Showing papers on "Young's modulus published in 2003"

Effect of high temperature on the change in color, dimensional stability and mechanical properties of spruce wood

Abstract: In this study the effect of high temperature on mechanical properties, dimensional stability and color of spruce was investigated. Wood specimens conditioned at different relative humidities (50, 65, 80 and 95 %) were subjected to heat treatment at 200 degreesC for 2, 4, 8, 10 and 24 h and at 100, 150 and 200degreesC for 24 h. Color changes were measured in the Minolta Croma-Meter CR-300 color system. Bending strength and modulus of elasticity were determined according to DIN 52186. The results show that heat treatment mainly resulted in a darkening of wood tissues, improvement of the dimensional stability of wood and reduction of its mechanical properties. The darkening accelerated generally when treatment temperature exceeded approximately 200degreesC. Most of the darkening occurred within the first 4 h of exposure. For the specimens heated to high temperatures, the average decrease in bending strength was about 44-50 %, while modulus of elasticity was reduced by only 4-9 %. We found that treatment time and temperature were more important than relative humidity regarding the color responses. Strong correlations between total color difference and both modulus of elasticity and bending strength were found. Thus, the color parameters can be estimated quantitatively and used as a prediction of wood strength.

Ultrathin single-crystalline-silicon cantilever resonators: Fabrication technology and significant specimen size effect on Young’s modulus

Abstract: Ultrathin resonant cantilevers are promising for ultrasensitive detection. A technique is developed for high-yield fabrication of single-crystalline-silicon cantilevers as thin as 12 nm. The formed cantilever resonators are characterized by resonance testing in high vacuum. Significant specimen size effect on Young’s modulus of ultrathin (12–170 nm) silicon is detected. The Young’s modulus decreases monotonously as the cantilevers become thinner. The size effect is consistent with the published simulation results of direct-atomistic model, in which surface effects are taken into consideration.

Hirsch model for estimating the modulus of asphalt concrete

Abstract: The purpose of this paper is to present a new, rational and effective model for estimating the modulus of asphalt concrete using binder modulus and volumetric composition. The model is based upon an existing version of the law of mixtures, called the Hirsch model, which combines series and parallel elements of phases. In applying the Hirsch model to asphalt concrete, the relative proportion of material in parallel arrangement, called the contact volume, is not constant but varies with time and temperature. Several versions of the Hirsch model were evaluated, including ones using mastic as the binder, and one in which the effect of film thickness on asphalt binder modulus was incorporated into the equation. The most effective model was the simplest, in which the modulus of the asphalt concrete is directly estimated from binder modulus, voids in mineral aggregate, and voids filled with asphalt binder. Models are presented for both dynamic complex shear modulus and dynamic complex extensional modulus. Semi-empirical equations are also presented for estimating phase angle in shear loading and in extensional loading. The proposed model was verified by comparing predicted modulus and phase angles to values reported in the literature for a range of mixtures.

Single-Wall Carbon Nanotube Films

Abstract: An optically homogeneous solution/dispersion of single-wall carbon nanotubes (SWNTs) in oleum has been used to form isotropic films exhibiting fibrillar morphology. Tensile modulus, strength, and strain to failure of the film are 8 GPa, 30 MPa, and 0.5%, respectively. The electrical conductivity in the plane of the film is 1 × 105 S/m.

Nanomechanics of carbon nanotubes and composites

Abstract: Computer simulation and modeling results for the nanomechanics of carbon nanotubes and carbon nanotube-polyethylene composite materials are described and compared with experimental observations Young’s modulus of individual single-wall nanotubes is found to be in the range of 1 TPa within the elastic limit At room temperature and experimentally realizable strain rates, the tubes typically yield at about 5–10% axial strain; bending and torsional stiffness and different mechanisms of plastic yielding of individual single-wall nanotubes are discussed in detail For nanotube-polyethylene composites, we find that thermal expansion and diffusion coefficients increase significantly, over their bulk polyethylene values, above glass transition temperature, and Young’s modulus of the composite is found to increase through van der Waals interaction This review article cites 54 references @DOI: 101115/11538625#

Some characteristics of high strength fiber reinforced lightweight aggregate concrete

