Showing papers on "Elastic modulus published in 1995"
TL;DR: In this article, a concept for the design of novel nanocrystalline/amorphous composites is suggested based on recent theoretical and experimental results regarding the appearance of supermodulus phenomena in composition-modulated layered heterostructures and on a simple thermodynamic criterion for segregation in ternary nitride systems.
871 citations
TL;DR: Modulus in the radial or circumferential direction could not be predicted from modulus inThe S-I direction for cortical bone, but could be predicted for cancellous bone, and specific relationships, depending on the types of bone, that predict elastic modulus from density and CT numbers were suggested.
720 citations
TL;DR: The elastic modulus El of the crystalline regions of cellulose polymorphs in the direction parallel to the chain axis was measured by x-ray diffraction in this paper, which indicates that the skeletons of these polymorphs are completely different from each other in the mechanical point of view.
Abstract: The elastic modulus El of the crystalline regions of cellulose polymorphs in the direction parallel to the chain axis was measured by x-ray diffraction. The El values of cellulose I, II, IIII, IIIII, and IVI were 138, 88, 87, 58, 75 GPa, respectively. This indicates that the skeletons of these polymorphs are completely different from each other in the mechanical point of view. The crystal transition induces a skeletal contraction accompanied by a change in intramolecular hydrogen bonds, which is considered to result in a drastic change in the El value of the cellulose polymorphs. © 1995 John Wiley & Sons, Inc.
547 citations
TL;DR: In this article, thin films of novel superhard composite materials consisting of TiN nanocrystals in an amorphous Si3N4 matrix have been prepared by means of plasma chemical vapor deposition.
Abstract: Thin films of novel superhard composite materials consisting of TiN nanocrystals in an amorphous Si3N4 matrix have been prepared by means of plasma chemical vapor deposition. The films show a high Vickers hardness of 5000 kg/mm2 and elastic modulus of ≳500 GPa, and they are resistant against oxidation in air up to ≥800 °C. The theoretical background of these unusual properties are briefly discussed and practical rules suggested according to which similar properties should be expected for composites of other ternary systems.
482 citations
TL;DR: The resolution is best in pure propanol, on the order of 20 nm, and becomes worse for the softer samples, and the degradation in resolution can be understood by considering the elastic indentation of the gelatin caused by the AFM tip, which becomes larger the softer the sample is.
377 citations
TL;DR: In this paper, the influence of matrix properties on composite pseudo-strain-hardening has been studied and a new class of ECCs with improved elastic modulus by the addition of fine aggregates to the cementitious matrix is proposed.
Abstract: Pseudo-strain-hardening behaviour under direct tensile loading in short fibre reinforced cement composites designed with quantitative guidance from micromechanics has been demonstrated experimentally, and conditions for the ductile behaviour of such engineered cementitious composites (ECC) have been formulated theoretically. In this paper special focus is placed on the influence of matrix properties on composite pseudo-strain-hardening. An experimental program is undertaken to study the dependence of the matrix properties on its mix compositions governed by water/cement and the sand/cement ratios. The theoretical and experimental knowledge thus obtained are combined to propose an innovative procedure for the design of composites using different types of matrix. The study is motivated by the need to develop a new class of ECCs with improved elastic modulus by the addition of fine aggregates to the cementitious matrix. Finally, a new composite is designed, and shown experimentally to exhibit the desirable features of pseudo-strain-hardening behaviour and improved elastic modulus.
370 citations
TL;DR: In this article, the authors proposed techniques based on principles well established in hardness testing using spherical indenters, but not previously applied to depth-sensing instruments capable of measurements on a submicrometer scale.
Abstract: The stress/strain behavior of bulk material is usually investigated in uniaxial tension or compression; however, these methods are not generally available for very small volumes of material. Submicrometer indentation using a spherical indenter has the potential for filling this gap with, possibly, access to hardness and elastic modulus profiles, representative stress/strain curves, and the strain hardening index. The proposed techniques are based on principles well established in hardness testing using spherical indenters, but not previously applied to depth-sensing instruments capable of measurements on a submicrometer scale. These approaches are now adapted to the analysis of data obtained by stepwise indentation with partial unloading, a technique that facilitates separation of the elastic and plastic components of indentation at each step and is able to take account of the usually ignored phenomena of “piling up” and “sinking in”.
