Showing papers on "Flexural strength published in 1996"
TL;DR: In this article, several samples of poly(lactic acid) with different molecular weights and tacticity have been prepared, and some PLLA injection moulded specimens have been annealed to promote their crystallization.
Abstract: Several samples of poly(lactic acid) with different molecular weights and tacticity have been prepared, and some PLLA injection moulded specimens have been annealed to promote their crystallization. From the characterization data, poly(L-lactide) showed more interesting mechanical properties than poly(D, L-lactide), and its behavior significantly improves with crystallization. In fact, annealed specimens possess higher values of tensional and flexural modulus of elasticity, Izod impact strength, and heat resistance. The plateau region of flexural strength as a function of molecular weights appears around Mv = 35,000 for PDLLA and amorphous PLLA and at higher molecular weight, around Mv = 55,000, for crystalline PLLA. The study of temperature effect shows that at 56°C only crystalline PLLA still exhibits useful mechanical properties. © 1996 John Wiley & Sons, Inc.
541 citations
TL;DR: In this paper, a new class of phenolic-like thermosetting resins was developed that is based on the ring opening polymerization of a benzoxazine precursor, which is copolymerized with an epoxy resin in order to modify their performance.
425 citations
TL;DR: In this article, the effect of the replacement of mineral coarse aggregate by rubber tire aggregate is investigated, and the authors found that the incorporation of these rubber tire chips in concrete exhibited a reduction in compressive and flexural strengths, the reduction in compression strength was approximately twice the reduction of flexural strength.
Abstract: The effect of the replacement of mineral coarse aggregate by rubber tire aggregate is investigated in this paper. Four different volume contents of rubber tire chips were used: 25, 50, 75 and 100%. The incorporation of these rubber tire chips in concrete exhibited a reduction in compressive and flexural strengths, the reduction in compressive strength was approximately twice the reduction of the flexural strength. The specimens which contained rubber tire aggregate exhibited ductile failure and underwent significant displacement before fracture. The toughness of flexural specimens was evaluated for plain and rubber tire concrete specimens. The test revealed that high toughness was displayed by specimens containing rubber tire chips as compared to control specimens.
376 citations
TL;DR: In this paper, a comprehensive set of experimental data were generated regarding the effects of collated fibrillated polypropylene fibers at relatively low volume fractions (below 0.3%) on the compressive, flexural and impact properties of concrete materials with different binder compositions.
Abstract: A comprehensive set of experimental data were generated regarding the effects of collated fibrillated polypropylene fibers at relatively low volume fractions (below 0.3%) on the compressive, flexural and impact properties of concrete materials with different binder compositions. Statistical analysis of results produced reliable conclusions on the mechanical properties of polypropylene fiber reinforced, concrete and also on the interaction of fibers and pozzolanic admixtures in deciding these properties. Polypropylene fibers were observed to have no statistically significant effects on compressive or flexural strength of concrete, while flexural toughness and impact resistance showed an increase in the presence of polypropylene fibers. Positive interactions were also detected between fibers and pozzolans.
350 citations
TL;DR: In this article, a degree of hydration-based description for the compressive strength, Young's modulus, uniaxial tensile strength, splitting tensile and flexural tensile strengths, Poisson's ratio and peak strain are all worked out based on an extensive experimental program on hardening concrete elements.
Abstract: For the evaluation of the risk of thermal cracking in hardening massive concrete elements, knowledge of the development of strength and deformability of early-age concrete is extremely important. Based on an extensive experimental research program on hardening concrete elements, a degree of hydration-based description for the compressive strength, Young's modulus, the uniaxial tensile strength, the splitting tensile strength, the flexural tensile strength, Poisson's ratio and the peak strain are all worked out. An extension of the formulation of Sargin for the stress-strain relation for short-term compressive loading leads to a degree of hydration-based stress-strain relation for hardening concrete. Good agreement with experimental results is reported.
284 citations
TL;DR: In this article, the authors conducted an experimental and theoretical comparison between flexural behaviors of concrete beams reinforced with fiber reinforced plastic (FRP) reinforcing bars and identical conventionally reinforced ones.
Abstract: The authors conducted an experimental and theoretical comparison between flexural behaviors of concrete beams reinforced with fiber reinforced plastic (FRP) reinforcing bars and identical conventionally reinforced ones. Comparisons were made in relation to cracking behavior, load-carrying capacities and modes of failure, load-deflection response, flexural rigidity, and strain distribution. The results revealed that perfect bond exists between FRP reinforcing bars and the surrounding concrete. Also, American Concrete Institute (ACI) Code formulas for predicting deflection response, cracking-ultimate moments, and cracked-effective moments of inertia can easily be adapted for modeling the flexural behavior of concrete beams reinforced with FRP reinforcing bars if appropriate modifications are made.
283 citations
TL;DR: Three new ceramic crown core materials were tested to compare their biaxial flexural strength and indentation fracture toughness and it was revealed that both ceramics had significantly higher fracture toughness.
