Young's Modulus (young + modulus)

Distribution by Scientific Domains
Distribution within Polymers and Materials Science

Selected Abstracts

Nanostructure and nanomechanics of live Phaeodactylum tricornutum morphotypes

Grégory Francius
Summary The ultrastructure and mechanical properties of the fusiform, triradiate and ovoid morphotypes of Phaeodactylum tricornutum were investigated using atomic force microscopy. Using topographic imaging, we showed that the surface of the ovoid form is rougher than those of the two other specimens, and coated with an outer layer of extracellular polymers. Using spatially resolved force,indentation curves, we found that the valve of the ovoid form is about five times stiffer (Young modulus of ,500 kPa) than those of the other forms (,100 kPa), a finding fully consistent with the fact that only the ovoid form has a silica valve, whereas the valves in the other two consist mostly of organic material. Notably, the girdle region of both fusiform and ovoid forms was five times softer than the valve, suggesting that this region is poor in silica and enriched in organic material. For the triradiate form, we showed the arms to be softer than the core region, presumably as a result of organelle localization. Last, we observed mucilaginous footprints of moderate stiffness (,100 kPa) in the vicinity of ovoid diatoms, which we believe are secreted extracellular polymers. [source]

Nanometer-Scale Mapping of Elastic Modules in Biogenic Composites: The Nacre of Mollusk Shells

Haika Moshe-Drezner
Abstract In this study, a newly developed nanoscale modulus mapping is applied in order to visualize the 2D-distribution of mechanical characteristics in the aragonitic nacre layer of Perna canaliculus (green mussel) shells. Modulus maps provide lateral resolution of about 10 nm. They allow the aragonitic mineral (CaCO3) tablets and the interfaces between them to be clearly resolved, which are filled by an organic substance (mainly beta-chitin). The experimental data are compared with finite element simulations that also take into account the tip radius of curvature and the thickness of organic layers, as measured by means of scanning electron microscopy with back-scattered electrons. Based on this comparison, the Young modulus of beta-chitin is extracted. The obtained number, E, = 40 GPa, is higher than previously evaluated. The collected maps reveal that the elastic modules in the nacre layer change gradually across the ceramic/organic interfaces within a spatial range four times wider than the thickness of the organic layers. This is possibly due to inhomogeneous distribution of organic macromolecules within ceramic tablets. According to the data, the concentration of macromolecules gradually increases when approaching the organic/ceramic interfaces. A behavior of this type is unique to biogenic materials and distinguishes them from synthetic composite materials. Finally, three possible mechanisms that attempt to explain why gradual changes of elastic modules significantly enhance the overall resistance to fracture of the nacre layer are briefly discussed. The experimental findings support the idea that individual ceramic tablets, comprising the nacre, are built of the compositionally and functionally graded ceramic material. This sheds additional light on the origin of the superior mechanical properties of biogenic composites. [source]

Stress and elastic-constant analysis by X-ray diffraction in thin films

F. Badawi
Residual stresses influence most physical properties of thin films and are closely related to their microstructure. Among the most widely used methods, X-ray diffraction is the only one allowing the determination of both the mechanical and microstructural state of each diffracting phase. Diffracting planes are used as a strain gauge to measure elastic strains in one or several directions of the diffraction vector. Important information on the thin-film microstructure may also be extracted from the width of the diffraction peaks: in particular, the deconvolution of these peaks allows values of coherently diffracting domain size and microdistortions to be obtained. The genesis of residual stresses in thin films results from multiple mechanisms. Stresses may be divided into three major types: epitaxic stresses, thermal stresses and intrinsic stresses. Diffraction methods require the knowledge of the thin-film elastic constants, which may differ from the bulk-material values as a result of the particular microstructure. Combining an X-ray diffractometer with a tensile tester, it is possible to determine X-ray elastic constants of each diffracting phase in a thin-film/substrate system, in particular the Poisson ratio and the Young modulus. It is important to notice that numerous difficulties relative to the application of diffraction methods may arise in the case of thin films. [source]

Mechanical behavior of carbon nanofibre-reinforced epoxy composites

Sohel Rana
Abstract Epoxy resins are widely used in a variety of applications because of their high chemical and corrosion resistance and good mechanical properties. But few types of epoxy resins are brittle and possess low toughness which makes them unsuitable for several structural applications. In this work, carbon nanofibres have been dispersed uniformly into the epoxy resin at a very low concentration (0.07 vol. %). Improvement of 98% in Young modulus, 24% in breaking stress and 144% in work of rupture was achieved in the best sample. The emphasis is on achieving uniform dispersion of carbon nanofibers into epoxy resin using a combination of techniques such as ultrasonication, use of solvent and surfactants. The fracture surfaces of the specimens were studied under scanning electron microscope to see the fracture mechanism of nanocomposites under tensile load and correlate it to the enhancement in their properties. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source]

