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Showing papers on "Flexural strength published in 2004"


Journal ArticleDOI
TL;DR: In this paper, Zirconium diboride and ZrB 2 ceramics containing 10, 20, and 30 vol% SiC particulates were prepared from commercially available powders by hot pressing.
Abstract: Zirconium diboride (ZrB 2 ) and ZrB 2 ceramics containing 10, 20, and 30 vol% SiC particulates were prepared from commercially available powders by hot pressing. Four-point bend strength, fracture toughness, elastic modulus, and hardness were measured. Modulus and hardness did not vary significantly with SiC content. In contrast, strength and toughness increased as SiC content increased. Strength increased from 565 MPa for ZrB 2 to >1000 MPa for samples containing 20 or 30 vol% SiC. The increase in strength was attributed to a decrease in grain size and the presence of WC.

731 citations


Journal ArticleDOI
TL;DR: In this paper, the authors investigated the mechanical properties of high-strength steel fiber-reinforced concrete, including compressive and splitting tensile strength, modulus of rupture, and toughness index.

684 citations


Journal ArticleDOI
TL;DR: In this article, the effect of fiber alignment and alkalization on the mechanical properties of the composites were measured to observe the effects of fibre alignment and alkylation on fiber properties.

642 citations


Journal ArticleDOI
TL;DR: Double‐network (DN) hydrogels with high mechanical strength have been synthesized using the natural polymers bacterial cellulose and gelatin, and an enhancement in the mechanical strength was also observed for the combination of BC with polysaccharides, such as sodium alginate, gellan gum, and ι‐carrageenan.
Abstract: Double-network (DN) hydrogels with high mechanical strength have been synthesized using the natural polymers bacterial cellulose (BC) and gelatin. As-prepared BC contains 90 % water that can easily be squeezed out, with no more recovery in its swelling property. Gelatin gel is brittle and is easily broken into fragments under a modest compression. In contrast, the fracture strength and elastic modulus of a BC–gelatin DN gel under compressive stress are on the order of megapascals, which are several orders of magnitude higher than those of gelatin gel, and almost equivalent to those of articular cartilage. A similar enhancement in the mechanical strength was also observed for the combination of BC with polysaccharides, such as sodium alginate, gellan gum, and ι-carrageenan.

619 citations


Journal ArticleDOI
TL;DR: In this article, the authors evaluated how the degree of fibrillation of pulp fiber affects the mechanical properties of the final composites, using kraft pulp subjected to various levels of refining and high pressure homogenization treatments was used as raw material with different phenolic resin contents.
Abstract: Fibrillated kraft pulp impregnated with phenolic resin was compressed under an extremely high pressure of 100 MPa to produce high strength cellulose nanocomposites To evaluate how the degree of fibrillation of pulp fiber affects the mechanical properties of the final composites, kraft pulp subjected to various levels of refining and high pressure homogenization treatments was used as raw material with different phenolic resin contents It was found that fibrillation solely of the surface of the fibers is not effective in improving composite strength, though there is a distinct point in the fibrillation stage at which an abrupt increase in the mechanical properties of composites occurs In the range between 16 and 30 passes through refiner treatments, pulp fibers underwent a degree of fibrillation that resulted in a stepwise increment of mechanical properties, most strikingly in bending strength This increase was attributed to the complete fibrillation of the bulk of the fibers For additional high pressure homogenization-treated pulps, composite strength increased linearly against water retention values, which characterize the cellulose’s exposed surface area, and reached maximum value at 14 passes through the homogenizer

