Showing papers on "Elastic modulus published in 2008"

Universal Elastic Anisotropy Index

Abstract: Practically all elastic single crystals are anisotropic, which calls for an appropriate universal measure to quantify the extent of anisotropy. A review of the existing anisotropy measures in the literature leads to a conclusion that they lack universality in the sense that they are nonunique and ignore contributions from the bulk part of the elastic stiffness (or compliance) tensor. Proceeding from extremal principles of elasticity, we introduce a new universal anisotropy index that overcomes the above limitations. Furthermore, we establish special relationships between the proposed anisotropy index and the existing anisotropy measures for special cases. A new elastic anisotropy diagram is constructed for over 100 different crystals (from cubic through triclinic), demonstrating that the proposed anisotropy measure is applicable to all types of elastic single crystals, and thus fills an important void in the existing literature.

Elastic properties of chemically derived single graphene sheets.

Abstract: The elastic modulus of freely suspended graphene monolayers, obtained via chemical reduction of graphene oxide, was determined through tip-induced deformation experiments. Despite their defect content, the single sheets exhibit an extraordinary stiffness (E = 0.25 TPa) approaching that of pristine graphene, as well as a high flexibility which enables them to bend easily in their elastic regime. Built-in tensions are found to be significantly lower compared to mechanically exfoliated graphene. The high resilience of the sheets is demonstrated by their unaltered electrical conductivity after multiple deformations. The electrical conductivity of the sheets scales inversely with the elastic modulus, pointing toward a 2-fold role of the oxygen bridges, that is, to impart a bond reinforcement while at the same time impeding the charge transport.

Mechanical properties of silicones for MEMS

Abstract: This paper focuses on the mechanical properties of polydimethylsiloxane (PDMS) relevant for microelectromechanical system (MEMS) applications. In view of the limited amount of published data, we analyzed the two products most commonly used in MEMS, namely RTV 615 from Bayer Silicones and Sylgard 184 from Dow Corning. With regard to mechanical properties, we focused on the dependence of the elastic modulus on the thinner concentration, temperature and strain rate. In addition, creep and thermal aging were analyzed. We conclude that the isotropic and constant elastic modulus has strong dependence on the hardening conditions. At high hardening temperatures and long hardening time, RTV 615 displays an elastic modulus of 1.91 MPa and Sylgard 184 of 2.60 MPa in a range up to 40% strain.

Mechanical properties of polypropylene hybrid fiber-reinforced concrete

Abstract: This paper investigates the mechanical properties of polypropylene hybrid fiber-reinforced concrete. There are two forms of polypropylene fibers including coarse monofilament, and staple fibers. The content of the former is at 3 kg/m3, 6 kg/m3, and 9 kg/m3, and the content of the latter is at 0.6 kg/m3. The experimental results show that the compressive strength, splitting tensile strength, and flexural properties of the polypropylene hybrid fiber-reinforced concrete are better than the properties of single fiber-reinforced concrete. These two forms of fibers work complementarily. The staple fibers have good fineness and dispersion so they can restrain the cracks in primary stage. The monofilament fibers have high elastic modulus and stiffness. When the monofilament fiber content is high enough, it is similar to the function of steel fiber. Therefore, they can take more stress during destruction. In addition, hybrid fibers disperse throughout concrete, and they are bond with mixture well, so the polypropylene hybrid fiber-reinforced concrete can effectively decrease drying shrinkage strain.

An estimation of the Young's modulus of bacterial cellulose filaments

Abstract: An estimation, using a Raman spectroscopic technique, of the Young’s modulus of a single filament of bacterial cellulose is presented. This technique is used to determine the local molecular deformation of the bacterial cellulose via a shift in the central position of the 1095 cm–1 Raman band, which corresponds to the stretching of the glycosidic bond in the backbone of the cellulose structure. By calculating the shift rate with respect to the applied strain it is shown that the stiffness of a single fibril of bacterial cellulose can be estimated. In order to perform this estimation, networks of fibres are rotated through 360° and the intensity of the 1095 cm−1 Raman band is recorded. It is shown that the intensity of this band is largely independent of the angle of rotation, which suggests that the networks are randomly distributed. The modulus is predicted from a calibration of Raman band shift against modulus, using previously published data, and by using Krenchel analysis to back-calculate the modulus of a single fibril. The value obtained (114 GPa) is higher than previously reported values for this parameter, but lower than estimates of the crystal modulus of cellulose-I (130–145 GPa). Reasons for these discrepancies are given in terms of the crystallinity and structural composition of the samples.

