Showing papers on "Young's modulus published in 1985"

Analysis of stress-strain, fracture, and ductility behavior of aluminum matrix composites containing discontinuous silicon carbide reinforcement

Abstract: Mechanical properties and stress-strain behavior were evaluated for several types of commercially fabricated aluminum matrix composites, containing up to 40 vol pct discontinuous SiC whisker, nodule, or particulate reinforcement. The elastic modulus of the composites was found to be isotropic to be independent of type of reinforcement, and to be controlled solely by the volume percentage of SiC reinforcement present. The yield/tensile strengths and ductility were controlled primarily by the matrix alloy and temper condition. Type and orientation of reinforcement had some effect on the strengths of composites, but only for those in which the whisker reinforcement was highly oriented. Ductility decreased with increasing reinforcement content; however, the fracture strains observed were higher than those reported in the literature for this type of composite. This increase in fracture strain was probably attributable to cleaner matrix powder, better mixing, and increased mechanical working during fabrication. Comparison of properties with conventional aluminum and titanium structural alloys showed that the properties of these low-cost, lightweight composites demonstrated very good potential for application to aerospace structures.

Properties of concrete made with crushed concrete as coarse aggregate

Abstract: Synopsis Effects of using recycled concrete of different qualities as coarse aggregate upon the strength and deformation of concrete are reported. Tests on the aggregates showed that the recycled concrete aggregates have lower specific gravity and higher absorption capacity than the original crushed granite aggregate. The resistance to mechanical actions such as impact, crushing and abrasion for the recycled concrete aggregates is also lower. The effects of using recycled concrete aggregates instead of natural aggregates in concrete are: reduction in compressive strength up to 25%; reduction in modulus of elasticity up to 30%; improvement in damping capacity up to 30%; and higher amounts of drying shrinkage and creep. Available methods of predicting the modulus of elasticity on the basis of compressive strength for conventional concrete overestimate the modulus of elasticity for recycled-aggregate concretes.

Jute-reinforced polyester composites

Abstract: Raw jute fibre has been incorporated in a polyester resin matrix to form uniaxially reinforced composites containing up to 60 vol% fibre. The tensile strength and Young's modulus, work of fracture determined by Charpy impact and inter-laminar shear strength have been measured as a function of fibre volume fraction. These properties all follow a Rule of Mixtures relationship with the volume fraction of jute. Derived fibre strength and Young's modulus were calculated as 442 MN m−2 and 55.5 GN m−2 respectively. Polyester resin forms an intimate bond with jute fibres up to a volume fraction of 0.6, above which the quantity of resin is insufficient to wet fibres completely. At this volume fraction the Young's modulus of the composite is approximately 35 GN m−2, the tensile strength is 250 MN m−2, the work of fracture is 22 kJ m−2 and the inter-laminar shear strength is 24 MN m−2. The properties of jute and glass fibres are compared, and on a weight and cost basis jute fibres are seen in many respects to be superior to glass fibres as a composite reinforcement.

The temperature‐dependence of some mechanical properties of a cured epoxy resin system

Abstract: The tensile mechanical properties and fracture toughness of a Bisphenol-A type difunctional epoxy resin, cured with different amounts of metaphenylene diamine, using two cure cycles, were determined over a range of temperature. The tensile modulus in the glassy state was seen to be predominantly related to intermolecular packing, while in the rubbery state crosslink density was the important factor. Yielding appeared to be due to an increase in free volume as a result of dilatation during the tensile test and was related to a critical shear stress. The large strain properties like tensile strength, elongation-to-break, and toughness showed a more complex dependence on chemical structure, molecular architecture, intermolecular packing, and crosslink density. The roles played by the relaxation processes in determining mechanical properties are highlighted.

The use of a δ-alumina fibre for metal-matrix composites

Abstract: Composites formed by infiltration of an array of fine alumina fibres with aluminium alloy melts have been investigated in terms of fabrication characteristics, microstructural features and mechanical properties. A production method has been developed in which the application of pressure ensures very low porosity levels and strong fibre-matrix bonding. Details of the transport phenomena occurring during fabrication have been explored with a view to optimizing selection of applied pressure, thermal fields, alloy composition and the structure of the fibrous preform. Microstructural examinations revealed an intimate fibre-matrix bond, but the virtual absence of any chemical reaction at the interface. Comparison of property measurements with data from unreinforced alloys revealed increased elastic moduli and marked improvement in tensile strength at elevated temperature, accompanied by reductions in elongation.

