Showing papers on "Flexural strength published in 1993"
TL;DR: In this paper, the properties of nylon 6-clay hybrids, such as molecular composites of nylon and silicate layers of montmorillonite and saponite, NCH's and NCHP's, respectively, have been synthesized.
Abstract: Various nylon 6-clay hybrids, such as molecular composites of nylon 6 and silicate layers of montmorillonite and saponite, NCH's and NCHP's, respectively, have been synthesized. To estimate the mechanical properties of these hybrids, tensile, flexural, impact, and heat distortion tests were carried out. NCH was found superior in strength and modulus and comparable in impact strength to nylon 6. The heat distortion temperature (HDT) of NCH (montmorillonite: 4.7 wt. %) was 152 °C, which was 87 °C higher than that of nylon 6. In NCHP, saponite had a smaller effect on the increase of these mechanical properties. The modulus and HDT of NCH and NCHP increased with an increase in the amount of clay minerals. It was found that these properties were well described by the contribution of the constrained region calculated from the storage and loss modulus at the glass transition temperature. According to the mixing law on elastic modulus, the following expression was obtained between the modulus E at 120 °C and the fraction of the constrained region C, En = Ecn = C, where the values of n and Ec (modulus of the constrained region) were 0.685 and 1.02 GPa, respectively.
2,492 citations
TL;DR: In this article, the fracture behavior of Al2O3 containing 5 vol% 0.15μm SiC particles was investigated using indentation techniques, and a significant increase in strength was achieved by the addition of SiC particle to the base Al 2O3.
Abstract: The fracture behavior of Al2O3 containing 5 vol% 0.15μm SiC particles was investigated using indentation techniques. A significant increase in strength was achieved by the addition of SiC particles to the base Al2O3. Specifically, the strength increased from 560 MPa for Al2O3 to 760 MPa for the composite samples (average values for unindented hotpressed bars tested in four-point bending). After annealing for 2 h at 1300°C, the average strength of the composite samples increased to about 1000 MPa. Toughness was estimated using indentation-strength data. While there was a slight increase in toughness, the increase was not sufficient to account for the increase in the unindented strength on SiC particle addition. It is suggested that the observed strengthening and apparent toughening were due to a machining-induced compressive surface stress.
323 citations
TL;DR: In this paper, the α to γ transformation in ODS martensitic steel has been successfully achieved by introducing the α-to-γ transformation in 13Cr-3W ODS ferritic steels.
288 citations
TL;DR: In this article, 6 reinforced concrete columns were tested under cyclic flexure and shear while simultaneously subjected to a constant axial load, and it was concluded that the stub enhanced the adjacent section's flexural strength by more than 20%.
Abstract: The critical sections of columns in a framed structure subjected to earthquake loads are invariably adjacent to the beam-column/slab joints or the footings. External restraint provided by the heavy elements alters the behavior of the adjacent sections and may not always prove conservative. To simulate this behavior, 6 reinforced concrete columns were tested under cyclic flexure and shear while simultaneously subjected to a constant axial load. The variables in the test program were the amount of lateral steel, steel configuration, and level of axial load. From a comparison of the results with those from similar prismatic specimens tested earlier, it was concluded that the stub enhanced the adjacent section's flexural strength by more than 20%. The details of the study are described, and these and other findings are presented and discussed.
209 citations
TL;DR: In this article, the authors present tests on square and circular stainless steel tubular beams and quantify the increase in bending strength resulting from cold-work during the fabrication process using the concept of affinity factors.
Abstract: The paper presents tests on square and circular stainless steel tubular beams. An important part of the test program was to quantify the increase in bending strength resulting from cold‐work during the fabrication process. Tension and compression tests on coupons cut from finished tubes were also included in the test program. Stress‐strain curves for shear were obtained using the coupon test results and the concept of affinity factors. A design method is proposed for stainless steel tubular beams. The method incorporates the increase in strength produced by the cold‐rolling process and is validated by comparing it to the test strengths. Design rules are proposed for the bending and shear strengths and for combined bending and shear. The design procedure proposed is an extension of that described in the ASCE Specification for the Design of Stainless Steel Structural Members. The paper describes a simple noniterative method for calculating deflections of stainless steel tubular beams. The method is suitable...
