Showing papers on "Elastic modulus published in 2007"

Elastic Properties and Short-to Medium-Range Order in Glasses

Abstract: Very different materials are named “Glass,” with Young's modulus (E) and Poisson's ratio (ν) extending from 5 to 180 GPa and from 0.1 to 0.4, respectively, in the case of bulk inorganic glasses. Although glasses have in common the lack of long-range order in the atomic organization, they offer a wide range of structural features at the nanoscale and we show in this analysis that beside the essential role of elastic properties for materials selection in mechanical design, the elastic characteristics (E, ν) at the continuum scale allow to get insight into the short- and medium-range orders existing in glasses. In particular, ν, the atomic packing density (Cg) and the glass network dimensionality appear to be strongly correlated. Maximum values for ν and Cg are observed for metallic glasses (ν∼0.4 and Cg>0.7), which are based on cluster-like structural units. Atomic networks consisting primarily of chains and layers units (chalcogenides, low Si-content silicate, and phosphate glasses) correspond to ν>0.25 and Cg>0.56. On the contrary, ν<0.25 is associated with a highly cross-linked network, such as in a-SiO2, with a tri-dimensional organization resulting in a low packing density. Moreover, the temperature dependence of the elastic moduli brings a new light on the structural changes occurring above the glass transition temperature and on the depolymerization rate in the supercooled liquid. The softening rate depends on the level of cooperativity of atomic movements at the source of the deformation process, with an obvious correlation with the “fragility” of the liquid.

Imaging and estimation of tissue elasticity by ultrasound.

Abstract: Ultrasound (US) elasticity imaging is an extension of the ancient art of palpation and of earlier US methods for viewing tissue stiffness such as echopalpation. Elasticity images consist of either an image of strain in response to force or an image of estimated elastic modulus. There are 3 m

Studies on lignocellulosic fibers of Brazil. Part II: Morphology and properties of Brazilian coconut fibers

Abstract: Continuing the studies on the Brazilian lignocellulosic fibers, this paper presents chemical, physical, thermal and mechanical properties of curaua fibers, one of the unique fibers of the country. Stress–strain curves as a function of diameter of the fiber and static mechanical properties as functions of diameter, length of the fiber and as function of strain rate are determined for the first time. It was found that the tensile strength (TS) and Young’s modulus (YM) decrease while % strain at break remained constant as fiber diameter increases; decrease of TS and % strain at break and increase in YM as test length increased and an increase in TS and YM but without any change in % strain at break with increase of strain rate. Density, crystallinity, identification of chemical groups and degradation temperatures of these constituents of the fibers have been determined using pycnometer, X-ray diffraction, FTIR, UV and DTA/DSC instruments respectively. Dynamic mechanical analysis was also carried out, which revealed increase in modulus as the water present in the fiber is removed. All the results are discussed in terms of morphological observations including fractography.

Mechanics of Polymer−Clay Nanocomposites

Abstract: The mechanics of nanocomposites is critical in the design of nanomaterials with desirable properties In this paper, the mechanics of polymer−clay nanocomposites is studied using a designed polymer and solution nanocomposite synthesis A copolymer latex, with function groups that strongly interact with the surface of the clay nanoplatelet and glass-transition temperature lower than room temperature, was synthesized Uniformly dispersed nanocomposites were then generated using water as the intercalation agent through the solution process The chain mobility in the nanocomposites is greatly reduced as studied by dynamic mechanical thermal analysis (DMTA) and dielectric thermal analysis (DETA) The modulus of the composite increases significantly The modulus enhancement strongly relates to the volume of the added clay as well as the volume of the constrained polymer This modulus enhancement follows a power law with the content of the clay and is modeled well by Mooney's equation for this soft-polymer-based

Diameter-Dependent Radial and Tangential Elastic Moduli of ZnO Nanowires

Abstract: We show how contact resonance atomic force microscopy (CR-AFM) can be used to accurately determine the radial elastic moduli of [0001] ZnO nanowires with diameters smaller than 150 nm. Using a realistic tip−nanowire contact geometry, we find the radial indentation modulus from CR-AFM data and the tangential shear modulus from friction-type measurements. Both moduli show a pronounced increase when the wire diameter is reduced below 80 nm. The size dependence of the elastic properties can be explained by a core−shell model that accounts for a bulk-like core and an elastically stiffer surface layer.