358 citations
TL;DR: In this paper, the hardness and elastic modulus were measured using nanoindentation methods, and ultra-low load scratch tests were used to assess the scratch resistance of the films and measure friction coefficients.
Abstract: Nanoindentation and nanoscratching experiments have been performed to assess the mechanical properties of several carbon thin films with potential application as wear resistant coatings for magnetic disks. These include three hydrogenated-carbon films prepared by sputter deposition in a H{sub 2}/Ar gas mixture (hydrogen contents of 20, 34, and 40 atomic %) and a pure carbon film prepared by cathodic-arc plasma techniques. Each film was deposited on a silicon substrate to thickness of about 300 run. The hardness and elastic modulus were measured using nanoindentation methods, and ultra-low load scratch tests were used to assess the scratch resistance of the films and measure friction coefficients. Results show that the hardness, elastic modulus, and scratch resistance of the 20 and 34% hydrogenated films are significantly greater than the 40% film, thereby showing that there is a limit to the amount of hydrogen producing beneficial effects. The cathodic-arc film, with a hardness of greater than 59 GPa, is considerably harder than any of the hydrogenated films and has a superior scratch resistance.
342 citations
TL;DR: In this article, the authors investigated the relationship between microstructure and elastic properties in two-dimensional cellular materials (honeycombs) and proposed a finite element analysis (FEA) to determine effective elastic moduli for low density honeycombs.
327 citations
TL;DR: The constitutive equation of the aortic wall was constructed on the basis of three different hookean materials and two nonlinear functions, fA and fC, and the purely elastic stress-strain relation was assessed by subtracting the viscous and inertial behaviors.
Abstract: To evaluate arterial physiopathology, complete arterial wall mechanical characterization is necessary. This study presents a model for determining the elastic response of elastin (sigma E, where sigma is stress), collagen (sigma C), and smooth muscle (sigma SM) fibers and viscous (sigma eta) and inertial (sigma M) aortic wall behaviors. Our work assumes that the total stress developed by the wall to resist stretching is governed by the elastic modulus of elastin fibers (EE), the elastic modulus of collagen (EC) affected by the fraction of collagen fibers (fC) recruited to support wall stress, and the elastic modulus of the maximally contracted vascular smooth muscle (ESM) affected by an activation function (fA). We constructed the constitutive equation of the aortic wall on the basis of three different hookean materials and two nonlinear functions, fA and fC: sigma = sigma E + sigma C + sigma SM + sigma eta + sigma M = EE. (epsilon - epsilon 0E) + EC.fC.epsilon + ESM.fA.epsilon + eta. [equation: see text] + M.[equation: see text] where epsilon is strain and epsilon 0E is strain at zero stress. Stress-strain relations in the control state and during activation of smooth muscle (phenylephrine, 5 micrograms.kg-1.min-1 IV) were obtained by transient occlusions of the descending aorta and the inferior vena cava in 15 conscious dogs by using descending thoracic aortic pressure (microtransducer) and diameter (sonomicrometry) measurements. The fC was not linear with strain, and at the onset of significant collagen participation in the elastic response (break point of the stress-strain relation), 6.02 +/- 2.6% collagen fibers were recruited at 23% of stretching of the unstressed diameter. The fA exhibited a skewed unimodal curve with a maximum level of activation at 28.3 +/- 7.9% of stretching. The aortic wall dynamic behavior was modified by activation increasing viscous (eta) and inertial (M) moduli from the control to active state (viscous, 3.8 +/- 1.3 x 10(4) to 7.8 +/- 1.1 x 10(4) dyne.s.cm-2, P < .0005; inertial, 61 +/- 42 to 91 +/- 23 dyne.s2.cm-2, P < .05). Finally, the purely elastic stress-strain relation was assessed by subtracting the viscous and inertial behaviors.
317 citations
TL;DR: In this paper, the effect of hydrogen on dislocationdislocation and dislocationdashimpurity atom interactions is studied under conditions where hydrogen is in equilibrium with local stresses and in systems where hydrogen increases the shear modulus.
