Showing papers on "Ultimate tensile strength published in 2003"

Nanostructured artificial nacre

Abstract: Finding a synthetic pathway to artificial analogs of nacre and bones represents a fundamental milestone in the development of composite materials. The ordered brick-and-mortar arrangement of organic and inorganic layers is believed to be the most essential strength- and toughness-determining structural feature of nacre. It has also been found that the ionic crosslinking of tightly folded macromolecules is equally important. Here, we demonstrate that both structural features can be reproduced by sequential deposition of polyelectrolytes and clays. This simple process results in a nanoscale version of nacre with alternating organic and inorganic layers. The macromolecular folding effect reveals itself in the unique saw-tooth pattern of differential stretching curves attributed to the gradual breakage of ionic crosslinks in polyelectrolyte chains. The tensile strength of the prepared multilayers approached that of nacre, whereas their ultimate Young modulus was similar to that of lamellar bones. Structural and functional resemblance makes clay– polyelectrolyte multilayers a close replica of natural biocomposites. Their nanoscale nature enables elucidation of molecular processes occurring under stress.

An application of nanotechnology in advanced dental materials

Abstract: Background This article reports the authors' development of nanofillers and a resulting nanocomposite They measured the nanocomposite's properties in vitro in comparison with those of several existing composites (hybrids, microhybrids and microfill) Methods The authors developed two types of nanofillers: nanomeric particles and nanoclusters They used optimal combinations of these nanofillers in a proprietary resin matrix to prepare the nanocomposite system with a wide range of shades and opacities The properties they studied were compressive, diametral tensile and flexural strengths; in vitro three-body wear; fracture resistance; polish retention; and surface morphology after toothbrush abrasion They performed statistical analysis using analysis of variance/Tukey-Kramer paired analysis at a 95 percent confidence interval Results The compressive and diametral strengths and the fracture resistance of the nanocomposite were equivalent to or higher than those of the other commercial composites tested The three-body wear results of the nanocomposite system were statistically better than those of all other composites tested The nanocomposite showed better polish retention than the hybrids and microhybrids tested at the extended brushing periods After extended toothbrush abrasion, the dentin, body and enamel shades showed polish retention equivalent to that of the microfill tested, while translucent shades showed better polish retention than the microfill Conclusions The dental nanocomposite system studied showed high translucency, high polish and polish retention similar to those of microfills while maintaining physical properties and wear resistance equivalent to those of several hybrid composites Clinical Implications The strength and esthetic properties of the resin-based nanocomposite tested should allow the clinician to use it for both anterior and posterior restorations

Improving the Dispersion and Integration of Single-Walled Carbon Nanotubes in Epoxy Composites through Functionalization

Abstract: Considerable improvement in the dispersion of purified single-walled carbon nanotubes (SWNTs) in an epoxy composite was obtained through functionalization of the SWNTs by using an optimized H2SO4/70% HNO3 acid treatment and subsequent fluorination. Epoxy composites containing 1 wt % nanotubes were processed by dissolving the functionalized SWNTs in dimethylformamide and mixing with the epoxy resin thereafter. The functionalized nanotubes were observed to be highly dispersed and well integrated in the epoxy composites. The enhancement of mechanical properties of the latter was indicated by a 30% increase in modulus and 18% increase in tensile strength. This work demonstrates the practical use of combining acid treatment and fluorination to achieve functionalization and unroping of SWNTs. The functionalized SWNTs can be integrated into epoxy composites through the formation of strong covalent bonds in the course of epoxy ring-opening esterification and curing chemical reactions.