207 citations
TL;DR: In this paper, the authors argue that the working-stress method is better suited for FRP-reinforced concrete structures and that the predicted ultimate moment capacity represents a highly variable state only attainable at a high level of deformation and crack opening and that depends strictly on concrete ultimate strain.
Abstract: Flexural design for concrete members reinforced with fiber‐rein‐forced‐plastic (FRP) composites may be conducted using both the ultimate‐strength method and the working‐stress method. Since FRP reinforcement does not yield, there should be the explicit provision that failure be controlled by concrete crushing as opposed to reinforcement rupture. Deflection control may become as important as flexural strength for the design of FRP‐reinforced concrete structures. The paper contends that, at this stage of development, the working‐stress method is better suited to FRP‐reinforced concrete. The primary reasons are that the predicted ultimate moment capacity represents a highly variable state only attainable at a high level of deformation and crack opening and that it depends strictly on concrete ultimate strain. FRP reinforcement is better suited to pre‐ and posttensioned‐type concrete members; however, it cannot be ruled out that FRP should become the reinforcement of choice in special nonprestressed applicati...
195 citations
TL;DR: In this paper, the analysis of carbon fiber/epoxy composites with fiber volume fractions of 12, 17, 38 and 61 vol% were subjected to flexural deformation on a Dupont DMA 983 instrument.
Abstract: The application of dynamic mechanical analysis (DMA) for quantifying interfacial interactions in composites is briefly reviewed. Carbon fiber/epoxy composites with fiber volume fractions of 12, 17, 38 and 61 vol% were subjected to flexural deformation on a Dupont DMA 983 instrument. The dependencies of dynamic mechanical properties of the composites on experimental parameters such as oscillation mode, amplitude, frequency, and temperature were investigate. As opposed to the storage modulus, the loss modulus is found to be sensitive to all parameters. In a fixed multiple frequency mode, the loss modulus of the composites increases with oscillation amplitude and decreases with frequency and the number of tests. The information produced in the resonant mode is more reproducible. An additional damping at the interfaces, apart from those of the constituents, suggests a poor interface adhesion in these composites. A linear relationship between the excess damping at the interfaces and the fiber volume fraction shows a similar interface quality for these composites having different fiber volume fractions. The detection of interfacial properities was found to be more sensitive in the flexural deformation mode than in the torsional mode. At temperatures higher than the glass transition temperature of the matrix, the effective volume fraction of the matrix is reduced. Such a reduction can be interpreted from the mismatch of thermal expansion of the matrix and the fibers.
185 citations
Journal Article•
TL;DR: In this paper, the authors highlight aspects of structural design in which traditional procedures may need to be modified to account for the different characteristics of high-strength concrete, such as the stress-strain response of such concretes, as well as the capacity of columns and the minimum reinforcement and ductility in tension and flexural members.
Abstract: This paper highlights aspects of structural design in which traditional procedures may need to be modified to account for the different characteristics of high-strength concrete. The stress-strain response of such concretes is considered, as well as the capacity of columns and the minimum reinforcement and ductility in tension and flexural members. The shear strength of beams is also considered.
183 citations
TL;DR: In this article, an experimental research investigation of the fresh and hardened material properties of the fibrillated polypropylene fiber reinforced concrete is reported, where fiber lengths were 1/2 and 1/4 inch and volume fractions were 0.1, 0.3, and 0.5%.