Abstract: The effect of hydrogen on dislocationdashdislocation and dislocationdashimpurity atom interactions is studied under conditions where hydrogen is in equilibrium with local stresses and in systems where hydrogen increases the shear modulus. In the case of two edge dislocations (plane strain) the effect of hydrogen is modeled by a continuous distribution of dilatation lines whose strength depends on the local hydrogen concentration. The hydrogen distribution in the atmospheres is adjusted to minimize the energy of the system as the dislocations approach each other. The iterative finite element analysis used to calculate the hydrogen distribution accounts for the stress relaxation associated with the hydrogen induced volume and the elastic moduli changes due to hydrogen. The interactions between the dislocations are calculated accounting for all the stress fields due to dislocations and hydrogen atmospheres. Modeling of the hydrogen effects on the edge dislocationdashinterstitial solute atom interaction and on the screw dislocationdashinterstitial solute atom interaction is discussed using a finite element analysis and the atom interaction energies are calculated in the presence of hydrogen. For the case where hydrogen increases the shear modulus, a significant hydrogendashrelated decrease of the edge dislocationdashinterstitial solute atom interaction energy was observed when the edge dislocationdashsolute distance is approximately less than two Burgers vectors. Depending on the orientation of the tetragonal axis of the interstitial solute distortion field, hydrogen may strengthen or weaken the interaction between the screw dislocationdashinterstitial solute.
TL;DR: In this article, the elastic modulus of soft tissue based on ultrasonic displacement and strain images is reconstructed using a hybrid reconstruction procedure based on numerical solution of the partial differential equations describing mechanical equilibrium of a deformed medium.
Abstract: A method is presented to reconstruct the elastic modulus of soft tissue based on ultrasonic displacement and strain images. Incompressible and compressible media are considered separately. Problems arising with this method, as well as applications to real measurements on gel-based, tissue equivalent phantoms, are given. Results show that artifacts present in strain images can be greatly reduced using a hybrid reconstruction procedure based on numerical solution of the partial differential equations describing mechanical equilibrium of a deformed medium. >
TL;DR: Regression analysis showed that only three parameters, the elastic modulus, the maximum strain, and the strain intersect, are sufficient to define the nonlinear stress-strain relation up to failure.
TL;DR: In this paper, the dynamic viscoelasticity of silicone gels having many lines of dispersed iron particles under the influence of external magnetic fields was studied and the microscopic bondings between dispersed particles were analyzed using a simple model of induced dipole-induced dipole interactions.
Abstract: Dynamic viscoelasticity of silicone gels having many lines of dispersed iron particles under the influence of external magnetic fields was studied. The particulate composite enhanced its elastic modulus by action of magnetic fields. The magnetroviscoelastic behavior was caused by the cohesive forces between magnetically polarized particles and was analyzed using a simple model of induced dipole-induced dipole interactions. The presented results provide insight into the relationship between macroscopic viscoelastic behavior of the composite gels and the microscopic bondings between dispersed particles. © 1995 John Wiley & sons, Inc.
TL;DR: In this paper, the relationship between the structure and mechanical properties of both polyacrylonitrile (PAN) and pitch-based carbon fibres has been studied in detail.
TL;DR: In this paper, the elastic and mechanical properties of Stoichiometric polycrystalline magnesium aluminum spinel have been studied from room temperature up to 1300deg;C. Elastic modulus, fracture toughness, and modulus of rupture measurements and observations of polished and fracture surfaces have been performed.
Abstract: The elastic and mechanical behavior, from room temperature up to 1300deg;C, of Stoichiometric polycrystalline magnesium aluminum spinel is studied. Elastic modulus, fracture toughness, and modulus of rupture measurements and observations of polished and fracture surfaces have been performed. Two well-differentiated regions of fracture behavior as a function of temperature have been found. In the low-temperature region, this material behaves elastically, whereas in the high-temperature (>800deg;C) region, plastic phenomena take place.
TL;DR: In this article, a set of high performance concrete mixes, of low water cement ratio and fixed mortar composition, containing six different types of aggregates of constant volume fraction, has been used to check moduli of elasticity at 7, 28 and 91 days.
TL;DR: The proposed new type of inverse problem by which the spatial distribution of the relative elastic modulus of the tissue can be estimated only from the deformation or strain measurement seems promising for the quantitative differential diagnosis on the lesion in the tissue in vivo.
