Showing papers on "Young's modulus published in 2006"

Size dependence of Young's modulus in ZnO nanowires.

Abstract: We report a size dependence of Young's modulus in [0001] oriented ZnO nanowires (NWs) with diameters ranging from 17 to 550 nm for the first time. The measured modulus for NWs with diameters smaller than about 120 nm is increasing dramatically with the decreasing diameters, and is significantly higher than that of the larger ones whose modulus tends to that of bulk ZnO. A core-shell composite NW model in terms of the surface stiffening effect correlated with significant bond length contractions occurred near the {1010} free surfaces (which extend several layers deep into the bulk and fade off slowly) is proposed to explore the origin of the size dependence, and present experimental result is well explained. Furthermore, it is possible to estimate the size-related elastic properties of GaN nanotubes and relative nanostructures by using this model.

Surface effects on elastic properties of silver nanowires: Contact atomic-force microscopy

Abstract: Silver nanowires with different diameters were synthesized by a hydrothermal chemical method. The elastic properties of the nanowires with outer diameters ranging from 20 to $140\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ were measured using contact atomic force microscopy. The apparent Young modulus of the nanowires is found to decrease with the increase of the diameter. When the diameter of the silver nanowires is larger than $100\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$, the Young modulus approaches a constant value. The size dependence of the apparent Young modulus of the silver nanowires is attributed to the surface effect, which includes the effects of the surface stress, the oxidation layer, and the surface roughness. Thus, a theoretical analysis is presented to explain the size dependence. This analysis is different from the previous models in that both the surface stress and the surface moduli are included in it. We also show that the apparent surface modulus and the surface stress of the silver nanowires can be experimentally determined.

Engineering Properties of Alkali-Activated Fly Ash Concrete

Abstract: In this paper, results are reported from experimental research carried out on certain engineering properties of a new (portland cement-free) concrete made with alkali-activated fly ash Lab tests were conducted to determine its bending and compression mechanical strength, modulus of elasticity, bond strength, and shrinkage The results show that mortar and concrete made with portland cement-free activated fly ash develop a high mechanical strength in short periods of time, have a moderate modulus of elasticity, bond better to reinforcing steel, and shrink much less than ordinary portland cement concrete

Effect of Zr and Sn on Young's modulus and superelasticity of Ti-Nb-based alloys

Abstract: Quaternary Ti–(20–26)Nb–(2–8)Zr–(3.5–11.5)Sn (wt%) alloys were investigated to evaluate the effects of Zr and Sn on Young's modulus and superelasticity of Ti–Nb-based alloys. X-ray diffraction analysis showed that solution-treated alloys have β + α″, β + ω, α″ + ω, α″, or β microstructures. Zr and Sn increase the lattice parameters of the β phase; for orthorhombic α″ matensite, they increase the lattice parameter a but decrease both b and c . The martensitic start temperature of the α″ is depressed by Zr and Sn additions, whereas the formation of athermal ω is dependent on Zr and Sn contents. Differential scanning calorimetry (DSC) measurements show that 1 wt% of Nb, Zr or Sn addition decreases the martensitic start temperature by 17.6, 41.2 or 40.9 K, respectively, due to their negative effect on lattice parameter ratios of the martensite ( c / a and b / a ). Tensile tests were used to evaluate Young's modulus and superelasticity of the solution-treated alloys. Of the studied alloys Ti–24Nb–4Zr–7.5Sn with single β microstructure has the lowest Young's modulus of 52 GPa and recoverable elastic strain of about 2% at room temperature after cyclic strain.

Polyelectrolyte Multilayers with a Tunable Young's Modulus: Influence of Film Stiffness on Cell Adhesion

Abstract: Mechanical properties of model and natural gels have recently been demonstrated to play an important role in various cellular processes such as adhesion, proliferation, and differentiation, besides events triggered by chemical ligands. Understanding the biomaterial/cell interface is particularly important in many tissue engineering applications and in implant surgery. One of the final goals would be to control cellular processes precisely at the biomaterial surface and to guide tissue regeneration. In this work, we investigate the substrate mechanical effect on cell adhesion for thin polyelectrolyte multilayer (PEM) films, which can be easily deposited on any type of material. The films were cross linked by means of a water-soluble carbodiimide (EDC), and the film elastic modulus was determined using the AFM nanoindentation technique with a colloidal probe. The Young's modulus could be varied over 2 orders of magnitude (from 3 to 400 kPa) for wet poly(l-lysine)/hyaluronan (PLL/HA) films by changing the ED...

