Showing papers on "Young's modulus published in 1982"

Piezoelectricity of a high‐content lead zirconate titanate/polymer composite

Abstract: A binary system consisting of polyvinylidene fluoride (PVDF) and lead zirconate titanate (PZT) powder was investigated to determine its dielectric constant, piezoelectric constant, and Young’s modulus. An expression was obtained for the piezoelectric constant, and expressions for the dielectric constant and Young’s modulus were also mentioned. The calculated values had good agreement with the observed values for the composite with a large PZT volume fraction. The dielectric constant and the piezoelectric constant were 152 and 48.3×10−12 C/N, respectively, for the composite with the PZT volume fraction of 0.67. Changing the mixing ratio of PVDF and the fluorine elastomer, Young’s modulus was varied without changing the piezoelectric constant.

A method for fabrication of aluminum-alumina composites

Abstract: A process was used to produce Al-Mg alloy composites containing discontinuous A12O3 fibers. In the first step of the process, induced convection of the melt permits intimate contact between the fibers and the melt which invariably results in chemical interaction between the two. The presence of MgAl2O4 spinel on the fiber surface was confirmed. The composites produced contained randomly distributed fibers and were further processed both to increase the volume fraction of fibers and to align them in two dimensions (planar random alignment). Examination of composite specimens fractured under tension indicated that the interfaces were strong enough to permit transfer of load from the matrix to the fiber. For example, modulus of elasticity and ultimate tensile strength of the alloy were improved approximately 50 pct and 40 pct, respectively, by the addition of 23 vol pct A12O3 fibers.

Stresses and Displacements in Cross-Anisotropic Soils

Abstract: An analytic investigation is presented on the effect of soil cross-anistropy on surface displacements and stress distributions in a homogeneous thick soil deposit (halfspace) subjected to axisymmetric parabolic vertical surface loading. Rigorous treatment is given to deformational soil anisotropy and particular emphasis is accorded to the sensitivity of calculated stresses and deformations to assumed realistic values of the five independent material constants, under both drained and undrained loading conditions. For a given vertical Young's modulus, it is found that the horizontal Young's modulus, the shear modulus on vertical planes and the Poisson's ratio for horizontal due to vertical strain have a profound effect on all stress and displacement components, especially under undrained conditions. The dependence of normal vertical stresses on material properties and particularly on one of the Poisson's ratios disproves the opposite conclusion of isotropic elasticity.

The effect of addition of high-density polyethylene on the crystallization and mechanical properties of polypropylene and glass-fiber-reinforced polypropylene

Abstract: High-density polyethylene up to about 30% by weight was melt-mixed with polypropylene and short-glass-fiber-reinforced polypropylene. The presence of high-density polyethylene and glass fibers in the polypropylene matrix affects its crystallization characteristics, which were studied with the help of differential scanning calorimetry. The blend and composite samples have a large number of polypropylene domains apparently due to an abundance of surface nuclei; as a result, the tensile strength, tensile modulus, and toughness are enhanced. The temperature dependence of shear modulus and logarithmic decrement indicate that high-density polyethylene can have plasticizing effect below the glass transition temperature of polypropylene. The scanning electron micrographs of fractured ends show the presence of dispersed domains in the composite samples.

Determination of the primary elastic constants from thin foils having a strong texture

Abstract: A new method is described for determining the primary elastic constants (stiffnesses cij’s and compliances sij’s) with respect to the crystallographic axes. Although we will consider only cubic materials the method can be applied to materials of lower symmetry. The method utilizes the symmetry present in a textured (preferred growth) foil and can be used for cases when bulk single crystals are difficult to prepare for ultrasonic experiments. The method involves the use of expressions, that have not been previously derived, relating the biaxial, flexural, Young’s and shear modulus to the primary elastic constants for textured foils. The agreement of the experimentally observed moduli with ones calculated from the expressions to be presented demonstrates that the accuracy is comparable with existing methods.

Saint-Venant End Effects In Composites

Abstract: In this paper, we demonstrate that the neglect of elastic end effects, usually justified by appealing to Saint-Venant's principle, cannot be applied routine ly in problems involving composite materials. In particular, for fiber rein forced composites, the characteristic decay length over which end effects are significant is, in general, several times longer than the corresponding length for isotropic materials. For plane strain or generalized plane stress of a highly anisotropic transversely isotropic (or orthotropic) material, modeling a fiber- reinforced composite, the characteristic decay length is of order b(E/G) 1/2, where b is the maximum dimension perpendicular to the fibers and E, G are the longitudinal Young's modulus and shear modulus respectively. Thus when E/G is large, as for fiber-reinforced composites, end effects are transmitted over a distance which is of the order of several specimen widths. This is in marked contrast with the situation for isotropic materials where decay lengths of one ...

