Showing papers on "Flexural strength published in 1999"
TL;DR: The results indicate that sandblasting may provide a powerful technique for strengthening Y-TZP in clinical practice and grinding may lead to substantial strength degradation and reduced reliability of prefabricated zirconia elements, therefore, sandblasted of ground surfaces is suggested.
724 citations
TL;DR: In this article, the authors evaluated the mechanical properties of woven jute fabric-reinforced composites using hand lay-up techniques as per the ASTM standard, including tensile strength, compressive strength, flexural strength, impact strength, inplane shear strength, interlaminar shear and hardness.
Abstract: This research work is concerned with the evaluation of the mechanical properties—modulus, Poisson's ratio and strength—of woven jute fabric-reinforced composites. The specimens are prepared using hand lay-up techniques as per the ASTM standard. This is the first report by any single group of researchers in which tensile strength, compressive strength, flexural strength, impact strength, inplane shear strength, interlaminar shear strength and hardness are given. This work being an experimental study on untreated (`as received' jute fabric) woven jute fabric-reinforced polyester composites, demonstrates the potential of this renewable source of natural fibre for use in a number of consumable goods.
517 citations
TL;DR: In this article, the results of a research project initiated to study the stability of these materials when exposed to aggressive solutions were presented, where prisms of mortar made of sand and alkali-activated metakaolin were immersed in deionized water, ASTM sea water, sodium sulfate solution (4.4% wt), and sulfuric acid solution (0.001 M).
510 citations
Book•
01 Jan 1999
TL;DR: In-Plane Stiffness Design. Failure Criteria for Laminated Composites as discussed by the authors, failure criteria for laminate composites, and strength design of laminate materials.
Abstract: Mechanics of Laminated Composite Materials. Hygrothermal Analysis of Laminated Composites. Laminate In-Plane Stiffness Design. Integer Programming Techniques. Failure Criteria for Laminated Composites. Strength Design of Laminates. Laminate Design for Flexural and Combined Response.
501 citations
TL;DR: Novel glass fiber reinforcements may considerably enhance flexural properties of multiphase dental polymers, which is due to proper impregnation of fibers with polymer matrix.
Abstract: Statement of problem. Fiber-reinforced plastics for dental applications have been under development for some time. A major difficulty in using reinforcing fibers with multiphase acrylic resins, such as powderliquid resins, has been improper impregnation of fibers with the resin. Purpose. The aim of this study was to describe and test a novel system to use polymer-preimpregnated reinforcing fibers with commonly used multiphase acrylic resins. Material and methods. Continuous unidirectional and woven preimpregnated glass fiber reinforcements (Stick and Stick Net) were used to reinforce heat-curing denture base and autopolymerizing denture base polymers. A temporary fixed partial denture polymer was also reinforced with Stick reinforcement material. Five test specimens were fabricated for unreinforced control groups and for Stick- and Stick Net-reinforced groups. A 3-point loading test was used to measure transverse strength and flexural modulus of the materials and ultimate strain at fracture was calculated. Cross-sections of test specimens were examined with a SEM to evaluate degree of impregnation of fibers with polymer matrix. Quantity of fibers in test specimens was determined by combustion analysis. Results. Transverse strength of heat-curing denture base polymer was 76 MPa, Stick reinforcement increased it to 341 MPa, and flexural modulus increased from 2550 to 19086 MPa. Stick Net reinforcement increased transverse strength of heat-curing denture base polymer to 99 MPa and flexural modulus to 3530 MPa. Transverse strength of autopolymerizing denture base polymer was 71 MPa; Stick increased it to 466 MPa; and flexural modulus increased from 2418 to 16749 MPa. Stick Net increased the transverse strength of autopolymerizing denture base polymer to 96 MPa and flexural modulus to 3573 MPa. Transverse strength of temporary fixed partial denture polymer increased from 58 to 241 MPa and flexural modulus from 1711 to 7227 MPa. ANOVA showed that reinforcement type and polymer brand affected transverse strength and modulus ( P Conclusions. Novel glass fiber reinforcements may considerably enhance flexural properties of multiphase dental polymers, which is due to proper impregnation of fibers with polymer matrix. By using Stick or Stick Net reinforcement, the strain at fracture of the material can be modified. (J Prosthet Dent 1999;81:318-26.)