Abstract: An experimental research investigation of the fresh and hardened material properties of the fibrillated polypropylene fiber reinforced concrete is reported. Fiber lengths were 1/2 and 1/4 inch, and volume fractions were 0.1, 0.3, and 0.5%. Fiber effects on concrete properties were assessed. Properties studied were slump, inverted slump cone time, air content, compressive and flexural behaviors, impact resistance and rapid chloride permeability, and volume percent of permeable voids. An innovative method of characterizing the flexural behavior of fibrillated polypropylene fiber concrete was proposed. The new method was dependent on the post-peak flexural resistance of concrete. For impact resistance and flexural behavior, it was concluded that 1/4-inch-long fibers were more effective than 1/2-inch-long fibers for volumes of 0.3% or less, while 1/2-inch-long fibers were more effective for 0.5% volume.
179 citations
TL;DR: In this paper, the use of short pitch-based carbon fibres (0.5% by weight of cement, 0.189 volume % (vol%) of concrete), together with a dispersant, chemical agents and silica fume, in concrete with fine and coarse aggregates, resulted in a flexural strength increase of 85%, flexural toughness increase of 205, a compressive strength increase, and a material price increase of 39%.
153 citations
TL;DR: In this paper, the effects of wound angle on the strength of E-glass fiber reinforced epoxy resin tubes were investigated under various combinations of internal pressure and axial tension or compression.
01 Jan 1993
TL;DR: In this article, a series of (0/90) 4s laminates with varying void content were fabricated and two quasistatic mechanical tests, short beam shear and three-point flexure, were used for evaluation and the results correlated to void volume fraction.
Abstract: A series of (0/90) 4s , laminates with varying void content were fabricated. Two quasistatic mechanical tests, short beam shear and three-point flexure, were used for evaluation and the results correlated to void volume fraction. Accurately quantifying the strength fall off proved difficult. Values of strength drop-of recorded were: 9.7% per percent void for interlaminar shear, 10.3% per percent void for flexural strength, and 5.3% per percent void for flexural modulus. In a manufacturing setting, a 2% void content increase will cause an approximate 20% decrease in both interlaminar shear strength and flexural strength, accompanied by an approximate 10% drop in flexural modulus
TL;DR: In this paper, Young's modulus, 73 GPa, Poisson's ratio, 0.25, tensile strength, −14 MPa, unconfined compressive strength, 262 MPa; fracture toughness, 1-3 MPa m½ cohesion, 66 MPa.
Abstract: Laboratory measurements of rock deformation in the brittle regime provide constraints on the response of rocks to stress. These values are essential parameters in tectonic models of near-surface deformation because they influence both the stress state and the conditions for predicting the types and occurrences of brittle structures such as joints and faults. However, additional parameters must be included before the laboratory values can be used to construct brittle strength envelopes for near-surface materials. The properties of basaltic rock masses provide a more precise estimate of the strengths of basaltic lava flows on the terrestrial planets than other, more widely used approaches (intact rock or frictional strength of a through-going surface). Rock mass strength is defined by three parameters including unconfined compressive strength of intact basalt and two others related to the degree of fracturing of the material. Experimental results for elevated temperature extend the applicability of these parameters to the near-surface environment of Venus. Representative values of strength parameters for intact basalt at ambient temperature (20°C)and negligible confining pressure are: Young's modulus, 73 GPa; Poisson's ratio, 0.25; tensile strength, −14 MPa; unconfined compressive strength, 262 MPa; fracture toughness, 1–3 MPa m½ cohesion, 66 MPa; and coefficient of friction, 0.6. At elevated temperature (∼450°C) and zero confining pressure, reference values for the strength of intact basalt are: Young's modulus, 57 GPa; Poisson's ratio, 0.25; unconfined compressive strength, 210 MPa; and fracture toughness, 2–2.8 MPa m½. Corresponding values for a basaltic rock mass that incorporate the weakening effects of scale (but not elevated temperature) are: Deformation modulus, 5–50 GPa; Poisson's ratio, 0.3; tensile strength, −0.2 to −2 MPa; uniaxial compressive strength, 12–63 MPa; cohesion, 0.5–6 MPa. Values of tensile and cohesive strength for the basaltic rock mass are approximately one to two orders of magnitude lower than corresponding values for intact basalt. Temperatures comparable to those at the Venus surface may slightly increase the deformation modulus but decrease the compressive strength of the rock mass. Brittle strength envelopes for the rock mass as a function of depth are typically stronger in both extension and compression than conventional envelopes that assume a simple frictional strength. These results indicate that the strengths of basaltic rocks on planetary surfaces and in the shallow subsurface are significantly different from strength values commonly used in tectonic modeling studies which assume properties of either intact rock samples or single planar shear surfaces.