The effect of crosslinking on the mechanical properties of polylactic acid/polycaprolactone blends

Abstract: The improvement of the brittle behavior of Polylactic acid (PLA) resin was studied by blending it with Polycaprolactone (PCL) resin. These materials were fabricated into the compressed films and injection moldings. The values of tensile modulus and strength were appropriate, judging from the rule of mixtures. However, the ultimate tensile strain was very small. Dicumyl peroxide (DCP) was added to this blend system to improve its ultimate tensile strain. It was found that the value of ultimate tensile strain peaked at low DCP concentration. The samples at low DCP contents show yield point and ductile behavior under tensile test. The impact strength of the optimum composition was 2.5 times superior to neat PLA, and ductile behavior such as plastic deformation was observed at its fracture surface. It was found that the carbonyl groups of the blend material with DCP were altered by using FTIR spectroscopy. Dynamic mechanical analysis data revealed the dual phase nature of PLA/PCL blend albeit with good interfacial adhesion, and the DCP enhanced the viscous property in PCL phase, which agreed with tensile ductility and impact strength. The mechanical properties of this blend are comparable to those of general purpose HIPS and ABS. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1816–1825, 2006

Rigid-rod polymeric fibers

Abstract: This paper traces the historical development of high temperature resistant rigid-rod polymers. Synthesis, fiber processing, structure, properties, and applications of poly(p-phenylene benzobisoxazole) (PBO) fibers have been discussed. After nearly 20 years of development in the United States and Japan, PBO fiber was commercialized with the trade name Zylon® in 1998. Properties of this fiber have been compared with the properties of poly(ethylene terephthalate) (PET), thermotropic polyester (Vectran®), extended chain polyethylene (Spectra®), p-aramid (Kevlar®), m-aramid (Nomex®), aramid copolymer (Technora®), polyimide (PBI), steel, and the experimental high compressive strength rigid-rod polymeric fiber (PIPD, M5). PBO is currently the highest tensile modulus, highest tensile strength, and most thermally stable commercial polymeric fiber. However, PBO has low axial compressive strength and poor resistance to ultraviolet and visible radiation. The fiber also looses tensile strength in hot and humid environment. In the coming decades, further improvements in tensile strength (10–20 GPa range), compressive strength, and radiation resistance are expected in polymeric fibers. Incorporation of carbon nanotubes is expected to result in the development of next generation high performance polymeric fibers. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 100: 791–802, 2006

An experimental investigation of humidity and temperature effects on the mechanical properties of perfluorosulfonic acid membrane

Abstract: The mechanical properties of a perfluorosulfonic acid (PFSA) membrane have been investigated at different humidities and temperatures in a custom-designed environmental chamber. Tensile tests were conducted to determine Young's modulus, the proportional limit stress (“yield strength”), break stress, and break strain. In-plane dimensional changes of the membrane at different temperature and humidities were also determined. The results indicate that Young's modulus and the proportional limit stress of the PFSA membrane decrease as humidity and temperature increase. Higher temperature leads to lower break stress and higher break strain. However, humidity has little effect on the break stress and break strain. A nonparametric statistical analysis, Kruskal–Wallis test, is applied to the experimental results, which shows that the effects of temperature and humidity on Young's modulus and proportional limit stress are statistically significant.