Abstract: The effect of polypropylene and steel fibers on high strength lightweight aggregate concrete is investigated. Sintered fly ash aggregates were used in the lightweight concrete; the fines were partially replaced by fly ash. The effects on compressive strength, indirect tensile strength, modulus of rupture, modulus of elasticity, stress–strain relationship and compression toughness are reported. Compared to plain sintered fly ash lightweight aggregate concrete, polypropylene fiber addition at 0.56% by volume of the concrete, caused a 90% increase in the indirect tensile strength and a 20% increase in the modulus of rupture. Polypropylene fiber addition did not significantly affect the other mechanical properties that were investigated. Steel fibers at 1.7% by volume of the concrete caused an increase in the indirect tensile strength by about 118% and an increase in the modulus of rupture by about 80%. Steel fiber reinforcement also caused a small decrease in the modulus of elasticity and changed the shape of the stress–strain relationship to become more curvilinear. A large increase in the compression toughness was recorded. This indicated a significant gain in ductility when steel fiber reinforcement is used.

Transient elastography in anisotropic medium: Application to the measurement of slow and fast shear wave speeds in muscles

Abstract: From the measurement of a low frequency (50–150 Hz) shear wave speed, transient elastography evaluates the Young’s modulus in isotropic soft tissues. In this paper, it is shown that a rod source can generate a low frequency polarized shear strain waves. Consequently this technique allows to study anisotropic medium such as muscle. The evidence of the polarization of low frequency shear strain waves is supported by both numeric simulations and experiments. The numeric simulations are based on theoretical Green’s functions in isotropic and anisotropic media (hexagonal system). The experiments in vitro led on beef muscle proves the pertinent of this simple anisotropic pattern. Results in vivo on man biceps shows the existence of slow and fast shear waves as predicted by theory.

Size-dependent elastic moduli of platelike nanomaterials

Abstract: A semicontinuum model is presented for nanostructured materials that possess a platelike geometry, such as ultra-thin films. In contrast to the classical continuum theory, the current model accounts for the discrete nature in the thickness direction. In-plane Young’s modulus, and in-plane and out-plane Poisson’s ratios are investigated with this model. It is found that the values of the Young’s modulus and Poisson’s ratios depend on the number of atom layers in the thickness direction and approach the respective bulk values as the number of atom layers increases.

Effect of Fiber Orientation and Strain Rate on the Nonlinear Uniaxial Tensile Material Properties of Tendon

Abstract: Tendons are exposed to complex loading scenarios that can only be quantified by mathematical models, requiring a full knowledge of tendon mechanical properties. This study measured the anisotropic, nonlinear, elastic material properties of tendon. Previous studies have primarily used constant strain-rate tensile tests to determine elastic modulus in the fiber direction. Data for Poisson's ratio aligned with the fiber direction and all material properties transverse to the fiber direction are sparse. Additionally, it is not known whether quasi-static constant strain-rate tests represent equilibrium elastic tissue behavior. Incremental stress-relaxation and constant strain-rate tensile tests were performed on sheep flexor tendon samples aligned with the tendon fiber direction or transverse to the fiber direction to determine the anisotropic properties of toe-region modulus (E0), linear-region modulus (E), and Poisson's ratio (v). Among the modulus values calculated, only fiber-aligned linear-region modulus (E1) was found to be strain-rate dependent. The E1 calculated from the constant strain-rate tests were significantly greater than the value calculated from incremental stress-relaxation testing. Fiber-aligned toe-region modulus (E(1)0 = 10.5 +/- 4.7 MPa) and linear-region modulus (E1 = 34.0 +/- 15.5 MPa) were consistently 2 orders of magnitude greater than transverse moduli (E(2)0 = 0.055 +/- 0.044 MPa, E2 = 0.157 +/- 0.154 MPa). Poisson's ratio values were not found to be rate-dependent in either the fiber-aligned (v12 = 2.98 +/- 2.59, n = 24) or transverse (v21 = 0.488 +/- 0.653, n = 22) directions, and average Poisson's ratio values in the fiber-aligned direction were six times greater than in the transverse direction. The lack of strain-rate dependence of transverse properties demonstrates that slow constant strain-rate tests represent elastic properties in the transverse direction. However, the strain-rate dependence demonstrated by the fiber-aligned linear-region modulus suggests that incremental stress-relaxation tests are necessary to determine the equilibrium elastic properties of tendon, and may be more appropriate for determining the properties to be used in elastic mathematical models.