Effects of Surface Chemistry on the Nanomechanical Properties of Commercial Float Glass

Pavan V. Kolluru
Nanoindentation was used to evaluate the mechanical properties of commercial float glass surfaces that were subjected to various surface cleaning treatments and other short-term corrosion conditions. The changes in the plane strain elastic modulus, where ,s and Es are the Poisson ratio and Young modulus of the specimen, respectively) and hardness after exposure to dilute hydrochloric acid (pH 0.9), reverse osmosis water (pH 7.1), and commercial cleaning solutions (pH 9.5) were found to be 0.5%,9% and 2%,35%, respectively. Similarly, weathering in a humid atmosphere and leaching in hot deionized water also had a distinct effect on the measured properties of the float glass surfaces. Moreover, both the surface cleaning treatments and the short-term corrosion exposures affected the tin side of the float glass differently than the air side. This work suggests that many of the discrepancies in the literature on the effect of tin concentration on the nanomechanical properties of float glass surfaces are likely due to variability in the surface cleaning and exposure history of the samples and calibration glasses that have been used. [source]

Structural, Mechanical, and Reactivity Properties of Tricalcium Aluminate Using First-Principles Calculations

Hegoi Manzano
Although tricalcium aluminate (C3A) is one of the most important components of Portland cement, neither its reactivity nor its elastic moduli tensor have been fully determined yet. This work aims to shed some insights on these questions by means of ab-initio simulations. First our simulations have reproduced the details of its crystalline structure. Second, we have computed the full elastic moduli tensor of C3A, where we found that our value for the Young modulus (E=138.7 GPa) is in agreement with the values obtained by nanoindentation measurements. Finally, we have identified which atoms and sites are more suitable to suffer chemical attacks. [source]

Sintering Behavior and Properties of Iron-Rich Glass-Ceramics

Alexander Karamanov
Iron-rich glass-ceramics were obtained by the sintering of two glass powders, labeled G1 and G2, at heating rates of 5° and 20°C/min followed by an isothermal step in the 850°,1050°C temperature interval. The sintering process was evaluated by the linear shrinkage; the closed porosity was estimated by density measurements; the structure and the morphology of the glass ceramics were observed by scanning electron microscopy. The bending strength, the Young modulus, and Vickers hardness of the glass-ceramics materials were evaluated. The results showed that the sintering process and morphology of the glass-ceramics depends on the amount of magnetite and pyroxene formed. With a low percentage of crystal phase formed (25%,30% typical of G1) the structure is characterized by closed porosity; at higher crystallization (45%,50% typical of G2) open porosity is mainly formed. The properties of the glass-ceramics were not influenced by the heating rate but improved with an increase in the degree of crystallization. [source]

High-Temperature Resistant Composites in the AlN,SiC,MoSi2 System

Diletta Sciti
Two fully dense composites containing AlN, SiC, and MoSi2 in different amounts were produced by hot pressing. Young modulus, hardness, electrical conductivity, and thermal expansion coefficient were measured at room temperature. Strength and toughness were evaluated up to 1300°C in air. According to statistical analysis, the temperature has little or no effect on high-temperature fracture behavior of the composites. These electroconductive materials are suitable for thermomechanical applications at high temperature, the strength being about 600 MPa at 1300°C. [source]

Elastic constant measurement for standard and photosensitive single mode optical fibres

P. Antunes
Abstract In this work we determine the elastic constant, the Young modulus, and the strain limit of commercial optical fibers. The fiber rupture limit in standard and Boron codoped photosensitive optical fibers, usually used in FBG-based sensors, is also quantified. The estimation of such values is extremely relevant, providing useful experimental values to be used in the design and modeling of the sensors. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 2467,2469, 2008; Published online in Wiley InterScience ( DOI 10.1002/mop.23660 [source]

Study of the modification of the properties of (PP/EPR) blends with a view to preserving natural resources when elaborating new formulation and recycling polymers

