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Strength Properties (strength + property)
Selected AbstractsStrength Properties of Poled Lead Zirconate Titanate Subjected to Biaxial Flexural Loading in High Electric FieldJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2010Hong Wang The mechanical strength of poled lead zirconate titanate (PZT) has been studied using ball-on-ring (BoR) biaxial flexure tests with a high electric field applied concurrently. Both the as-received and the aged PZT specimens were tested. The Weibull plot and a 95% confidence ratio ring were used to characterize the responses of mechanical strength under various electric loading conditions. A fractographical study has been conducted at the same time, and the fracture origins or strength-limiting flaws of tested PZT specimens have been identified and characterized accordingly. The fracture toughness was further estimated to correlate with the obtained fracture stresses and flaws. It has been observed that electric field affects the mechanical strength of poled PZT, and the degree of the effect depends on the sign and magnitude of the applied electric field. Within the examined electric field range of ,3 to +3 times the coercive field, an increasing electric field resulted in a rapid strength decrease and a sharp increase with the turning point around the negative coercive field. Surface-located volume-distributed flaws were identified to be strength limiting for this PZT material. Variations of the mechanical strength with the electric field were believed to be related to the domain switching and amount of switchable domains. An aging effect on the mechanical strength of poled PZT could be significant, especially in the OC condition. These results and observations have the potential to serve probabilistic reliability analysis and design optimization of multilayer PZT piezo actuators. [source] Modification of High Lignin Content Kraft Pulps with Laccase to Improve Paper Strength Properties.BIOTECHNOLOGY PROGRESS, Issue 1 2004Laccase was reacted with gallic acid in the presence of a high-, (91) kraft pulp. The result was a modified pulp with 34%, 20%, and 72% improvements in burst, tensile, and wet tensile strength compared to untreated control samples. Fully bleached pulps were not responsive to the laccase treatment, indicating lignin was the major target for the fiber modification. The results indicate that the strength increases were a combined effect of improvements of hydrogen bonding between fibers and creation of phenoxy radical cross-links within the sheet. [source] Characterization of strength properties of thin polycrystalline silicon films for MEMS applicationsFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 1 2007R. Boroch ABSTRACT The aim of this work is to characterize the strength properties of polycrystalline silicon (polysilicon) with the use of tensile and bending test specimens. The strength of thin polysilicon films with different geometry, size and stress concentrations has been measured and correlated with the effective size of the specimen and its stress distribution. The test results are evaluated using a probabilistic strength approach based on the weakest link theory with the use of STAU software. The use of statistic methods of strength prediction of polysilicon test structures with a complex geometry and loading based on test values for standard material tests specimen has been evaluated. [source] Brittle-to-Ductile Transition in Uniaxial Compression of Silicon Pillars at Room TemperatureADVANCED FUNCTIONAL MATERIALS, Issue 15 2009Fredrik Östlund Abstract Robust nanostructures for future devices will depend increasingly on their reliability. While great strides have been achieved for precisely evaluating electronic, magnetic, photonic, elasticity and strength properties, the same levels for fracture resistance have been lacking. Additionally, one of the self-limiting features of materials by computational design is the knowledge that the atomistic potential is an appropriate one. A key property in establishing both of these goals is an experimentally-determined effective surface energy or the work per unit fracture area. The difficulty with this property, which depends on extended defects such as dislocations, is measuring it accurately at the sub-micrometer scale. In this Full Paper the discovery of an interesting size effect in compression tests on silicon pillars with sub-micrometer diameters is presented: in uniaxial compression tests, pillars having a diameter exceeding a critical value develop cracks, whereas smaller pillars show ductility comparable to that of metals. The critical diameter is between 310 and 400,nm. To explain this transition a model based on dislocation shielding is proposed. For the first time, a quantitative method for evaluating the fracture toughness of such nanostructures is developed. This leads to the ability to propose plausible mechanisms for dislocation-mediated fracture behavior in such small volumes. [source] Calibration of a discrete element model for intact rock up to its peak strengthINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 5 2010Yuannian Wang Abstract When three dimensional, bonded discrete element models (DEMs) are deployed to model intact rock, a basic question is how to determine the micro parameters that control macro properties of the modeled rock. After briefly describing the authors' DEM code, this paper describes algorithms to calibrate the model's micro parameters against standard laboratory tests, such