Role of collagen and other organics in the mechanical properties of bone

Abstract: Relevant mechanical properties of bone The mechanical properties of bone material are determined by the relative amounts of its 3 major constituents: mineral, water, and organics (mainly type I collagen); by the quality of these components; and by how the resulting material is arranged in space. For our purposes, the mechanical properties of bone can be summed up as follows: modulus of elasticity, yield stress and yield strain, post-yield stress and post-yield strain, and the total area under the stress-strain curve. Also important are some fracture mechanics properties, but these are not discussed here. A typical tensile stress-strain curve for a bone specimen is shown in Fig. 1. The modulus of elasticity shows how stiff the bone material is. Indeed, stiffness is the prime property of bone, distinguishing it from tendon, which has much less tensile stiffness, almost no shear stiffness, but which is nearly as strong and is much tougher. Yield stress and strain determine how much energy can be absorbed before irreversible changes take place. Post-yield stress and strain determine mainly how much energy can be absorbed after yield but before fracture. Irreversible changes take place at yield, caused by microdamage. The total area under the stress-strain curve is equivalent to the work that must be done per unit volume on the specimen before it breaks. Fracture mechanics properties show the extent to which bone is resistant to crack initiation and to crack travel (which are different things and governed by somewhat different features). In fact, crack travel resistance is given rather well by post-yield stress and strain.

Elastic properties of polyelectrolyte capsules studied by atomic-force microscopy and RICM.

Abstract: Mechanical properties of polyelectrolyte multilayer capsules were studied using a new method combining atomic-force microscopy and reflection interference contrast microscopy. By measuring the force vs. deformation for poly(styrene sulfonate)/poly(allylamine) capsules the existence of different deformation regimes depending on the applied deformation was shown. The present paper focuses on the small-deformation regime. The elastic response of the deformed capsule was studied as a function of the wall thickness and the capsule size, and showed the theoretically expected variations. The Young modulus obtained from the experiments ranges between 1.3 and 1.9 GPa.

Effects of cooling rate on the microstructure and tensile behavior of a Sn-3.5wt.%Ag solder

Abstract: The tensile behavior and microstructure of bulk, Sn-3.5Ag solders as a function of cooling rate were studied. Cooling rate is an important processing parameter that affects the microstructure of the solder and, therefore, significantly influences mechanical behavior. Controlled cooling rates were obtained by cooling specimens in different media: water, air, and furnace. Cooling rate significantly affected secondary dendrite-arm size and spacing of the Sn-rich phase, as well as the aspect ratio of Ag3Sn. The Sn-rich dendrite-arm size and spacing were smaller for water-cooled specimens than for air-cooled specimens. Furnace cooling yielded a nearly eutectic microstructure because the cooling rate approached equilibrium cooling. The morphology of Ag3Sn also changed from spherical, at a fast cooling rate, to a needlelike morphology for slower cooling. The changes in the microstructure induced by the cooling rate significantly affected the mechanical behavior of the solder. Yield strength was found to increase with increasing cooling rate, although ultimate tensile strength and strain-to-failure seemed unaffected by cooling rate. Cooling rate did not seem to affect Young’s modulus, although a clear coorelation between modulus and porosity was obtained. The mechanical behavior was correlated with the observed microstructure, and fractographic analysis was employed to elucidate the underlying damage mechanisms.

Characterization of PVA cryogel for intravascular ultrasound elasticity imaging

Abstract: The present study characterizes the mechanical properties of polyvinyl alcohol (PVA) cryogel in order to show its utility for intravascular elastography. PVA cryogel becomes harder with an increasing number of freeze-thaw cycles, and Young's modulus and Poisson's ratio are measured for seven samples. Mechanical tests were performed on cylindrical samples with a pressure column and on a hollow cylinder with the calculation of an intravascular elastogram. An image of the Young's modulus was obtained from the elastogram using cylinder geometry properties. Results show the mechanical similitude of PVA cryogel with the biological tissues present in arteries. A good agreement between Young's modulus obtained from pressure column and from elastogram was also observed.