425 citations
TL;DR: In this paper, the performance of concrete columns conbined with carbon and glass FRP composite tubes was evaluated under uniaxial compressive load and showed that external confinement of concrete by FRP tubes can significantly enhance the strength, ductility, and energy absorption capacity of concrete.
Abstract: New types of structural columns are being developed for new construction. They are made of concrete-encased fiber reinforced polymer (FRP) tubes. The concrete-filled FRP tubes are cast in place. The tube acts as formwork, protective jacket, confinement, and shear and flexural reinforcement. It can also be used to complement or replace conventional steel reinforcement of the column. This paper presents the results of experimental and analytical studies of the performance of concrete columns conbined with carbon and glass FRP composite tubes. Concrete-filled FRP tubes are instrumented and tested under uniaxial compressive load. Test variables include type of fiber, thickness of tube, and concrete compressive strength. Results show that external confinement of concrete by FRP tubes can significantly enhance the strength, ductility, and energy absorption capacity of concrete. Equations to predict the compressive strength and failure strain, as well as the entire stress-strain curve of concrete-filled FRP tubes were developed. A comparison between the experimental results and those of analytical results indicate that the proposed model provides satisfactory predictions of ultimate compressive strength, failure strain, and stress-strain response. The study shows that the available models generally overestimate the strength of concrete confined by FRP tubes, resulting in unsafe design.
403 citations
TL;DR: In this paper, the results of an investigation on concrete containing alkali activated slag (AAS) as the binder, with emphasis on achievement of reasonable workability and equivalent one-day strength to portland cement concrete at normal curing temperatures.
320 citations
TL;DR: The average interfacial shear strength between the pineapple fiber and poly(hydroxybutyrate-co-valerate) (PHBV) was 8.23 MPa as measured by the microbond technique as mentioned in this paper.
Abstract: Physical and tensile properties of pineapple fibers were characterized. Tensile properties of pineapple fibers, like most natural fibers, showed a large variation. The average interfacial shear strength between the pineapple fiber and poly(hydroxybutyrate-co-valerate) (PHBV) was 8.23 MPa as measured by the microbond technique. Scanning electron microscopy (SEM) photomicrographs of the microbond specimens revealed an adhesive failure of the interface. Fully degradable and environment-friendly “green” composites were prepared by combining pineapple fibers and PHBV with 20 and 30% weight content of fibers placed in a 0°/90°/0° fiber arrangement. Tensile and flexural properties of these “green” composites were compared with different types of wood specimens. Even though tensile and flexural strength and moduli of these “green” composites were lower than those of some wood specimens tested in grain direction, they were significantly higher than those of wood specimens tested in perpendicular to grain direction. Compared to PHBV virgin resin, both tensile and flexural strength and moduli of these “green” composites were significantly higher. SEM photomicrographs of the fracture surface of the “green” composites, in tensile mode, showed partial fiber pull-out indicating weak bonding between the fiber and the matrix.
314 citations
TL;DR: In this paper, the possibility of in situ detection of damage in unidirectional CFRP by means of electric resistance measurements was investigated by changing the electrode location and conduction occurred both along the fibre and in the transverse direction by virtue of fibre-to-fibre contacts.
312 citations
TL;DR: In this article, the effect of test specimen size on the unnotched strength of continuous fiber reinforced composites is considered, and different fundamental failure mechanisms of fibre direction tension, fibre direction compression, and matrix dominated transverse tension and shear are discussed in turn.
283 citations
TL;DR: In this article, the effect of curing temperature on microstructure, shrinkage, and compressive strength of AAS concrete was investigated, and it was found that pretreatment at room temperature before elevated temperature curing further improved early strength and considerably decreased shrinkage in AAScrete.
TL;DR: In this article, the results of an experimental study on 111 under-reinforced concrete beams were presented to determine their residual flexural capacity after undergoing different degrees of reinforcement corrosion. But the results showed marked reductions in flexural strength due to reinforcement corrosion, which was caused primarily by the breakdown of bond at the steel/concrete interface.