Elastic constants and structure of the vitreous system Co3O4P2O5

Abstract: The elastic moduli of the entire vitreous range of the system CoPO that can be prepared by melting together Co3O4 and P2O5 oxides in open crucibles, have been measured by ultrasonic techniques at 15 MHz. The bulk, shear, longitudinal and Young's moduli and the Poisson ratio are found to be rather sensitive to the glass composition. It is found from this ultrasonic data, that the glass system can be divided into “three compositional regions”. This behaviour is qualitatively interpreted in terms of the cobalt co-ordination, crosslink densities, interatomic force constants and atomic ring sizes. Also presented is a full discussion of effects of annealing on elastic properties.

Mechanical properties of composition modulated Cu‐Ni foils

Abstract: Measurements have been made of the Young’s, flexural, and torsional moduli of compositionally modulated Cu‐Ni foils. The average composition of the foils was 50‐at. % Ni and the wavelength of the modulation ranged from 8 to 80 A. At a wavelength of 20 A, the flexural modulus exhibited a maximum and had a value two times greater than that measured at shorter or longer wavelengths or that calculated from the bulk single‐crystal elastic constants of a homogeneous alloy. The Young’s and torsion moduli exhibited two maxima at 12 and 28 A. These results are consistent with earlier measurements of the biaxial modulus using a bulge tester. It was also observed that at a wavelength of 20 A there was a threefold increase in the breaking stress of the foils as compared with homogeneous bulk alloys.

Laminated Glass Units under Uniform Lateral Pressure

Abstract: Laminated flat glass is gaining popularity as an architectural glazing product. Despite its increased use as a cladding material, its structural properties are not well known. Research undertaken to advance understanding of the behavior of laminated glass units under lateral pressure representing wind loads is reported. Laminated glass units are comprised of two layers of glass connected by a thin interlayer of polyvinyl butyral. The material properties of the interlayer are very different from the properties of the glass plates which it joins together; its modulus of elasticity in shear is only about 1/10,000th that of glass. Experimental stress analyses were conducted on several laminated glass units to ascertain whether their behavior was similar to a monolithic glass plate of the same nominal thickness, or to a layered glass unit consisting of two glass plates with no interlayer. At room temperature the laminated glass unit behaves much like a monolithic glass plate of the same nominal thickness. At elevated temperatures [170°F (77°C)] the behavior changes, and approaches that of a layered glass unit with no interlayer. Results of the experimental stress analyses are compared with theoretical stress analyses designed to characterize the behavior of monolithic glass plates and layered glass units.

A novel concept in describing elastic and plastic properties of semicrystalline polymers: polyethylene

Abstract: An analysis of micro-hardness and elastic modulus data for different lamellar systems in the light of both eutectoid copolymer and chain folded lamellar microphases is presented. A novel thermodynamically derived expression offering a fair description of hardness (stress required to plastically deform a crystal) of autonomous non-homogeneous microphases in terms of the average crystal thickness, including a defective surface boundary is developed. The present results characterize the mechansim of plastic deformation as primarily governed by the initial mosaic-block structure controlling the “solid state” mechanism underlined. The average dimensions of the remaining blocks after crystal destruction are thus related to the original block dimensions before plastic deformation. Within this context it is shown that the dissipated energy for crystal destruction increases very rapidly with the molar mass-function of crystalline material.

Mechanical properties of polypropylene filled with calcium carbonate

Abstract: The tensile behavior of polypropylene (PP) filled with calcium carbonate particles has been studied using a tensile test. In particular, the effect of strain rate, filler content, and filler size upon the elastic modulus, yield stress, and strain of surface-modified and unmodified particles-filled PP were investigated. The results indicated that the elastic modulus and yield stress of an unmodified system were increased with an increase of strain rate and filler content, and with a decrease of filler size. The yield strain was decreased with an increase of filler content, and with a decrease of filler size, but did not depend on the strain rate. Although the dependence of elastic modulus on the filler size was maintained even by the surface-modified fillers, that dependence on the strain rate and filler content was decreased by such fillers. This may be because the modifier is present at the interface of filler and polymer matrix.