Single wall nanotube and vapor grown carbon fiber reinforced polymers processed by extrusion freeform fabrication

Abstract: Single wall carbon nanotubes (SWNTs) and vapor grown carbon fibers (VGCFs) were compounded with poly(acrylonitrile-co-butadiene-co-styrene) (ABS) to create composite materials for use with Extrusion Freeform Fabrication (EFF). The composite materials possessed homogeneously dispersed fibers that were oriented with EFF processing. The VGCF and SWNT reinforced materials processed by EFF displayed improved tensile modulus compared to similarly processed ABS and composite material with isotropic fiber orientation, and the SWNT reinforced material displayed the highest properties, strength and modulus, of the materials studied. The materials containing oriented VGCFs and SWNTs showed modulus improvements of 44 and 93%, respectively.

The Effects of Filler Content and Size on the Properties of PTFE/SiO2 Composites

Abstract: A study on PTFE reinforced with SiO2 was described. It included the manufacturing process of SiO2-reinforced PTFE and the effects of the SiO2 content and size on the properties of the composite material, such as thermal, dielectric, tensile strength and morphology, etc. PTFE/SiO2 composites loaded with two sizes (5 µm or 25 µm SiO2) of filler contents varied from 0–60 wt% were mixed by a high-speed dispersion mixer and made via a two-roll milling machine. Our results showed that the composite filled with 25 µm SiO2 at 60 wt% filler content had the highest modulus, lowest CTE z and acceptable dielectric properties. Composites with different sizes of filler showed a similar trend of decreasing tensile strength and coefficient of thermal expansion (CTE z ), and increasing tensile modulus, water absorption and dielectric properties as the filler content increased. Furthermore, the composites filled with small-size filler showed higher water absorption and dielectric loss properties due to the presence of higher SiO2 surface area. Poor adhesion between filler and matrix is a primary cause of low tensile properties and lack of increase in thermal stability. Such phenomenon was also confirmed by fracture surface analysis of scanning electron microscope (SEM). Experimental data were compared with theoretical models from the literatures, which are used to predict the properties of two component mixtures. The results revealed that experimental values of dielectric constant and CTE z agreed with the theoretical calculated values. It was also found that the modified Nicolais-Narkis equation provided a good estimation for the tensile strength of composite.

Aging response of the young’s modulus and mechanical properties of Ti-29Nb-13Ta-4.6Zr for biomedical applications

Abstract: Alloys for implant devices require improved strength but a reduced Young’s modulus, in order to become mechanically more compatible with adjacent bone tissues. In this study, a new metastable β-type titanium alloy, Ti-29Nb-13Ta-4.6Zr (wt pct), was subjected to aging treatment to produce different microstructures, and the resulting mechanical properties, including the Young’s modulus, were measured. The Young’s modulus of this alloy is found to be sensitive to microstructures generated by various heat treatments. For microstructures varying from (α + β) to (α + β + ω) and (β + ω), the Young’s modulus increases with an accompanying increase in tensile strength and hardness, but decreases in ductility. The (β + ω) microstructure has a low strength, high modulus, and poor ductility and cannot be used for biomedical applications. For an (α + β) microstructure, the volume fraction of the phases is shown to be the main factor that determines the mechanical properties.

Ab initio study of elastic properties of Ir and Ir3X compounds

Abstract: Elastic constants and moduli of face-centered cubic Ir and its L12 intermetallic compounds Ir3X (X=Ti, Ta, Nb, Zr, Hf, V) have been determined using ab initio density functional theory calculations within the generalized gradient approximation. With the tetragonal, trigonal, and isotropical lattice distortions, elastic constants C11, C12, C44, and bulk modulus B are derived from the second derivative of the total energy as a function of volume. The calculated Young’s modulus E, shear modulus G, Poisson’s ratio ν, and the ratio RG/B of G over B are then used to examine mechanical properties of Ir and Ir3X compounds. By analyzing RG/B and Cauchy pressure C12–C44, the brittle-ductile behavior of the materials is assessed. Based on the modulus difference ΔG between the γ matrix (Ir) and γ′ precipitates (Ir3X), the γ′ strengthening effect in the γ matrix is studied.