Nizar Mnif
The aim of the present work is to study how CaCO3, very abundant on earth, can be blended with polypropylene/ethylene propylene rubber (PP/EPR) either to preserve natural resources when elaborating virgin formulations or to simulate mixtures of waste made of CaCO3 filled PP with PP/EPR which could result from end-of-life-vehicles (ELV). The article focuses on the studies of PP/EPR blends, used in the manufacture of automobile fenders, in the presence of nano-CaCO3 and compatibilizers. Blends of various compositions (with and without compatibilizer and nanoparticles) were prepared using a corotating twin-screw extruder. The results were compared with the ones presented by a commercial (PP/EPR) blend. The experiments included mechanical tests, differential scanning calorimetry, scanning electron microscopy, and dynamic mechanical analysis experiments. The presence of the compatibilizers in the (PP/EPR) blends decreases the size of elastomer particles, improves the adherence to the interface and improves the mechanical properties. The nano-CaCO3 would also seem to act as a nucleating agent in the PP/EPR matrix; it increases the cristallinity and the Young modulus of the blends. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers [source]

Morphology and properties of SAN-clay nanocomposites prepared principally by water-assisted extrusion

Michaël Mainil
An efficient extrusion process involving the injection of water while processing was used to prepare poly (styrene- co -acrylonitrile) (SAN)/clay nanocomposites with a high degree of nanoclay delamination. The usefulness of water-assisted extrusion is highlighted here, in comparison with classical extrusion and roll mill processes. Cloisite® 30B (C30B), a montmorillonite clay organomodified with alkylammonium cations bearing 2-hydroxyethyl chains, and pristine montmorillonite were melt blended with SAN (25 wt% AN) in a semi-industrial scale extruder specially designed to allow water injection. XRD analysis, visual and TEM observations were used to evaluate the quality of clay dispersion. The relationship between the nanocomposite morphology and its mechanical and thermal properties was then investigated. The superiority of the SAN/C30B nanocomposite extruded with water has been evidenced by cone calorimetry tests and thermogravimetric measurements (TGA). These analyses showed a substantial improvement of the fire behavior and the thermal properties, while a 20% increase of the Young modulus was recorded. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers [source]

Excited-State Dynamics of a Hemicyanine Dye in Polymer Blends

CHEMPHYSCHEM, Issue 4 2010
Ah-Young Jee
The twisting motion of trans -4-[4-(dimethylamino)-styryl]-1-methylpyridinium iodide (4-DASPI) is studied in rigid environments. The elastic modulus of the medium is found to play a key role in the molecular rotor dynamics. The picture shows the isomerization rate constant of 4-DASPI as a function of the Young modulus of polystyrene/1-octene copolymer (PS/EOC) blends. [source]

On the Use of the Nanoindentation Unloading Curve to Measure the Young's Modulus of Polymers on a Nanometer Scale

Davide Tranchida
Abstract Summary: The nanoindentation test is a fundamental tool to assess the link between morphology and mechanical properties. The preliminary results of a more exhaustive study about the applicability to polymers of the most used procedure to determine elastic modulus by indentation are reported in this short communication. A departure of the experimental conditions from the theoretical assumptions and results that give rise to the Oliver and Pharr analysis is shown to occur under a wide range of experimental conditions, with applied loads and penetration depths covering several orders of magnitude and using different indenter geometries. Unloading curves with exponents significantly larger than 2 are observed in disagreement with the contact mechanics approach used by Oliver and Pharr. An AFM image obtained in non contact mode of an indentation induced by a sharp AFM tip with a maximum applied load of ca 1.2 µN on amorphous PET. [source]

Hochdynamische Materialeigenschaften von Ultrahochleistungsbeton (UHPC)

