Showing papers on "Elastic modulus published in 1997"
TL;DR: In this article, the elastic properties of carbon nanotubes and nanoropes were investigated using an empirical force-constant model and it was shown that the tensile Young's modulus and the torsion shear modulus of tubes are comparable to that of the diamond, while the bulk modulus is smaller.
Abstract: Elastic properties of carbon nanotubes and nanoropes are investigated using an empirical force-constant model. For single and multiwall nanotubes the elastic moduli are shown to be insensitive to structural details such as the helicity, the radius, and the number of walls. The tensile Young's modulus and the torsion shear modulus of tubes are comparable to that of the diamond, while the bulk modulus is smaller. Nanoropes composed of single wall nanotubes have the ideal elastic properties of high tensile stiffness and light weight.
1,431 citations
TL;DR: It is shown that multiwalled carbon nanotubes can be bent repeatedly through large angles using the tip of an atomic force microscope, without undergoing catastrophic failure.
Abstract: The curling of a graphitic sheet to form carbon nanotubes produces a class of materials that seem to have extraordinary electrical and mechanical properties. In particular, the high elastic modulus of the graphite sheets means that the nanotubes might be stiffer and stronger than any other known material, with beneficial consequences for their application in composite bulk materials and as individual elements of nanometre-scale devices and sensors. The mechanical properties are predicted to be sensitive to details of their structure and to the presence of defects, which means that measurements on individual nanotubes are essential to establish these properties. Here we show that multiwalled carbon nanotubes can be bent repeatedly through large angles using the tip of an atomic force microscope, without undergoing catastrophic failure. We observe a range of responses to this high-strain deformation, which together suggest that nanotubes are remarkably flexible and resilient.
1,430 citations
TL;DR: The elastic and tensile behavior of high-density, high-purity nanocrystalline Cu and Pd was determined in this paper, showing that porosity increases with decreasing porosity, and may be significantly affected by a few large processing flaws.
791 citations
TL;DR: In this article, a device and procedure for measuring elastic properties of gelatin for elasticity imaging (elastography) was described. And the measured compression forces were comparable to results obtained from finite element analysis when linear elastic media are assumed.
Abstract: Acoustic and mechanical properties are reported for gelatin materials used to construct tissue-like phantoms for elasticity imaging (elastography). A device and procedure for measuring elastic properties are described. The measured compression forces were comparable to results obtained from finite element analysis when linear elastic media are assumed. Also measured were the stress relaxation, temporal stability, and melting point of the materials. Aldehyde concentration was used to increase the stiffness of the gelatin by controlling the amount of collagen cross-linking. A broad range of tissue-like elastic properties was achieved with these materials, although gels continued to stiffen for several weeks. The precision for elastic modulus measurements ranged from less than 0.1% for 100 kPa samples to 8.9% for soft (<10 kPa), sticky samples.
511 citations
TL;DR: The elastic constants of an open-cell foam model, having tetrakaidecahedral cells on a BCC lattice, were derived, as functions of the edge cross section and the foam density, by considering the bending, twisting and extension of the cell edges.
Abstract: The elastic constants of an open-cell foam model, having tetrakaidecahedral cells on a BCC lattice, were found The Young's modulus, shear modulus and Poisson's ratio were derived, as functions of the edge cross section and the foam density, by considering the bending, twisting and extension of the cell edges If edge bending were the only mechanism the moduli would vary with the square of the foam density The other deformation mechanisms are predicted to reduce the power law exponent by 3–5%, and the effect of edge torsion on the modulus level is small The foam bulk modulus is predicted to vary linearly with its relative density, so Poisson's ratio approaches 05 at low densities The lattice model is elastically isotropic, whereas other lattice models of foams are highly anisotropic
446 citations
TL;DR: The structural and elastic properties of MgO periclase were studied up to 150 GPa with the first-principles pseudopotential method within the local density approximation as mentioned in this paper.
