Showing papers on "Volume fraction published in 1971"

Stress-strain behavior of styrene-acrylonitrile/glass bead composites in the glassy region

Abstract: The effects of temperature, strain rate and filler content on tensile properties of SAN/glass bead composites are studied. A point of discontinuity on the stress-strain curves for unannealed composites is investigated, annealing results in smooth curves with no discontinuities. A simple model for the filler effect on yield stress is suggested and shown to be in a good agreement with experimental data. A double shifting procedure to account for the temperature and filler effects on yield stress as a function of strain rate is proposed. A single master curve that can be represented by the equation: relates composite yield stress to strain rate, temperature and filler volume fraction.

Fracture energy of an epoxy composite system

Abstract: Fracture energy data are presented for an epoxy-alumina trihydrate composite system in which both the volume fraction and particle size of the dispersion were changed. These data show that the fracture energy of a brittle epoxy composite can be significantly increased by choosing the proper volume fraction and particle size of the dispersed second phase. The results are discussed in terms of several mechanisms which could account for the observed increase in fracture energy. A recently proposed mechanism of crack interaction with a second phase dispersion is qualitatively consistent with these results.

The effect of omega phase on the mechanical properties of titanium alloys

Abstract: The effect of the precipitation of the metastable ω phase on the tensile properties of β-phase titanium alloys has been studied. The volume fraction of ω phase was varied by controlling the heat treatment temperature and the alloy content. It is shown that provided the volume of ω phase is less than 0.6, significant increases in yield strength can be obtained while retaining reasonable ductility. Higher volume fractions results in complete macroscopic embrittlement, but fracture still occurs by microvoid coalescence. Thin film microscopy of deformed samples shows that dislocations bypass the omega particles. The results are discussed in relation to current theories of deformation and fracture of two-phase alloys.

The mechanical properties of an epoxy resin with a second phase dispersion

Abstract: The mechanical strength of an anhydride-cured epoxy resin was studied by means of tensile tests as a function of particle size and volume fraction of an alumina trihydrate particulate-dispersed phase. These results and those of the microscopic examination imply that the poor strength of the system may be attributed to the intrinsically low strength of the dispersion. The tensile strength can be maximised by correct formulation on the basis of either particle size or volume fraction of the dispersed second phase. The modulus increases with increasing volume fraction, but is unaffected by particle-size variation at a constant volume fraction. The addition of a silane coupling agent increases the modulus of the composite, while having a negligible or adverse effect on the other properties.

Effect of gamma-gamma prime mismatch, volume fraction gamma prime, and gamma prime morphology on elevated temperature properties of Ni, 20 Cr, 5.5 Mo, Ti, Al alloys

Abstract: This study was designed to provide a critical test for the postulate that the mismatch between the lattices of austenite (γ) and the age-hardening gamma-prime (γ′) precipitates and the resultant coherency strains have a significant influence on the elevated temperature, particularly stress rupture, properties of a nickel-base superalloy. Two experimental alloys with a base analysis of Ni, 20 Cr, 5.5 Mo were designed with variable titanium and aluminum additions. To discern the effect of mismatch, an alloy without molybdenum was also experimented with. By manipulating the mismatch and volume fraction γ′ by heat treatment and chemistry, it was shown that a lower γ-γ′ mismatch indeed is beneficial to stress rupture life. Importance of volume fraction γ′ on this elevated temperature was also established.

Matrix strengthening mechanisms of an iron fiber-copper matrix composite as a function of fiber size and spacing.

Abstract: Copper matrix-iron fiber composites of fiber diameters from 10 to 5 × 10−3 mils and volume fractions from 0.03 to 0.97 were fabricated in order to study the dependence of mechanical properties on these variables. Composite elastic moduli agreed well with the predictions of the rule of mixtures. However, matrix and composite yielding and plastic flow were quite dependent on fiber diameter and spacing, exhibiting positive deviations from the simple rule of mixtures by factors of more than five in some cases. Yielding behavior may be explained by a combination of dislocation extrusion and pileup models for low volume fractions of fiber. Triaxiality generated by the difference in Poisson coefficients of the phases inhibits matrix yielding in higher volume fraction composites, allowing matrix flow only when the fibers also yield.