Markus Nöldgen Dipl.-Ing.
Baustoffe; Versuche; Dynamische Einwirkungen Abstract Der vorliegende Bericht liefert einen Beitrag zur Werkstoffbeschreibung von Ultrahochleistungsbetonen unter hochdynamischer Belastung. Grundlage für die Ermittlung der Werkstoffeigenschaften ist eine Hopkinson-Bar Versuchsreihe, die Werte für die dynamische Zugfestigkeit, den dynamischen E-Modul und die dynamische Bruchenergie unter Dehnraten von 102 · s,1 liefert. Ein Vergleich mit den Ergebnissen dieser Parameter für Normalbeton und hochfesten Betonen ermöglicht eine Einordnung des Ultrahochleistungsbetons in etablierte Ansätze und Berechnungsvorschriften und liefert einen Bewertungsansatz für die maßgebenden mechanischen Vorgänge. Unter Einbeziehung der Bruchenergie und der Spannungs-Rissöffnungs-Beziehung für UHPC in das RHT-Betonmodell werden Hydrocode Simulationen durchgeführt, die den Versuch am Hopkinson-Bar adäquat abbilden können. Material Properties of Ultra High Performance Concrete (UHPC) at High Strain Rates The presented paper is a contribution to the material description of Ultra High Performance Concrete (UHPC) under high-speed dynamical loading conditions. Based on a series of Hopkinson-Bar experiments dynamical material parameters such as the Tensile Strength, Young's Modulus and Fracture Energy are derived at high strain rates of 102 · s,1. A comparison with the results of these parameters for normal and high strength concrete leads to a qualitative and quantitative evaluation of UHPC at high strain rates. With the extension of the established RHT material model for UHPC by the material's Fracture Energy and Stress-Crack-Opening-Relation the Hopkinson-Bar experiments are simulated appropriately. [source]

Wave propagation in an inhomogeneous cross-anisotropic medium

Cheng-Der Wang
Abstract Analytical solutions for wave velocities and wave vectors are yielded for a continuously inhomogeneous cross-anisotropic medium, in which Young's moduli (E, E,) and shear modulus (G,) varied exponentially as depth increased. However, for the rest moduli in cross-anisotropic materials, , and ,, remained constant regardless of depth. We assume that cross-anisotropy planes are parallel to the horizontal surface. The generalized Hooke's law, strain,displacement relationships, and equilibrium equations are integrated to constitute governing equations. In these equations, displacement components are fundamental variables and, hence, the solutions of three quasi-wave velocities, VP, VSV, and VSH, and the wave vectors, , and , can be generated for the inhomogeneous cross-anisotropic media. The proposed solutions and those obtained by Daley and Hron, and Levin correlate well with each other when the inhomogeneity parameter, k, is 0. Additionally, parametric study results indicate that the magnitudes and directions of wave velocity are markedly affected by (1) the inhomogeneous parameter, k; (2) the type and degree of geomaterial anisotropy (E/E,, G,/E,, and ,/,,); and (3) the phase angle, ,. Consequently, one must consider the influence of inhomogeneous characteristic when investigating the behaviors of wave propagation in a cross-anisotropic medium. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Analysis of micro fracture in human Haversian cortical bone under transverse tension using extended physical imaging

É. Budyn
Abstract We propose a procedure to investigate local stress intensity factors at the scale of the osteons in human Haversian cortical bone. The method combines a specific experimental setting for a three-point bending millimetric specimen and a numerical method using the eXtended Finite Element Method (X-FEM). The interface between the experimental setting and the numerical method is ensured through an imaging technique that analyses the light microscopy observations to import the geometrical heterogeneity of the Haversian microstructures, the boundary conditions and appearing crack discontinuities into the numerical model. The local mechanical elastic Young's moduli are measured by nano-indentation, and the Poisson ratios are determined by an imaging technique of the stress,strain fields. The model is able to access three scales of measurement: the macro scale of the material level (mm), the micro scale inside the Haversian material for stress,strain fields (10,100µm), and the sub-micro scale for the crack opening profiles (1,10µm ) and fracture parameters (stress intensity factors). The model is applied to several patients at different aging stages. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Synthesis and properties of novel organosoluble aromatic poly(ether ketone)s containing pendant methyl groups and sulfone linkages

Shou-Ri Sheng
Abstract Several novel aromatic poly(ether ketone)s containing pendant methyl groups and sulfone linkages with inherent viscosities of 0.62,0.65 dL/g were prepared from 2-methyldiphenylether and 3-methyldiphenylether with 4,4,-bis(4-chloroformylphenoxy)diphenylsulfone and 4,4,-bis (3-chloroformylphenoxy)diphenylsulfone by electrophilic Friedel,Crafts acylation in the presence of N,N -dimethylformamide with anhydrous AlCl3 as a catalyst in 1,2-dichloroethane. These polymers, having weight-average molecular weights in the range of 57,000,71,000, were all amorphous and showed high glass-transition temperatures ranging from 160.5 to 167°C, excellent thermal stability at temperatures over 450°C in air or nitrogen, high char yields of 52,57% in nitrogen, and good solubility in CHCl3 and polar solvents such as N,N -dimethylformamide, dimethyl sulfoxide, and N -methyl-2-pyrrolidone at room temperature. All the polymers formed transparent, strong, and flexible films, with tensile strengths of 84.6,90.4 MPa, Young's moduli of 2.33,2.71 GPa, and elongations at break of 26.1,27.4%. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