as uniaxial and triaxial tests. Sensitivity analysis is used to identify the deformability micro parameters by obtaining relationships between microscopic and macroscopic deformability properties. The strength model parameters are identified by a global optimization process aimed at minimizing the difference between computed and experimental failure envelopes. When applied to the experimental results of Lac du Bonnet granite, this calibration process produced a good agreement between simulated and experimental results for both deformability and strength properties. Copyright © 2009 John Wiley & Sons, Ltd. [source] Determination of rock mass strength properties by homogenizationINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 13 2001A. Pouya Abstract A method for determining fractured rock mass properties is presented here on the basis of homogenization approach. The rock mass is considered to be a heterogeneous medium composed of intact rock and of fractures. Its constitutive model is studied numerically using finite element method and assimilating the fractures to joint elements (Coste, Comportement Thermo-Hydro-Mécanique des massifs rocheux fracturés. Thèse de Doctorat, Ecole Nationale des Ponts et Chaussées, Paris, 1997). The method has been applied to a granite formation in France. Geological data on different families of fractures have been used for the statistical representation of the fractures. A mesh-generating tool for the medium with high density of fractures has been developed. The mechanical behaviour of the rock mass (elasticity, ultimate strength and hardening law) has been determined assuming linear elasticity and Mohr,Coulomb strength criterion both for the intact rock and the fractures. Evolution of the mechanical strength in different directions has been determined as a function of the mean stress, thanks to various numerical simulations. The mechanical strength appears to be anisotropic due to the preferential orientation of the fractures. The numerical results allowed us to determine an oriented strength criterion for the homogenized rock mass. A 2D constitutive law for the homogenized medium has been deduced from numerical data. A 3D extension of this model is also presented. Copyright © 2001 John Wiley & Sons, Ltd. [source] Compatible blends of ethylene-vinyl acetate copolymer and hydrogenated nitrile rubberADVANCES IN POLYMER TECHNOLOGY, Issue 1 2004P. Thavamani Abstract The miscibility and some physico-mechanical characteristics of ethylene vinyl acetate (EVA) copolymer and hydrogenated nitrile rubber (HNBR) have been investigated using differential scanning calorimetry, dynamic mechanical and thermal analysis, and electrical conductivity. EVA was found to be miscible with HNBR at all properties. Infrared spectroscopic studies revealed that there is some chemical interaction between the constituent polymers. Scanning electron microscopic observations on the morphology of preferential solvent extracted samples indicated that in the blend the major constituent forms a continuous matrix in which the minor one is dispersed. At equal proportions, both EVA and HNBR exist as discontinuous phase. Variation of strength properties with blend composition is also discussed. © 2004 Wiley Periodicals, Inc. Adv Polym Techn 23: 5,17, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.10066 [source] Flexural Strength, Elastic Modulus, and pH Profile of Self-etch Resin Luting CementsJOURNAL OF PROSTHODONTICS, Issue 4 2008Egle Saskalauskaite DDS Abstract Purpose: To determine the flexural strength, modulus of elasticity, and 24-hour pH profile of three self-etching resin luting cements and to obtain comparative data for representative conventional resin and resin-modified glass ionomer luting cements. Materials and Methods: Three self-etching resin luting cements [RelyX Unicem (3M ESPE), Maxcem (Kerr), Embrace Wetbond (Pulpdent)] were tested and compared with two conventional resin cements [RelyX ARC (3M ESPE), Linkmax (GC)] plus two resin-modified glass ionomer luting cements [Fuji Plus (GC), RelyX Luting Plus (3M ESPE)]. Flexural strength and modulus of elasticity were determined using bar-shaped specimens (2 × 2 × 25 mm3) at 24 hours, using an Instron universal testing machine. Setting pH was measured using a flat-surface pH electrode at 0, 2, 5, 15, and 30 minutes and 1, 2, 4, 6, and 24 hours after mixing. Testing was performed under both dual-cured and self-cured conditions for all dual-cure cements. Data analysis included ANOVA and Tukey's test (p < 0.05). Results: The self-etching cements showed similar flexural strength to the conventional resin cements, except for Embrace Wetbond self-cured, which was considerably lower. Modulus of elasticity results were both higher and lower than for conventional resin cements. All photopolymerized conventional and self-etch dual-cure cements showed markedly higher flexural strength and modulus than when solely self-cured. The resin-modified glass ionomer cements were characterized by lower flexural strength and elastic modulus. Self-etching resin cements showed lower initial pH (2.0 to 2.4) than conventional resin cements (4.8 to 5.2) and a wide range of final pH values (3.9 to 7.3) at 24 hours. One self-etching cement (Unicem) revealed a unique pH profile characterized by a more rapid rise in pH to neutrality both when dual-cured (15 minutes) and when auto-cured (1 hour). Conclusions: The self-etching resin cements evaluated in this study displayed disparate properties and cannot be considered a homogeneous