Showing papers on "Composite number published in 1993"

Fibre-matrix adhesion and its relationship to composite mechanical properties

Abstract: Two major areas of enquiry exist in the field of fibre-matrix adhesion in composite materials. One is the fundamental role that fibre-matrix adhesion plays on composite mechanical properties. The other is what is the “best” method used to measure fibre-matrix adhesion in composite materials. Results of an attempt to provide an experimental foundation for both areas are reported here. A well-characterized experimental system consisting of an epoxy matrix and carbon fibres was selected in which only the fibre surface chemistry was altered to produce three different degrees of adhesion. Embedded single-fibre fragmentation tests were conducted to quantify the level of fibre-matrix adhesion. Observation of the events occurring at the fibre breaks led to the documentation of three distinct failure modes coincident with the three levels of adhesion. The lowest level produced a frictional debonding, the intermediate level produced interfacial crack growth and the highest level produced radial matrix fracture. High fibre volume fraction composites made from the same material were tested for on- and off-axis, as well as fracture, properties. Results indicate that composite results can be explained if both differences in adhesion and failure mode are considered. It will be further demonstrated that fibre-matrix adhesion is an “optimum” condition which has to be selected for the stress state that the interface will experience. The embedded single-fibre fragmentation test is both a valuable measurement tool for quantifying fibre-matrix adhesion as well as the one method which provides fundamental information about the failure mode necessary for understanding the role of adhesion on composite mechanical properties.

Mechanical behavior of alumina-silicon carbide «Nanocomposites»

Abstract: The fracture behavior of Al2O3 containing 5 vol% 0.15μm SiC particles was investigated using indentation techniques. A significant increase in strength was achieved by the addition of SiC particles to the base Al2O3. Specifically, the strength increased from 560 MPa for Al2O3 to 760 MPa for the composite samples (average values for unindented hotpressed bars tested in four-point bending). After annealing for 2 h at 1300°C, the average strength of the composite samples increased to about 1000 MPa. Toughness was estimated using indentation-strength data. While there was a slight increase in toughness, the increase was not sufficient to account for the increase in the unindented strength on SiC particle addition. It is suggested that the observed strengthening and apparent toughening were due to a machining-induced compressive surface stress.

Dielectric constant for binary piezoelectric 0‐3 composites

Abstract: In this article an analytic expression is presented for the dielectric constant of a binary piezoelectric 0‐3 composite by modifying the well known Kerner expression [Proc Phys Soc London Sec B 69, 802 (1956)] to include interactions The developed expression is a function of the constituent dielectric constants and their volume fractions only and compares very favorably with available experimental data for piezoelectric ceramic inclusions in a dielectric continuum having widely differing dielectric constants

Composite elastic nonwoven fabric

Abstract: The invention provides composite elastic nonwoven fabrics and the process of making them. The elastic nonwoven composite fabrics of the invention are formed from the combination of a plurality of cooperative elastic layers including an elastomeric meltblown web and an elastomeric spunbonded web. The elastomeric layers are joined together in a unitary elastic fabric structure to provide a composite having a desirable combination of elastic and barrier properties.

Thermal conductivity of a polymer composite

Abstract: A prediction equation for thermal conductivity of polymer composites reported in our previous papers has been revised in terms of two view points: (1) estimation of thermal conductivity of a composite using an idea of reduced thermal conductivity; and (2) the effect of ease in forming conductive filler chains on thermal conductivity is related to the CVF value in electric conductivity of the composite. The new equation was confirmed to be adaptable to thermal conductivities of varieties of polymer composite systems filled with spherical or irregular fillers. The equation was also considered to explain thermal conductivity of polymer composites filled with fibers. Further, it was found that thermal conductivities of fiber composites can be estimated by introducing a factor of the CVF value or aspect ratio (L/D) into the new equation. © 1993 John Wiley & Sons, Inc.

Wrapped composite gasket material

Abstract: A composite gasket material (10) composed of a core of elongated polytetrafluoroethylene (11) wrapped with a high strength porous expanded polytetrafluoroethylene film (12) is provided. The composite gasket material exhibits increased resistance to creep while in use so that thickness of the composite gasket material and thus gasket stress is maintained.