Chemical, Physical, and Mechanical Characterization of Isocyanate Cross-linked Amine-Modified Silica Aerogels

Abstract: We describe a new mechanically strong lightweight porous composite material obtained by encapsulating the skeletal framework of amine-modified silica aerogels with polyurea. The conformal polymer coating preserves the mesoporous structure of the underlying silica framework and the thermal conductivity remains low at 0.041 plus or minus 0.001 W m(sup -1 K(sup -1). The potential of the new cross-linked silica aerogels for load-carrying applications was determined through characterization of their mechanical behavior under compression, three-point bending, and dynamic mechanical analysis (DMA). A primary glass transition temperature of 130 C was identified through DMA. At room temperature, results indicate a hyperfoam behavior where in compression cross-linked aerogels are linearly elastic under small strains (less than 4%) and then exhibit yield behavior (until 40% strain), followed by densification and inelastic hardening. At room temperature the compressive Young's modulus and the Poisson's ratio were determined to be 129 plus or minus 8 MPa and 0.18, respectively, while the strain at ultimate failure is 77% and the average specific compressive stress at ultimate failure is 3.89 x 10(exp 5) N m kg(sup -1). The specific flexural strength is 2.16 x 10(exp 4) N m kg(sup -1). Effects on the compressive behavior of strain rate and low temperature were also evaluated.

Measurement of the Bending Strength of Vapor-Liquid-Solid Grown Silicon Nanowires

Abstract: The fracture strength of silicon nanowires grown on a [111] silicon substrate by the vapor-liquid-solid process was measured. The nanowires, with diameters between 100 and 200 nm and a typical length of 2 Im, were subjected to bending tests using an atomic force microscopy setup inside a scanning electron microscope. The average strength calculated from the maximum nanowire deflection before fracture was around 12 GPa, which is 6% of the Young’s modulus of silicon along the nanowire direction. This value is close to the theoretical fracture strength, which indicates that surface or volume defects, if present, play only a minor role in fracture initiation. Nanowires (NWs) are of interdisciplinary interest to applications in the fields of biomedical sensing, nano- and optoelectronics and photovoltaics due to their electrical, optical, mechanical, and geometrical properties that may deviate substantially from bulk. 1 To name some particularly exciting applications, the reader is referred to the following list: (i) high-frequency electromechanical resonators, 2 (ii) high-aspect ratio tips for surface probe microscopy, 3 (iii) sensor array for electrical detection of cancer markers, 4 (iv) Si NW arrays for photovoltaics, 5 and (v) nanoscale light-emitting diodes. 6 For all these applications the mechanical stability of the NWs is essential for their atomic scale manipulation, functionalization, or integration into device schemes. Several methods were used in the past to access the mechanical properties of silicon NWs and nanobeams. An atomic force microscope (AFM) was used for bending tests of single crystal, micromachined silicon beams (from 1 mm down to 200 nm in width, beam axis oriented in [110] direction). No change in Young’s modulus, but an increase in bending strength by a factor of up to 38 was observed from the millimeter down to the nanometer scale. 7 AFM measurements were also done on silicon NWs (from 10 to 100 nm in diameter, grown along the [111] direction) where a bending modulus of 186 GPa (188 GPa in bulk) was measured. 8

Effects of processing on microstructure and properties of SLS Nylon 12

Abstract: There currently exists the requirement to improve reproducibility and mechanical properties of SLS Nylon parts for rapid manufacturing (RM). In order to achieve this, further fundamental research is needed and this paper addresses this need by investigating effects of potential sources of the lack of reproducibility and reports effects in relation to crystal structure, microstructure, chemical structure (molecular weight) and mechanical properties. Different γ crystal forms were identified and related to the unmolten particle cores and the melted/crystallised regions of the microstructure. The melt point of the γ-form varied depending on processing conditions. Observable differences were also present when comparing the microstructure of the parts. Molecular weight of parts was significantly higher than virgin powder but used powder also showed an increase in molecular weight. This was related to improved elongation at break of parts built from the used powder, consistent with previous studies. Tensile strength showed some increase with machine parameters selected for improved strength but Young's modulus values were broadly similar.