The Mechanical Properties of Human Dentin: a Critical Review and Re-evaluation of the Dental Literature:

Abstract: The past 50 years of research on the mechanical properties of human dentin are reviewed. Since the body of work in this field is highly inconsistent, it was often necessary to re-analyze prior studies, when possible, and to re-assess them within the framework of composite mechanics and dentin structure. A critical re-evaluation of the literature indicates that the magnitudes of the elastic constants of dentin must be revised considerably upward. The Young's and shear moduli lie between 20-25 GPa and 7-10 GPa, respectively. Viscoelastic behavior (time-dependent stress relaxation) measurably reduces these values at strain rates of physiological relevance; the reduced modulus (infinite relaxation time) is about 12 GPa. Furthermore, it appears as if the elastic properties are anisotropic (not the same in all directions); sonic methods detect hexagonal anisotropy, although its magnitude appears to be small. Strength data are re-interpreted within the framework of the Weibull distribution function. The large coefficients of variation cited in all strength studies can then be understood in terms of a distribution of flaws within the dentin specimens. The apparent size-effect in the tensile and shear strength data has its origins in this flaw distribution, and can be quantified by the Weibull analysis. Finally, the relatively few fracture mechanics and fatigue studies are discussed. Dentin has a fatigue limit. For stresses smaller than the normal stresses of mastication, approximately 30 MPa, a flaw-free dentin specimen apparently will not fail. However, a more conservative approach based on fatigue crack growth rates indicates that if there is a pre-existing flaw of sufficient size (approximately 0.3-1.0 mm), it can grow to catastrophic proportion with cyclic loading at stresses below 30 MPa.

Influence of Recycled Aggregate on Interfacial Transition Zone, Strength, Chloride Penetration and Carbonation of Concrete

Abstract: This study is conducted (1) to examine the influence of recycled aggregate on interfacial transition zone (ITZ), strength, chloride penetration, and carbonation of concrete, and (2) to propose a method for improving strength, chloride penetration, and carbonation resistances of concrete using recycled aggregates Five types of recycled aggregate, and four levels of water-binder ratio are used in this study The recycled aggregate concrete is evaluated according to compressive strength, tensile strength, chloride penetration depth, and carbonation depth The characteristics of ITZs in recycled aggregate concrete are also measured and used to explain the influence of recycled aggregate on the mentioned properties Additionally, the double-mixing method for improving strength, chloride penetration, and carbonation resistances of recycled aggregate concrete is evaluated in this study

Surface-stress-induced phase transformation in metal nanowires.

Abstract: Several researchers have demonstrated, through experiments and analysis, that the structure and properties of nanometre-scale materials can be quite different to those of bulk materials due to the effect of surfaces. Here we use atomistic simulations to study a surface-stress-induced phase transformation in gold nanowires. The emergence of the transformation is controlled by wire size, initial orientation, boundary conditions, temperature and initial cross-sectional shape. For a initial crystal orientation and wire cross-sectional area below 4 nm(2), surface stresses alone cause gold nanowires to transform from a face-centred-cubic structure to a body-centred-tetragonal structure. The transformation occurs roughly when the compressive stress caused by tensile surface-stress components in the length direction exceeds the compressive stress required to transform bulk gold to its higher energy metastable crystal structure.

Cell-wall recovery after irreversible deformation of wood

Abstract: The remarkable mechanical properties of biological materials reside in their complex hierarchical architecture and in specific molecular mechanistic phenomena1,2,3. The fundamental importance of molecular interactions and bond recovery has been suggested by studies on deformation and fracture of bone and nacre4,5,6. Like these mineral-based materials, wood also represents a complex nanocomposite with excellent mechanical performance, despite the fact that it is mainly based on polymers. In wood, however, the mechanistic contribution of processes in the cell wall is not fully understood7,8,9. Here we have combined tensile tests on individual wood cells and on wood foils with simultaneous synchrotron X-ray diffraction analysis in order to separate deformation mechanisms inside the cell wall from those mediated by cell–cell interactions. We show that tensile deformation beyond the yield point does not deteriorate the stiffness of either individual cells or foils. This indicates that there is a dominant recovery mechanism that re-forms the amorphous matrix between the cellulose microfibrils within the cell wall, maintaining its mechanical properties. This stick–slip mechanism, rather like Velcro operating at the nanometre level, provides a 'plastic response' similar to that effected by moving dislocations in metals. We suggest that the molecular recovery mechanism in the cell matrix is a universal phenomenon dominating the tensile deformation of different wood tissue types.