Control of γ′ particle size and volume fraction in the high temperature superalloy Udimet 700

Abstract: Experiments were conducted to determine the chemical composition, volume fraction and particle size of the γ′ precipitate in Udimet 700 as a function of temperature and time Growth of the γ′ particles was found to followt 1/3 diffusion controlled coarsening kinetics The composition of γ′ varied only slightly with temperature and was independent of time From this information, a method was developed to estimate the volume fraction and average particle size of the γ′ precipitate for any given heat treatment It is suggested that this approach could be applied to other γ′ strengthened superalloys

The importance of mechanical twinning in the stress-strain behavior of swaged high purity fine-grained titanium below 424°K

Abstract: Zone-refined iodide titanium specimens, swaged and annealed at different temperatures to give a range of grain sizes from 2.4 to 22 μ, were deformed to fracture between 77° and 424°K. A metallographic study of the fractured specimens revealed that mechanical twinning is an important factor in the plastic deformation of this grade of titanium at subambient temperatures. In all cases, the volume fraction of twins increased steadily with strain as well as with decreasing deformation temperature. At 77°K and at a grain size of 22 μ, the twin volume fraction was greater than 0.5 at a strain of 0.5. Furthermore, each of the 77°K stress-strain curves showed a linear work-hardening character with an associated high ductility similar to that originally reported by Wasilewski for commercial purity titanium. The nearly linear stress-strain curve in this latter case has been rationalized earlier in terms of deformation twinning. The present results are in good agreement with this point of view.

Fracture mechanics of a composite with ductile fibers

Abstract: F racture mechanics of a metal-matrix composite containing ductile-metallic fibers is described. Experimental verification of the proposed descriptions has been established with an aluminum-base composite containing uni-directional stainless-steel fibers. Theoretical description of the plastic energy dissipation shows that crack propagation across fibers is very difficult because of the high energy density represented by the fiber. The fiber contribution is an increasing function of volume fraction which results in the critical stress-intensity factor increasing with fiber content. On the other hand, crack propagation between fibers is very easy because the inter-fiber spacing limits the plastic energy dissipation in the matrix. The critical stress intensity for crack propagation between fibers is a decreasing function of volume fraction.

Work-hardening theory of fibre-reinforced composities

Abstract: The work-hardening rate dσM/d∊ is calculated of a composite of a plastic matrix between elastic fibres. A model is used of dislocations piling up on slip planes spaced by Dy and forming an angle of 45° with the fibre direction. The resulting dσM/d∊ are shown to fit experimental data by Kelly and Lilholt as a function of fibre diameter and volume fraction of fibres with Dy as the only parameter of the theory.

Stress Concentrations Near a Discontinuity in Fibrous Composites

Abstract: Stress concentration factors are defined for the fiber and matrix in an axially loaded unidirectional composite which has a discontinuous fiber Effects of variations in fiber volume fraction, end-gap size, and modulus ratio are studied by using a linearly elastic finite-element analysis Results show that the fiber stress concentration factors reach a maximum value of 1.5 and then remain relatively unchanged The matrix stress concentration factors, however, are shown to increase rapidly with decreasing end-gap size and increasing modulus ratio.

Structure of liquid cadmium-antimony alloys

Abstract: The structure of liquid Cd-Sb alloys was determined with the help of the Kumar-Samarin technique of centrifuging liquid metals. Alloys containing 7, 29, 50, 57 and 79 at. % Sb were examined in the range 350 to 650° C. It shows that (i) all alloys except in the vicinity of equi-atomic composition, consist of a colloidal dispersion of compound clusters in a random monatomic matrix, and (ii) the cluster size depends on composition with minima occurring at the two eutectic compositions. The volume fraction of clusters and their heat of formation were determined. The composition of the compound cluster was deduced as Cd40Sb30. Concentration gradient was not established in the equi-atomic alloy during centrifuging. The investigation shows that residual structure can exist far into the liquid state and is not confined to liquids of stoichiometric compound compositions.