Abstract: The structural and elastic properties of MgO periclase were studied up to 150 GPa with the first-principles pseudopotential method within the local density approximation. The calculated lattice constant of the B1 phase over the pressure range studied is within 1% of experimental values. The observed B1 phase of MgO was found to be stable up to 450 GPa, precluding the B1-B2 phase transition within the lower mantle. The calculated transition pressure is less than one-half of the previous pseudopotential prediction but is very close to the linearized augmented plane-wave result. All three independent elastic constants, c(11), c(12), and c(44) for the B1 phase are calculated from direct computation of stresses generated by small strains. The calculated zero-pressure values of the elastic moduli and wave velocities and their initial pressure dependence are in excellent agreement with experiments. MgO was found to be highly anisotropic in its elastic properties, with the magnitude of the anisotropy first decreasing between 0 and 15 Gpa and then increasing from 15 to 150 GPa. Longitudinal and shear-wave velocities were found to vary by 23 and 59%, respectively, with propagation direction at 150 Gpa. The character of the anisotropy changes qualitatively with pressure. At zero pressure longitudinal and shear-wave propagations are fastest along [111] and [100], respectively, whereas above 15 GPa, the corresponding fast directions are [100] and [110]. The Cauchy condition was found to be strongly violated in MgO, reflecting the importance of noncentral many-body forces.
412 citations
TL;DR: In this paper, the material coefficients of Biot's anisotropic poroelasticity are interpreted following micromechanical considerations, which leads to a most practical model for laboratory measurement: the material is defined within 21 drained elastic constants M ijkl, a solid grain bulk modulus K s and a Biot modulus M.
389 citations
TL;DR: In this article, the authors show the application of five approximation functions for this purpose: linear, exponential, reciprocal exponential, Gao's, and the Doerner and Nix functions.
Abstract: Elastic modulus of thin homogeneous films can be determined by indenting the specimen to various depths and extrapolating the measured (apparent) E-values to zero penetration. The paper shows the application of five approximation functions for this purpose: linear, exponential, reciprocal exponential, Gao’s, and the Doerner and Nix functions. Comparison of the results for 26 film/substrate combinations has shown that the indentation response of film/substrate composites can, in general, be described by the Gao analytical function. In determining the thin film modulus from experimental data, satisfactory results can also be obtained with the exponential function, while linear function may be used only for thick films where the relative depths of penetration are small. The article explains the pertinent procedures and gives practical recommendations for the testing.
346 citations
TL;DR: In this paper, a unified method based on the inclusion formulation is proposed to determine the magnetic, electric, and elastic fields in a composite with piezoelectric and piezomagnetic phases.
Abstract: A unified method based on the inclusion formulation is proposed to determine the magnetic, electric, and elastic fields in a composite with piezoelectric and piezomagnetic phases. The composite reinforcements are treated as ellipsoidal inclusions that enable the reinforcement geometries ranging from thin flakes to continuous fibers. Utilizing the proposed method, the magneto-electro-elastic tensors analogous to Eshelby tensors for elastic ellipsoidal inclusions are obtained. With these tensors, the magnetic, electric, and elastic fields around the inclusion as well as concentration factors are determined. Furthermore, based upon the Mori–Tanaka mean-field theory [Acta Metall. 21, 571 (1973)] to account for the interaction between inclusions and matrix, the effective magneto-electro-elastic constants (elastic moduli, piezoelectric coefficients, dielectric constants, piezomagnetic coefficients, magnetoelectric, and magnetic permeability) of the composites are expressed explicitly in terms of phase propertie...
340 citations
TL;DR: The dependence of phase contrast in tapping-mode scanning force microscopy on elastic and inelastic interactions is studied in this article, where the cantilever-tip ensemble is simulated as a driven, damped harmonic oscillator.