Effects of wood fiber characteristics on mechanical properties of wood/polypropylene composites

Abstract: Commercial wood flour, the most common wood-derived filler for thermoplastics, is produced in a mixture of particle sizes and generally has a lower aspect ratio than wood and other natural fibers. To understand how wood flour and fiber characteristics influence the mechanical properties of polypropylene composites, we first investigated the effect of different sizes of wood flour particles on the mechanical properties of wood-flour-filled polypropylene composites. We then compared the properties of wood-flour-filled composites to those of composites reinforced with refined wood fiber. We also studied the effect of a maleated polypropylene coupling agent on composite properties. Wood flour particles (35, 70, 120, and 235 mesh) were compounded at 40% by weight with polypropylene. Increases in tensile and flexural strength and modulus of the wood flour composites were found to correspond with increases in aspect ratio. Notched impact energy increased with increasing particle size, whereas unnotched impact energy decreased with increasing particle size. Refined wood fiber and 40-mesh wood flour was compounded at 20% and 40% by weight with polypropylene. Wood fiber resulted in higher strengths at both filler levels and higher moduli at the 40% level compared to the strength properties of wood flour composites. The higher aspect ratio of the wood fiber had little effect on impact energy. The maleated polypropylene coupling agent caused greater strength increases in wood fiber composites than in wood flour composites. The coupling agent did not significantly affect tensile or flexural moduli. Our results clearly support the use of higher aspect ratio wood fibers and coupling agents for increasing the strength of wood/plastic composites.

Nanofiber-reinforced polymers prepared by fused deposition modeling

Abstract: Vapor-grown carbon fibers (VGCFs), a practical model nanofiber for single-walled carbon nanotubes, were combined with an acrylonitrile–butadiene–styrene (ABS) copolymer to create a composite material for use with fused deposition modeling (FDM). Continuous filament feedstock materials were extruded from Banbury mixed composites with a maximum composition of 10 wt % nanofibers. Issues of dispersion, porosity, and fiber alignment were studied. SEM images indicated that the VGCFs were well dispersed and evenly distributed in the matrix and that no porosity existed in the composite material following FDM processing. VGCFs aligned both in the filament feedstock and in the FDM traces suggested that nanofibers, in general, can be aligned through extrusion/shear processing. The feedstock materials were processed into test specimens for mechanical property comparisons with unfilled ABS. The VGCF-filled ABS swelled less than did the plain ABS at similar processing conditions due to the increased stiffness. The tensile strength and modulus of the VGCF-filled ABS increased an average of 39 and 60%, respectively, over the unfilled ABS. Storage modulus measurements from dynamic mechanical analysis indicated that the stiffness increased 68%. The fracture behavior of the composite material indicated that the VGCFs act as restrictions to the chain mobility of the polymer. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3081–3090, 2003

Review Mechanical properties of ice and snow

Abstract: The mechanical properties of ice and snow are reviewed. The tensile strength of ice varies from 0.7–3.1 MPa and the compressive strength varies from 5–25 MPa over the temperature range −10°C to −20°C. The ice compressive strength increases with decreasing temperature and increasing strain rate, but ice tensile strength is relatively insensitive to these variables. The tensile strength of ice decreases with increasing ice grain size. The strength of ice decreases with increasing volume, and the estimated Weibull modulus is 5. The fracture toughness of ice is in the range of 50–150 kPa m1/2 and the fracture-initiating flaw size is similar to the grain size. Ice-soil composite mixtures are both stronger and tougher than ice alone. Snow is a open cellular form of ice. Both the strength and fracture toughness of snow are substantially lower than those of ice. Fracture-initiating flaw sizes in snow appear to correlate to the snow cell size.