Pressure-densification of powder composites*

Abstract: A preliminary investigation of the pressure-densification behaviour of iron and nickel powders both with and without added alumina or zirconia particles has been made. The importance of some relevant parameters is assessed in the light of experimental results obtained on different powder composites, prepared by mechanical mixing of powders followed by compaction in a die using a hydraulic press.The degree of pressure-densification decreases with increasing volume fraction of the added oxide particles, the decrease being also a function of the matrix and oxide particle-size ratio. These data are interpreted in terms of reductions in the number and area of the contact surfaces deforming as a result of the presence of non-deforming particles.

Order and Disorder in Monodisperse Latexes

Abstract: Iridescence due to Bragg diffraction of visible light is exhibited by electrolyte-free monodisperse polymer latexes, and also by redispersions of the polymer spheres in certain polar organic media The center-to-center particle separation D, the particle diameter Do, and the volume fraction ϕ are related by ϕ(D/Do)3 = 074, the value 074, being the volume fraction occupied by spheres in a close-packed lattice The structure responsible for the diffraction is thus identified as a lattice-like array which pervades the entire suspension, and is due to long-range coulombic forces between charged particles Addition of electrolyte shortens the range of inter-particle forces through a screening action, thereby destroying the lattice and producing a disordered, non-diffracting suspension At intermediate electrolyte levels, ordered and disordered phases coexist at equilibrium; the volume fractions of the coexisting phases are functions of the ionic strength

Reinforced elastomer compositions

Abstract: A NEW RUBBER COMPOSITION COMPRISING RUBBER REINFORCED BY DISTRIBUTING THEREIN CARBON FIBERS, CARBON BLACK AND SOFTENED IN COMBINATION RESPECTIVELY IN A PARTICULAR AMOUNT. THE SUITABLE AMOUNTS ARE 0.02 TO 0.10 VOLUME FRACTION OF CARBON FIBERS, 0.05 TO 0.25 VOLUME FRACTION OF CARBON BLACK AND 0.02 TO 0.30 VOLUME FRACTION OF SOFTENER. SUBSTANTIALLY UNIFORMLY DISTRIBUTED CARBON FIBERS, CARBON BLACK FINE PARTICLES AND FURTHER FINER SOFTENER PARTICLES DISPERSE THE CONCENTRATED STRAIN LOCALLY GENERATED IN THE RUBBER COMPOSITION TO EFFECTIVELY PREVENT THE SUDDEN DETERIORATION OF THE RUBBER ARTICLE WHICH PHENOMENON CAN BE OBSERVED IN SOME TYPES OF RUBBER. THUS THE VULCANIZED RUBBERS MADE OF SAID COMPOSITION HAVE HIGH RESISTANCE OF FATIGUE, ELONGATION, MECHANICAL STRENGTH AND ELASTICITY IN COMBINATION WHICH MAKES THEM VERY USEFUL FOR TIRES, CONVEYOR BELTS ETC. TO BE SUBJECTED TO SEVERE DYNAMIC CONDITIONS.

Fracture Mechanics Studies of Composite Systems.

Abstract: : A combined theoretical and experimental research program for investigating the application of fracture mechanics to composite systems is carried out. Preliminary results are presented which include the development of two fiber reinforced composite crack models, one with a low-fiber volume fraction and the other a high fiber volume fraction, and corresponding experimental data. The qualitative features of the theoretical prediction are in agreement with the experimental data indicating that there exists an optimum fiber volume fraction for which the composite achieves maximum fracture toughness. Tests were performed on uni-directional fiber reinforced composites with the crack running parallel to the fibers. For this arrangement, the current theory of fracture mechanics is shown to apply with good accuracy for FRP/epoxy composites. This is accomplished by performing two independent fracture tests the results of which are checked by an analysis of the crack system. A more elaborate analytical model is required for studying the graphite fiber/epoxy composite. (Author, modified-PL)

Effect of Deposition Temperature on Condensed Phases in Sputtered Ni–Cr Thick Films