585 citations


Journal ArticleDOI
TL;DR: In this article, the authors fabricated polycrystalline bulk samples of Ti 3 Al 1.1 C 1.8 by reactively hot isostatically pressing a mixture of titanium, graphite, and Al 4 C 3 powders at a pressure of 70 MPa and temperature of 1400°C for 16 h.
Abstract: Polycrystalline bulk samples of Ti 3 Al 1.1 C 1.8 have been fabricated by reactively hot isostatically pressing a mixture of titanium, graphite, and Al 4 C 3 powders at a pressure of 70 MPa and temperature of 1400°C for 16 h. The hot isostatically pressed samples are predominantly single phase (containing ∼4 vol% Al 2 O 3 ), fully dense, and have a grain size of ∼25 μm. This carbide is similar to Ti 3 SiC 2 , with which it is isostructural, and has an unusual combination of properties. It is relatively soft (Vickers hardness of ∼3.5 GPa) and elastically stiff (Young's modulus of 297 GPa and shear modulus of 124 GPa); yet, it is lightweight (density of 4.2 g/cm 3 ) and easily machinable. The room-temperature electrical resistivity is 0.35 ± 0.03 μΩ.m and decreases linearly as the temperature decreases. The temperature coefficient of resistivity is 0.0031 K -1 . The coefficient of thermal expansion, in the temperature range of 25°-1200°C, is 9.0 (± 0.2) x 10 -6 K -1 . The room-temperature compressive and flexural strengths are 560 ± 20 and 375 ± 15 MPa, respectively. In contrast to flexure, where the failure is brittle, the failure in compression is noncatastrophic and is accompanied by some plasticity. The origin of that plasticity is believed to be the formation of a shear band that is oriented at an angle of ∼45° to the applied load. Ti 3 Al 1.1 C 1.8 also is a highly damage-tolerant material; a 10-kg-load Vickers indentation made in a bar 1.5 mm thick reduces the postindentation flexural strength by ∼7%. This material also is quite resistant to thermal shock. At temperatures of >1000°C, the deformation in compression is accompanied by significant plasticity and very respectable ultimate compressive stresses (200 MPa at 1200°C).

583 citations


Journal ArticleDOI
Rafat Siddique1
TL;DR: In this paper, the results of an experimental investigation dealing with concrete incorporating high volumes of Class F fly ash Portland cement was replaced with three percentages (40, 45, and 50%) of Class-F fly ash Tests were performed for fresh concrete properties: slump, air content, unit weight, and temperature Compressive, splitting tensile, and flexural strengths, modulus of elasticity, and abrasion resistance were determined up to 365 days of testing.

478 citations


Journal ArticleDOI
TL;DR: A transparent and slight yellow chitosan (CS)/hydroxyapatite (HA) nanocomposite with high performed, potential application as internal fixation of bone fracture was prepared by a novel and simple in situ hybridization, which solves the problem of the nano-sized particle aggregation in polymer matrix.

436 citations


Journal ArticleDOI
TL;DR: In this paper, a high density polyethylene (HDPE) reinforced with continuous henequen fibres (Agave fourcroydes) was studied and it was found that the resulting strength and stiffness depended on the amount of silane deposited on the fibre.
Abstract: The mechanical behaviour high density polyethylene (HDPE) reinforced with continuous henequen fibres (Agave fourcroydes) was studied. Fibre-matrix adhesion was promoted by fibre surface modifications using an alkaline treatment and a matrix preimpregnation together with a silane coupling agent. The use of the silane coupling agent to promote a chemical interaction, improved the degree of fibre-matrix adhesion. However, it was found that the resulting strength and stiffness of the composite depended on the amount of silane deposited on the fibre. A maximum value for the tensile strength was obtained for a certain silane concentration but when using higher concentrations, the tensile strength did not increase. Using the silane concentration that resulted in higher tensile strength values, the flexural and shear properties were also studied. The elastic modulus of the composite did not improve with the fibre surface modification. The elastic modulus, in the longitudinal fibre direction obtained from the tensile and flexural measurements was compared with values calculated using the rule of mixtures. It was observed that the increase in stiffness from the use of henequen fibres was approximately 80% of the calculated values. The increase in the mechanical properties ranged between 3 and 43%, for the longitudinal tensile and flexural properties, whereas in the transverse direction to the fibre, the increase was greater than 50% with respect to the properties of the composite made with untreated fibre composite. In the case of the shear strength, the increase was of the order of 50%. From the failure surfaces it was observed that with increasing fibre-matrix interaction the failure mode changed from interfacial failure to matrix failure.

416 citations


Journal ArticleDOI
TL;DR: The aim of this study was to investigate the flexural properties of different types of FRC posts and compare those values with a novel FRC material for dental applications, and found commercial prefabricated FRC Posts showed lower Flexural properties than an individually polymerised FRCMaterial.