Abstract: In order to obtain noninvasively quantitative static mechanical properties of living tissue, the authors propose a new type of inverse problem by which the spatial distribution of the relative elastic modulus of the tissue can be estimated only from the deformation or strain measurement. The living tissue is modeled as a linear isotropic incompressible elastic medium which has the spatial distribution of the shear modulus, and the deformation or strain is supposedly measured ultrasonically. Assuming that there is no mechanical source in the region of interest, the authors derive a set of linear equations in which unknowns are the spatial derivatives of the relative shear modulus, and the coefficients are the strain and its spatial derivatives. By solving these equations, the spatial derivatives of the relative shear modulus are determined throughout the region, from which the spatial distribution of the relative shear modulus is obtained by spatial integration. The feasibility of this method was demonstrated using the simulated deformation data of the simple inclusion problem. The proposed method seems promising for the quantitative differential diagnosis on the lesion in the tissue in vivo. >
TL;DR: In this paper, Young's modulus of conventional and re-entrant open cell foams are obtained by modeling the three-dimensional unit cell as an idealized 14-sided unit cell.
TL;DR: It is concluded that, in the species studied, the flexural stiffness of the whole rachis is principally controlled by its cross-sectional morphology rather than by the material properties of the keratin.
Abstract: The flexural stiffness of the rachis varies along the length of a primary feather, between primaries and between species; the possible contribution of variations in the longitudinal Young's modulus of feather keratin to this was assessed. Tensile tests on compact keratin from eight species of birds belonging to different orders showed similar moduli (mean E=2.50 GPa) in all species apart from the grey heron (E=1.78 GPa). No significant differences were seen in the modulus of keratin from primaries 710 in any species. There was a systematic increase in the modulus distally along the length of the rachis from swan primary feathers. Dynamic bending tests on swan primary feather rachises also showed that the longitudinal elastic modulus increases with increasing frequency of bending over the range 0.110 Hz and decreases monotonically with increasing temperature over the range -50 to +50 °C. The position-, frequency- and temperature-dependent variations in the modulus are, however, relatively small. It is concluded that, in the species studied, the flexural stiffness of the whole rachis is principally controlled by its cross-sectional morphology rather than by the material properties of the keratin.
TL;DR: In this article, a simplified constitutive model is presented that recognizes and incorporates the properties of microstructure and its influence on mechanical response of plain concrete, and the model evaluates uniaxial compressive stress at any level of axial strain, using a straindependent estimate of material stiffness.
Abstract: A simplified constitutive model is presented that recognizes and incorporates the properties of microstructure and its influence on mechanical response of plain concrete. The model evaluates uniaxial compressive stress at any level of axial strain, using a strain-dependent estimate of material stiffness. The initial elastic modulus of uncracked concrete is assessed, based on water-cement ratio, age, volume fraction of aggregates, paste porosity, degree of hydration, and paste-aggregate interface properties. Reduction of the initial modulus with increasing load is modeled by the application of a factor that depends on the natural porosity of the material and mechanically induced porosity as it is assessed by the area strain that develops in the cross section supporting the load. Using this approach, it is possible to model the change effected on the initial resistance of the material from progressive microcrack growth and internal damage occurring in the concrete. The sensitivity of the proposed model to several variables was evaluated from parametric studies and by comparisons with available experimental data.
TL;DR: In this paper, a composite model has been developed in which water ingress may be estimated by changes in overall elastic behaviour of the polymer, and the composite model gives values of the coefficient of diffusion, D, for the bulk adhesive in satisfactory agreement with those obtained by gravimetric analysis.
TL;DR: In this paper, a multiphase B4C/A1 composites containing 5-10 vol% free metal are compared to ceramics, and the highest hardness (88 Rockwell A) and Young's modulus (310 GPa) are obtained in Al4BC-rich samples.
Abstract: B4C/A1 offers a family of engineering materials in which a range of properties can be developed by postdensiflcation heat treatment. In applications where hardness and high modulus are required, heat treatment above 600°C provides a multiphase ceramic material containing only a small amount of residual metal. Heat treatment between 600° and 700°C produces mainly A1B2; 700° and 900°C results in a mixture of A1B2 and A14BC; 900° and 980°C produces primarily A14BC; and 1000° to 1050°C results in A1B24C4 with small amounts of A14C3 if the heating does not exceed 5 h. Deleterious A14C3 is avoided by processing below 1000°C. All of these phases tend to form large clusters of grains and result in lower strength regardless of which phase forms. Toughness is also reduced; the least determinal phase is A1B2. The highest hardness (88 Rockwell A) and Young's modulus (310 GPa) are obtained in Al4BC-rich samples. AlB2-containing samples exhibit lower hardness and Young's modulus but higher fracture toughness. While the modulus, Poisson's ratio, and hardness of multiphase B4C/A1 composites containing 5–10 vol% free metal are comparable to ceramics, the unique advantage of this family of materials is low density (>2.7 g/cm3) and higher than 7 MPa-m1/2 fracture toughness.
