Showing papers on "Composite number published in 1997"

Stress analysis of fiber-reinforced composite materials

Abstract: 1 Fiber-Reinforced Composite Materials2 Linear Elastic Stress-Strain Characteristics of Fiber-Reinforced Material3 Prediction of Engineering Properties Using Micromechanics4 The Plane-Stress Assumption5 Plane-Stress, Stress-Strain Relations in a Global Coordinate System6 Classical Lamination Theory: The Kirchoff Hypothesis7 Classical Lamination Theory: Lamination Stiffness Matrix8 Classical Lamination Theory: Additonal Examples9 Failure Theories for Fiber-Reinforced Materials Maximum Stress Criterion10 Failure Theories for Fiber-Reinforced Materials The TSAI-Wu Criterion11 Environmentally-Induced Stresses in Laminates12 Through-Thickness Laminate Strains13 Introduction to Fiber-Reinforced Laminated Planes14 Appendix Manufacturing Composite Laminates

Biofiber‐reinforced polypropylene composites

Abstract: Biofibers, natural lignocellulosics, have an outstanding potential as a reinforcement in thermoplastics. This study deals with the preparation of lignocellulosic composites by reactive extrusion processing in which good interfacial adhesion is generated by a combination of fiber modification and matrix modification methods. PP matrix was modified by reacting with maleic anhydride and subsequently bonded to the surface of the modified lignocellulosic component, in-situ. The fiber surface was modified by reacting it with a silane in a simple and quick aqueous reaction system, similar to that employed for glass fibers. The modified fibers are then extruded with the modified polymer matrix to form the compatibilized composite. The various reactions between the lignocellulosic fiber/filler and modified polymer chains, is expected to improve the interfacial adhesion significantly as opposed to simple mixing of the two components, since new covalent bonds between the fiber surface and matrix are created in the former case. These composite blends were then injection molded for mechanical characterization. Typical mechanical tests on strength, toughness and Izod impact energy were performed and the results are reported. These findings are discussed in view of the improved adhesion resulting from reactions and enhanced polar interactions at phase boundaries.

Representative volume element size for elastic composites: A numerical study

Abstract: Monte Carlo (MC) runs are employed to generate statistically independent realizations of a periodic elastic composite with a disordered unit cell made up of 8, 27, and 64 nonoverlapping identical spheres. In the limit of an infinite number of spheres in the disordered unit cell, this periodic composite obeys the Percus-Yevick hard-sphere statistics. By construction, the MC realizations studied have the same inclusion fraction. A constant-strain-tetrahedra displacement-based finite element code with an iterative solver is used to calculate the overall elastic constants of these periodic MC realizations. It appears that the scatter in the individual elastic constants already obtained with a few dozen spheres in the disordered unit cell is remarkably small and the averages obtained with varying numbers of spheres are practically stationary.

Composite memory material comprising a mixture of phase-change memory material and dielectric material

Abstract: A composite memory material (36) comprising a mixture of active phase-change memory material and inactive dielectric material. The phase-change material includes one or more elements selected from the group consisting of Te, Se, Ge, Sb, Bi, Pb, Sn, As, S, Si, P, O and mixtures of alloys thereof. A single cell memory element (30) comprising the aforementioned composite memory material (36), and a pair of spacedly disposed contacts (6, 8).

Thermoplastic Nanocomposites Filled With Wheat Straw Cellulose Whiskers. Part II: Effect of Processing and Modeling

Abstract: The reinforcing effect of cellulose microcrystals, or whiskers, dispersed in a thermoplastic matrix is analyzed. In Part I [Polym. Compos., 17, 604 (1996)], the preparation and the characterization of cellulose whiskers obtained from wheat straw were detailed. Composite films were processed by freeze-drying and molding a mixture of aqueous suspension of these microcrystals and a film forming latex of poly(Styrene-co-ButylAcrylate). Using the same filler and latex, materials were processed by casting and evaporating the mixture of aqueous suspensions. It was found that the reinforcing effect is greater in the latter case. This behavior is ascribed to the sedimentation of the filler during evaporation, evidenced by scanning electron microscopy, wide angle X-ray scattering, and dynamic mechanical analysis, and to the formation of a network of whiskers governed by a percolation mechanism. The behavior of the composite is modeled by subdividing the sample into layers with different whisker contents lying parallel to the film surface.

