, in general, occurred in the interior of G-10CR glass-epoxy laminates. A finite element method was used to study the influence of weave geometry and cryogenic temperatures on the edge and interlaminar stresses of two-layer woven laminates under uniform axial strain. Numerical calculations are carried out and the stress distributions along the free edge and midplane of the woven laminates are shown graphically for various values of the temperature Φ and warp angle θ. The stress distributions of woven and nonwoven laminates are also compared. Finite element results demonstrated that the weave geometry reduced edge stresses, and the tendency was more pronounced with increasing θ. The large debonding stress tended to increase with increasing θ and decreasing Φ.

Surface charging limit for a woven fabric on a ground plane

Abstract This paper investigates the problem of depositing the maximum possible charge on a sheet of porous material, such as cloth, using a corona discharge. In the experiments, 50 to 75 μm-thick samples of nylon parachute fabric of varying porosity were charged over a ground plane using corona ions generated by a pin array energized at 6 kV – 9 kV dc and 0.5 cm gap spacing. The cloth exhibited a material-dependent maximum surface potential that was independent of the potential of the corona electrodes. This characteristic maximum surface potential was larger for low-porosity fabrics (tighter weave pattern), reaching a high of approximately 600V for 65 μm-thick, “zero porosity”, calendared ripstop nylon. Maximum surface potentials on the order of 200–500 V were observed on higher-porosity, “standard-issue” parachute fabrics of similar thicknesses. The experiments suggest a fundamental limit to surface charge that depends on the properties of the cloth, but not on the corona charging voltage. The observed results can be explained, in part, by a back ionization discharge mechanism that limits the indefinite build up of surface charge. The onset of back ionization is predicted from the Paschen breakdown curve and the weave geometry of the cloth. Breakdown field strengths inside the pores of the material were estimated using a simple dielectric layer model.

An analytical method for plain weave fabric composites

A two-dimensional closed-form analytical method has been developed for the thermoelastic analysis of two-dimensional orthogonal plain weave fabric laminae. Strand undulation and continuity in both the warp and fill directions, actual strand cross-section and weave geometry, strand fibre volume fraction and possible gap between the two adjacent strands have been considered in the analysis. Good correlation is observed between the predicted thermoelastic properties and experimental results.

Morphological description of coating cracks in SiC coated carbon-carbon composites

Thermal expansion mismatch between silicon carbide coatings on carbon-carbon composites creates a complex pattern of microcracks in the coatings. A better understanding of the mechanics and environmental performance of these coatings requires an improved ability to quantify the coating crack morphology. The work described here proposes and measures a variety of coating crack descriptions, such as crack type, spacing, width, cell area, and cell feret orientation. Characterization has been done from a section view and a plan view. Specialized specimen preparation techniques and computer-aided image analysis approaches were developed to make the measurements feasible. Data from a multilayer chemical vapor deposited SiC coated carbon-carbon composite illustrate the techniques. From the section views it is found that about 67% of the cracks do not penetrate to the surface of the specimen. From the plan view it is found that the crack pattern is systematically influenced by the underlying weave geometry of the cloth reinforcement. This result, along with the measured crack area/surface area, can be explained with simple thermal expansion mismatch arguments. The data is used to build two tractable but realistic models of coating crack morphology that would be useful in oxidation rate predictions. The observation also suggest several strategies for tailoring the coating crack morphology.

Mechanisms of breakdown of the structure of glass cloth during impregnation with polymer binders

The basic sources of worsening of the quality indexes of insulating glass cloth and the requirements for the properties of the cloth and binder during impregnation were determined: short pile, gas inclusions, thermodynamic characteristics of binder and monofilament on the binder—monofilament, binder—air, and air—monofilament interface, internal stresses in the structure of the cloth, weave geometry, and position of monofilaments in the complex fibre.