Abstract: The dependence of phase contrast in tapping-mode scanning force microscopy on elastic and inelastic interactions is studied. The cantilever–tip ensemble is simulated as a driven, damped harmonic oscillator. It is found that for tip–sample elastic interactions, phase contrast is independent of the sample’s elastic properties. However, phase contrast associated with elastic modulus variations are observed if viscous damping or adhesion energy hysteresis is considered during tip–sample contact. The phase shift versus tip–sample equilibrium separation was measured for a compliant material (polypropylene) and for a stiff sample (mica). The agreement obtained between theory and experiment supports the conclusions derived from the model. These results emphasize the relevance of energy dissipating processes at the nanometer scale to explain phase contrast imaging in tapping-mode force microscopy.
274 citations
TL;DR: In this article, a one-dimensional model able to reproduce the shape-memory-alloy superelastic behavior, taking into account the different elastic properties between austenite and martensite, is presented.
Abstract: The present work addresses a one-dimensional model able to reproduce the shape-memory-alloy superelastic behavior, taking into account the different elastic properties between austenite and martensite. The model is based on a single scalar internal variable, the martensite fraction, for which evolutionary equations in rate form are proposed. The dependency of the elastic modulus in terms of the martensite fraction is computed through different homogenization techniques. Integration in time leads to the time-discrete evolutionary equations, for which a detailed analysis in terms of admissible roots is presented, together with the expression of the consistent tangent modulus. The solution of the time-discrete model is approached through a return map algorithm, properly modified for the case of phase transitions of the type occurring in shape-memory materials. Finally, the ability of the model to simulate one-dimensional experimental data is assessed.
TL;DR: In this paper, the authors present a new apparatus to measure elastic properties and internal friction of materials using a light mechanical impact (impulse excitation) and perform a software-based analysis of the resulting vibration.
Abstract: This paper presents a new apparatus to measure elastic properties and internal friction of materials. The apparatus excites the test specimen by a light mechanical impact (impulse excitation) and performs a software-based analysis of the resulting vibration. The resonant frequencies fr of the test object are determined and, in the case of isotropic and regular shaped specimens, the elastic moduli are calculated. The internal friction value (Q−1) is determined for each fr as Q−1=k/(πfr) with k the exponential decay parameter of the vibration component of frequency fr. A furnace was designed and equipped with automated impulse excitation and vibration detection devices, thus allowing computer-controlled measurements at temperatures up to 1750 °C. The precision of the measured fr depends on the size and stiffness of the specimen, and varies from the order of 10−3 (that is ±1 Hz at 1 kHz) in soft, high damping materials or light specimens, to values as precise as 10−5 (that is ±0.1 Hz at 10 kHz) in larger or ...
TL;DR: The Young's modulus and the shear modulus are comparable to that of the diamond, but the bulk modulus is almost twice as large as the diamond's as mentioned in this paper.
TL;DR: Load-dependent studies of the frictional properties of the carbon compounds graphite, diamond, amorphous carbon, and C${}_{60}$ were performed by friction force spectroscopy in air and dry argon.
Abstract: Load-dependent studies of the frictional properties of the carbon compounds graphite, diamond, amorphous carbon, and C${}_{60}$ were performed by friction force spectroscopy in air and dry argon. During the experiments, the surface was profiled at low loads without wear or plastic deformation. The tips used for profiling were fabricated according to a special production procedure in order to obtain apexes with a well-defined spherical shape and known apex radius. The data obtained were compared with a theoretical model based on the contact mechanical analysis of a Hertzian-type tip/sample contact with small tip radius, low surface energies, but not too low elastic moduli of the tip and sample material. Our experimental results are in excellent agreement with a ${F}_{\mathrm{f}}\ensuremath{\sim}{F}_{\mathrm{n}}^{2/3}$ dependence of the frictional force ${F}_{\mathrm{f}}$ on the normal force ${F}_{\mathrm{n}}$ as predicted for this case. These findings suggest that contact mechanical models, in spite of being based on continuum elasticity theory, are valid for tip radii down to a few nanometers and that the shear stress is constant within the elastic regime. Additionally, it was shown that the friction coefficient $\ensuremath{\mu}{=F}_{\mathrm{f}}{/F}_{\mathrm{n}}$ is not well suited for comparing the tribological behavior of different materials in the case of single-asperity friction. Therefore, an effective friction coefficient for point-contact-like single-asperity friction was introduced for the classification of the microscopic frictional properties of materials. As quantitative results, high microscopic friction was found for C${}_{60}$ thin films, medium friction for amorphous carbon and diamond, and very low friction for graphite.