TL;DR: In this paper, a connected-grain model developed earlier to study the modulus of elasticity as a power-law of density was extended to consider the dependence of the flexural strength of polycrystalline ceramics on porosity.
Abstract: A connected-grain model developed earlier to study the modulus of elasticity as a power-law of density was extended to study the dependence of the flexural strength of polycrystalline ceramics on porosity. Relations were derived for specific surface fracture energy, fracture toughness and flexural strength as power laws of (1 −p), wherep is porosity. Model validity was confirmed with data on α-alumina, UO2, Si3N4, and the YBa2Cu3O7−δ superconductor.
TL;DR: In this article, the effectiveness of steel fibers used alone as shear reinforcement in lightweight concrete beams was evaluated and a truss model was proposed to predict the ultimate shear strength of both lightweight and normal weight concrete beams.
Abstract: The paper assesses the effectiveness of steel fibers used alone as shear reinforcement in lightweight concrete beams. The tests were carried out on full-size I-beams with thin webs and varying tension steel and shear span. The fibers reduced the beam deformations substantially at all load levels, controlled dowel and shear cracking, reduced spalling in the cover, and helped to preserve the ductility and overall integrity of the structural member. The ultimate shear strength was increased by amounts of 60 to 200 %., but flexural failure was achieved only in beams with 1.55 % tension steel and in beams with 2.76 % tension steel tested at large shear spans. A truss model is proposed to predict the the ultimate shear strength, and it is shown that the model predicts satisfactorily the shear resistance of both lightweight and normal weight concrete beams.
TL;DR: In this paper, the texture of the fracture surfaces was quantified using image analysis techniques to compute a roughness parameter and fractal dimension, and a positive correlation between fracture surface roughness and fracture toughness was demonstrated.
Abstract: Fracture surfaces of cement and mortar specimens were characterized using a confocal microscope to create three-dimensional computer-based topographic maps. The texture of the fracture surfaces was quantified using image analysis techniques to compute a roughness parameter and fractal dimension. Total porosity, pore-size distribution, compressive strength, and fracture properties of the specimens were determined and compared with the roughness parameter. Fracture properties were determined by notched-beam tests and the results were analyzed both by using conventional linear elastic fracture mechanics as well as a compliance-based approach that incorporated R-curve type of behavior. A positive correlation between fracture surface roughness and fracture toughness was demonstrated.
TL;DR: It is concluded that zirconia can be used clinically because it retains a bending strength of over 700 MPa under any experimental conditions for over 3 years.
Abstract: Zirconia has received special attention, mainly because of its high strength and toughness. However, there is some controversy about the time-dependent deterioration of its mechanical properties. To examine the change in mechanical properties of zirconia ceramics in vivo and in vitro, tetragonal zirconia polycrystal pieces were introduced into the medullary cavity of the tibia in Japanese rabbits and animals were sacrificed after 2, 4 and 6 weeks and 6, 12, and 30 mo, respectively. Alumina ceramic and hydroxyapatite (HAP) pieces were used as controls to investigate the differences in biocompatibility. Zirconia showed a bending strength of over 1000 MPa initially, and little time-dependent change in strength was found in both in vivo environments. x-Ray analysis showed little change in the transformation rate, i.e., less than 5 mol % in vivo and in vitro over a period of 3 years. To estimate time-dependent changes in zirconia over a longer period, zirconia pieces were placed in 95°C saline solution for over 3 years and their mechanical properties examined at chosen intervals. No serious decrease of bending strength was found over the 3-year period under these conditions. It is concluded that zirconia can be used clinically because it retains a bending strength of over 700 MPa under any experimental conditions for over 3 years. © 1993 John Wiley & Sons, Inc.