Molecular dynamics study of the stress–strain behavior of carbon-nanotube reinforced Epon 862 composites

Abstract: Single-walled carbon nanotubes (CNTs) are used to reinforce epoxy Epon 862 matrix. Three periodic systems – a long CNT-reinforced Epon 862 composite, a short CNT-reinforced Epon 862 composite, and the Epon 862 matrix itself – are studied using the molecular dynamics. The stress–strain relations and the elastic Young's moduli along the longitudinal direction (parallel to CNT) are simulated with the results being also compared to those from the rule - of - mixture . Our results show that, with increasing strain in the longitudinal direction, the Young's modulus of CNT increases whilst that of the Epon 862 composite or matrix decreases. Furthermore, a long CNT can greatly improve the Young's modulus of the Epon 862 composite (about 10 times stiffer), which is also consistent with the prediction based on the rule - of - mixture at low strain level. Even a short CNT can also enhance the Young's modulus of the Epon 862 composite, with an increment of 20% being observed as compared to that of the Epon 862 matrix.

Processing and mechanical properties of SiC reinforced cast magnesium matrix composites by stir casting process

Abstract: Elemental Mg and Mg-alloy (AZ91D) based composites reinforced with 15 vol.% silicon carbide (SiC) particulates (average particle size 15 μm and 150 μm) were synthesised by stir casting technique. Particle distribution, particle–matrix interfacial reaction, hardness and mechanical properties in the as cast as well as T4 heat-treated conditions were investigated. The composite materials show uniform distribution of SiC particulates. The average grain size decreases with the presence of SiC particulates and the grain size further decreases as the particle size decreases. The AZ91D alloy composite shows an increase in hardness and elastic modulus compared to monolithic alloys. The improvement in elastic modulus of composite containing 15 μm size SiC particles is significantly higher than the composite with 150 μm size particles. The ultimate tensile strength and ductility of composite materials were reduced compared to unreinforced alloy.

Direct Force Measurements and Kinking under Elastic Deformation of Individual Multiwalled Boron Nitride Nanotubes

Abstract: Individual multiwalled boron nitride nanotubes of different diameters (40−100 nm) were bent inside a 300 kV high-resolution transmission electron microscope (TEM) using a new fully integrated TEM−atomic force microscope (AFM) piezodriven holder under continuous recording of force−piezodisplacement curves. The tubes were gently compressed in situ (i.e., inside the electron microscope) between a piezomovable aluminum wire and a silicon cantilever. Typically, bending stress values ranging from ∼100 to ∼260 MPa, and corresponding to elastic moduli of 0.5−0.6 TPa, were estimated. Tube gross failures were absent up to very large bending angles (in excess of 115°). Extending the bending angles beyond 30−40° resulted in the elastic deformation of BN nanotubes, which proceeded through the propagation of consecutive momentary kinks. These had the effect of accumulating a bending curvature rather then uniformly curl the tube under the compression load. These kinks were found to be entirely reversible on reloading wi...

Synthesis of TiO2−PMMA Nanocomposite: Using Methacrylic Acid as a Coupling Agent

Abstract: Inorganic−polymer nanocomposites are of significant interest for emerging materials due to their improved properties and unique combination of properties. Methacrylic acid (MA), a functionalization agent that can chemically link TiO2 nanomaterials (n-TiO2) and polymer matrix, was used to modify the surface of n-TiO2 using a Ti−carboxylic coordination bond. Then, the double bond in MA was copolymerized with methyl methacrylate (MMA) to form a n-TiO2−PMMA nanocomposite. The resulting n-TiO2−PMMA nanocomposite materials were characterized by using thermal analysis, electron microscopy, and elemental analysis. The dynamic mechanical properties (Young's and shear modulus) were measured using an ultrasonic pulse technique. The electron microscopy results showed a good distribution of the nanofillers in the polymer matrix. The glass transition temperature, thermal degradation temperature, and dynamic elastic moduli of the nanocomposites were shown to increase with an increase in the weight percentage of nanofibe...