TL;DR: The authors investigated the morphology and the elastic properties of living cultured rat liver macrophages with an atomic force microscope (AFM) and found the importance of the cytoskeleton for the mechanical properties of the cell has been investigated by measuring the cell's elasticity as a function of position.
TL;DR: This study used a two-dimensional finite element mesh of a lower first premolar to model two different tooth loading systems which measured either the vertical or the horizontal displacements of this particular tooth.
TL;DR: In this paper, the effective Young's (E ∗ ) and shear moduli and Poisson's ratio of some materials of interest for solid oxide fuel cells (SOFC), namely 10 and 20 mol% Gd2O3 doped CeO2 (GCO), 3 and 8 mol% Y 2O3 stabilized ZrO2 and YSZ, and 75 mol% NiO-YSZ, were measured.
Abstract: Measurements are presented for the effective Young's ( E ∗ ) and shear ( G ∗ ) moduli and Poisson's ratio of some materials of interest for solid oxide fuel cells (SOFC), namely 10 and 20 mol% Gd2O3 doped CeO2 (GCO), 3 and 8 mol% Y2O3 stabilized ZrO2 (TZP and YSZ), and 75 mol% NiO-YSZ. The dependence of moduli on porosity was characterized by employing both theoretical (composite sphere method, CSM) and empirical (exponential, nonlinear, and linear) equations. The theoretical and empirical equations were tested by determining the goodness of fit of the equations to the experimental data and the standard error of estimation. All the equations described the modulus-porosity relationships equally well, except that, for NiOYSZ, the empirical equations yield better fits than the CSM equations. This was attributed to the fact that the CSM equations, derived for two-phase composites, might not hold for calculating the effective moduli of three-phase composites, such as these NiO- YSZ materials.
TL;DR: In this paper, real-time FTIR spectroscopy and in situ dynamic rheology were used to characterize the UV curing kinetics of a thiol-ene system containing trimethylolpropane tris(2-mercaptoacetate) and trimethyllpropane diallyl ether.
Abstract: Real-time FTIR spectroscopy and in situ dynamic rheology were used to characterize the UV curing kinetics of a thiol-ene system containing trimethylolpropane tris(2-mercaptoacetate) and trimethylolpropane diallyl ether. The combination of these two techniques offered a powerful approach for monitoring changes in the chemical and rheological properties of the system during UV curing. Comparable gel times were independently obtained from both FTIR spectroscopy and rheology, thereby validating the comparison of data obtained from each method. The thiol conversion determined from FTIR spectroscopy was correlated with the elastic modulus obtained from rheology. The conversion increased very rapidly during the initial stages of UV curing. However, the elastic modulus did not have an appreciable value until after 65% of the thiol functional groups have reacted, following which the elastic modulus increased at a rapid rate. From the Flory−Stockmayer theory of gelation, the critical thiol conversion at the gel poi...
Journal Article•
TL;DR: The current status of particulate-reinforced titanium matrix composites is reviewed in this paper, where different types of reinforcements are used, together with the alternative processing routes, and the mechanical properties of these composites are influenced by a wide range of factors.