Modeling 1-3 composite piezoelectrics: hydrostatic response

Abstract: A simple physical model of 1-3 composite piezoelectrics that was advanced for the material properties relevant to thickness-mode oscillations is extended to address the hydrostatic response. The model is valid when the lateral spatial scale of the composite is sufficiently fine that the composite can be treated as an effective homogeneous medium. Expressions are derived for the composite's material parameters in terms of the volume fraction of piezoelectric ceramic and the properties of the constituent piezoelectric ceramic and passive polymer. The results are similar to those derived by Haun and Newnham (1983, 1986) using a parallel-series connectivity model. The model is illustrated by analyzing composites made from conventional PZT5 and anisotropic modified lead titanate piezoelectric ceramics. For PZT5, the composite structure enhances its hydrostatic charge coefficient, hydrostatic voltage coefficient, hydrophone figure of merit, and hydrostatic coupling coefficient, while three of these quantities fall short of their pure ceramic values in the modified lead titanate composites. The shortfall is due to an enhanced composite that arises from lateral stress on the polymer being transferred to a longitudinal stress along the ceramic rods by the Poisson effect in the polymer, thus producing a charge through the ceramic's d/sub 33/. >

Micromechanical modeling of large plastic deformation and texture evolution in semi-crystalline polymers

Abstract: A micromechanically-based composite model is proposed to study large plastic deformation and texture evolution in semi-crystalline polymers. The microstructure of many semi-crystalline polymers consists of co-existing crystalline and amorphous phases locally associated with each other in a fine plate-like morphological structure. An aggregate of two-phase composite inclusions is used to model these materials. Special consideration is given to molecular chain inextensibility within the crystalline phase. The introduction of a back stress tensor in the constitutive model of the amorphous phase accounts for hardening due to deformation-induced molecular alignment. Interface compatibility and traction equilibrium are enforced within each composite inclusion. A Sachs-like model and two newly-developed self-consistent-like hybrid models are proposed to relate volume-average deformation and stress within the two-phase composite inclusion to the remote (macroscopic) fields. Applications of these composite models arc made to predict stress strain behavior and texture evolution in initially isolropic high density polyethylene (HOPE) under different modes of straining.

Genetic Algorithms with Local Improvement for Composite LaminateDesign

Abstract: This paper describes the application of a genetic algorithm to the stacking sequence optimization of a composite laminate plate for buckling load maximization Two approaches for reducing the number of analyses are required by the genetic algorithm are described First, a binary tree is used to store designs, affording an efficient way to retrieve them and thereby avoid repeated analyses of designs that appeared in previous generations Second, a local improvements scheme based on approximations in terms of lamination parameters is introduced Two lamination parameters are sufficient to define the flexural stiffness and hence the buckling load of a balanced, symmetrically laminated plate Results were obtained for rectangular graphite-epoxy plates under biaxial in-plane loading The proposed improvements are shown to reduce significantly the number of analyses required for the genetic optimization

Breathable non-woven composite barrier fabric and fabrication process

Abstract: A breathable non-woven composite fabric having barrier capabilities to biological liquids comprised of at least one non-woven layer bonded to at least one surface of a thermoplastic microporous film, the non-woven composite fabric providing a barrier to passage of biological liquid when the composite fabric is subjected to contact with synthetic blood under the dictates of testing procedure ASTM ES21-92 and ES22-92 while maintaining a moisture of vapor transmission rate of greater than about 450 grams per square meter for 24 hours at about 75° F. and about 65% relative humidity, the non-woven composite fabric having a breaking strength of at least about 14 pounds. A process is provided for forming the non-woven composite fabric which has been adhesively bonded by unwinding and contacting at least one continuous thermoplastic non-woven web to at least one side of a continuous thermoplastic microporous film with spot adhesive or pattern adhesive applications between the film and webs, continuously transporting said contacted webs and film through a bonding and curing zone and bonding the webs and film at multiple spaced-apart locations, said bonding zone having a dwell time sufficient to cure the adhesive bond of the composite while avoiding degradation of the film and webs.