400 citations


Journal ArticleDOI
TL;DR: In this paper, the second part of a two-part study, the authors report on the mechanical behavior of Ti3SiC2 in simple compression and flexure tests, and compared the results with those of coarse-grained (100-200 μm) Ti3 SiC2.
Abstract: In this article, the second part of a two-part study, we report on the mechanical behavior of Ti3SiC2. In particular, we have evaluated the mechanical response of fine-grained (3–5 μm) Ti3SiC2 in simple compression and flexure tests, and we have compared the results with those of coarse-grained (100–200 μm) Ti3SiC2. These tests have been conducted in the 25°–1300°C temperature range. At ambient temperature, the fine- and coarse-grained microstructures exhibit excellent damage-tolerant properties. In both cases, failure is brittle up to ∼1200°C. At 1300°C, both microstructures exhibit plastic deformation (>20%) in flexure and compression. The fine-grained material exhibits higher strength compared with the coarse-grained material at all temperatures. Although the coarse-grained material is not susceptible to thermal shock (up to 1400°C), the fine-grained material thermally shocks gradually between 750° and 1000°C. The results presented herein provide evidence for two important aspects of the mechanical behavior of Ti3SiC2: (i) inelastic deformation entails basal slip and damage formation in the form of voids, grain-boundary cracks, kinking, and delamination of individual grains, and (ii) the initiation of damage does not result in catastrophic failure, because Ti3SiC2 can confine the spatial extent of the damage.

Journal ArticleDOI
TL;DR: One hundred eighty different mortars made with a natural hydraulic lime (NHL) and different kinds of aggregates were prepared to be used in restoration works and the factors affecting the mechanical behavior have been studied at long-term test.

Journal ArticleDOI
TL;DR: In this article, the authors investigated compressive strength, splitting tensile strength, and bending strength of high-strength concrete (HSC) after being heated to temperatures of 200, 400, 600, 800, and 1000 °C.

Journal ArticleDOI
Lin-Hai Han1
TL;DR: In this article, a form of unified theory, where a confinement factor was introduced to describe the composite action between the steel tube and filled concrete, is used in the analysis of concrete-filled hollow structural section (HSS) beams.

Journal ArticleDOI
TL;DR: In this article, the authors present the results of experimental tests carried out on rectangular simply supported beams made of hooked steel fibre reinforced concrete with and without stirrups, subjected to two-point symmetrically placed vertical loads.
Abstract: This paper presents the results of experimental tests carried out on rectangular simply supported beams made of hooked steel fibre reinforced concrete with and without stirrups, subjected to two-point symmetrically placed vertical loads. The tests, carried out with controlled displacements, allow one to record complete load–deflection curves by means of which it is possible to deduce information on dissipative capacity and ductile behaviour up to failure. Depending on the amount of transverse reinforcement, volume fraction of fibres added in the mix and shear span, the collapse mechanism is due to predominant shear or flexure, thus showing the influence of the aforementioned structural parameters on the load carrying capacity and the post-peak behaviour of the beam. In particular, the results show that the inclusion of fibres in adequate percentage can change the brittle mode of failure characterizing shear collapse into a ductile flexural mechanism, confirming the possibility of achieving analogous performance by using reinforcing fibres instead of increasing the amount of transverse reinforcement. The ultimate values of the shear stresses recorded experimentally are compared with the corresponding values deduced by semiempirical expressions available in the literature and the correlation is satisfactory.

Journal ArticleDOI
TL;DR: In this article, a petrophysical durability estimator (PDE) is proposed, which is the ratio between parameters and estimators, which are based on pore structure and the strength of the material.