Effect of high temperature treatment on the mechanical properties of birch (Betula papyrifera)

Abstract: The thermal treatment of wood is an alternative to the chemical treatment for preservation purposes. The heat treatment process improves wood’s resistance to decay and its dimensional stability. However, mechanical strength decreases as a result of heat treatment. Therefore, the treatment parameters have to be optimized to keep this loss at a minimum while improving other properties. Thermal treatment is new in North America, and its parameters are not yet adjusted for the Canadian species. Carrying out the parameter adjustment in an industrial furnace requires many trials which are costly in terms of material and man-power. A laboratory study was carried out to determine the effect of different parameters of the heat treatment on the mechanical properties of birch in order to optimize this process. A thermogravimetric analyzer was built to carry out the laboratory tests. The impact of the process parameters–such as maximum treatment temperature, holding time at this temperature, heating rate, and gas humidity–on the mechanical properties of birch was investigated. Temperature distributions in wood and in gas as well as the weight loss of wood were measured during the experiments. Afterwards, hardness, modulus of elasticity, modulus of rupture, and resistance to screw withdrawal of the samples were measured. The relation between the process parameters and the resulting mechanical properties was examined.

Thermal conductivity of diamond-like carbon films

Abstract: The authors report the thermal conductivity (K) of a variety of carbon films ranging from polymeric hydrogenated amorphous carbons (a-C:H) to tetrahedral amorphous carbon (ta-C). The measurements are performed using the 3ω method. They show that thermal conduction is governed by the amount and structural disorder of the sp3 phase. If the sp3 phase is amorphous, K scales linearly with the C–C sp3 content, density, and elastic constants. Polymeric and graphitic films have the lowest K (0.2–0.3W∕mK), hydrogenated ta-C:H has K∼1W∕mK, and ta-C has the highest K (3.5W∕mK). If the sp3 phase orders, even in small grains such as in micro- or nanodiamond, a strong K increase occurs for a given density, Young’s modulus, and sp3 content.

Atomic force microscopy and nanoindentation of cement pastes with nanotube dispersions

Abstract: Since their discovery in 1991 by lijima [1], carbon nanotubes (CNTs) have probably become the most promising nanomaterials due to their unique mechanical, electronic and chemical properties. Our aim is to improve the mechanical properties of cement pastes by the addition of CNTs, giving rise to a new and higher-performance composite material. To reach an efficient cement-based composite with nanotubes, we have studied the addition of different CNT concentrations in the mix design in order to obtain enhanced mechanical properties with respect to plain cement pastes. We have measured the micro-hardness and Young's modulus of the composites by nanoindenting with a sharp diamond three-sided pyramidal tip mounted on an Atomic Force Microscope probe. These measurements have been correlated with the average macroscopic Young's modulus.

Beneficial effects of an ultra-fine α-SiC incorporation on the sinterability and mechanical properties of ZrB2

Abstract: A fully dense ZrB2 ceramic containing 10 vol. % ultra-fine α-SiC particulate was successfully hot pressed at 1900 °C for 20 min and 40–50 MPa of applied pressure. Faceted ZrB2 grains (average size ≈3 μm) and SiC particles dispersed regularly characterized the base material. No extra secondary phases were found. The introduction of the ultra-fine α-SiC particulate was recognized as the key factor that enabled both the control of the diboride grain growth and the achievement of full density. The mechanical properties offered an interesting combination of data: 4.8±0.2 MPa $\surd{m}$ fracture toughness, 507±4 GPa Young’s modulus, 0.12 Poisson’sratio, and 835±35 MPa flexural strength at room temperature. The flexural strength measured at 1500 °C (in air) provided values of 300±35 MPa. The incorporated ultra-fine α-SiC particulate was fundamental, sinterability apart, to enhancing the strength and oxidation resistance of ZrB2. The latter property was tested at 1450 °C for 20 h in flowing dry air. In such oxidizing conditions, the formation of a thin external borosilicate glassy coating supplied partial protection for the faces of the material exposed to the hot environment. The oxidation attack penetrated into the material’s bulk and created a 200-μm-thick zirconia scale. The SiC particulate included in the oxide scale, lost by active oxidation, left carbon-based inclusions in the formerly occupied sites.