Optical properties of gold nanocluster composites formed by deep ion implantation in silica

Abstract: Planar layers of Au clusters with diameters between 5 and 30 nm were synthesized by implanting 2.75‐MeV Au+ ions in fused silica. The metal‐glass composite layer was 0.85 μm below the surface and had a width of 0.5 μm. Thermal annealing enhanced the optical absorption of the annealed samples near 2.4 eV. The third‐order nonlinear optical response time is ≤35 ps; the magnitude of the effective nonlinear susceptibility is 200 times that of similar clusters embedded in ruby‐gold melt glass.

Method for preparing color-clear composite coatings having resistance to acid etching

Abstract: A color-plus-clear coating system is disclosed. A pigmented or colored basecoat is first applied to a substrate followed by the application of a transparent topcoat to the basecoat. The transparent topcoat composition is a crosslinkable composition comprising (1) a material containing a plurality of carbamate and/or urea functional groups and (2) an aminoplast crosslinking agent. The topcoat composition provides a composite coating with improved acid etch resistance, making the composite coating particularly useful as an automotive topcoat.

Enhanced Mechanical Properties of TiNi Shape Memory Fiber/Al Matrix Composite

Abstract: A design concept of shape memory TiNi fiber reinforced/Al metal matrix composite (SM-MMC) was proposed. Mechanical tensile properties such as stiffness and yield strength, were improved by the strengthening mechanisms: back stress in the Al matrix induced by stiffness of TiNi fibers and the compressive stress in the matrix caused by shape memory shrinkage of TiNi fibers. Damping capacity of the composite was also increased. These results suggest that this composite with prestrain can be applicable and is suitable for machinery, especially engine components where the material becomes stronger at higher temperatures owing to the shape memory effect

Composite resins in the 21st century

Abstract: Human enamel and dentin should be used as the physiologic standards with which to compare composite resins, especially in the posterior region. The intrinsic surface roughness of composite resins must be equal to or lower than the surface roughness of human enamel on enamel-to-enamel occlusal contact areas (Ra = 0.64 microns). Roughness determines the biologic strength of composite resins. The nanoindentation hardness value of the filler particles (2.91 to 8.84 GPa) must not be higher than that of the hydroxyapatite crystals of human enamel (3.39 GPa). Composite resins intended for posterior use should have a Young's modulus at least equal to, and preferably higher than, that of dentin (18.500 MPa). The compressive strength of enamel (384 MPa) and dentin (297 MPa) and the fracture strength of a natural tooth (molar = 305 MPa; premolar = 248 MPa) offer excellent mechanical standards to select the optimal strength for posterior composite resins. The in vivo occlusal contact area wear rate of composite resins must be comparable to the attritional enamel wear rate (about 39 microns/y) in molars. Differential wear between enamel and composite resin on the same tooth is a new criterion for visualizing and quantifying the wear resistance of composite resins in a biologic way. Posterior resins must have a radiographic opacity that is slightly in excess of that of human enamel (198% Al). Based on these standard criteria, it can be concluded that in the 21st century the ultrafine compact-filled composite resins may be the materials of choice for restoring posterior cavities.

Advanced polymer wood composite

Abstract: A composition in the form of pellets comprising a thermoplastic and wood fiber composite material suitable for forming structural members as a replacement for wood in the manufacture of doors and windows. The composite has less than about 10 wt % water based on pellet weight and a Young's modulus of at least about 500,000. Structural members are typically formed from the composite in an extrusion or an injection molding process.

Low resistance device element and interconnection structure

Abstract: A composite semiconductor structure which replaces polysilicon for conductive device elements and provides lower resistance interconnections between devices. The preferred structure is a conductive adhesion layer deposited in place of polysilicon in contact with a conductive metal layer traversing the interconnection. The preferred material for the adhesion layer is tungsten nitride, and for the metal layer--tungsten. If polysilicon is retained for device elements, the adhesion and metal layers may be placed in contact with the polysilicon element and along the interconnect structure providing an interconnect with lower resistance. Increased adhesion may be obtained by adding a cap layer of dielectric material atop the metal layer.