Journal ArticleDOI
TL;DR: In this paper, the authors used finite element models to predict material response in internally heated nozzle tests, and the results of the modeling suggest that HfB2 should survive the high thermal stresses generated during the nozzle test primarily because of its superior thermal conductivity.
Abstract: The thermal conductivity, thermal expansion, Young's Modulus, flexural strength, and brittle-plastic deformation transition temperature were determined for HfB2, HfC0.98, HfC0.67, and HfN0.92 ceramics. The mechanical behavior of αHf(N) solid solutions was also studied. The thermal conductivity of modified HfB2 exceeded that of the other materials by a factor of 5 at room temperature and by a factor of 2.5 at 820°C. The transition temperature of HfC exhibited a strong stoichiometry dependence, decreasing from 2200°C for HfC0.98 to 1100°C for HfC0.67 ceramics. The transition temperature of HfB2 was 1100°C. Pure HfB2 was found to have a strength of 340 MPa in 4 point bending, that was constant from room temperature to 1600°C, while a HfB2 + 10% HfCx had a higher room temperature bend strength of 440 MPa, but that dropped to 200 MPa at 1600°C. The data generated by this effort was inputted into finite element models to predict material response in internally heated nozzle tests. The theoretical model required accurate material properties, realistic thermal boundary conditions, transient heat transfer analysis, and a good understanding of the displacement constraints. The results of the modeling suggest that HfB2 should survive the high thermal stresses generated during the nozzle test primarily because of its superior thermal conductivity. The comparison the theoretical failure calculations to the observed response in actual test conditions show quite good agreement implying that the behavior of the design is well understood.

Journal ArticleDOI
TL;DR: The study, which was conducted with sample configurations that reproduce the clinical situation of crowns and fixed partial dentures, indicates that the material which lies on the bottom surface dictates the strength, reliability and fracture mode of the specimens.

Journal ArticleDOI
TL;DR: The glassy alloy rods exhibit ultra-high fracture strength of 5185 MPa, high Young's modulus of 268 GPa and high specific strength of 6.5B31.

Journal ArticleDOI
TL;DR: In this paper, two types of carbon composite were developed and characterized in terms of bulk and contact resistance, flexural strength, density, gas tightness, water absorption, and depth deviation of the flow channel.

Journal ArticleDOI
TL;DR: Using plant microfiber bundles with a nanometer unit web-like network, a moulded product with a bending strength of 250 MPa was obtained without the use of binders.
Abstract: Using plant microfiber bundles with a nanometer unit web-like network, a moulded product with a bending strength of 250 MPa was obtained without the use of binders. High interactive forces seem to be developed between pulp fibers owing to their nanometer unit web-like network. In other words, the area of possible contact points per fiber are increased, so that more hydrogen bonds might be formed or van der Waals forces increased. When 2% oxidized tapioca starch, by weight, was added, the yield strain doubled and the bending strength reached 310 MPa. The starch mixed moulded product had a similar stress strain curve to that for magnesium alloy, and three to four times higher Young's modulus and bending strength values than polycarbonate and GFRP (chopped). The mouldings have a combination of environmentally friendly and high strength properties.

Journal ArticleDOI
TL;DR: A detailed review of the strain rate dependence of some mechanical properties of polymer composite materials is given in this article, where an attempt is made to present and summarize much of the published work relating to the effect of strain rate studies done in the past on the tensile, shear, compressive, and flexural properties of composite materials.
Abstract: This paper is a detailed review of the strain rate dependence of some mechanical properties of polymer composite materials. An attempt is made to present and summarize much of the published work relating to the effect of strain rate studies done in the past on the tensile, shear, compressive, and flexural properties of composite materials to better understand the strain rate effects on these mechanical properties of fiber-reinforced polymer composite materials. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 296–301, 2004

Journal ArticleDOI
TL;DR: In this article, the authors present test results at failure of 16 reinforced concrete (RC) continuous beams with different arrangements of internal steel bars and external carbon fibre reinforced polymer (CFRP) laminates.
Abstract: This paper presents test results at failure of 16 reinforced concrete (RC) continuous beams with different arrangements of internal steel bars and external carbon fibre reinforced polymer (CFRP) laminates. All test specimens had the same geometrical dimensions and were classified into three groups according to the amount of internal steel reinforcement. Each group included one unstrengthened control beam designed to fail in flexure. Different parameters including the length, thickness, position and form of the CFRP laminates were investigated. Three failure modes of beams with external CFRP laminates were observed, namely laminate rupture, laminate separation and peeling failure of the concrete cover attached to the laminate. The ductility of all strengthened beams was reduced compared with that of the respective unstrengthened control beam. Simplified methods for estimating the flexural load capacity and the interface shear stresses between the adhesive and concrete at failure of beams tested are presented. Comparisons between results from experiments and those obtained from the simplified methods show that most beams were close to achieving their full flexural capacity and the longitudinal elastic shear stresses at the adhesive/concrete interface calculated at beam failure conformed to the limiting value recommended in the Concrete Society Technical Report 55.