Abstract: The current status of particulate-reinforced titanium matrix composites is reviewed. The different types of reinforcements being used, together with the alternative processing routes, are described. The mechanical properties of these composites are influenced by a wide range of factors. Particulate reinforcements can affect properties by enhancing modulus and strength or by refining the grain size. Mechanical properties such as elastic modulus, low and high temperature strength, fracture toughness and compressive creep are discussed as functions of reinforcement size/shape and volume fraction. The review concludes by underlining the importance of further research in some critical areas to fully realise the industrial potential of these composites.
TL;DR: In this paper, the hardness and elastic modulus of tracheid walls in the longitudinal direction of spruce wood were obtained by continuously measuring force and displacement as a diamond indenter impressed a cell wall.
Abstract: Using a mechanical properties microprobe, measurements of hardness and elastic modulus of tracheid walls in the longitudinal direction of spruce wood were obtained by continuously measuring force and displacement as a diamond indenter impressed a cell wall. Maximum mechanical properties were found at the edges of the walls of angular shaped tracheids. Both the hardness and elastic modulus of latewood cell walls were higher than cell walls in the earlywood. The high spatial resolution of this new concept of mechanical testing allows a direct comparison with ultrastructural and microchemical parameters of lignified cells which opens a wider area of applications for the understanding of intrinsic wood properties.
TL;DR: In the lamellipodal region investigated here in detail, the elastic moduli range from around 10 up to 200 kPa on top of stress fibers, which means that to what extent the elastic properties of this type of cell are determined by the actin network is unknown.
TL;DR: The diurnal time course of tension in the water columns in the xylem of the trunk of mature Scots pine (Pinus sylvestris L.) was measured during the summer of 1995 by means of a displacement transducer mounted on a rigid steel frame.
Abstract: According to the cohesion theory for the ascent of water in vascular plants, significant tensions should develop in the water columns of transpiring trees. These tensions cause small but detectable changes in the diameter of the xylem as a consequence of adhesive forces between water molecules and the inner xylem walls. The diurnal time course of tension in the water columns in the xylem of the trunk of mature Scots pine (Pinus sylvestris L.) was measured during the summer of 1995 by means of a displacement transducer mounted on a rigid steel frame. The apparent elastic modulus of Scots pine wood in the radial direction (E
′
r
) was determined in the laboratory and then used to estimate tensions from the measured displacement. Laboratory measurements on logs indicated that only the sapwood contributed to dimensional changes of the xylem. Corrections for thermal expansion of the system were included. Water tensions fell by 0.19 MPa over the course of the day, when needle water potentials fell by 0.50 MPa. Such data are consistent with the cohesion theory, and with the view that the hydraulic resistances to flow in above- and below-ground plant parts are of similar magnitude.
01 Apr 1997
TL;DR: The photoluminescence (PL) peaks superimposed upon the Raman scattering spectrum were observed at a hydrogen content of ca. 34%, and increases exponentially thereafter, driven by the progressive saturation of carbon dangling bonds.
Abstract: a-C:H films prepared by DC-magnetron sputtering in an H/sub 2/:Ar mixture exhibit strong photoluminescence (PL) peaks superimposed upon the Raman scattering spectrum. PL becomes observable at a hydrogen content of ca. 34%, and increases exponentially thereafter, driven by the progressive saturation of carbon dangling bonds. In this %H range, hardness and elastic modulus decrease and CSS durability reaches an optimum. The Raman G peak position is very sensitive to deposition temperature (shift of 0.1 cm/sup -1///spl deg/C) and was found to correlate with the sp/sup 3//sp/sup 2/ bonding ratio as measured by EELS, and therefore can also be used as a predictor of carbon tribological performance.
TL;DR: In this article, the shear and compressive properties of aggregated alumina particles are determined as functions of volume fraction and the strength of the interparticle attraction, and the links between compressive and shear properties are well described by linear elastic models where the Py and τy are a function of Poisson's ratio which, for the suspensions investigated, has a value near 0.49.