Interfacial effects in carbon-epoxies

Abstract: Carbon fibre-reinforced epoxy resin samples made with aligned fibres, with lengths of 1 to 5 mm, had strengths and Young's moduli that were affected by fibre length, and surface condition and well as fibre volume fraction. Stress-strain trajectories were all linear, except when the fibres were coated with silicone resin. Fibre critical lengths were found to be affected by the surface condition, but composite strength could not be accounted for when the critical length was inserted into the usual equations, based on fibre slip. The results indicate that existing theoretical treatments for strength and modulus should take more account of the overstressing of fibres adjacent to fibre ends.

Model copolymers of ethylene with butene‐1 made by hydrogenation of polybutadiene: Chemical composition and selected physical properties

Abstract: Hydrogenation of polybutadienes with from 8 to nearly 100% vinyl content was used to prepare a series of model copolymers of ethylene and butene-1 with uniform microstructures and narrow molecular weight distributions. They range from readily crystallizable to completely amorphous, depending on the frequency of ethyl side branches (2–50 per 100 skeletal carbons). Melting temperature, secondary transition temperature, density, plateau modulus for the melt, and elastic modulus for the solid were obtained as functions of branch content. The effect of crystallinity on the secondary transition and modulus of the solid is discussed.

Improvements in fibre reinforced plastics structures

Abstract: An air permeable sheet-like structure comprising 20 to 60% by weight of reinforcing fibres having a high modulus of elasticity (as herein defined), and being between about 7 and about 50 millimetres long, and 40 to 80% by weight of wholly or substantially unconsolidated particulate plastics material, and in which the fibrous and plastics components are bonded into an air permeable structure.

High-modulus-high-strength poly-(p-phenylene benzobisthiazole) fibres

Abstract: Heat-treatment processing of dry-jet wet-spun poly-(p-phenylene benzobisthiazole) fibres was undertaken to enhance fibre tensile mechanical properties. The effects of fibre tension and temperature and time of heat treatment in a nitrogen atmosphere on fibre mechanical properties were systematically investigated. Fibres possessing a tensile modulus as high as 300 GPa along with a tensile strength of 3 GPa have been produced. To attain this level of tensile properties, heat-treatment temperatures of 630 to 680° C for residence times of under one minute were required while applying tensions approaching fibre breaking stress at the elevated temperatures; conditions bordered on fibre degradation. Fibre structural changes associated with heat treatment and enchancement of mechanical properties are discussed in Part 2 of this work.

Wood tensile strength at temperatures and moisture contents simulating fire conditions

Abstract: The immediate tensile strength parameters for spruce parallel to the grain and for hardboard have been determined at equilibrium conditions at temperatures up to 250°C. Below 100°C the moisture content has been varied between 0 and 30%. Above 100°C dry samples have been studied. An increase in moisture content up to about 12% leads to a slight increase in the tensile strength of spruce whereas the modulus of elasticity remains constant. With a further increase in moisture content, both properties decrease significantly. At any given moisture content, both properties decrease with increasing temperature. The corresponding strain at rupture is constant. An increase in temperature leads to a more or less linear decrease in the tensile strength and in the modulus of elasticity up to about 200°C. Above 200°C there is a more rapid decrease due to thermal softening. It is most relevant to consider the relative strength decrease since the absolute levels may be quite high due to the fact that wood samples without any irregularities were used. Such relative strength data are compared with the small amount of similar data found in the literature. The effects on the modulus of elasticity are discussed in terms of thermal softening and of water as a softener for the cellulose/hemicellulose polymers. The glass transition temperature is determined as a function of the moisture content.