The mechanical properties of atomic layer deposited alumina for use in micro- and nano-electromechanical systems

Abstract: Mechanical characterization of atomic layer deposited (ALD) alumina (Al2O3) for use in micro- and nano-electromechanical systems has been performed using several measurement techniques including: instrumented nanoindentation, bulge testing, pointer rotation, and nanobeam deflection Using these measurement techniques, we determine Young's modulus, Berkovitch hardness, universal hardness and the intrinsic in-plane stress for ALD Al2O3 Specifically, measurements for ALD Al2O3 films deposited at 177 degrees C with thicknesses between 50 and 300 nm are reported The measured Young's modulus is in the range of 168-182 GPa, Berkovitch hardness is 123 GPa, universal hardness is 8 GPa, and the intrinsic in-plane stress is in the range of 383-474 MPa Multiple measurements of the same material property from different measurement techniques are presented and compared ALD Al2O3 is an advantageous material to use over various forms of silicon nitride, for micro- and nano-electromechanical systems due in part to the low deposition temperature that allows for integration with CMOS processing Also, Al2O3, unlike silicon nitride, has a high chemical resistance to dry-chemistry Si etchants Although ALD Al2O3 has recently been used as both a coating and a structural layer for micro- and nano-electromechanical systems, its mechanical properties were not previously described

Cell Mechanics Using Atomic Force Microscopy-Based Single-Cell Compression

Abstract: We report herein the establishment of a single-cell compression method based on force measurements in atomic force microscopy (AFM). The high-resolution bright-field or confocal laser scanning microscopy guides the location of the AFM probe and then monitors the deformation of cell shape, while microsphere-modified AFM probes compress the cell and measure the force. Force and deformation profiles of living cells reveal a cubic relationship at small deformation (<30%), multiple peaks at 30-70% compression, and a rapid increase at over 80% deformation. The initial compression may be described qualitatively and quantitatively using a simple model of a nonpermeable balloon filled with incompressible fluid. Stress peaks reflect cell membrane rupture, followed by the deformation and rupture of intracellular components, beyond which the cell responses become irreversible. The Young's modulus and bending constant of living cell membranes are extracted from the balloon models, with 10-30 MPa and 17-52 kT, respectively. The initial compression of dead and fixed cells is modeled using Hertzian contact theory, assuming that the cell is a homogeneous sphere. Dead cells exhibit a cytoskeleton elasticity of 4-7.5 kPa, while fixation treatment leads to a dramatic increase in the cytoskeletal Young's modulus (150-230 kPa) due to protein cross-linking by imine bonds. These results demonstrate the high sensitivity of the single-cell compression method to the molecular-level structural changes of cells, which suggests a new generic platform for investigating cell mechanics in tissue engineering and cancer research.

On the determination of residual stress and mechanical properties by indentation

Abstract: Residual stresses are of practical importance in bulk materials and coatings, which critically affects their mechanical integrity and reliability Comparing with traditional techniques, the depth-sensing indentation technique provides a quick and effective method of measuring the residual stress field In this study, we have used the finite element method to investigate the effect of in-plane residual stress on hardness and stiffness measurements of a bulk material/thick coating It is found that the contact hardness, stiffness, and indentation work are sensitive to the residual stress, in particular for materials with a relatively high yield strain Based on the reverse analysis, a new technique is proposed for measuring the yield strength, Young's modulus, and in-plane residual stress in bulk material and thick coatings through one simple indentation test The effectiveness of this method is demonstrated through numerical examples The effect of residual stress on indentation stress, plastic zone, and surface profile are also investigated It is found that when the indentation is dominated by elastic deformation, the large recovery makes the surface profile measured after unloading an unreliable parameter in characterizing the properties

Young's Modulus of ZnO Nanobelts Measured using Atomic Force Microscopy and Nanoindentation Techniques

Abstract: The bending Young's modulus of ZnO nanobelts was measured by performing three-point bending tests directly on individual nanobelts with an atomic force microscope (AFM). The surface-to-volume ratio has no effect on the bending Young's modulus of the ZnO nanobelts for surface-to-volume ratios ranging from 0.017 to 0.035 nm(2) nm(-3), with a belt size of 50-140 nm in thickness and 270-700 nm in width. The bending Young's modulus was measured to be 38.2 +/- 1.8 GPa, which is about 20% higher than the nanoindentation Young's modulus of 31.1 +/- 1.3 GPa. The ZnO nanobelts exhibit brittle fracture failure in bending but some plastic deformation in indentation.