Abstract: A modified triode sputtering technique was used to deposit nickel-chromium alloys on pure nickel substrates maintained at temperatures varying from 550 to 1050 °C by controlled, low energy electron bombardment heating. The coatings (110–200 μ thick), deposited at rates between 960 and 1400 A/min, were evaluated utilizing metallographic, chemical analysis, electron microprobe, x-ray diffraction, and electron diffraction techniques. A new phase, designated e, was found when Ni-22 at.% Cr was deposited at temperatures above 750 °C. The volume fraction of the new phase increased from 10% at 750 °C to 13% at 1050 °C. Heat treatment for 200 h at 1050 °C showed no change in volume fraction of e previously deposited at that temperature, indicating that e is the equilibrium phase. The e phase containing 87 at.% chromium had a tetragonal structure with a c/a=0.55, and a columnar-plate habit and grew perpendicular to the interface. The alloy target containing 12 at.% chromium condensed as e+γ between 750 ° and 950 °...

Molecular Configuration of Spherical, Non-Polar, Dense Gases and Liquids

Abstract: IN a previous communication1, I discussed the coordination of equal spheres in a random assemblage and liquid structure and supported Bernal's idea2,3 that the liquid structure can be characterized as a homogeneous, coherent and essentially irregular assemblage of particles. In view of the bulk-mean particle volume fraction, this communication provides a comparison between the random assemblage of equal spheres and the molecular configuration of spherical, non-polar, dense gases and liquids.

Effect and Detection of Loose Chain Ends in Crosslinked Polyurethane Elastomers

Abstract: The effect of loose chain ends on tensile properties and equilibrium swelling of crosslinked polyurethane rubbers is studied. As in plasticized elastomers, tensile strength and elastic modulus are reduced approximately by a factor (1−νE,P)2, where νE,P is the volume fraction of loose chain ends, plasticizer, or both. This effect is much larger than predicted by present theory. Also the equilibrium volume swelling ratio, V0/V, of rubbers having terminal chains or an equal volume of plasticizer is the same, provided they do not differ in crosslink density. However, the volume fraction of “network rubber” in the equilibrium swollen specimen, ν2, differs owing to the non-extractability of terminal chains. On this basis a method is proposed which allows experimental determination of the volume fraction of loose ends. Elastomers abounding in loose chain ends show markedly less long term stress relaxation. This effect is not clearly understood but is useful to detect the presence of non load-bearing net...

Cast microstructure and fatigue behavior of a grain-refined Mg−Zn−Zr alloy

Abstract: Microstructure studies were conducted on grain-refined Mg-5.1 pct Zn-0.6 pct Zr alloy plates, sand-cast and end-chilled. Grains in this alloy are spherical, nondendritic and increase in diameter with distance from the chill. Coring in these, grains is spherical. The volume fraction of interspherical nonequilibrium secondary phase decreases with distance from the chill, whereas the volume fraction of microporosity increases. Solution kinetics of the secondary phase were found to depend on the dimensionless parameterDt/a2, where:D is the diffusivity of zinc in this alloy,a the sphere radius andt the solutionizing time. The fatigue strength of this alloy at room temperature was measured in reversed bending at a stress level of 10,000 psi and was found to decrease with increasing distance from the chill, both in the as-cast and the cast-and-solutionized conditions. Solutionizing was found to increase fatigue life. Fatigue cracks were found to initiate in shear bands, most frequently at micropores, and to propagate transgranularly.

Dielectric Properties of Polymer–Solvent Systems

Abstract: Measurements of the dielectric absorption of solutions, poly(vinyl acetate)–toluene and poly(vinyl chloride)–dioxane systems were carried out. Based on the effects of temperature, frequency, and concentration of the polymer in the dielectric absorption, the mechanism of this absorption is discussed. The frequency at which the maximum loss occurs depends largely upon the concentration of the polymer. This dependence is described successfully in terms of the free volume model. The activation enthalpy and entropy of this dielectric relaxation process were obtained as functions of the volume fraction of the polymer. These values increase with the volume fraction of the polymer and approach those for the α-relaxation process observed in pure polymers. The variation of free energy with volume fraction in this process can be explained by the change of free volume. Observed relaxation times show apparent molecular weight dependence and this effect can also be explained in terms of the free volume variation.