Inhomogeneous cartilage properties enhance superficial interstitial fluid support and frictional properties, but do not provide a homogeneous state of stress

Abstract: It has been well established that articular cartilage is compositionally and mechanically inhomogenous through its depth. To what extent this structural inhomogeneity is a prerequisite for appropriate cartilage function and integrity is not well understood. The first hypothesis to be tested in this study was that the depth-dependent inhomogeneity of the cartilage acts to maximize the interstitial fluid load support at the articular surface, to provide efficient frictional and wear properties. The second hypothesis was that the inhomogeneity produces a more homogeneous state of elastic stress in the matrix than would be achieved with uniform properties. We have, for the first time, simultaneously determined depth-dependent tensile and compressive properties of human patellofemoral cartilage from unconfined compression stress relaxation tests. The results show that the tensile modulus increases significantly from 4.1 +/- 1.9 MPa in the deep zone to 8.3 +/- 3.7 MPa at the superficial zone, while the compressive modulus decreases from 0.73 +/- 0.26 MPa to 0.28 +/- 0.16 MPa. The experimental measurements were then implemented with the finite-element method to compute the response of an inhomogeneous and homogeneous cartilage layer to loading. The finite-element models demonstrate that structural inhomogeneity acts to increase the interstitial fluid load support at the articular surface. However, the state of stress, strain, or strain energy density in the solid matrix remained inhomogeneous through the depth of the articular layer, whether or not inhomogeneous material properties were employed. We suggest that increased fluid load support at the articular surface enhances the frictional and wear properties of articular cartilage, but that the tissue is not functionally adapted to produce homogeneous stress, strain, or strain energy density distributions. Interstitial fluid pressurization, but not a homogeneous elastic stress distribution, appears thus to be a prerequisite for the functional and morphological integrity of the cartilage.

Temperature dependence of thermal expansion and elastic constants of single crystals of ZrB2 and the suitability of ZrB2 as a substrate for GaN film

Abstract: Coefficients of thermal expansion (CTE) and elastic constants of single crystals of ZrB2 have been determined in the temperature ranges from room temperature to 1073 K and from room temperature to 1373 K, respectively. The elastic constants of ZrB2 are best characterized by the large value of the Young modulus (as high as 500 GPa) and the small values of the Poisson ratio (0.13–0.15), indicating the high stiffness and hardness and the brittleness, respectively. The values of CTE along the a- and c-axis directions are 6.66×10−6 and 6.93×10−6 K−1, respectively, when averaged over the temperature range from room temperature to 1073 K. The CTE value along the a-axis direction of ZrB2 is only moderately larger than the corresponding value for GaN. This together with the small lattice mismatch along the a-axis direction between ZrB2 and GaN in the heteroepitaxial orientation relationship of (0001)GaN//(0001)ZrB2 and 〈1120〉GaN//〈1120〉ZrB2 indicate that only a small compressive stress develops in the GaN thin-film crystal grown on the (0001) surface of the ZrB2 substrate. The stresses developed in the GaN thin-film crystal are evaluated with the values of CTE and elastic constants of ZrB2 determined in the present study. The evaluation verifies the suitability of ZrB2 as a substrate for heteroepitaxial growth of GaN.

Molecular dynamics analysis of temperature effects on nanoindentation measurement

Abstract: A three-dimensional molecular dynamics (MD) model is carried out to study the effects of temperature on the atomic-scale nanoindentation process. The model utilizes the Morse potential function to simulate interatomic forces between the sample and tool. The results show that both Young's modulus and hardness become smaller as temperature increases. The results also indicate that elastic recovery is smaller at higher temperatures. The softening behavior is similar to the prior experiment and the estimated elastic moduli are much higher than the prior experiment. The discrepancy may be due to simulations performed on defect-free single crystals. In addition, some defects of vacancies, atomic steps and plastic indent are observed on the surface region.

Mechanical properties of sputtered silicon nitride thin films

Abstract: Silicon nitride thin films were prepared by reactive sputtering from different sputtering targets and using a range of Ar/N2 sputtering gas mixtures. The hardness and the Young’s modulus of the samples were determined by nanoindentation measurements. Depending on the preparation parameters, the obtained values were in the ranges 8–23 and 100–210 GPa, respectively. Additionally, Fourier-transform infrared spectroscopy, Rutherford backscattering spectroscopy, and x-ray diffraction were used to characterize samples with respect to different types of bonding, atomic concentrations, and structure of the films to explain the variation of mechanical properties. The hardness and Young’s modulus were determined as a function of film composition and structure and conditions giving the hardest film were found. Additionally, a model that assumes a series coupling of the elastic components, corresponding to the Si–O and Si–N bonds present in the sample has been proposed to explain the observed variations of hardness and Young’s modulus.