Abstract: The shear and compressive properties of aggregated alumina particles are determined as functions of volume fraction and the strength of the interparticle attraction. Over a range of volume fractions, yield stresses, τy, elastic moduli, the strain delimiting the extent of the linear elastic response, and compressive yield stress, Py, are well described by power-law functions of volume fraction, while the role of interparticle attractions can be accounted for by expressing these mechanical properties as (ϕ/ϕg − 1)n, where ϕg captures the strength of particle attractions and n the microstructure. The links between compressive and shear properties are well described by linear elastic models where the Py and τy are a function of Poisson's ratio which, for the suspensions investigated, has a value near 0.49.
TL;DR: In this article, the authors used the inhomogeneous ITZ model to analyze the data of Wang et al. on the bulk modulus of mortar containing sand inclusions, and inferred that the elastic moduli at the interface with the inclusions is 30-50% less than in the bulk cement paste.
Journal Article•
TL;DR: In this article, the current status of our knowledge of electromechanical effects that take place in smart polymer gels is reviewed, and the mechanism of polyelectrolyte gel behavior in electric fields is investigated experimentally and then theoretically.
Abstract: “Smart” polymer gels actively change their size, structure, or viscoelastic properties in response to external signals. The stimuli-responsive properties, indicating a kind of intelligence, offer the possibility of new gel-based technology. The article attempts to review the current status of our knowledge of electromechanical effects that take place in smart polymer gels. Deformation and the mechanism of polyelectrolyte gel behavior in electric fields are first studied experimentally and then theoretically. In particular, the swelling or bending is discussed in detail. Particulate composite gels whose modulus of elasticity can vary in electric fields are revealed as a new smart material. The driving force causing varying elastic modulus in electric fields is explained by a qualitative model based upon polarized particles. Finally, applications of the two electromechanical effects are presented.
TL;DR: In this paper, a multi-mode analysis of micro-cantilever dynamics is presented, where the power spectral density of the cantilever displacement due to a thermal noise source is derived.
Abstract: A multi-mode analysis of micro-cantilever dynamics is presented. We derive the power spectral density of the cantilever displacement due to a thermal noise source and predict the cantilevers’s fundamental resonant frequency and higher harmonics. The first mode in the multi-mode model is equivalent to the traditional single-mode model. Experimental results obtained with a silicon nitride cantilever at 300 K are in excellent qualitative agreement with the multi-mode model. The multi-mode model may be used to obtain accurate values of the cantilever properties such as the elastic modulus,effective mass, thickness and moment of inertia.
TL;DR: Shear relaxation data do not indicate the presence of a long-term elastic modulus, indicating fluid-like behavior, and the strain sweep experiment showed that the viscoelastic strain limit is of the order of 0.1% strain.
TL;DR: In this paper, a finite/infinite element scheme was employed to investigate the effectiveness of three different wave barriers, i.e., the open trench, in-filled trench, and elastic foundation, in reducing the ground vibrations caused by the passage of trains.
Abstract: In this paper, a finite/infinite element scheme developed previously by the authors is employed to investigate the effectiveness of three different wave barriers, i.e., the open trench, in-filled trench, and elastic foundation, in reducing the ground vibrations caused by the passage of trains. The mathematical model adopted herein is the two-dimensional profile that contains the cross-section of the railway, barrier and underlying soils, with the moving train loads simulated as a vertical harmonic line load. Concerning the effect of isolation, the geometric and material parameters of the three barriers investigated include the distance to rail, depth, width and thickness, damping ratio, shear modulus, mass density, Poisson's ratio, elastic modulus, etc. Also examined is the effectiveness of the three barriers with respect to different exciting frequencies. Conclusions are made regarding the selection of optimal parameter values for the three barriers in isolating the train-induced ground vibrations. © 1997 John Wiley & Sons, Ltd.
TL;DR: Cholinergic synaptic vesicles from Torpedo californica have been probed with the atomic force microscope in aqueous buffers to map and measure their elastic properties, showing that Vesicular centers were hardest in calcium-containing buffer and softest in isoosmotic buffer.