Analysis, design, and optimization of composite structures

Abstract: ANALYSIS OF COMPOSITE MATERIALS AND STRUCTURAL MEMBERS OF A PERIODIC STRUCTURE. Asymptotic Methods in the Mechanics of Composites. Analysis of the Effective Properties of Highly Porous Composite Materials and Structures. Homogenization Models for Thin-Walled Composite Structural Members. Effective Properties of Thin-Walled Composite Structural Members. Strength Criteria for Composite Materials. DESIGN OF COMPOSITE MATERIALS AND STRUCTURAL MEMBERS. Design of Laminated Composites with Given Effective Characteristics. Design of High-Stiffness, Fibre-Reinforced Composites. Design of Composite Structural Members with Given Effective Characteristics. Smart Composite Structures. Appendices. References. Index.

Optical recognition of CO and H2 by use of gas-sensitiveAu–Co3O4 composite films

Abstract: Gold–cobalt oxide (Au–Co 3 O 4 ) composite films have been prepared by the sputter-deposition of gold onto a glass plate substrate followed by pyrolysis of spin-coated cobalt 2-ethylhexanoate. The films comprise small Au particles and Co 3 O 4 nanocrystals, and exhibit different and independent optical responses to CO and H 2 in air. Carbon monoxide caused only a decrease in absorbance, while H 2 caused both a decrease and an increase in absorbance at different wavelengths. Among solid-state gas sensor materials, this Au–Co 3 O 4 composite film is probably the first example of an inorganic material which can be used for the recognition of CO and H 2 molecules through optical absorbance changes.

Influence of filament winding parameters on composite vessel quality and strength

Abstract: An experimental design investigation of manufacturing and design variables that affect composite vessel quality, strength, and stiffness was conducted. Eight 20-in. cylinders (with one additional cylinder as a replicate) were manufactured and tested for hoop strength, hoop stiffness, fiber and void volume fraction distribution through thickness, residual stress, and interlaminar shear strength. Material and processing variables were divided into five categories: (a) resin, (b) fiber, (c) fabrication process, (d) design, and (e) equipment. Five variables were selected (from a list of 12) for study using a 1 4 fractional factorial design of experiment setup. The five variables were: (a) winding tension, (b) stacking sequence, (c) winding-tension gradient, (d) winding time, and (e) cut-versus-uncut helicals. Statistical analysis of the data shows that the composite vessel strength was affected by the manufacturing and design variables. In general, it was found that composite strength was significantly affected by the laminate stacking sequence, winding tension, winding-tension gradient, winding time, and the interaction between winding-tension gradient and winding time. The mechanism that increased composite strength was related to the strong correlation between fiber volume in the composite and vessel strength. Cylinders with high fiber volume in the hoop layers tended to deliver high fiber strength.

Method and apparatus for producing high efficiency fibrous media incorporating discontinuous sub-micron diameter fibers, and web media formed thereby

Abstract: A composite filtration medium web of fibers containing a controlled dispersion of a mixture of sub-micron and greater than sub-micron diameter polymeric fibers is described. The filtration medium is made by a two dimensional array of cells, each of which produces a single high velocity two-phase solids-gas jet of discontinuous fibers entrained in air. The cells are arranged so that the individual jets are induced to collide in flight with neighboring jets in their region of fiber formation, to cause the individual nascent fibers of adjacent jets to deform and become entangled with and partially wrap around each other at high velocity and in a localized fine scale manner before they have had an opportunity to cool to a relatively rigid state. The cells are individually adjusted to control the mean diameters, lengths and trajectories of the fibers they produce. Certain cells are adjusted to generate a significant percentage of fibers having diameters less than one micron diameter, and which are relatively shorter in length and certain other cells are adjusted to generate a significant percentage of structure-forming reinforcing fibers having diameters greater than one micron diameter which are relatively longer in length. By employing appropriate close positioning and orientation of the cells in the array, the sub-micron fibers are caused to promptly entangle with and partially wrap around the larger reinforcing fibers. The larger fibers thereby trap and immobilize the sub-micron diameter fibers in the region of formation, to minimize the tendency of sub-micron diameter fibers to clump, agglomerate, or rope together in flight. Also, the larger fibers in flight are made to form a protective curtain to prevent the sub-micron fibers from being carried off by stray air currents.