TL;DR: The stress-strain and Young's modulus curves showed the typical hysteresis and nonlinearity seen previously in other vocal fold tissues (muscle and mucosa), but the non linearity was most profound for the vocal ligament.
Abstract: The longitudinal elastic properties of the human vocal ligament were quantified by stress-strain measurements and by modeling the response mathematically. Human ligaments were obtained from surgery and autopsy cases. They were dissected, mounted, and stretched with a dual-servo ergometer to measure force versus elongation and to convert the results into stress and strain. To calculate a longitudinal Young's modulus, the stress-strain curves were fitted with polynomial and exponential functions and differentiated. Young's modulus was separately defined in the low- and high-strain regions. The mean Young's modulus for the low-strain region was 33.1 ± 10.4 kilopascals. In the high-strain region, A and B parameters for an exponential fit were 1.4 ± 1.0 and 9.6 ± 1.2 kilopascals, respectively. The stress-strain and Young's modulus curves showed the typical hysteresis and nonlinearity seen previously in other vocal fold tissues (muscle and mucosa), but the nonlinearity was most profound for the vocal ligament.
TL;DR: In this paper, a series of experiments were conducted to measure the physical properties, tensile and shear strengths and elastic moduli of stem between nodes of wheat straw (var Mercia).
TL;DR: In this paper, the second-order elastic stiffness coefficients of a Ti{sub 44}Al{sub 56} single crystal (ital L}1{sub 0} structure were measured at room temperature using a resonant ultrasonic spectroscopy (RUS) technique.
Abstract: The six independent second-order elastic stiffness coefficients of a Ti{sub 44}Al{sub 56} single crystal ({ital L}1{sub 0} structure) have been measured at room temperature for the first time using a resonant ultrasonic spectroscopy (RUS) technique. These data were used to calculate the orientation dependence of Young`s modulus and the shear modulus. The Young`s modulus is found to reach a maximum near a [111] direction, close to the normal to the most densely packed planes. The elastic moduli and the Poisson`s ratio for polycrystalline materials, calculated by the averaging scheme proposed by Hill, are in good agreement with experimental data and theoretical calculations.
TL;DR: In this article, the elastic behavior of mortar and concrete as a composite material and the influence of the transition zone on the elastic modulus is studied, and the theoretical bounds of Hashin-Shtrikman for the modulus of elasticity of two-phase composite material are used as a criteria in the analysis.
TL;DR: In this paper, elastic moduli of granular material with anisotropic packing structures are derived in explicit terms of inter-particle properties using two different methods, namely the kinematic method and the static method.
TL;DR: The strength of alumina materials that had been subjected to varying degrees of densification was determined in this paper, showing that significant increases occur during the initial stage of sintering, showing a strong correlation with the strength data.
Abstract: The strength of alumina materials that had been subjected to varying degrees of densification was determined. Significant increases in strength were obtained for these materials even when there was minimal densification. For the most porous materials, the Weibull modulus values were similar but showed a significant increase for materials that were close to the theoretical density. Young's modulus data were found to be similar to previous work, in that significant increases occur during the initial stage of sintering, showing a strong correlation with the strength data. A simple modi fication to a previous theory allowed the Young's modulus data to be fitted with excellent accuracy.
01 Dec 1995-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, Young's modulus for nanocrystalline Fe samples produced by inert-gas condensation and warm consolidation was measured using nanindentation techniques and shown to be reduced relative to that of conventional, fully dense Fe.
Abstract: Nanoindentation techniques were used to measure Young's modulus for nanocrystalline Fe samples produced by inert-gas condensation and warm consolidation. The samples had grain sizes of 4–20 nm and residual porosity of 2–30% calculated relative to conventional Fe. Values of Young's modulus for the nanocrystalline Fe are reduced relative to that of conventional, fully dense Fe. A review of Young's modulus for other nanocrystalline materials showed similar trends. Published results for porous conventional Fe showed similar reductions in Young's modulus for samples with comparable porosity levels. The observed reductions in Young's modulus for both the nanocrystalline and the conventional porous Fe can be described adequately by several theories utilizing spheroidal porosity.