Improvement of Thermal and Mechanical Properties of Carbon Nanotube Composites through Chemical Functionalization

Abstract: Chemically functionalized multiwalled carbon nanotubes were incorporated into a polymer matrix by in situ polymerization, to improve the transfer of mechanical load through a chemical bond, which was demonstrated by Raman and infrared spectroscopies. The resulting composite shows higher storage modulus (E‘) and tensile strength than existing similar composites, with only 1 wt % of functionalized nanotubes. E‘ at 90 °C is increased by an outstanding 1135% and the glass transition temperature is exceptionally raised by ≅40 °C.

Strain-induced band gap shrinkage in Ge grown on Si substrate

Abstract: Band gap shrinkage induced by tensile strain is shown for Ge directly grown on Si substrate. In Ge-on-Si pin diodes, photons having energy lower than the direct band gap of bulk Ge were efficiently detected. According to photoreflectance measurement, this property is due to band gap shrinkage. The origin of the shrinkage is not the Franz–Keldysh effect but rather tensile strain. It is discussed that the generation of such a tensile strain can be ascribed to the difference of thermal expansion between Ge and Si. Advantages of this tensile Ge for application to photodiode are also discussed.

Ultimate limit state design of steel-plated structures

Abstract: Preface. About the Authors. How to Use This Book. Principles of Limit State Design. Buckling and Ultimate Strength Behavior of Plate Stiffener Combinations: Beams, Columns and Beam Columns. Elastic and Inelastic Buckling of Plates under Complex Circumstances. Post Buckling and Ultimate Strength Behavior of Plates. Elastic and Inelastic Buckling of Stiffened Panels and Grillages. Post buckling and Ultimate Strength Behavior of Stiffened Panels and Grillages. Ultimate Strength of Plate Assemblies: Plate Girders, Box Columns/Girders and Corrugated Panels. Ultimate Strength of Ship Hulls. Impact Mechanics and Structural Design for Accidents. Fracture Mechanics and Ultimate Strength of Cracked Structures. A Semi analytical Method for the Elastic Plastic Large deflection Analysis of Plates under Combined Loading. The Nonlinear Finite Element Method. The Idealized Structural Unit Method. Appendices. Index.

Microstructural Effects on the Tensile and Fracture Behavior of Aluminum Casting Alloys A356/357

Abstract: The tensile properties and fracture behavior of cast aluminum alloys A356 and A357 strongly depend on secondary dendrite arm spacing (SDAS), Mg content, and, in particular, the size and shape of eutectic silicon particles and Fe-rich intermetallics. In the unmodified alloys, increasing the cooling rate during solidification refines both the dendrites and eutectic particles and increases ductility. Strontium modification reduces the size and aspect ratio of the eutectic silicon particles, leading to a fairly constant particle size and aspect ratio over the range of SDAS studied. In comparison with the unmodified alloys, the Sr-modified alloys show higher ductility, particularly the A356 alloy, but slightly lower yield strength. In the microstructures with large SDAS (>50 µm), the ductility of the Sr-modified alloys does not continuously decrease with SDAS as it does in the unmodified alloy. Increasing Mg content increases both the matrix strength and eutectic particle size. This decreases ductility in both the Sr-modified and unmodified alloys. The A356/357 alloys with large and elongated particles show higher strain hardening and, thus, have a higher damage accumulation rate by particle cracking. Compared to A356, the increased volume fraction and size of the Fe-rich intermetallics (π phase) in the A357 alloy are responsible for the lower ductility, especially in the Sr-modified alloy. In alloys with large SDAS (>50 µm), final fracture occurs along the cell boundaries, and the fracture mode is transgranular. In the small SDAS (<30 µm) alloys, final fracture tends to concentrate along grain boundaries. The transition from transgranular to intergranular fracture mode is accompanied by an increase in the ductility of the alloys.