A Microscopic Model for the Reinforcement and the Nonlinear Behavior of Filled Elastomers and Thermoplastic Elastomers (Payne and Mullins Effects)

Abstract: We extend a model regarding the reinforcement of nanofilled elastomers and thermoplastic elastomers. The model is then solved by numerical simulations on mesoscale. This model is based on the presence of glassy layers around the fillers. Strong reinforcement is obtained when glassy layers between fillers overlap. It is particularly strong when the corresponding clusters—fillers + glassy layers—percolate, but it can also be significant even when these clusters do not percolate but are sufficiently large. Under applied strain, the high values of local stress in the glassy bridges reduce their lifetimes. The latter depend on the history, on the temperature, on the distance between fillers, and on the local stress in the material. We show how the dynamics of yield and rebirth of glassy bridges account for the nonlinear Payne and Mullins effects, which are a large drop of the elastic modulus at intermediate deformations and a progressive recovery of the initial modulus when the samples are subsequently put at ...

Anisotropic Elastic Properties of Cellulose Measured Using Inelastic X-ray Scattering

Abstract: Plant fibers such as linen are remarkably stiff materials in the longitudinal direction of the fiber. As plant cell walls are composites made of cellulose nanocrystals, the so-called microfibrils, embedded in a disordered matrix, those nanocrystals should exhibit an even higher elastic modulus G. We have determined the elastic properties of cellulose microfibrils via the sound velocities measured by inelastic X-ray scattering (IXS). The IXS technique is particularly sensitive to crystal properties by discriminating the contribution of disordered material. A strong anisotropy is observed, with a much lower elastic modulus perpendicular to the fiber direction (G1 = 15 GPa) than parallel to it (G2 = 220 GPa). The latter modulus is considerably higher than all values previously determined and will have a significant impact on models for the elastic properties of cellulose microfibrils and of composites based on them.

Nanostructured YSZ thermal barrier coatings engineered to counteract sintering effects

Abstract: Thermal spray zirconia–8 wt% yttria (YSZ) deposits have been employed as thermal barrier coatings (TBCs) in the hot sections of gas turbines. The use of nanostructured YSZ represents an alternative for improving the performance of these coatings. Despite some initial positive research results, there are still fundamental questions to be answered on the applicability of nanostructured YSZ coatings as TBCs. These questions are related to sintering effects, which could significantly increase the thermal diffusivity/conductivity and elastic modulus values of these types of coatings in high temperature environments. In this study, nanostructured and conventional YSZ coatings were heat-treated at 1400 °C for 1, 5 and 20 h. It was observed that the nanostructured coatings counteract sintering effects, due to the presence of a bimodal microstructure exhibiting regions with different sintering rates: (i) matrix (low rate) and (ii) nanozones (high rate). Important sintering-affected properties, like thermal diffusivity and elastic modulus were studied. The thermal diffusivity and elastic modulus values of the nanostructured YSZ coatings were significantly lower than those of conventional YSZ coatings, even after an exposure to a temperature of 1400 °C for 20 h. This study demonstrates that nanostructured YSZ coatings can be engineered to counteract sintering effects and exhibit significantly lower increases in thermal diffusivity and elastic modulus values in high temperature environments when compared to those of conventional YSZ coatings.

Strength, Modulus of Elasticity, and Brittleness Index of Rubberized Concrete

Abstract: This paper presents a study of rubberized concretes designed by replacing coarse aggregate in normal concrete with ground and crushed scrap tire rubber in various volume ratios. The objective of the study was to investigate the effect of rubber types and rubber content on strength and deformation properties. The compressive strength, static, and dynamic modulus of elasticity of rubberized concrete were tested and studied. The stress-strain hysteresis loops were obtained by loading, unloading, and reloading on specimens. Brittleness index values were calculated based on the hysteretic loops. The experiments revealed that strength and modulus elasticity of rubberized concrete decreased with the increasing amount of rubber content. Compressive strength and modulus of elasticity of crushed rubberized concrete were lower than that of ground rubberized concrete. An American Concrete Institute equation could reasonably predict modulus of elasticity of rubberized concrete. Brittleness index values of rubberized concrete were lower than that of normal concrete, which means that rubberized concrete had higher ductility performance than that of normal concrete.