TL;DR: In this article, the sintering behavior of hydroxyapatite (HAP) for various compositions and its resultant flexural strength was investigated. And the best results were obtained for HAP containing tricalcium phosphate (TCP), whereas for nearly pure HAP, the flexure strength decreases to the lowest results corresponding to HAP with CaO.
Abstract: This paper reports results on the sintering behaviour of hydroxyapatite (HAP) for various compositions and its resultant flexural strength. The HAP decomposition occurs at higher temperatures for sintered compacts than for powder and their OH stoichiometry depends on the porosity-closing temperature. The mechanical behaviour of HAP depends on its composition: the best results are obtained for HAP containing tricalcium phosphate (TCP), whereas for nearly pure HAP the flexural strength decreases to the lowest results corresponding to HAP containing CaO. It is suggested that the strengthening of HAP by TCP involves surface compression due to the β → α TCP transformation.
TL;DR: In this article, the effects of morphology on the fracture toughness of modified epoxy resins were investigated and the co-continuous structure and morphology of the PEI spherical domain dispersed in the epoxy matrix were obtained.
TL;DR: In this article, fabrication tests of thin-walled cladding tubes were carried out from a viewpoint of future industrial manufacturing, and the manufactured claddings within the specification limit exhibited a superior high temperature strength and sufficient Charpy impact properties.
TL;DR: In this paper, the residual mechanical properties and damage tolerance of carbon fiber-reinforced composites containing unmodified and rubber-modified epoxy resins were evaluated after drop-weight impact damage.
TL;DR: In this paper, the fracture parameters of limestone at loading rates ranging over four orders of magnitude in the static regime were determined using the size effect method using three sizes of three-point bend notched specimens were tested under crackmouth opening displacement control.
TL;DR: It appears that chemical etching can improve the retention of ceramic laminate veneers without significant loss of strength.
Abstract: This project studied the effect of altering surface topography by chemical etching on the strength of a feldspathic porcelain and castable glass ceramic. Fifty specimens of each ceramic material were subjected to five different etch times (in groups of 10). A silane coupling agent and composite resin cement were applied. Specimens were then subjected to a three-point flexural strength test. Representative specimens were examined under scanning electron microscope to elucidate more information on the effect and the depth of etch. There was no significant difference in the mean flexural strengths between the etched and nonetched groups and no significant difference between the different etching times for either material. Photomicrographs revealed dissimilar etch depths and selective dissolution of the phases. It appears that chemical etching can improve the retention of ceramic laminate veneers without significant loss of strength.
TL;DR: In this paper, a nonlinear analysis model was developed for the prediction of the complete moment versus deformation response of concrete beams containing bonded prestressing tendons, unbonded tendons (metallic or otherwise), and nonprestressed conventional reinforcing bars.
Abstract: The present study describes a nonlinear analysis model developed for the prediction of the complete moment versus deformation response of concrete beams containing bonded prestressing tendons, unbonded prestressing tendons (metallic or otherwise), and nonprestressed conventional reinforcing bars. The model uses an extensive iterative procedure for calculating the stress in unbonded tendons, \If\dp\ds\N, by performing a nonlinear analysis at various locations along the beam. The analysis is performed several times during any loading stage until the stress \If\dp\ds\N is calculated within a reasonable tolerance. Two important issues not addressed in previous investigations are considered in modeling the curvature distribution, namely: (1) The effects of member span-to-depth ratio and the level of shear force on the flexural deformations; and (2) the change in eccentricity under load (i.e., second-order effects) for beams containing external tendons. Experimental verification was carried out using beam tests taken from 15 different investigations that occurred between 1962 and 1990. Excellent correlation was observed between predicted results and experimental observations.