A compliant, high failure strain, fibre-reinforced glass-matrix composite

Abstract: It is demonstrated that a unique form of composite material can be achieved by reinforcing glass matrices with discontinuous graphite fibres. The graphite fibres were utilized in the form of a paper, purchased in large sheets, and composites were formed by hot-pressing glass-powder-impregnated paper plys. The resultant composites exhibit high strength, high fracture toughness (compared to ceramics), low density and low thermal expansion coefficient. Of particular note is the unique tensile stress-strain curve achieved which exhibits both high strength and high failure strain. Its very non-linear shape differs markedly from that of either the unreinforced glass or a similarly reinforced epoxymatrix composite. In addition, the elastic modulus of the resultant composite, despite being reinforced with a high stiffness fibre, is lower than that of the parent matrix resulting in an unusually compliant ceramic material.

Residual stresses in polymers III: The influence of injection‐molding process conditions

Abstract: Following the evaluation of Residual Stresses (R.S.) in quenched specimens (Part I) and the resulting mechanical-physical properties (Part II), the, present study deals with the effect of injection-molding process conditions on R.S. and the respective properties of amorphous polymers. Melt temperature, mold temperature, injection rate, and injection pressure were the parameters studied. Experimental results indicated that the melt temperature caused two maxima in R.S. The second one reverses from compressive to tensile. In general, most changes occur in the surface regions, while R.S. decreases with increasing melt temperature, as is the case in zones far away from the gate. Furthermore, tensile modulus increased, in general, with rising melt temperature. In the case where the effect of mold temperature was studied, it was found that R.S. are compressive in the surface layers and tend to decrease upon increase in mold temperature and distance from the entrance region. Significant changes in R.S. were also detected in the interior layers. As the mold temperature approached Tg, low values of R.S. were measured, as was the case in quenched specimens. Injection rate affects surface R.S. to a large extent. With low flow rates, tensile stresses were developed in the exterior, reversing to compressive stresses at higher speeds. The reversal in sign depends on the location relative to the gate. Once compressive stresses were formed, further increase in rate caused a reduction in R.S. In addition, variations in tensile modulus, as high as 30 percent, were measured at high injection rates. As far as injection and holding pressures are concerned, experimental results showed that a maximum in R.S. was obtained, with increasing pressure, at the surface. Close to the gate entrance, a reverse from compressive to tensile R.S. was detected at high injection pressures. As in the other cases, injection pressure influenced mostly the exterior layers. Only in zones close to the entrance and at high pressures were high levels of R.S. measured in the core regions.

Cylindrical Shells of Bimodulus Composite Materials

Abstract: Certain fiber-reinforced materials, especially those with slightly curved fibers in very soft matrices, exhibit considerably smaller stiffnesses when loaded in compression than when loaded in tension. Examples are tire cord-rubber, wire-reinforced solid propellants, and certain soft biological tissues. For purposes of analysis and design, such materials can be modeled as a bimodulus material, i.e., one having one set of stiffnesses when the fiber direction strain is tensile and another set when this strain is compressive. Using the fiber-governed bimodulus-material model introduced several years ago and verified for cord-rubber composites, the previous work is extended on the deflection of single-layer and cross-ply laminated rectangular plates to circular cylindrical shells of the same construction. A closed-form solution is presented for the case of a simply supported cylindrical panel under sinusoidally distributed loading. Numerical results are presented to show the effect of shell curvature on the neutral-surface position and deflection.

Ultrasonically delaminated and coarse mica particles as reinforcements for polypropylene

Abstract: The effect of the size of mica platelets used, at 30% by mass, to reinforce polypropylene was studied by comparing ultrasonically delaminated mica (diameter 5μ aspect ratio about 40) with a coarser mica (150–420μ) with and without the coupling agent 3-(triethoxysilyl)-1-propanamine (Union Carbide A-1100). Reducing the particle size of the mica (treated with coupling agent) significantly increased the tensile modulus and strength but did not affect elongation at break; it gave a small improvement in Izod impact strength; the heat distortion temperature was lower and the melt flow index was increased. Dynamic mechanical evaluation (Rheovibron) was done with a series of coarse micas (>44μ, 45–150μ, 150–250μ, and one with a broad distribution around 100μ), and an ultrasonically delaminated mica made in a continuous process (>20μ), all treated with N-(4-vinylphenyl) methyl-N′-(3-trimethoxysilylpropyl)ethylenediamine (Dow Corning Z-6032), at 20% by mass in polypropylene. Except for the disappearance of a peak at 0°C in the loss tangent due to the glass transition, the composite with delaminated mica did not differ from pure polypropylene, melting at 175°C. Use of the coarser micas raised the melting temperature to 200°C, increased the storage modulus, and lowered the loss tangent in the case of the three fractionated samples. The results were concordant with theories of reinforcement and microheology. The hoped-for improvement in some properties on changing to the finer mica may not have been realized because of incomplete dispersion.