Correlation between hardness and elastic moduli of the ultraincompressible transition metal diborides RuB2, OsB2, and ReB2

Abstract: The ultraincompressible transition metal diborides RuB 2 , OsB 2 , and ReB 2 were synthesized by arc melting the elemental metals and boron under an argon atmosphere at ambient pressure The hardness and Young’s modulus were measured using nanoindentation with a Berkovich diamond indenter The bulk modulus and shear modulus were derived based on an isotropic model and then plotted as a function of hardness A strong correlation is observed between the hardness and shear modulus for these transition metal diborides © 2008 American Institute of Physics DOI: 101063/12946665

Yield stress and elastic modulus of suspensions of noncolloidal particles in yield stress fluids

Abstract: We study experimentally the behavior of isotropic suspensions of noncolloidal particles in yield stress fluids. This problem has been poorly studied in the literature, and only on specific materials. In this paper, we manage to develop procedures and materials that allow us to focus on the purely mechanical contribution of the particles to the yield stress fluid behavior, independently of the physicochemical properties of the materials. This allows us to relate the macroscopic properties of these suspensions to the mechanical properties of the yield stress fluid and the particle volume fraction, and to provide results applicable to any noncolloidal particle in any yield stress fluid. We find that the elastic modulus-concentration relationship follows a Krieger-Dougherty law, and we show that the yield stress-concentration relationship is related to the elastic modulus-concentration relationship through a very simple law, in agreement with results from a micromechanical analysis.

Homogenization approach to the behavior of suspensions of noncolloidal particles in yield stress fluids

Abstract: The behavior of suspensions of rigid particles in a non-Newtonian fluid is studied in the framework of a nonlinear homogenization method. Estimates for the overall properties of the composite material are obtained. In the case of a Herschel–Bulkley suspending fluid, it is shown that the properties of a suspension with overall isotropy can be satisfactorily modeled as that of a Herschel–Bulkley fluid with an exponent equal to that of the suspending fluid. Estimates for the yield stress and the consistency at large strain rate levels are proposed. These estimates compare well to both experimental data obtained by Mahaut et al. [J. Rheol. 52(1), 287–313 (2008)] and to experimental data found in the literature.

Motion of ferroparticles inside the polymeric matrix in magnetoactive elastomers

Abstract: Ferroelastic composites are smart materials with unique properties including large magnetodeformational effects, strong field enhancement of the elastic modulus and magnetic shape memory On the basis of mechanical tests, direct microscopy observations and magnetic measurements we conclude that all these effects are caused by reversible motion of the magnetic particles inside the polymeric matrix in response to an applied field The basic points of a model accounting for particle structuring in a magnetoactive elastomer under an external field are presented

Internal lattice relaxation of single-layer graphene under in-plane deformation

Abstract: For noncentrosymmetric crystals, internal lattice relaxation must be considered for theoretical predictions of elastic properties. This paper develops a molecular dynamics approach for determination of the internal relaxation displacement in a single-layer graphene sheet under macroscopically homogeneous in-plane deformation. Based on an analytical interatomic potential, a generally nonlinear relationship between the internal relaxation displacement and the applied macroscopic strain is obtained explicitly from molecular dynamics simulations with a rhombic unit cell under finite deformation. A linear relationship is derived for relatively small strains, which can be conveniently incorporated into a continuum description of the elastic behavior of graphene. It is found that the internal relaxation has a strong effect on theoretical elastic moduli of graphene. In addition, the relationship between elastic properties for graphene and carbon nanotubes is discussed.

High-resolution and large dynamic range nanomechanical mapping in tapping-mode atomic force microscopy

Abstract: High spatial resolution imaging of material properties is an important task for the continued development of nanomaterials and studies of biological systems. Time-varying interaction forces between the vibrating tip and the sample in a tapping-mode atomic force microscope contain detailed information about the elastic, adhesive, and dissipative response of the sample. We report real-time measurement and analysis of the time-varying tip-sample interaction forces with recently introduced torsional harmonic cantilevers. With these measurements, high-resolution maps of elastic modulus, adhesion force, energy dissipation, and topography are generated simultaneously in a single scan. With peak tapping forces as low as 0.6 nN, we demonstrate measurements on blended polymers and self-assembled molecular architectures with feature sizes at 1, 10, and 500 nm. We also observed an elastic modulus measurement range of four orders of magnitude (1 MPa to 10 GPa) for a single cantilever under identical feedback conditions, which can be particularly useful for analyzing heterogeneous samples with largely different material components.

Elasticity of (Mg,Fe)O Through the Spin Transition of Iron in the Lower Mantle

Abstract: Changes in the electronic configuration of iron at high pressures toward a spin-paired state within host minerals ferropericlase and silicate perovskite may directly influence the seismic velocity structure of Earth's lower mantle. We measured the complete elastic tensor of ferropericlase, (Mg(1-x),Fe(x))O (x = 0.06), through the spin transition of iron, whereupon the elastic moduli exhibited up to 25% softening over an extended pressure range from 40 to 60 gigapascals. These results are fully consistent with a simple thermodynamic description of the transition. Examination of previous compression data shows that the magnitude of softening increases with iron content up to at least x = 0.20. Although the spin transition in (Mg,Fe)O is too broad to produce an abrupt seismic discontinuity in the lower mantle, the transition will produce a correlated negative anomaly for both compressional and shear velocities that extends throughout most, if not all, of the lower mantle.