Effect of composite type, light intensity, configuration factor and laser polymerization on polymerization contraction forces

Abstract: PURPOSE To investigate the effect of composite type, light intensity, configuration factor and laser polymerization on polymerization contraction force. MATERIALS AND METHODS Glass rods (10 pairs/group) were etched with HF acid, silanated, unfilled resin applied and light cured for 20 s. Rods were held vertically in chucks on a Zwick machine. A cylindrical matrix was filled with Silar chemical cure, Silux Plus microfill or Z-100 hybrid composite and the crosshead of the UTM positioned at an inter-rod distance corresponding to a specific ratio of bound to unbound composite surface area (configuration factor or C). Exposure time with the Demetron 401 conventional visible light curing unit (D401) was 40 s/side (80 s total). Exposure times for the ILT Model D5500 air cooled laser (LAC) and Model 5500ABL water cooled laser (LWC) was 20 s/side (40 s total). Experimental groups, n = 10 with constant factors in parentheses, included: (1) Silar chemical-cured (C = 3); (2) Z-100 hybrid (C = 3, D401, 100% intensity); (3) Silux Plus microfill (C = 3, D401, 100% intensity); (4) D401 100% light intensity = 476 mW (Z-100, C = 3, D401); (5) D401 50% intensity = 238 mW (Z-100, C = 3, D401); (6) D401 25% intensity = 119 mW (Z-100, C = 3, D401); (7-9) C = 5, 3 & 1 respectively (Z-100, D401, 100% intensity); (10) D401 with 13 mm tip = 391 mW/cm2 (Z-100, C = 3; D401); (11) D401 with Turbo Tip = 811 mW/cm2 (Z-100, C = 3; D401); (12) LAC = 265 mW, 689 mW/cm2 (Z-100, C = 3); (13) LWC = 365 mW, 1100 mW/cm2 (Z-100, C = 3). One Way ANOVA and Duncan's Multiple Range Test (alpha = 0.05) were performed separately for each variable. RESULTS Homogeneous subsets by variable were: composite type Group 1 (25N) < Group 3 (65.8N) < Group 2 (90.4N); intensity Group 6 (73.9N) = Group 5 (77.7N) < Group 4 (90.4N); C-Factor Group 7 (81.8N) < Group 8 (90.4N) < Group 9 (103.4N); light source Group 12 (77.4N) = Group 13 (79.1N) < Group 10 (90.4N) = Group 11.(89.4N). The chemical-cured composite had the lowest maximum polymerization contraction force, the microfill was intermediate and the hybrid composite had the highest recorded force. Increases in light intensity increased the maximum force on the force/time curve. Maximum forces were inversely related to C-factor (C5 < C3 < C1) and directly related to composite volume in a non-rigid system which allowed compliance. Maximum force was not significantly different with the two tips tested on the conventional curing light. Forces obtained with laser polymerization were similar for the two laser groups, which were both statistically lower than the conventional light tested.

Analytical and experimental studies on the characteristics of composite solid-state laser rods in diode-end-pumped geometry

Abstract: In this paper, we report analytical and experimental studies on the characteristics of end-pumped composite laser rods with undoped end, using mainly Nd:YAG rods as an example. It is found that the peak temperature rise in a composite rod decreases to <70% of that in a noncomposite crystal. Thermal stress is dramatically reduced to <60% by employing the composite rod structure, We also demonstrate high-power operation of the diode-end-pumped composite Nd:YVO/sub 4/ rod and a maximum CW output power of 9.3 W was achieved, which is about 1.5 times higher than that in the noncomposite rod. This high-power performance of the composite rod is primarily attributed to the reduction of thermal stress inside the rod.