Journal ArticleDOI
TL;DR: In this article, a resin transfer molding (RTM) process was used to produce fiber mat with a moisture content of 4.3% at 50% relative humidity, and the fiber mat was dry in the mold under vacuum to reach a moisture level of around 1.2%.

Journal ArticleDOI
TL;DR: In this paper, the effect of moisture content on the mechanical properties of composite foams was investigated and it was shown that the flexural strength and flexural modulus of elasticity appeared to be markedly improved with addition of 5-10% by weight of the fibers.

Journal ArticleDOI
TL;DR: In this article, a method to fabricate short bamboo fiber reinforced "green" composites (BFGC) and evaluate their mechanical properties was described. And the composites were prepared by hot-pressing a mixture of starch-based resin and short bamboo fibers.
Abstract: This paper describes a method to fabricate short bamboo fiber reinforced “green” composites (BFGC) and evaluate their mechanical properties. The composites were prepared by hot-pressing a mixture of starch-based resin and short bamboo fibers. Their tensile strength and flexural strength were characterized. The effects of fiber content and fiber length on the mechanical properties of BFGC were investigated in detail. Both tensile and flexural strengths of BFGC were strongly affected by fiber aspect ratio and fiber content. Bamboo fibers with a small aspect ratio of 20 do not act as reinforcement but as filler.

Proceedings ArticleDOI
N. E. Dowling1
01 Apr 2004
TL;DR: In this article, the authors compared various approaches to estimating mean stress effects on stress-life and strain-life behavior with test data for engineering metals and concluded that the Smith, Watson, and Topper (SWT) method is a reasonable choice that avoids the above difficulties.
Abstract: Various approaches to estimating mean stress effects on stress-life and strain-life behavior are compared with test data for engineering metals. The modified Goodman equation with the ultimate tensile strength is found to be highly inaccurate, and the similar expression of Morrow using the true fracture strength is a considerable improvement. However, the Morrow expression employing the fatigue strength coefficient ′ σ f may be grossly non-conservative for metals other than steels. The Smith, Watson, and Topper (SWT) method is a reasonable choice that avoids the above difficulties. Another option is the Walker approach, with an adjustable exponent γ that may be fitted to test data, allowing superior accuracy. Handling mean stress effects for strainlife curves is also discussed, including the issue of mathematical consistency with mean stress equations expressed in terms of stress. A new and mathematically consistent method for incorporating the Walker approach into strainlife curves is developed. With γ = 0.5, this result gives a new strain-based interpretation of the SWT method.

Journal ArticleDOI
01 Mar 2004-Polymer
TL;DR: Electrospun Nylon 6 nanofibers, in the form of nonwoven fabrics, were impregnated with the dental methacrylate of BIS-GMA/TEGDMA (50/50, mass ratio), to prepare the restorative composite resins, suggesting that the presence of nan ofibers deflected the crack.

Journal ArticleDOI
01 Jun 2004-Wear
TL;DR: The sliding wear performance of epoxy composites filled with nano-sized Al2O3 particles was studied in this paper, where the nanoparticles were pretreated by either silane coupling agent or graft polymerization to enhance the interfacial interaction between the fillers and the matrix polymer.

Journal ArticleDOI
TL;DR: In this article, an experimental work and analytical modeling for concrete-filled steel tubes (CFSTs) subjected to concentric axial compression and combined axial compressive and lateral cyclic loading is presented.
Abstract: This paper presents an experimental work and analytical modeling for concrete-filled steel tubes (CFSTs) subjected to concentric axial compression and combined axial compression and lateral cyclic loading. The objective of the study is to evaluate the strength and ductility of CFST short columns and beam-column members under different bond and end loading conditions. Both bonded and unbonded specimens were tested, including application of the axial load to the composite steel-concrete section and to the concrete core only. Research findings indicate that the bond and end loading conditions did not affect the flexural strength of beam-column members significantly. On the other hand, the axial strengths of the unbonded short columns were slightly increased, compared to those of the bonded ones, while the stiffness of the unbonded specimens was slightly reduced. Test results were compared with the available design specifications, which were found to be conservative. The paper also presents an analytical model capable of predicting the flexural and axial load strength of CFST members. Experimental results were found to be in good agreement with the predicted values.