Physicochemical properties and application of pullulan edible films and coatings in fruit preservation

Tony Diab
Abstract The effects of water, sorbitol and a sucrose fatty acid ester (SE) on the water sorption behaviour and thermal and mechanical properties of pullulan-based edible films as well as the physiological responses of fruit coated with pullulan have been studied. Incorporation of sorbitol or SE in pullulan films resulted in lower equilibrium moisture contents at low to intermediate water activities (aw), but much higher moisture contents at aw,>,0.75; estimates of monolayer values (within 4.1,5.9,gH2O,kg,1 solids) were given by application of the Brunauer,Emmett,Teller (BET) and Guggenheim,Anderson,DeBoer (GAB) models. A single glass,rubber transition (Tg), attributed to the polysaccharide component, was detected by calorimetry and dynamic mechanical thermal analysis (DMTA) at a sorbitol level of 15,30% DM. With both tests the strong plasticising action of water and polyol was evident in the thermal curves, and the Tg vs moisture content data were successfully fitted to the Gordon,Taylor empirical model. Multifrequency DMTA measurements provided estimates for the apparent activation energy of the glass transition in the range of , 300,488,kJ,mol,1. With large-deformation mechanical testing, large decreases in Young's moduli (tensile and three-point bend tests) were observed as a result of water- and/or polyol-mediated glass-to-rubber transition of the polymeric films. In the moisture content range of 2,8%, increases in flexural modulus (E) and maximum stress (,max) with small increases in moisture content were found for films made of pullulan or pullulan mixed with 15% DM sorbitol; a strong softening effect was observed when the water content exceeded this range. Addition of sorbitol increased the water vapour transmission rate of the films, whereas addition of SE had the opposite effect. Application of a pullulan/sorbitol/SE coating on strawberries resulted in large changes in internal fruit atmosphere composition which were beneficial for extending the shelf-life of this fruit; the coated fruit showed much higher levels of CO2, a large reduction in internal O2, better firmness and colour retention and a reduced rate of weight loss. In contrast, similar studies on whole kiwifruits showed increased levels of internal ethylene, which caused acceleration of fruit ripening during storage. © 2001 Society of Chemical Industry [source]

Polyamides X.34: A New Class of Polyamides with Long Alkane Segments

Moritz Ehrenstein
Abstract A new series of semi-crystalline polyamides (PA), which comprise extended aliphatic segments between the amide moieties and which display an interesting amphiphilic character has been synthesized and characterized. The polymers PA-2.34, PA-4.34, PA-8.34, PA-10.34, and PA-12.34 were prepared by melt-polycondensation of salts of tetratriacontanedioic acid and the respective short-chain diamine. The thermal properties of these polymers were investigated by differential scanning calorimetry, thermogravimetric analysis, and dynamic mechanical thermal analysis. The new polyamides exhibit melting temperatures that depend on the length of the diamine and range between 166 (PA-12.34) and 190,°C (PA-2.34). Solid transitions were observed between 38 and 57,°C. The materials displayed a rather limited solubility in common polyamide solvents, but readily dissolved in alkylsulfonic acids. All members of the series formed thermo-reversible gels in the highly polar sulfuric acid and 1,2,3,4-tetrahydronaphthalene, reflecting their interesting amphiphilic character. Young's moduli and tensile strengths of melt-processed, isotropic films of the polyamides investigated were in the range of 0.5,0.7 GPa and 20.30 MPa, respectively, independent of the length of the diamine used. Melting temperatures of polyamides PA-X.34 (x) and 1,2,3,4-tetrahydronaphthalene/PA-X.34 gels (37.5 wt.-% polyamide, determined from the second DSC heating scans) (+). [source]

Effect of synthesis process on the Young's modulus of titanate nanowire

Ming Chang
Abstract Nanocrystalline materials have attracted a great deal of attention because of their intriguing size-/shape-dependent properties. Titanate nanowires have been synthesized from titania (TiO2) nanoparticles using conventional hydrothermal process. Young's moduli of as-prepared titanate nanowires have been determined in situ from the buckling instability of the nanowires due to application of axial compressive load using a nanomanipulator inside a scanning electron microscope. Based on Euler's buckling model, the Young's moduli of the nanowires are determined to be 32,±,11,GPa. The obtained Young's moduli have been compared to that of the titanate nanowires prepared with microwave hydrothermal process to study the effect of synthesis process on the mechanical behavior of nanomaterials. The prolonged holding time of a conventional hydrothermal process helps in the significant enhancement of the Young's modulus of nanowire in comparison to that prepared with microwave hydrothermal process. [source]