Abstract: The paper presents the results of an experimental study on 111 under-reinforced concrete beams to determine their residual flexural capacity after undergoing different degrees of reinforcement corrosion. Corrosion was induced in the laboratory by an accelerated corrosion technique using two sources of external power supply. The beams were precured for different periods of up to I year before accelerated corrosion was induced in the reinforcement. Different degrees of reinforcing bar corrosion were induced in increments, ranging from 1.25 to 10 percent at corrosion rates off, 2, 3, and 4 mA/cm(2). The beams were reinforced with two longitudinal bars. Shear reinforcement was provided by external means using steel collars. The results show marked reductions in flexural strength due to reinforcement corrosion, which is caused primarily by the breakdown of bond at the steel/concrete interface.
TL;DR: In this paper, the mechanical and thermal properties of green composites made from pineapple fibers and poly(hydroxybutyrate-co-valerate) (PHBV) resin are investigated.
Abstract: This paper presents the mechanical and thermal properties of unidirectional, degradable, environment-friendly “green” composites made from pineapple fibers and poly(hydroxybutyrate-co-valerate) (PHBV) resin. Tensile and flexural properties of the “green” composites with different fiber contents were measured in both longitudinal and transverse directions. Compared to those of virgin resin, the tensile and flexural strengths of “green” composites are significantly higher in the longitudinal direction while they are lower in the transverse direction. However, the mechanical properties are lower than those predicted by simple models. Scanning electron microscope (SEM) photomicrographs of the tensile fracture surfaces demonstrate fibers being pulled out from the matrix, the interfacial failure, fiber fibrillation, and the nonunidirectional nature of the “green” composites. The thermal behavior of the “green” composites, studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), showed that the presence of pineapple fibers does not affect the nonisothermal crystallization kinetics, crystallinity, and thermal decomposition of PHBV resin.
TL;DR: Cements differed considerably with respect to mechanical properties, including compressive proportional limit, compressive resilience, compressed strength, compression toughness, diametral tensile strength, flexural strength, and flexural toughness.
Abstract: Statement of problem. Dental luting cements fail by microcrack formation and bacterial ingress or by gross failure and crown dislodgment. Both of these failure modes are related to mechanical properties and deformation. Purpose. This study evaluated those mechanical properties of cements. Methods and material. Elastic modulus for 8 representative cements (zinc phosphate, polycarboxylate, glass ionomer, encapsulated glass ionomer, resin-modified glass ionomer, resin composite, and adhesive resin composite) was measured by using a nondestructive technique and evaluated for cement type and storage time (1 hour, 1 day, 1 week, 1 month, 1 year) by 2-way ANOVA ( P P Results. Cements varied with respect to elastic moduli, compressive proportional limit, compressive resilience, compressive strength, compressive toughness, diametral tensile strength, flexural strength, and flexural toughness. Storage time affected the elastic moduli of different materials in different ways. Elastic moduli of polycarboxylate and glass ionomer cements increased over time, whereas the other materials changed little after the first day. Crosshead rate only significantly affected compressive proportional limit and resilience. Conclusions. Luting cements differed considerably with respect to mechanical properties. (J Prosthet Dent 1999;81:597-609.)
TL;DR: The impact strength of denture base acrylic resins was increased with fibers in woven form, and there were significant differences among the test groups, but no significant differences in transverse strength were found.