Elastic constants of monocrystal iron from 3 to 500 K

Abstract: Resonant ultrasound spectroscopy was used to measure the monocrystal elastic constants of iron over a temperature range of 3–500K. All the moduli behave normally as a function of temperature and are well described by the semiempirical Einstein-oscillator model. Values at 300K are bulk modulus=166.2±0.9GPa; shear constant C′=(C11−C12)∕2=48.15±0.9GPa; shear constant C44=115.87±0.17GPa. The Poisson ratio (ν100) is 0.3679±0.0005. Representation surfaces of Young’s and torsion moduli are presented. The Debye temperature (θD) is 476.3K as calculated from 3K measured elastic constants. A thermodynamic Gruneisen parameter γth=1.65 is calculated. The temperature dependence of the internal friction associated with C′ is very different from that associated with C44. Possible reasons for this difference are suggested.

Shear strength of FRP-reinforced concrete beams without transverse reinforcement

Abstract: This paper studied the behavior and shear strength of concrete slender beams reinforced with fiber-reinforced polymer (FRP) bars. Nine large-scale reinforced concrete beams without stirrups were constructed and tested to failure. The beams measured 3250 mm long, 250 mm wide, and 400 mm deep and were tested in 4-point bending. Test variables were the reinforcement ratio and modulus of elasticity of the longitudinal reinforcing bars. The test beams included 3 reinforced with glass FRP bars, 3 reinforced with carbon FRP bars, and 3 control beams reinforced with conventional steel bars. Test results were compared with predictions provided by the different available codes, manuals, and design guidelines, indicating that the relatively low modulus of elasticity of FRP bars results in reduced shear strength compared to that of control beams reinforced with steel. The current ACI 440.1R design method offered very conservative predictions, particularly for beams reinforced with glass FRP bars. Based on obtained experimental results, a proposed modification to the current ACI 440.1R design equation is given and verified against test results from other research.

A comprehensive closed form micromechanics model for estimating the elastic modulus of nanotube-reinforced composites

Abstract: This paper describes an approximate, yet comprehensive, closed form micromechanics model for estimating the effective elastic modulus of carbon nanotube-reinforced composites. The model incorporates the typically observed nanotube curvature, the nanotube length, and both 1D and 3D random arrangement of the nanotubes. The analytical results obtained from the closed form micromechanics model for nanoscale representative volume elements and results from an equivalent finite element model for effective reinforcing modulus of the nanotube reveal that the reinforcing modulus is strongly dependent on the waviness, wherein, even a slight change in the nanotube curvature can induce a prominent change in the effective reinforcement provided. The micromechanics model is also seen to produce reasonable agreement with experimental data for the effective tensile modulus of composites reinforced with multi-walled nanotubes (MWNTs) and having different MWNT volume fractions.

Tensile properties of glass microballoon-epoxy resin syntactic foams

Abstract: The effect of hollow glass particle (microballoon) volume fraction in the range of 0.3–0.6 on the tensile properties and fracture mode of syntactic foams is characterized in the present research. Sixteen types of syntactic foams have been fabricated and tested. Four types of glass microballoons, having 220, 320, 380, and 460 kg/m3 density, are used with epoxy resin matrix for making the syntactic foam samples. These foams contain 30, 40, 50 and 60% microballoons by volume. All types of microballoons have the same size but different wall thickness, which reflects as a difference in their density. It is observed that the tensile strength increases with a decrease in the volume fraction of microballoons. All types of syntactic foams showed 60–80% decrease in the tensile strength compared with that of the neat resin. The foams containing low strength microballoons showed lower tensile modulus compared with that of the neat resin, but the presence of high strength microballoons led to an increase in the tensile modulus of the composites. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1254–1261, 2006