Elastic properties of nanowires

Claus-Christian Röhlig
Abstract The elastic properties of metallic and semiconducting nanowires were analyzed by different techniques employing static and dynamic loads. The reliability of the methods is verified by analyzing well defined microstructures and a good agreement for the values of the Young's modulus determined by the different methods was achieved. For the investigated materials systems (Au, W, Si, InN), basically no differences in the Young's moduli were observed between microstructures, bulk material, and nanowires with radii of 20,300,nm. Microstructure, morphological undulation, defects, and contaminations, however, can drastically change the apparent Young's moduli of nanowires. Examples are given, where an apparent increasing or decreasing of the Young's modulus with decreasing diameter is caused by such effects. The same effects have also influence on the fracture strength in nanowires. While perfect Au nanowires exhibit fracture strengths exceeding the bulk values up to two orders of magnitude, any anomaly causes earlier failure. In addition, failure mechanisms are observed to be dependent on the microstructure. While single crystalline Au nanowires have shown a pure elastic deformation upon load, polycrystalline nanowires show a remarkable plastic deformation before breaking. [source]

Synthesis of poly(aryl ether ketone)s containing diphenyl moieties by electrophilic Friedel,Crafts solution polycondensation

Mingzhong Cai
Abstract A new monomer, 4,4,-bis(4-phenoxybenzoyl)diphenyl (BPOBDP), was prepared by Friedel,Crafts reaction of 4-bromobenzoyl chloride and diphenyl, followed by condensation with potassium phenoxide. Novel poly(ether ketone ketone) (PEKK)/poly(ether ketone diphenyl ketone ether ketone ketone) (PEKDKEKK) copolymers were synthesized by electrophilic Friedel,Crafts solution copolycondensation of isophthaloyl chloride (IPC) with a mixture of diphenyl ether (DPE) and BPOBDP, in the presence of anhydrous aluminum chloride and N -methyl-pyrrolidone (NMP) in 1,2-dichloroethane (DCE). The copolymers obtained were characterized by various analytical techniques such as FT-IR, DSC, TGA, and wide-angle X-ray diffraction (WAXD). The results showed that the resulting copolymers exhibited excellent thermal stability due to the existence of diphenyl moieties in the main chain. The glass transition temperatures are above 152°C, the melting temperatures are above 276°C, and the temperatures at a 5% weight loss are above 548°C in nitrogen. The copolymers with 50,70,mol% BPOBDP had tensile strengths of 101.5,102.7,MPa, Young's moduli of 3.23,3.41,GPa, and elongations at break of 12,17%. All these copolymers were semicrystalline and insoluble in organic solvents. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Structure and mechanical properties of nanocrystalline boron nitride thin films ,

Paolo M. Ossi
Abstract Boron nitride thin films have been deposited on (100) Si wafers, kept at low temperature, by radio frequency (r.f.) magnetron sputtering. The r.f. target power was fixed at 150,W and the substrate bias voltage ranged between ,50 and ,130,V. Film composition was checked by Auger electron spectroscopy; the structure was investigated by Fourier transform IR spectroscopy, glancing-angle X-ray diffraction and micro-Raman spectroscopy. Film hardness and Young's modulus were measured by nanoindentation. Film composition is nearly equiatomic, with a low degree of gaseous contamination. All samples are very fine grained, and nanocrystalline. Film coordination is mixed sp2,sp3, and the fraction of tetrahedral coordination depends critically on the bias voltage value. In hexagonal sp2 -bonded films the hardnesses and Young's moduli are low and increase considerably with the content of sp3 -coordinated cubic phase. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Mechanical properties of single crystalline and glassy lithium triborate