Abstract: Statement of problem. Fracture strength of denture base resins is of great concern, and many approaches have been used to strengthen acrylic resin dentures. Purpose. This study measured the effect of 5 fiber strengtheners on the fracture resistance of denture base acrylic resin material. Impact strength, transverse strength, deflection, and elasticity modulus values of a heat-polymerized denture base resin (Trevalon), reinforced with glass, carbon, thin Kevlar, thick Kevlar, and polyethylene fibers in woven form were studied. Material and methods. One hundred acrylic resin test specimens reinforced with woven fibers were fabricated. The control group consisted of 20 specimens with no fiber reinforcement. For the impact strength test, a Charpy-type impact tester was used. Transverse strength was assessed with a 3-point bending test by using a screw-driven mechanical testing machine. Ten specimens were used for each test. Results. The highest impact test values were produced by polyethylene-reinforced group, and the lowest values were obtained from specimens containing no fibers. There were significant differences among the test groups, but no significant differences in transverse strength were found. The lowest transverse strength values were obtained for specimens strengthened with polyethylene fibers, which also insignificantly decreased transverse strength of the acrylic resin. Conclusion. The impact strength of denture base acrylic resins was increased with fibers in woven form. Tested fibers did not have a significant effect on the transverse strengths. (J Prosthet Dent 1999;81:616-20.)
TL;DR: In this paper, pyrograf-derived carbon fibers (VGCF, Pyrograf III) were formulated in various fiber volume fractions into epoxy (thermoset) and poly(phenylene sulfide) (thermoplastic) composites.
Abstract: Vapor grown carbon fibers (VGCF, Pyrograf III™ from Applied Sciences, Inc.), with 100–300 nm diameters and ∽10–100 μm lengths, were formulated in various fiber volume fractions into epoxy (thermoset) and into poly(phenylene sulfide) (thermoplastic) composites. Increases in stiffness were observed as with previous VGCF/organic matrix composites. Large increases in flexural strengths were achieved in both systems demonstrating for the first time that discontinuous randomly oriented Pyrograf III™ can give strength increases and has substantial potential as a reinforcement in composites. Here-to-fore, addition of VGCF caused strength decreases. Voids, residual thermal strains (as the fiber surface area is ∽35 times greater than 7 μm-diameter PAN fiber), or uncertainties about fiber strength, fiber–matrix bonding and the degree of fiber dispersion, could cause losses of strength. Thermal conductivity properties of VGCF/ABS (acrylonitrile–butadiene–styrene from GE Plastics) and VGCF/epoxy composites with various fiber volume fractions were measured. Thermal conductivity increased with an increase in fiber volume fraction. However, these increases were not significant enough to make these VGCF fiber/organic matrix composites candidates for thermally conductive materials.
TL;DR: The bending strength of a wide variety of bony types is shown to be nearly linearly proportional to Young's modulus of elasticity/100, which strongly suggests that bending strength is determined by the yield strain.
Abstract: The bending strength of a wide variety of bony types is shown to be nearly linearly proportional to Young's modulus of elasticity/100. A somewhat closer and more satisfactory fit is obtained if account is taken of the variation of yield strain with Young's modulus. This finding strongly suggests that bending strength is determined by the yield strain. The yield stress in tension, which might be expected to predict the bending strength, underestimates the true bending strength by approximately 40 %. This may be explained by two phenomena. (1) The post-yield deformation of the bone material allows a greater bending moment to be exerted after the yield point has been reached, thereby increasing the strength as calculated from beam formulae. (2) Loading in bending results in a much smaller proportion of the volume of the specimens being raised to high stresses than is the case in tension, and this reduces the likelihood of a weak part of the specimen being loaded to failure.
TL;DR: A correlation was established between the decrease in their physical properties and the water uptake, and it should not be concluded that resin-modified GICs are not adequate for use in applications in direct contact with oral fluids.
TL;DR: In this paper, the strength and modulus properties of pultruded glass-fiber-reinforced vinyl ester matrix composite coupons were evaluated for bending perpendicular to the 0° orientations.
Abstract: Pultruded glass–fiber-reinforced vinyl ester matrix composite coupons were subjected to environmental aging in order to study their durability since such composites are of interest for infrastructure applications. Specimens were tested as-received and after aging in water or salt solutions at room temperature (25°C) or in water at 75°C for various times. The flexural properties (strength and modulus) were determined for bending perpendicular to the 0° orientations (0° being the pull direction) for all aging conditions. In addition, flexural properties in the 90° orientation and tensile properties in the 0° orientation were also measured for the as-received specimens and the specimens exposed to selected aging conditions. Both strengths and moduli were generally found to decrease with environmental aging. Comparing the size of the fracture mirrors on the broken ends of the fibers in aged and un-aged samples suggested that environmental aging decreased the in situ fiber strength. In addition, examination of the failure surfaces and comparisons between the strength of the 90° specimens suggested that degradation of the fiber/matrix interphase region also occurred during the aging process.