Modelling weave and stacking configuration effects on interlaminar shear stresses in fabric laminates

In an effort to improve out-of-plane properties, such as shear delamination strength, laminated composites have often incorporated laminae in which the fibres have been woven into a cloth. There are, however, many possible weave geometries for the cloth reinforcement, and many possible ply stacking configurations with these laminae. It is not well understood which combinations of weave and stacking can significantly improve, or inadvertently degrade, properties. This paper models the laminate geometry for woven-reinforced composites. Commonly available weave types, such as twills and five-harness satins, are considered. Stacking configurations include effects of weave pattern offset, folded vs. unfolded, and alternate stacking of different weaves. A rudimentary model is used to estimate the shear stress distribution within these various laminates. These distributions suggest the effectiveness of the various geometries. It is found that there may be significant effects due to weave offsets, that a folded configuration is undesirable, and that mixed weave types are unlikely to provide much improvement. A new quantity is defined—the lacing number—that has potential for quantifying the waviness of weave types.

Mechanical Properties of Fabric Woven from Yarns Produced by Different Spinning Technologies: Yarn Failure in Woven Fabric

A study has been conducted on the mechanisms of in-situ tensile failure of staple yams during uniaxial tensioning, as in a conventional ravel strip test. The yarns were PET/cotton blends processed on ring, rotor, and airjet spinning systems, and then woven into plain or twill weave fabrics. Load-extension behaviors of the yarns were recorded for the in-fabric state as well as for the free state (out-of-fabric), and SEM comparisons were made of the fractured yam ends obtained in the two states. When the tensioned yarns became jammed between cross yarns before straightening, the fracture ends were abrupt, similar to those observed in near zero gauge length tests of free-state yarns. However, when fabric structure was such that tensioned yams could straighten without cross yam jamming, the resulting failure zones were considerably longer, with a mixture of fiber fracture and slippage similar to that observed in long gauge length tests of free-state yams. The interaction between yarn properties and weave geometry had a strong influence on the local disturbance of cloth structure resulting from isolated yam failure during fabric tensioning. The extent of such dis turbance permitted estimates of the stress recovery length of the failed yam and showed its dependence on cloth tightness and yarn type.

極低温における織物複合材料の内部および縁応力解析

This paper deals with stress states at the laminate interior and free edges of woven glass-epoxy laminates with temperature-dependent properties. The composite material in generalized plane strain is assumed. The finite element method is used to study the influence of weave geometry and thermal effects on internal and edge stresses in G-10 CR glass-epoxy laminates at low temperatures. Numerical results on the influence of the warp angles on the distribution of internal and edge stresses at different temperatures are obtained and presented in a graph form.

Deflection-Force Measurements and Observations on Kevlar 29® Parachute Fabrics

Deflection-force relations for plain weave Kevlar® fabrics have been determined under conditions of uniaxial loading. In these experiments, the loading is stopped at a given level and a portion of the fabric is encapsulated. The fabric is then unloaded, sectioned, and photographed. Measurements on the photographs reveal the changes in weave geometry and yarn cross section with loading. The initial geometrical data are used in a large deformation mechanical model, which couples yarn bending and stretching effects to predict theoretical displacement-force relations for the fabric. Experimental and theoretical deflection-force curves are in good agreement; they show that during initial loading the response is dominated by yarn bending, while for large loads the response is dominated by yarn stretching.

The large deformation elastic response of woven kevlar fabric

AbstractThe large deformation elastic response of a plane woven Kevlar fabric is investigated analytically and experimentally. The analysis assumes the undeformed geometry to be a sequence of interlaced arcs of circles that reverse at each yarn midpoint, and each yarn is modeled as an extensible elastica subject to certain compatibility conditions. Deflection‐force relations for the fabric are determined in terms of the initial weave geometry and the elastic properties of the individual yarns. The theoretical results agree well with the results of experiments performed on a fabric woven from 400 denier Kevlar yarns under conditions of uniaxial loading in both warp and fill directions.