I. P. Shakhverdova
Abstract Mechanical properties of LiB3O5 single crystal plates with different orientation as well as of glass with the same composition have been investigated. The nano- (H) and microhardness (HM), the reduced Young's modulus (Er) and the crack behaviour of the samples were studied. Both hardness and Young's modulus of glass appeared smaller in comparison to corresponding single crystal data (H , 7 , 8 GPa, HM , 6 GPa, Er , 70 , 80 GPa for glass and H , 10 , 15 GPa, HM , 6 ,11 GPa, Er , 93 , 155 GPa for single crystal). H, Er, and the plane of crack propagation proved orientation-dependent. Cracks in the glass sample were not observed up to 0.49 N microindentation load, whereas for the single crystal the cracks appeared already at 0.098N. In single crystals the observed cleavage planes {211} and/or {412} are oriented nearly parallel to planes of B-O rings. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Evidence for axonemal distortion during the flagellar beat of Chlamydomonas

CYTOSKELETON, Issue 8 2007
Charles B. Lindemann
Abstract In order to understand the working mechanism that governs the flagellar beat it is essential to know if the axoneme undergoes distortion during the course of the beat cycle. The rapid fixation method employed by Mitchell was able to preserve the waveform of Chlamydomonas flagella much as it appears during normal flagellar beating [Mitchell, Cell Motil Cytoskeleton 2003;56:120,129]. This conservation of the waveform suggests that the stress responsible for the production of bending is also trapped by the fixation procedure. Longitudinal sections of these well-preserved flagella were used to document variations in the relative axonemal diameter. Sections aligned to the plane of bending, showing both the central pair microtubules and outer doublets, were examined for this purpose. Micrographs were selected that continuously showed both the outer doublets and the central pair from a straight region to a curved region of the flagellum. Axoneme diameters measured from these select micrographs showed an increase in relative diameter that averaged 39 nm greater at the crest of the bent region. This constituted a 24% increase in the axoneme diameter in the bends. The transverse stress acting across the axoneme during bending was calculated from the Geometric Clutch computer model for a simulated Chlamydomonas -like flagellar beat. If we assume that this is representative of the transverse stress acting in a real flagellum, then the Young's modulus of the intact axoneme is ,0.02 MPa. The possibility that the distortion of the axoneme during the beat could play a significant role in regulating dynein function is discussed. Cell Motil. Cytoskeleton 2007. © 2007 Wiley-Liss, Inc. [source]

Sensitivity of alveolar macrophages to substrate mechanical and adhesive properties

CYTOSKELETON, Issue 6 2006
Sophie Féréol
Abstract In order to understand the sensitivity of alveolar macrophages (AMs) to substrate properties, we have developed a new model of macrophages cultured on substrates of increasing Young's modulus: (i) a monolayer of alveolar epithelial cells representing the supple (,0.1 kPa) physiological substrate, (ii) polyacrylamide gels with two concentrations of bis-acrylamide representing low and high intermediate stiffness (respectively 40 kPa and 160 kPa) and, (iii) a highly rigid surface of plastic or glass (respectively 3 MPa and 70 MPa), the two latter being or not functionalized with type I-collagen. The macrophage response was studied through their shape (characterized by 3D-reconstructions of F-actin structure) and their cytoskeletal stiffness (estimated by transient twisting of magnetic RGD-coated beads and corrected for actual bead immersion). Macrophage shape dramatically changed from rounded to flattened as substrate stiffness increased from soft ((i) and (ii)) to rigid (iii) substrates, indicating a net sensitivity of alveolar macrophages to substrate stiffness but without generating F-actin stress fibers. Macrophage stiffness was also increased by large substrate stiffness increase but this increase was not due to an increase in internal tension assessed by the negligible effect of a F-actin depolymerizing drug (cytochalasine D) on bead twisting. The mechanical sensitivity of AMs could be partly explained by an idealized numerical model describing how low cell height enhances the substrate-stiffness-dependence of the apparent (measured) AM stiffness. Altogether, these results suggest that macrophages are able to probe their physical environment but the mechanosensitive mechanism behind appears quite different from tissue cells, since it occurs at no significant cell-scale prestress, shape changes through minimal actin remodeling and finally an AMs stiffness not affected by the loss in F-actin integrity. Cell Motil. Cytoskeleton 2006. © 2006 Wiley-Liss, Inc. [source]

Determination of mechanical properties of traditional masonry walls in dwellings of Faial Island, Azores

Aníbal Costa
Abstract The determination of mechanical properties of masonry walls is a fundamental pre-requisite for the characterization of the seismic response of traditional buildings, which helps on the definition of adequate rehabilitation and strengthening procedures. This paper presents a testing campaign carried out in the Cedros region of Faial Island, Azores, hit by the July 98 earthquake, aiming at the determination of physical and mechanical properties of stone masonry walls, namely the mass density and Young's modulus. The paper describes the developed testing techniques as a contribution to the study and the preservation of traditional masonry buildings. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Universal foliage-stem scaling across environments and species in dicot trees: plasticity, biomechanics and Corner's Rules