TL;DR: The results suggest that crack-bridging is the most likely mechanism for the strengthening of ceramic dental restorations through surface treatments and cement coatings of the fracture-initiating surface.
TL;DR: In this article, the use of external prestressing tendons as a means of strengthening or upgrading concrete flexural members was experimentally investigated 16 beam specimens were first subjected to cyclic fatigue loading at a constant load range to induce fatigue deformations Then, they were externally prestressed and subjected to monotonically increasing load to failure.
Abstract: The use of external prestressing tendons as a means of strengthening or upgrading concrete flexural members was experimentally investigated 16 beam specimens were first subjected to cyclic fatigue loading at a constant load range to induce fatigue deformations Then, they were externally prestressed and subjected to monotonically increasing load to failure As a result of external prestressing, the nominal strengths of the beams were increased by up to 146 percent and the induced fatigue deflections were reduced by up to 75 percent External tendons using a draped profile were relatively more effective in increasing the flexural strength than tendons with a straight profile The stress ranges and mean stress levels in the internal tension reinforcement decreased considerably, which imply a significant improvement in the fatigue life of the strengthened beams
TL;DR: The coefficient of thermal expansion (α), Young's and rigid moduli (E and G), Poisson's ratio (v), compressive yield and fracture strengths (σ y and σ f ), fracture toughness (K), Vickers hardness (H v ) and cleavage fracture mode were examined along two-, three-and five-fold symmetry axes for an Al 70 Pd 20 Mn 10 single-quasicrystal prepared by the Czochralski method as discussed by the authors.
Abstract: The coefficient of thermal expansion (α), Young's and rigid moduli (E and G), Poisson's ratio (v), compressive yield and fracture strengths (σ y and σ f ), fracture toughness (K), Vickers hardness (H v ) and cleavage fracture mode were examined along two-, three- and five-fold symmetry axes for an Al 70 Pd 20 Mn 10 single-quasicrystal prepared by the Czochralski method. In the temperature range below 600 K, α is 1.3×10 -5 K -1 which is about 50% as high as that for conventional Al-based alloys
TL;DR: In this paper, a semi-empirical equation is proposed to estimate the effective moment of inertia of simply supported high-strength fiber reinforced concrete beams, and the estimated deflections using this equation agree well with the experimental values.
Abstract: Eight high-strength concrete beams with different fiber contents and shear span-depth ratios were tested to study the influence of fiber addition on ultimate load, crack propagation, flexural rigidity, and ductility. The addition of steel fibers enhanced the strength and increased the ductility and flexural stiffness of the tested beams. A semi-empirical equation is proposed to estimate the effective moment of inertia of simply supported high-strength fiber reinforced concrete beams. The estimated deflections using this equation agree well with the experimental values. At ultimate conditions, the length of the plastic hinge developed was found to be proportional to the fiber content.
TL;DR: In this article, the influence of maleicanhydride-modified polypropylene (m-PP) on monotonic mechanical properties of continuous-glass-fibre-reinforced poly-propylene composites was investigated.
DOI•
01 Jan 1993
TL;DR: In this article, a preliminary study was designed to reveal those aspects of the 3D printing process which must be modified for use with fine ceramic powders, and the basic elements of the modified process are to spread submicron alumina powder and print Jatex binder.
Abstract: The Three Dimensional Printing (3DP) Process hasbe~nadapted for processing of fine ceramic powders to •• prepare structllraLceramic components. Our preliminary study was designed to reveal those aspects ofthe.3DPprocesswhichmust be modified for use with fine ceramic powders. The basic elements of the modified process are to spread submicron alumina powder and printJatex binder. Several methods were used to spread thin layers of submicron powders. Gre.enparts are isostaticaUypressed followed by thermal decomposition prior to sintering to remove the polymer. The fired alumina components are greater than 99.2% dense and have·average flexural strength of324 MPa. This is lower than the best conventionally prepared alumina, but we believe that the strength results will improve as we learn more about the relationship between strength limiting flaws and the 3DP build process.