TL;DR: In this article, the authors synthesized polycrystalline Ti3SiC2 by reactive HIPing of Ti, SiC and C powders, which was obtained when treated at 1500°C, 40 MPa for 30 min The density was 99% of the theoretical value.
Abstract: The dense polycrystalline Ti3SiC2 has been synthesized by reactive HIPing of Ti, SiC and C powders The bulk material with the highest Ti3SiC2 content about 97 vol % was obtained when treated at 1500°C, 40 MPa for 30 min The density was 99% of the theoretical value The Ti3SiC2 grains had the columnar and plate-like shapes The grains were well boned to form a network structure Many stacking faults were observed along the (001) plane of Ti3SiC2 The Vickers hardness, Young's modulus, flexural strength and fracture toughness were 4 GPa, 283 GPa, 410 MPa and 112 MPa m1/2, respectively The Ti3SiC2 was stable up to 1100°C in air The electrical resistivity was 27 × 10−7 Ω·m at room temperature The resistivity increased linearly with the increasing temperature It may be attributed to a second order phase transition The Seebeck coefficient was from 4 to 20 μV/K in the temperature range 300–1200 K It seems that Ti3SiC2 is semi-metallic with hole carriers from this small positive value
TL;DR: In this paper, a combination of experiment and analysis was used to investigate the compressive response of polymer matrix fiber reinforced unidirectional composites (PMC's) and found that this failure mode is favorable for glass fiber composites, which is in agreement with test results and is able to show the influence of fiber mechanical properties, fiber volume fraction and fiber geometry on the splitting failure mode.
Abstract: The compressive response of polymer matrix fiber reinforced unidirectional composites (PMC's) is investigated via a combination of experiment and analysis The study accounts for the nonlinear constitutive response of the polymer matrix material and examines the effect of fiber geometric imperfections, fiber mechanical properties and fiber volume fraction on the measured compressive strength and compressive failure mechanismGlass and carbon fiber reinforced unidirectional composite specimens are manufactured in-house with fiber volume fractions ranging over 10∼60 percent Compression test results with these specimens show that carbon fiber composites have lower compressive strengths than glass fiber composites Glass fiber composites demonstrate a splitting failure mode for a range of low fiber volume fractions and a simultaneous splitting/kink banding failure mode for high fiber volume fractions Carbon fiber composites show kink banding throughout the range of fiber volume fractions examined Nonlinear material properties of the matrix, orthotropic material properties of the carbon fiber, initial geometric fiber imperfections and nonuniform fiber volume fraction are all included in an appropriate finite element analysis to explain some of the observed experimental results A new analytical model predictionof the splitting failure mode shows that this failure mode is favorable for glass fiber composites, which is in agreement with test results Furthermore, this modelis able to show the influence of fiber mechanical properties, fiber volume fraction and fiber geometry on the splitting failure mode
TL;DR: In this paper, the authors investigated the effects of corrosion products on bond strength of reinforced concrete (RC) structures and quantified the effect of deterioration of the bar surface on development length.
Abstract: Corrosion damage of reinforced concrete (RC) structures is a serious problem responsible for billions of dollars in repairs of highway structures every year. Corrosion of reinforcing steel in RC affects structural performance in two different ways: by loss of steel section and through deterioration of steel-concrete bond. This experiment investigated the effects of corrosion products on bond strength. To test the strength of corroded reinforcing bar anchorages and to quantify the effect of deterioration of the bar surface on development length, RC slabs were cast with the ends of the reinforcing bars anchored in the concrete for a known length. Bond breakers were used over the center portion of the bars to control the force demand input to the test anchorage. This measure also served to protect those regions from corrosion. The anchorage zones were corroded to various degrees by applying electrical voltage to the bar ends. Specimens were tested in flexure to assess strength and mode of failure. Results were summarized by means of simple parametric design expressions that relate bond strength to steel area loss.