An analytic model for the shock Hugoniot in porous materials

Abstract: A simplified analytic model for the Shock Hugoniot in porous materials is developed. The model is most accurate in the limits in which the pressure is dominated by either the elasticity (low pressure) or by the thermal motion (high pressure). The compressed density is expressed as a function of the pressure, the initial solidity and density of the material, the cold compression coefficient (Young’s Modulus)−1, and the Gruneisen coefficient. The model is validated over a wide range of materials, pressures, and solidities.

Heat-resistant spring made of fiber-reinforced metallic composite material

Abstract: A spring useful as various machine parts or elements for various machines and apparatuses, which is made of a fiber-reinforced metallic composite material comprising a matrix metal (e.g. a metal having a melting point of not higher than 1,700° C.) and a reinforcement of an inorganic fiber having high modulus of elasticity and high strength selected from a ceramic fiber and a metallic fiber, particularly an alumina or alumina-silica fiber containing alumina of 100 to 72% by weight, preferably 98 to 75% by weight, and silica of 0 to 28% by weight, preferably 2 to 25% by weight, and having substantially no α-alumina reflection by X-ray diffraction. The spring of the present invention is light in weight and has far greater heat resistance and mechanical properties in comparison with the conventional metallic or non-metallic springs, and hence is particularly valuable from the standpoint of saving energy and saving resources.

The effect of strain upon the velocity of sound and the velocity of free retraction for natural rubber

Abstract: Measurements have been made of the velocity of sound and the velocity of free retraction for stretched strips of vulcanized natural rubber. Both of these velocities are found to increase markedly with increasing strain, in agreement with earlier work. The velocity of sound is shown to be related to the appropriate modulus of elasticity, defined by the slope of the curve relating true stress to tensile strain. Values obtained range from about 50 to about 800 m/s. The effects of prior stretching and of stress relaxation on the velocity of sound are shown to arise from corresponding changes in the modulus of elasticity at a given strain. The velocity of free retraction is shown to be directly related to the velocity of sound in the stretched strip and to the imposed tensile strain, increasing from zero up to about 100 m/s at high strains.

Evaluation of in-situ moduli and pavement life from deflection basins --proceedings of the fifth international conference on the structural design of asphalt pavements held deflt university of technology, august 23-26 1982. vol 1 and 2. -- netherlands

Abstract: The determination of the in-situ pavement material moduli is an essential step in the non-destructive structural evaluation of flexible pavements. If the modulus values of the various layers can be determined, then the remaining pavement service life can also be predicted. This mechanistic evaluation can then serve as a rational basis for pavement management systems. This paper describes the results of a research project designed to determine the in-situ modulus values and remaining pavement life based upon the deflection basin obtained from a road rater device. Elastic layer theory and the Gaussian method of elimination were used to formulate surface deflections in terms of elastic modulus, load intensity, and layer thickness. The resulting equations were used to analyze the effect of changing layer modulus on the surface deflection. On the basis of this analysis, a computer program for calculating in-situ modulus values from road rater deflection basins was developed. The calculated in-situ modulus values were then used to calculate the maximum tensile strain in the bituminous concrete base layer of a four layer pavement system. The road rater deflection basin was used to calculate the surface curvature index, sci, the base curvature index, bci, and the base damage index, bdi. These criteria were correlated with the maximum tensile strain, the fatigue cracking of the pavement sections and the traffic loading. A relationship was established between the sci and the traffic loading resulting in the prediction of remaining pavement life. Results are presented graphically in terms of the structural number (sn) of the pavement section.(a) for the covering abstract of the conference see IRRD 815640.

Bulk stiffnesses of metallic glasses

Abstract: Determinations of density, Vickers microhardness, Young’s modulus, and Poisson’s ratio are reported for a series of Fe‐B glasses, for glassy Fe40Ni38Mo4B18, and for glassy Cu68Zr32. From the last two parameters, one may calculate the shear and bulk stiffnesses of the glasses. For the Fe‐B series the shear stiffness decreases by ∼13% when the B concentration decreases from 23 to 15 at.%; the bulk stiffness simultaneously decreases by ∼45%. As a result, the bulk stiffness of the near‐eutectic alloy Fe85B15 (≃111 GPa) is strongly depressed relative to that for pure crystalline Fe (≃169 GPa) and that for crystalline Fe3B (≳163 GPa). The ratios of bulk stiffness to shear stiffness for Cu68Zr32 (≃4.7) and Fe40Ni38Mo4B18 (≃2.6) are relatively large and similar to those previously observed for other metallic glasses. For Fe85B15 the observed ratio is ≃1.9, which is quite close to that ( (5)/(3) ) expected for a solid bonded by centrally directed interatomic forces (a Cauchy solid). For the glasses examined here, ...

Biaxially stretched polyolefin film with an elasticity modulus in the longitudinal direction of more than 4000 N/mm2

Abstract: 1. Biaxially oriented plastic film made from polypropylene containing an additive comprising a natural or synthetic resin with a softening point of between 70 and 170 degrees C, characterized in that the film has a modulus of elasticity of between 4,000 and 6,000 N/mm**2 in the longitudinal direction.