Effect of Chemical Crosslinks on the Thermal Stability of Conformation in Swollen Gelatin Films (Summary)

Abstract: The temperature dependence of tensile modulus, swelling, and specific optical rotation of cold-dried gelatin films hardened with formaldehyde and swollen in water has been determined over the temperature range 10°-60°C. Results indicate the following: (1) The films undergo structural transitions over the temperature range studied, with the transitions broadening and shifting to higher temperatures as the hardener level is increased. (2) Chemical crosslinks stabilize ordered structure in the films in a manner more specific than merely reducing swell. This is indicated by the fact that crosslinked, cold-dried films maintain high levorotation not found in hot-dried films or in uncrossedlink gelatin at the same temperatures and volume fraction. (3) The combination of chemical crosslinks and ordered structure contribute far more to the modulus of elasticity and to the suppression of swell than chemical crosslinks alone.

Effect of buoyancy on fuel containment in an open-cycle gas-core nuclear rocket engine.

Abstract: Analysis aimed at determining the scaling laws for the buoyancy effect on fuel containment in an open-cycle gas-core nuclear rocket engine, so conducted that experimental conditions can be related to engine conditions. The fuel volume fraction in a short coaxial flow cavity is calculated with a programmed numerical solution of the steady Navier-Stokes equations for isothermal, variable density fluid mixing. A dimensionless parameter B, called the Buoyancy number, was found to correlate the fuel volume fraction for large accelerations and various density ratios. This parameter has the value B = 0 for zero acceleration, and B = 350 for typical engine conditions.

Hall coefficient and resistivity of an amorphous palladium-silicon alloy

Abstract: The Hall coefficient and resistance in several specimens of an amorphous metallic alloy containing 80 at.% palladium and 20 at.% silicon have been investigated at temperatures between 4.2°K and room temperature. An ideal limiting behavior of these transport coefficients was analyzed on the basis of the nearly free electron model to yield a carrier density of 9 x 1022 cm.-3, or about 1.7 electrons per palladium atom, and a mean free path of about 9A which is almost constant with temperature. The deviations of the individual specimens from this ideal behavior, which were small but noticeable in the relative resistivity and much greater in the Hall coefficient, can be explained by invoking disk-shaped crystalline regions with low resistivity and a positive Hall coefficient. A detailed calculation shows how a volume fraction of such crystalline material too small to be noticed in X-ray diffraction could have a significant effect on the resistivity and a much greater effect on the Hall coefficient.

Correlation of creep elongation and substructure in aluminum-stainless steel composites

Abstract: The tensile creep behavior and associated substructural detail have been characterized in aluminum-stainless steel composites at ambient temperature. Volume fractions in the range 0 to 0.33 were tested under constant load conditions (in the range 1.0 to 4.0 times macroscopic yield stress) with the load applied parallel to the direction of reinforcement. In both unreinforced aluminum and the composites, steady-state creep conditions are established in <100 hr; creep rates are in the range 1.2×10−7 in. per in. per hr to 5×10−4 in. per in. per hr, depending on stress and volume fraction reinforcement. The stainless steel reinforcement significantly reduces the creep rate at a given stress level. The steady-state creep rates are in good agreement with behavior predicted by an exponential form of the rule-of-mixtures equation relating creep rate to applied stress and volume fraction reinforcement. The matrix (experimental) and stainless steel wire (rule-of-mixtures analysis) give an exponential dependence of creep rate on stress with power exponents of 2.7 and 3.3, respectively. At a given level of creep strain dislocation substructure in the aluminum matrix is independent of distance from the interface; alternatively, the substructure is independent of volume fraction of reinforcement and is controlled only by the total strain in the composite. Similar behavior has been established previously in this system for time-independent uniaxial tensile or compressive loading.