Polyethylene fibers‐polyethylene matrix composites: Preparation and physical properties

Abstract: Drawing on the difference in melting points of UHMPE fiber (150°C) and HDPE matrix (130°C), single-polymer composites were fabricated under various processing conditions. Because of the chemical similarity of the composite components, good bonding at the fiber-matrix interface could be expected. The matrix, the fiber, and unidirectional composite laminae were studied using TMA and DSC analyses, a hot-stage crystallization unit attached to a polarizing microscope, and an universal tensile testing machine. The TMA showed negative thermal expansion of the fiber over the complete temperature range of the experiment. Three regimes of contraction according to the values of the thermal expansion coefficient were detected. DSC analyses of either the fiber or the composite specimens did not show any appreciable changes after various thermal treatments. They also showed no evidence of fiber relaxation during manufacture, probably because of the pressure-related transverse constraint. The tensile strength and modulus values of the composite appeared to be fairly high and close to those reported for other composites reinforced with polyethylene (PE) fibers. An apparent maximum on the temperature dependencies of tensile properties was observed. A study of the matrix microstructure did not give any proof of transcrystalline growth at the fiber-matrix interface even for chemical or plasma surface-treated fibers. © 1993 John Wiley & Sons, Inc.

Synthesis of stable quasicrystalline particle-dispersed Al base composite alloys

Abstract: We report the preparation of the quasicrystalline particle-dispersed Al base composite alloys for the first time. Icosahedral AlCuFe quasicrystalline (i-AlCuFe) particles were homogeneously dispersed in a crystalline Al matrix using a novel process which combined mechanical alloying and hot press techniques. Hardness of the composite alloy increases with increasing volume fraction of the i-AlCuFe particle, i.e., increases from 25 kg/mm2 for pure Al to about 120 kg/mm2 for a 25 vol. % i-AlCuFe particle dispersed alloy.

Thermomechanical response of shape memory composites

Abstract: The Mori-Tanaka micromechanics method is used to predict the effective properties of composite materials consisting of a polymer matrix reinforced by a fiber made of a transformation shape memory effect (SME) material. The composite response is plotted for combinations of the following scenarios: (1) isothermal longitudinal and transverse stress input, (2) stress-free thermal loading, (3) constant fiber thermoelastic properties, and (4) thermoelastic fiber properties that vary with the martensite volume fraction. For the case of an isothermal stress input, the composite transformation stress, the maximum transformation strain, and the hysteresis are all reduced vis-a-vis the monolithic SME material. In contrast to a monolithic SME material, stress-free thermal loading of a SME composite can produce a transformation strain. It is shown that closed form solutions for the effective martensite and austenite start temperatures can be derived, that they are sensitive to the stress-free reference temperature of the fiber, and that the stress-free austenite and martensite start temperatures are higher than those of the monolithic SME material.

Method for making piezoelectric ceramic/polymer composite transducers

Abstract: A net-shape process for fabricating a fully dense ceramic preform for a piezoelectric or electrostrictive composite transducer exhibiting 1-3 or 2-2 connectivity. The process involves preparing a homogeneous, granulated, thermoplastic powder/binder mixture from a strongly piezoelectric or electrostrictive ceramic material powder and a thermoplastic organic binder selected to be nondestructively removed from the mixture by heating. The mixture is injection molded to form a self-supporting green body including a planar ceramic base with parallel ceramic elements extending perpendicularly from the base in a preselected array. Each element has a rod-like or lamellar shape. The body is released from the preform mold, heated to a temperature of 300°-700° C. for a time sufficient to completely remove the binder, and sintered to at least about 95% of theoretical density. To fabricate a piezoelectric or electrostrictive composite transducer exhibiting 1-3 or 2-2 connectivity and including a fully dense piezoelectric or electrostrictive ceramic phase, the preform is encapsulated in a polymeric material to form a 2-phase ceramic/polymer composite. The ceramic base is removed from the lower planar surface of the composite and the elements are exposed at each of the upper and lower planar surfaces. The composite is electroded to establish electrical contact with the elements. The elements may be poled to produce a piezoelectric composite transducer exhibiting 1-3 or 2-2 connectivity.