Mark E. Olson
Abstract Trees range from small-leaved, intricately branched species with slender stems to large-leaved, coarsely branched ones with thick stems. We suggest a mechanism for this pattern, known as Corner's Rules, based on universal scaling. We show similar crown area,stem diameter scaling between trunks and branches, environments, and species spanning a wide range of leaf size and stem biomechanics. If crown and stem maintain metabolically driven proportionality, but similar amounts of photosynthates are produced per unit crown area, then the greater leaf spacing in large-leaved species requires lower density stem tissue and, meeting mechanical needs, thicker stems. Congruent with this scenario, we show a negative relationship between leaf size and stem Young's modulus. Corner's Rules emerge from these mutual adjustments, which suggest that adaptive studies cannot consider any of these features independently. The constancy of scaling despite environmental challenges identifies this trait constellation as a crucial axis of plant diversification. [source]

Functional consequences of cartilage degeneration in the equine metacarpophalangeal joint: quantitative assessment of cartilage stiffness

Summary Reasons for performing study: No quantitative data currently exist on the relationship of the occurrence of cartilage degeneration and changes in site-specific biomechanical properties in the metacarpophalangeal (MCP) joint in the horse. Objectives: To gain insight into the biomechanical consequences of cartilage deterioration at 2 differently loaded sites on the proximal articular surface of the proximal phalanx (P1). Hypothesis: Static and dynamic stiffness of articular cartilage decreases significantly in degenerated cartilage. Methods: Cartilage degeneration index (CDI) values were measured at the lateral dorsal margin (Site 1), lateral central fovea (Site 2) and entire joint surface of P1 (CDIP1) in 30 horses. Group 1 contained joints without (CDIP1 values <25%, n = 22) and Group 2 joints with (CDIP1 values >25%, n = 8) signs of cartilage degeneration. Cartilage thickness at Sites 1 and 2 was measured using ultrasonic and needle-probe techniques. Osteochondral plugs were drilled out from Sites 1 and 2 and subsequently tested biomechanically in indentation geometry. Young's modulus at equilibrium and dynamic modulus were determined. Results: Cartilage thickness values were not significantly different between the 2 groups and sites. Young's modulus at Site 1 was significantly higher in Group 1 than in Group 2; at Site 2, the difference was not significant. Dynamic modulus values were significantly higher in Group 1 than in Group 2 at both sites. Conclusions: Degenerative cartilage changes are clearly related to loss of stiffness of the tissue. Absolute changes in cartilage integrity in terms of CDI are greatest at the joint margin, but concomitant changes are also present at the centre, with a comparable decrease of the biomechanical moduli at the 2 sites. Therefore, significant cartilage degradation at the joint margin not only reflects local deterioration of biomechanical properties, but is also indicative of the functional quality in the centre. Potential relevance: These findings may be important for improving prognostication and developing preventative measures. [source]

Ab Initio Guided Design of bcc Ternary Mg,Li,X (X,=,Ca, Al, Si, Zn, Cu) Alloys for Ultra-Lightweight Applications

William Art Counts
Abstract Ab initio calculations are becoming increasingly important for designing new alloys as these calculations can accurately predict basic structural, mechanical, and functional properties using only the atomic composition as a basis. In this paper, fundamental physical properties (like formation energies and elastic constants) of a set of bcc Mg,Li and Mg,Li-based compounds are calculated using density functional theory (DFT). These DFT-determined properties are in turn used to calculate engineering parameters such as (i) specific Young's modulus (Y/,) or (ii) shear over bulk modulus ratio (G/B) differentiating between brittle and ductile behavior. These parameters are then used to identify those alloys that have optimal mechanical properties for lightweight structural applications. First, in case of the binary Mg,Li system, an Ashby map containing Y/, versus G/B shows that it is not possible to increase Y/, without simultaneously increasing G/B (i.e., brittleness) by changing only the composition of a binary alloy. In an attempt to bypass such a fundamental materials-design limitation, a set of Mg,Li,X ternaries (X,=,Ca, Al, Si, Cu, Zn) based on stoichiometric Mg,Li with CsCl structure was studied. It is shown that none of the studied ternary solutes is able to simultaneously improve both specific Young's modulus and ductility. [source]