Acoustic Oscillations and Elastic Moduli of Single Gold Nanorods

Abstract: We present the first acoustic vibration measurements of single gold nanorods with well-characterized dimensions and crystal structure The nanorods have an average size of 90 nm × 30 nm and display two vibration modes, the breathing mode and the extensional mode Correlation between the dimensions obtained from electron microscope images and the vibrational frequencies of the same particle allows us to determine the elastic moduli for each individual nanorod Contrary to previous reports on ensembles of gold nanorods, we find that the single particle elastic moduli agree well with bulk values

On The Elastic Modulus of Metallic Nanowires

Abstract: Previous atomistic simulations and experiments have attributed size effects in the elastic modulus of Ag nanowires to surface energy effects inherent to metallic surfaces. However, differences in experimental and computational trends analyzed here imply that other factors are controlling experimentally observed modulus changes. This study utilizes atomistic simulations to determine how strongly nanowire geometry and surface structure influence nanowire elastic modulus. The results demonstrate that although these factors do influence the elastic modulus of Ag nanowires to some extent, they alone are insufficient to explain current experimental trends in nanowire modulus with decreasing dimensional scale. Future work needs to be done to determine whether other factors, such as surface contaminants or oxide layers, contribute to the experimentally observed elastic modulus increase.

Static, stability and dynamic analysis of gradient elastic flexural Kirchhoff plates

Abstract: The governing equation of motion of gradient elastic flexural Kirchhoff plates, including the effect of in-plane constant forces on bending, is explicitly derived. This is accomplished by appropriately combining the equations of flexural motion in terms of moments, shear and in-plane forces, the moment–stress relations and the stress–strain equations of a simple strain gradient elastic theory with just one constant (the internal length squared), in addition to the two classical elastic moduli. The resulting partial differential equation in terms of the lateral deflection of the plate is of the sixth order instead of the fourth, which is the case for the classical elastic case. Three boundary value problems dealing with static, stability and dynamic analysis of a rectangular simply supported all-around gradient elastic flexural plate are solved analytically. Non-classical boundary conditions, in additional to the classical ones, have to be utilized. An assessment of the effect of the gradient coefficient on the static or dynamic response of the plate, its buckling load and natural frequencies is also made by comparing the gradient type of solutions against the classical ones.

Selective Electron Beam Melting of Cellular Titanium: Mechanical Properties

Abstract: Cellular titanium seems to be a promising material for medical implant applications due to an elastic modulus comparable with human bone and an interconnected porosity which facilitates bone ingrowth. This paper reports the mechanical properties of non-stochastic cellular Ti-6Al-4V structures fabricated by Selective Electron Beam Melting depending on different unit cell sizes and varying energy input per unit length of the electron beam.

Elastic modulus of biomedical titanium alloys by nano-indentation and ultrasonic techniques—A comparative study

Abstract: The elastic modulus of near β and β titanium alloys was measured by nano-indentation and ultrasonic techniques The data obtained from both the experiments were analyzed and compared with each other The effects of composition and heat treatment on elastic modulus of the material are discussed The elastic modulus of β Ti–35Nb–57Ta–72Zr (TNTZ) was found to be half of the elastic modulus of the titanium Near β Ti–13Zr–13Nb (TZN) alloy hot worked at 800 °C and solution treated at 800 °C followed by water quenching also showed low elastic modulus value The accuracy of these two elastic modulus measurement techniques is discussed in terms of microstructures

Young's modulus of some SOFCs materials as a function of temperature

Abstract: Solid oxide fuel cells (SOFCs) have been under great consideration during this last decade and much effort has been dedicated to model their thermo-mechanical behavior, trying to take into account the different properties of the materials, such as their elasticity. In this paper, we report the elastic behavior of three classical materials used in SOFCs as a function of temperature: Yttria stabilized zirconia (YSZ), La0.8Sr0.2MnO3 (LSM) and Ni-YSZ. Both YSZ and LSM present unusual behaviors. The elastic modulus of YSZ first decreases slowly up to 150 °C, then dramatically up to 550 °C (certainly due to atomic motion) and finally increases probably because of an order–disorder transition (oxygen vacancies). The state of the art on zirconia was reviewed. For the LSM material, Young's modulus could not be determined below 600 °C. Above this temperature, samples with totally closed porosity present a continuously increasing modulus, while the other samples have a quite constant modulus.