TL;DR: In this paper, a total of nine beams have been tested to investigate the influence of fibre reinforcement on the mechanical behaviour of reinforced concrete beams in shear, and the results show that the first crack shear strength increases significantly as fibre content increases and the improvement in ultimate shear performance is also achieved.
TL;DR: In this article, the authors present the damage of concrete and its dependence on different strength grades of concrete under the simultaneous action of load and freeze-thaw cycles, and analyzes the inhibiting effect of air entrainment and steel fibers on damage.
TL;DR: The average tensile strength of polysilicon is 1.45±0.19 GPa (210 ±28 ksi) for the 27 specimens that could be broken with electrostatic gripping.
Abstract: Tensile specimens of polysilicon are deposited on a silicon wafer; one end remains affixed to the wafer and the other end has a relatively large paddle that can be gripped by an electrostatic probe. The overall length of the specimen is less than 2 mm, but the smooth tensile portion can be as small as 1.5×2μm in cross section and 50μm long. The specimen is pulled by a computer-controlled translation stage. Force is recorded with a 100-g load cell, whereas displacement is recorded with a capacitance-based transducer. Strain can be measured directly on wider specimens with laser-based interferometry from two small gold markers deposited on the smooth portion of the specimen. The strength of this linear and brittle material is measured with relative ease. Young's modulus measurement is more difficult; it can be determined from either the stress-strain curve, the record of force versus displacement or the comparison of the records of two specimens of different sizes. Specimens of different sizes—thicknesses of 1.5 or 3.5 μm, widths from 2 to 50 μm and lengths from 50 to 500 μm—were tested. The average tensile strength of this polysilicon is 1.45±0.19 GPa (210 ±28 ksi) for the 27 specimens that could be broken with electrostatic gripping. The average Young's modulus from force displacement records of 43 specimens is 162±14 GPa (23.5 ±2.0×103 ksi). This single value is misleading because the modulus values tend to increase with decreasing specimen width; that is not the case for the strength. The three methods for determining the modulus agree in general, although the scatter can be large.
TL;DR: In this article, a comprehensive study on the mechanical properties of expansive-cement concrete containing silica fume and polypropylene fibers was performed, and the results showed that the use of 5% silica and 10% fiber volume fraction results in optimum mixture design for repair applications from the standpoints of workability, bond, strength, length change and permeability.
TL;DR: In this paper, a hand operated hydraulic electrically heated press was used and the composites were cured at 100°C for 60min and post cured overnight in the oven at 80°C.
TL;DR: The compressive strength of modified and unmodified mortars depends on water-cement ratio and, to a lesser extent, on the cement content of the mortars as discussed by the authors.
TL;DR: A commercial acrylic bone cement was modified by the incorporation of different weight fractions of polycrystalline hydroxyapatite (HA) to find that up to 15 wt% HA could be added for increases in flexural modulus and fracture toughness.
Abstract: A commercial acrylic bone cement was modified by the incorporation of different weight fractions of polycrystalline hydroxyapatite (HA), and the modified formulation was investigated. The influence of the filler proportion on the flow characteristics and the mechanical behavior of the resultant composite was evaluated. The residual monomer present in the cured materials was measured by gas chromatography. The comparison of the residual monomer present in the cements with and without reinforcement demonstrated that the degree of polymerization was not affected by the addition of HA. Porosity morphology was analyzed by optical and scanning electron microscopy. Image examination revealed that the porosity and the pore size of the hardened cement increased with an increasing amount of particulate filler. Flexural, compressive, and fracture properties of the cement with varying amounts of HA reinforcement were measured. It was found that up to 15 wt% HA could be added for increases in flexural modulus and fracture toughness. HA acts as a rigid filler that enhances fracture resistance and flexural modulus. Our results show that the workability of the modified formulation limited the incorporation of the ceramic filler to a maximum value of 15 wt%.
TL;DR: In this paper, the effect of low-density metal filler, such as aluminum foam or honeycomb, on the bending collapse resistance of thin-walled prismatic columns was studied and closed-formed solutions for the bending-rotation characteristics were constructed in terms of the geometrical parameters and the filler strength.