The Elastic Longitudinal Modulus and Poisson's Ratio of Fiber Composites:

Abstract: A simplified theoretical approach for the prediction of the longitudinal elastic modulus and Poisson's ratio in fiber-reinforced composites is developed in this paper. The method considers that the main parameter affecting the elastic behaviour of com posite materials is the existence of the mesophase layer, between fiber and matrix, which possesses different physico-chemical properties than those of the constituent phases. The simplest and most convenient laws of variation are a linear, a parabolic, a hyperbolic and a logarithmic variation of E, and v, for the mesophase material, versus the polar radius from the fiber-surface. In this paper, therefore, these laws are con sidered for evaluating the overall moduli of the composite. Each one of these laws is applied to the representative volume element of the fiber composite and compares favorably with the unfolding model, introduced by one of the authors (PST), as well as with respective data existing in literature.

Elastic moduli of ultradrawn polyethylene

Abstract: Les cinq modules d'elasticite independants du PEhd oriente avec un taux d'etirage de 1 a 27, sont determines de −60 a 100°C par une methode ultrasonore a 10 MHz

Hardening non-linear behaviour in longitudinal tension of unidirectional carbon composites

Abstract: Uniaxial tensile tests of unidirectional carbon-epoxy coupons are conducted in the longitudinal direction. It is observed that the longitudinal modulus increases with axial stress or strain up to the intermediate level of tension. A fractional constitutive relation with a quadratic denominator is derived by the method of the theory of non-linear elasticity. This equation adopting the estimated higher-order compliance coefficients exhibits an excellent agreement with the experimental results. An empirical strain-based equation is also proposed as a simpler alternative. Averaging formulae for both types of relation are provided for a practical application. The present phenomenon includes the behaviour in a low-stress region discovered by some early work. The consideration of the present non-linear behaviour improves the correlation between theory and experiments in stress-strain relationships of fabric composites with carbon fibres.

Comparison of Interlocked Fabric and Laminated Fabric Kevlar 49/Epoxy Composites

Abstract: The mechanical properties of a multilayered, interlocked Kevlar 49 fabric reinforced epoxy composite with roughly a 4% fiber volume fraction in the through-the-thickness direction are reported. These results are compared to those of a standard Kevlar fabric laminate containing the same overall fiber volume fraction. Through-the-thickness reinforcement increases the apparent short beam shear strength by 25%. Actually, the shear failure mode is suppressed by the through-the-thickness reinforcement, and failure is due to yarn kinking on the compressive side of the beam. In contrast, the in-plane properties of the interlocked fabric reinforced composite are lower than those of the standard fabric laminate. For example, the initial tensile modulus is reduced by 35% while the ultimate tensile strength is reduced by roughly 25%. This loss in properties is thought to be due to both the relatively greater crimp in the interlocked fabric used in this study and fiber stress concentrations introduced by the binder yarns.

Elastic properties of SiC, AIN, and their solid solutions and particulate composites

Abstract: The elastic properties of SiC and AIN were determined at room temperature as a function of porosity by the resonant sphere technique. For an exponential relation, a zero porosity Young's modulus value (E0) of 437 GPa (63.4 X 10W psi) and an experimental constant (b) of 2.73 were found for SiC, and an E0 = 322 GPa (46.7 X 10W psi) and b = 2.44 for AIN. The elastic moduli of SiC-AIN solid solutions varied nearly linearly as a function of composition. The elastic moduli of SiC-AIN two-phase particulate composites were lower than those of the corresponding solid solutions and also lower than values calculated from composite theory, with the largest deviation at approx. =25% AIN and a gradual decrease to zero deviation at 100% AIN.

Temperature and stress dependence of Young’s modulus in semiconducting barium titanate ceramics

Abstract: In order to study the temperature and stress dependence of Young’s modulus in semiconducting barium titanate ceramics, the longitudinal sound velocity was measured at a frequency of 5 MHz in the temperature range of 20–180 °C. It is striking that at temperatures above the Curie point (Tc=120 °C) the sound velocity reaches values that are 10–20% higher than those at room temperature. Furthermore, a shift of the Curie point of about 2×10−8 K/Pa is observed if uniaxial stress is applied perpendicular to the sound propagation. Both effects can be understood by means of the phenomenological theory of Devonshire.

Cell wall elasticity: I. A critique of the bulk elastic modulus approach and an analysis using polymer elastic principles.