Physico-mechanical properties and water absorption of cement composite containing shredded rubber wastes

Abstract: The main objective of this study was to investigate the potential utilisation of rubber waste in cementitious matrix, as fine aggregates, to develop lightweight construction materials. Composites containing different amounts of rubber particles, as partial replacement to cement by volume, were characterised by destructive and non-destructive testing. Five designated rubber contents varying from 10% to 50% by volume were used. The 28-days physical, mechanical and hydraulic transport properties of the cement composite were determined. Analyses included dry unit weight, elastic dynamic modulus, compressive and flexural strengths, strain capacity, and water absorption. Test results of the physico-mechanical behaviour indicated that the increase in rubber content decreases the sample unit weight with a large reduction in the strengths and elastic modulus values of the composites. Results have only shown that the introduction of rubber particles significantly increases the strain capacity of the materials. However, rubbers into cement paste enhances the toughness of the composite. Although the mechanical strengths were reduced, the composite containing 50% of rubber particles satisfies the basic requirement of lightweight construction materials and corresponds to “class II”, according to the RILEM classification. Test-results of the hydraulic transport properties revealed that the addition of rubber particles tends to restrict water propagation in the cement matrix and reduces water absorption of the composite. The decrease of the sorptivity-value is favourable to the durability of the specimen structures.

Evaluation of interphase properties in a cellulose fiber-reinforced polypropylene composite by nanoindentation and finite element analysis

Abstract: The hardness and elastic modulus of the cellulose fiber and polypropylene (PP) matrix in a cellulose fiber-reinforced PP composite were investigated by nanoindentation with a continuous stiffness technique. Nanoindentation with different indentation depths and spacings was conducted to measure hardness and elastic modulus in the interphase region, which was modified by maleic anhydride-grafted PP and γ-amino propyltrimethoxy silane (γ-APS) sizing. A line of indents was produced from the fiber to the matrix. There was a gradient of hardness and modulus across the interphase region. The distinct properties of the transition zone were revealed by 1–4 indents, depending on nanoindentation depth and spacing. Based on the results of nanoindentation, it was assumed that the width of the property transition zone is less than 1 μm. However, three dimensional finite element analysis shows that even a perfect interface without property transition has almost same interphase width as that measured by nanoindentation. Using existing nanoindentation techniques, it will be difficult to calculate exact mechanical properties without the effect of neighboring material property in at least 8 times smaller region than indent size.

Elastic constants and internal friction of martensitic steel, ferritic-pearlitic steel, and α-iron

Abstract: The elastic constants and internal friction of induction hardened and unhardened SAE 1050 plain-carbon steel at ambient temperatures were determined by resonant ultrasonic spectroscopy. The hardened specimen contained only martensite and the unhardened specimen was ferrite-pearlite. Using an inverse Ritz algorithm with assumed orthorhombic symmetry, all nine independent elastic-stiffness coefficients were determined, and, from the resonance peak widths, all nine components of the internal-friction tensor were determined. Similar measurements and analysis on monocrystalline α-iron were performed. The steel has slight elastic anisotropy, and the isotropically approximated elastic moduli were lower in the martensite than in ferrite-pearlite: shear modulus by 3.6%, bulk modulus by 1.2%, Young modulus by 3.2%, and Poisson ratio by 1.5%. Isotropically approximated elastic moduli of α-iron were 0.6–1.3% higher than ferrite-pearlite. All components of the internal-friction in martensite were higher than those of ferrite-pearlite, but lower than those of α-iron.

Acoustoelasticity in soft solids: assessment of the nonlinear shear modulus with the acoustic radiation force.

Abstract: The assessment of viscoelastic properties of soft tissues is enjoying a growing interest in the field of medical imaging as pathologies are often correlated with a local change of stiffness. To date, advanced techniques in that field have been concentrating on the estimation of the second order elastic modulus (mu). In this paper, the nonlinear behavior of quasi-incompressible soft solids is investigated using the supersonic shear imaging technique based on the remote generation of polarized plane shear waves in tissues induced by the acoustic radiation force. Applying a theoretical approach of the strain energy in soft solid [Hamilton et al., J. Acoust. Soc. Am. 116, 41-44 (2004)], it is shown that the well-known acoustoelasticity experiment allowing the recovery of higher order elastic moduli can be greatly simplified. Experimentally, it requires measurements of the local speed of polarized plane shear waves in a statically and uniaxially stressed isotropic medium. These shear wave speed estimates are obtained by imaging the shear wave propagation in soft media with an ultrafast echographic scanner. In this situation, the uniaxial static stress induces anisotropy due to the nonlinear effects and results in a change of shear wave speed. Then the third order elastic modulus (A) is measured in agar-gelatin-based phantoms and polyvinyl alcohol based phantoms.