group. Flexural strength properties were most uniform and were similar to those of the conventional resin cements, whereas moduli of elasticity showed greater variation. Setting pH profiles differed, depending on the brand and mode of cure, even within the same category of luting cement. All cements with dual-cure capability, both conventional and self-etch, showed significantly superior properties when photopolymerized. [source] Aqueous Colloidal Processing of ZTA CompositesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2009Susana M. Olhero Two different zirconia-alumina composites, ZTA-30 (70 wt% Al2O3+30 wt% ZrO2) and ZTA-60 (40 wt% Al2O3+60 wt% ZrO2), with potential for orthopedic applications, were processed in aqueous media and consolidated by slip casting (SC), hydrolysis-assisted solidification (HAS), and gelcasting (GC) from suspensions containing 50 vol% solids loading. For comparison purposes, the same ceramic compositions were also consolidated by die pressing of freeze-dried granules (FG). In the HAS process, 5 wt% of Al2O3 in the precursor mixture was replaced by equivalent amounts of AlN to promote the consolidation of the suspensions. Ceramics consolidated via GC exhibited higher green (three-point bend) strengths (,17 MPa) than those consolidated by other techniques. Further, these ceramics also exhibited superior fracture toughness and flexural strength properties after sintering for 1 h at 1600°C in comparison with those consolidated by other techniques, including conventional die pressing (FG). [source] Effect of Flaw State on the Strength of Brittle Coatings on Soft SubstratesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2001Hae-Won Kim A study is made of the role of flaw state on the strength properties of brittle ceramic coating layers bonded to soft polycarbonate substrates. We introduce Vickers radial cracks at prescribed loads into the coating undersurfaces prior to bonding to control the sizes and locations of the starting flaws. A spherical indenter is then loaded on the top bilayer surfaces, directly above the Vickers indentation sites, subjecting the radial cracks to flexural tensile stress. Radial crack responses are monitored in situ, using a camera located below the transparent substrate. Critical loads to cause radial crack instability, and ensuing growth of the arrested cracks, are recorded. Conventional biaxial flexure tests on corresponding monolith coating materials provide a baseline for data comparison. Relative to the monolith flexure specimens, the bilayers show higher strengths, the more so the larger the flaw, indicating enhanced flaw tolerance. A simple fracture mechanics analysis of the radial crack evolution in the concentrated-load field, with due account for distribution of flexural tensile stresses at the coating undersurface, is unable to account completely for the enhanced bilayer strengths for the larger Vickers flaws. It is hypothesized that the epoxy used to bond the bilayer components enters the cracks, causing crack-wall adherence and providing an increased resistance to radial crack instability. The fracture mechanics are nevertheless able to account for the arrest and subsequent stable extension of the radial cracks beyond the critical loads once this extraneous adherence has been overcome. [source] Temperature Dependence of Tensile Strength for a Woven Boron-Nitride-Coated Hi-NicalonÔ SiC Fiber-Reinforced Silicon-Carbide-Matrix CompositeJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2001Shuqi Guo The temperature dependence of tensile fracture behavior and tensile strength of a two-dimensional woven BN-coated Hi-NicalonÔ SiC fiber-reinforced SiC matrix composite fabricated by polymer infiltration pyrolysis (PIP) were studied. A tensile test of the composite was conducted in air at temperatures of 298 (room temperature), 1200, 1400, and 1600 K. The composite showed a nonlinear behavior for all the test temperatures; however, a large decrease in tensile strength was observed above 1200 K. Young's modulus was estimated from the initial linear regime of the tensile stress,strain curves at room and elevated temperatures, and a decrease in Young's modulus became significant above 1200 K. The multiple transverse cracking that occurred was independent of temperature, and the transverse crack density was measured from fractographic observations of the tested specimens at room and elevated temperatures. The temperature dependence of the effective interfacial shear stress was estimated from the measurements of the transverse crack density. The temperature dependence of in situ fiber strength properties was determined from fracture mirror size on the fracture surfaces of fibers. The decrease in the tensile strength of the composite up to 1400 K was attributed to the degradation in the strength properties of in situ fibers, and to the damage behavior exception of the fiber properties for 1600 K. [source] Stress induced mechanical anisotropy in tetragonal zirconia polycrystalsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 3 2004V. I. Barbashov Abstract Microhardness and fracture toughness of polycrystalline ceramic on the basis of ZrO2 were measured using the microindentation technique. Obtained dependencies testify to the anisotropy of strength properties of partially stabilised zirconia specimens. In the authors' opinion, such anisotropy is caused by the initiation of tetragonal,monoclinic phase transition in the field of external stresses. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The influence of fiber formation conditions on the structure and properties of nanocomposite alginate fibers containing tricalcium phosphate or montmorillonitePOLYMER COMPOSITES, Issue 8 2010Maciej Bogu The authors devised conditions for the formation of nanocomposite calcium alginate fibers containing tricalcium phosphate (TCP) or montmorillonite (MMT). The rheological, sorptive, and strength properties of these fibers, as well as their porous and supramolecular structures were subjected to analysis. It has been concluded that the presence of nanoadditives in the material of alginate fibers decreases their susceptibility to distortion in the drawing stage. The obtained fibers are characterized by an even distribution of the nanoadditive on the fiber surface. POLYM. COMPOS., 31:1321,1331, 2010. © 2009 Society of Plastics Engineers [source] Maleated polypropylene film and wood fiber handsheet laminates,POLYMER COMPOSITES, Issue 12 2009Sangyeob Lee The grafting effect of maleic anhydride (MA) as an interfacial bonding agent and its influence on the tensile strength properties of thermomechanical pulp handsheet-isotactic polypropylene (iPP) film laminates was studied. For the MA treated with benzoyl peroxide (BPO) as an initiator, tensile strength properties increased 76% with PP film over untreated laminates. The optimal strength properties were obtained with a MA and BPO ratio of 2:1. A strong correlation was observed between the number of fibers in the web and tensile strength properties for both handsheet drying conditions. The R2 values were 0.95 for air-dry conditions and 0.94 from oven-dry conditions. Scanning electron microscopy images also showed the effectiveness of MA loading on the surface of thermomechanical pulp fibers due to increased fiber failure, which occurred without fiber being pulled out from the PP matrixes. Crystallinity and heat flow were determined using differential scanning calorimetry (DSC) and increased as expected as the ratio of MA and BPO increased from 0:0 to 2:1. These results were also in accordance with the morphological observations at the fracture surface, Fourier transform infrared spectra, and thermal analysis. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers [source] Dynamically cured natural rubber/EVA blends: influence of NR- g -poly(dimethyl (methacryloyloxymethyl)phosphonate) compatibilizerPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 5 2010Punyanich Intharapat Abstract Graft copolymer of natural rubber and poly(dimethyl(methacryloyloxymethyl)phosphonate) (NR- g -PDMMMP) was prepared in latex medium via photopolymerization. It was then used to promote the blend compatibility of dynamically cured 40/60 natural rubber (NR)/ethylene vinylacetate copolymer (EVA) blends using various loading levels at 1, 3, 5, 7, 9, 12, and 15,wt%. It was found that the increasing loading levels of NR- g -PDMMMP in the blends caused the increasing elastic modulus and complex viscosity until reaching the maximum values at a loading level of 9,wt%. The properties thereafter decreased with the increasing loading levels of NR- g -PDMMMP higher than 9,wt%. The smallest vulcanized rubber particles dispersed in the EVA matrix with the lowest tan , value was also observed at a loading level of 9,wt%. Furthermore, the highest tensile strength and elongation at break (i.e., 17.06 MPa and 660%) as well as the lowest tension set value (i.e., 27%) were also observed in the blend using this loading level of the compatibilizer. Addition of NR- g -PDMMMP in the dynamically cured NR/EVA blends also improved the thermal stability of the blend. That is, the decomposition temperature increased with the addition of the graft copolymer. However, the addition of NR- g -PDMMMP in the blends caused the decreasing degree of crystallinity of the EVA phase in the blend. However, the strength properties of the blend are still high because of the compatibilizing effect. Copyright © 2009 John Wiley & Sons, Ltd. [source] Effect of silicon reinforcement on load-capacity of porous nanofiltersPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2008Ádám Kovács Square,form microfilters consisting of a two,layer porous membrane with nano,size pores and reinforced by silicon columns have been investigated. The change of layer thicknesses and reinforcement geometry modify the load,capacity of the device through the variation of strength properties. A simple thin plate model was constructed by substituting the effect of silicon columns by an equivalent third layer. Estimates for the load,capacity were made by finite element calculations. These estimates have been verified by experimental results. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Enzymatic Treatment of Mechanical Pulp Fibers for Improving Papermaking PropertiesBIOTECHNOLOGY PROGRESS, Issue 6 2000Ken K. Y. Wong Three enzyme preparations (crude cellulase, laccase, and proteinase) were evaluated for their potential to improve the papermaking properties of mechanical pulp. After treating a long fibre-rich fraction of the pulp with enzyme, the fibres were recombined with untreated fines for handsheet making and testing. None of the enzymes altered the retention of fines or the consolidation of the furnish mix during handsheet formation. All three enzymes increased tensile stiffness index, which is a measure of the initial resistance of the handsheets to strain. Only the laccase preparation, an enzyme that modifies pulp lignin, consistently increased fibre bonding to enhance other strength properties of the handsheets. [source] | |||||||||||||