Thermally conductive polytrafluoroethylene article

Abstract: A thermally conductive composite article is provided having a PTFE material or a PTFE matrix material which has disposed therein thermally conductive particles, and a phase change material.

Thermomechanical behaviour of composite materials and structures under high temperatures: 2. Structures

Abstract: This paper is devoted to modelling of the thermomechanical behaviour of composite structures under high-temperature heating up to the temperature of charring of the composite. Attention is focused on the peculiarities of the behaviour of composite shells under high temperatures. It is also shown that the internal heat-mass transfer of pyrolysis gases has an essential effect on the stress state of the shell under high temperatures. Transverse stresses, which are usually neglected for composite shells, under high temperatures are indicated to be the most dangerous. These stresses can cause delamination of composite shells. A numerical analysis of the conditions of delamination for composite shells is conducted, and computed results are compared with experimental data on the thermomechanical destruction of cylindrical composite shells.

Composite oxide, composite oxide carrier and catalyst

Abstract: The composite oxide and the composite oxide carrier are manufactured by the precursor forming step and firing step. The precursor forming step includes high speed mixing means. The composite oxide catalyst is obtained by preparing a composite of catalytic components simultaneously with the formation of the precursor of composite oxide in the step of forming the precursor of composite oxide. The composite oxide and the composite oxide carrier are composed of a composite oxide in which at least one of cerium and zirconium, and aluminium disperse with extremely high homogeneity. With this structure, the heat resistance of the carrier is improved and consequently, enlargement of particles of the composite oxide defining the carrier, and sintering of adjacent particles of the composite oxide can be restrained, whereby the catalyst using the composite oxide carrier in accordance with the present invention is excellent in heat resistance. With the present invention, the carrier is not limited to a general catalyst carrier. The carrier may be interpreted to indicate general formed bodies. For example, the carrier with the present invention can be also used as materials for sensors and electrodes, optical materials, semiconductors and structure materials. Furthermore, the carrier can be used for a three-way catalyst, NOx catalyst or oxidation catalyst or a part thereof, and a promoter.

Composition and method for polishing a composite of silica and silicon nitride

Abstract: A composition is provided for polishing a composite comprised of silica and silicon nitride comprising: an aqueous medium, abrasive particles, a surfactant, and a compound which complexes with the silica and silicon nitride wherein the complexing agent has has two or more functional groups each having a dissociable proton, the functional groups being the same or different.

Multi-layer, multi-grade multiple cutting surface pdc cutter

Abstract: An improved polycrystalline diamond composite ("PDC") cutter with secondary PDC cutting surfaces in addition to a primary PDC cutting surface is formed comprising of at least two wafers of cemented carbide bonded together. The secondary cutting surfaces are formed by compacting and sintering diamond in grooves formed at the surface of the wafers. Wafers of different grades of cemented carbide may be used. Moreover, different grades of diamond may be compacted and sintered in different grooves.

The humidity dependence of the electrical conductivity of a solublepolyaniline–poly(vinyl alcohol) composite film

Abstract: A humidity-sensitive composite film has been synthesized that consists of soluble polyaniline (PAn) and poly(vinyl alcohol) (PVA). PAn gave a percolation threshold where the electrical conductivity rose sharply at a volume fraction of 0.1%. This value is very small compared with that (about 5 vol%) reported in general for composite films consisting of conducting and non-conducting polymers, indicating that the two polymers used in this study were mixing completely. The conductivity of the PAn–PVA composite was proportional to the relative humidity, and the linearity was valid from 3×10–5 to 1.5×10–1 S cm–1 . The response time of the composite for the humidity change was 45 s and 9 min for moistening and desiccating steps, respectively. The conductivity of the composite film varied depending on the doping level of PAn, which was affected by the concentration of water molecules surrounding the conducting polymer. At high humidity, the PAn was in the form of an emeraldine salt, and transformed into a non-conducting base with decreasing environmental humidity.

Composite construction design for buildings

Abstract: Introduction. Composite Systems. Composite Beams. Composite Columns. Lateral Resisting Systems. Design of Joints. Literature.