Integrated cross car structural duct cluster

Abstract: An automotive vehicle body has an integrated cross car structural duct cluster that is a composite that is connected to side pillars located on opposite sides of the vehicle body. The composite acts as a cross beam and provides four ducts that extend across the width of the vehicle body. Three ducts are related to the HVAC system of the vehicle and the fourth is a wiring duct. Five variations are disclosed. In two the composite comprises steel rods embedded in a molded plastic body. In the other three the composite comprises a steel plate that is attached to a molded plastic body.

The effective thermal conductivity of composites with coated reinforcement and the application to imperfect interfaces

Abstract: An analytical model is developed to predict the effective thermal conductivity of multiphase composites reinforced with coated fillers. The coated fillers are modeled as confocal spheroids, thus enabling the simulation of a wide range of reinforcement geometry ranging from thin flake to continuous fiber. The orientation of the coated fillers is described by a density distribution function which can simulate completely random, in‐plane random, and aligned distributions as special cases. The analytical approach appears to be the only one in the literature that renders closed‐form predictions of the effective thermal conductivity of composites with misoriented coated reinforcement and thus recourse to a numerical scheme is not required. The analytical approach is specialized to consider the effects of a thermal resistance at the filler‐matrix interface of a composite. Results of the proposed model are compared with those obtained by self‐consistent and differential estimates [Y. Benveniste and T. Miloh, J. Appl. Phys. 69, 1337 (1991)] for the effective thermal conductivity of a composite reinforced by completely random coated short fibers. The proposed model is in close agreement with the other two models for low conductivity coatings, but differs appreciably for high conductivity coatings. Finally, good agreement is shown to exist between analytical predictions and experimental results obtained from the literature for a diamond particle/zinc‐sulfide matrix composite with an interfacial thermal resistance.

Composite hydrogen separation metal membrane

Abstract: Composite hydrogen separation metal membranes are disclosed that contain an intermediate layer separating a base metal and a coating metal, wherein the intermediate layer is not a pure metal or metal alloy and is thermodynamically stable at operating temperatures.

Composite materials and methods for making the same

Abstract: The present invention generally relates to mechanisms for preventing undesirable oxidation (i.e., oxidation protection mechanisms) of reinforcement materials in composite bodies. The oxidation protection mechanisms include getterer materials which are added to the composite body which gather or scavenge undesirable oxidants which may enter the composite body. The getterer materials may be placed into at least a portion of the composite body such that any undesirable oxidant approaching, for example, a fiber reinforcement, would be scavenged by (e.g., reacted with) the getterer. In a preferred embodiment of the present invention, the getterer material(s) form at least one compound (e.g., at least one glassy material) which acts as a crack sealant, thereby further enhancing the oxidation protection of the composite body. One or more ceramic filler materials which serve as reinforcements may have a plurality of superimposed coatings thereon, at least one of which coatings may function as a getterer. The coated materials may be useful as reinforcing materials in ceramic matrix composites to provide improved mechanical properties such as fracture toughness. The present invention also relates to improved composites which incorporate these materials, and to their methods of manufacture.

Effects of particle shape and size distributions on the electrical and magnetic properties of nickel/polyethylene composites

Abstract: Electrical and magnetic properties of composite materials prepared by incorporating various nickel-based fillers of different shapes into polyethylene were investigated. The fillers used were nickel powders, nickel filamentary powders, nickel flakes, and nickel-coated graphite fibers. The particle-size distributions of the fillers were determined both before and after the processing of the composite samples. A wide range of filler volume fractions were used. In some cases, the volume fraction approached the maximum packing fraction of the solid phase to significantly exceed the percolation threshold. The composite samples were characterized in terms of their volume resistivity, dielectric constant, and magnetic permeability values. Filler particles of asymmetric shapes were very effective in terms of altering the electrical properties of the composite samples. At the highest loading levels of the nickel fillers, the volume resistivity values of the composites decreased by more than 17 orders of magnitude. AT such high filler concentrations, the dielectric constant values of the composite samples increased considerably, to values that were greater than 1,000. The permeability values of the samples increased linearly with the volume fraction of the nickel filler and were insensitive to the shape of the fillers. The highest relative permeability value measured was 5.8 for compositesmore » with 67% by volume of nickel powder.« less