Abstract: The traditional bulk elastic modulus approach to plant cell pressure-volume relations is inconsistent with its definition. The relationship between the bulk modulus and Young's modulus that forms the basis of their usual application to cell pressure-volume properties is demonstrated to be physically meaningless. The bulk modulus describes stress/strain relations of solid, homogeneous bodies undergoing small deformations, whereas the plant cell is best described as a thin-shelled, fluid-filled structure with a polymer base. Because cell walls possess a polymer structure, an alternative method of mechanical analysis is presented using polymer elasticity principles. This initial study presents the groundwork of polymer mechanics as would be applied to cell walls and discusses how the matrix and microfibrillar network induce nonlinear stress/strain relationships in the cell wall in response to turgor pressure. In subsequent studies, these concepts will be expanded to include anisotropic expansion as regulated by the microfibrillar network.

Elastic constants of two dental porcelains

Abstract: The development of stress that affects the bonding in porcelain-fused-to-metal (PFM) systems can be influenced by the temperature dependence of the elastic constants of both systems. Instead of using the normal, static procedure, e.g. determining the slope of a stress-strain curve, and measuring the lateral and vertical strains, in this study the sonic resonance technique was used to determine the elastic moduli for two dental bodyporcelains. The sonic resonance technique involves the determination of both the flexural as well as the torsional resonance frequencies. From these values both Young's,Y, and shear moduli,G, are determined. Since two elastic constants are sufficient to describe completely the elastic response of isotropic materials, it was also possible to compute, by usingY andG, the bulk modulus,B, and the Poisson's ratio. Resonant frequency measurements taken at elevated temperatures resulted in correspondingly lower values for the elastic constants. Young's and shear moduli for two dental porcelains obtained in the range from 20° C (293 K) to 500° C (773 K) are presented in this study. These data may in the future be used for refined stress calculations in PFM systems.

Mechanical properties of blends of nylon 6 with a chemically modified polyolefin

Abstract: Both tensile and impact properties were measured of a heterogeneous polymer blend system, consisting of nylon 6 and a chemically modified polyolefin, DuPont CXA3095, which is an ethylene-based multifunctional polymer. It was found, from the tensile testing, that the blends exhibited no signs of necking, and the addition of a soft resin (CXA3095) reduced the modulus and the tensile strength of nylon 6, whereas the percent elongation at break went through a minimum. When 20 wt % of CXA3095 was added to nylon 6, the impact strength was increased approximately three times. When the factors describing the interfacial adhesion were incorporated, the existing models for predicting the tensile modulus of blends were found to describe the experimental data rather well. In order to help explain the mechanical behavior observed, photomicrographs were taken of the fracture surfaces, using a scanning electron microscope.

Dynamic mechanical behavior of ultradrawn polyethylene films produced by gelation/crystallization from solution

Abstract: This paper is concerned with the temperature dependence of mechanical properties of ultradrawn polyethylene in terms of storage modulus E' and loss factor tanδ by the measurement of the complex dynamic tensile modulus over ranges of temperature from 20 to 140 ‡C. Interestingly, E' of a specimen with drawn ratio of 300 is about 120 GPa at 140 ‡C, when the measurement is carried out at a frequency of 100 Hz. This is a very high value. In addition, the drawn specimens were irradiated to try to produce ultra-drawn polyethylene films with more excellent mechanical and thermal properties. However, the melting peak shifts to a lower temperature with increasing radiation dose. This result is probably attributed to the considerably radiation-induced scission of extended chains constructing crystals.

Tensile properties of carbon fibers from acrylic fibers stabilized under isothermal conditions

Abstract: A series of carbon fibers were prepared from the acrylic fibers thermally stabilized in air under various temperature–time conditions, and the relation between the extent of stabilization and the tensile properties of carbon fibers was investigated. The density of stabilized fibers was adopted as a measure of the extent of stabilization. The tensile modulus of carbon fibers changed dependently on stabilization temperature. However, the variation of the tensile modulus of carbon fibers with the density of stabilized fibers was small if stabilization temperature was constant. In the relation between the tensile strength of carbon fibers and the density of stabilized fibers, a feature depending on stabilization temperature was not evident, and the tensile strength of carbon fibers showed a maximum in the density range from about 1.34 to 1.39 g/cm3 of stabilized fibers.