Abstract: The traditional gold and porcelain fused to metal crowns have been challenged by the esthetic all-ceramic crown materials. Only previous experience with poor mechanical properties, lack of standardized tooth preparation, and processing challenges have prevented universal acceptance of all-ceramic crowns. However, stronger and tougher ceramics and unique processing methods for ceramics have been developed in the past 20 years. In this study, three new ceramic crown core materials were tested to compare their biaxial flexural strength and indentation fracture toughness. Ten specimens of Empress, In-Ceram, and Procera AllCeram ceramics were prepared according to their manufacturers' recommendations. The results revealed significant differences in flexural strength for the three materials (p < or = 0.05). The average flexural strengths of AllCeram, In Ceram, and Empress ceramics were 687 MPa, 352 MPa, and 134 MPa respectively. There was no statistically significant difference between the fracture toughness of Procera (4.48 MPa x m1/2) and In-Ceram ceramics (4.49 MPa x m1/2); however, both ceramics had significantly higher fracture toughness (p < 0.005) than Empress ceramic (1.74 MPa x m1/2).
226 citations
TL;DR: In this paper, the mechanical properties of sisal fiber composites of several thermoset resin matrices, [polyester, epoxy, phenol-formaldehyde] and a thermoplastic matrix [low density polyethylene (LDPE)] were evaluated with respect to fibre length and fibre loading.
224 citations
TL;DR: It was found that, at lower light intensity, longer curing was required to provide comparable mechanical properties, and an accumulated irradiation energy obtained through a product of the light intensity and curing time may serve as a guideline to produce samples exhibiting equivalent fracture toughness as well as flexural strengths.
210 citations
TL;DR: In this paper, the microstructures, secondary phases, and grain boundaries were characterized using a range of analytical techniques including TEM, SEM, AES, and XRD, and the fracture toughness was derived either from bend tests of beam-shaped samples with a controlled surface flaw or from standard disk-shaped compact-tension specimens precracked in cyclic fatigue.
Abstract: “In situ toughened” silicon carbides, containing Al, B, and C additives, were prepared by hot pressing. Densification, phase transformations, and microstructural development were described. The microstructures, secondary phases, and grain boundaries were characterized using a range of analytical techniques including TEM, SEM, AES, and XRD. The modulus of rupture was determined from fourpoint bend tests, while the fracture toughness was derived either from bend tests of beam-shaped samples with a controlled surface flaw, or from standard disk-shaped compact-tension specimens precracked in cyclic fatigue. The R-curve behavior of an in situ toughened SiC was also examined. A steady-state toughness over 9 MPa·m1/2 was recorded for the silicon carbide prepared with minimal additives under optimum processing conditions. This increase in fracture toughness, more than a factor of three compared to that of a commercial SiC, was achieved while maintaining a bend strength of 650 MPa. The mechanical properties were found to be related to a microstructure in which platelike grain development had been promoted and where crack bridging by intact grains was a principal source of toughening.
204 citations
TL;DR: In this article, the authors investigated the effect of micro-fiber reinforcement on the strength and toughness of cement-based matrices and found significant strengthening, toughening and stiffening of the host matrix.
Abstract: Toughness and strength improvements in cementbased matrices due to micro-fiber reinforcement were investigated. Cement paste and cement mortar matrices were reinforced at 1, 2 and 3% by volume of carbon, steel and polypropylene micro-fibers, and these composites were then characterized in the hardened state under an applied flexural load. Both notched and unnotched specimens were tested in four-point bending. Considerable strengthening, toughening and stiffening of the host matrix due to micro-fiber reinforcement was observed. The test data from the notched specimens was used to construct crack growth resistance and crack opening resistance curves for these composites and to identify the conditions necessary for failure. This paper recognizes the potential of these composites in various applications and stresses the need for continued research.
TL;DR: In this article, the influence of retained moisture in recycled aggregates on the mechanical properties and durability of new concrete is determined experimentally and analyzed, and the effects of three different moisture conditions from the recycled agreggate are compared (dry, saturated and semi-saturated).
TL;DR: In this paper, the elastic modulus (E), flexural strength (MOR), and Vickers hardness (H v ) increase with the amount of carbon in the oxycarbide glasses reaching the maximum values (E≃115 GPa, MOR≃550 MPa, and H v ≃9 GPa).
Abstract: Silicon oxycarbide glasses have been fabricated, in the shape of thin rods suitable for flexural test experiments, by pyrolysis in an inert atmosphere at 1000 and 1200°C of sol-gel precursors containing Si-CH 3 and Si-H bonds The amount of carbon in the silicon oxycarbide network has been controlled by varying the carbon load in the precursor gel Density and surface area analysis revealed that all of the samples pyrolyzed at 1200°C were well-densified silicon oxycarbide glasses whereas for the glasses treated at 1000°C, compositions with low carbon loads showed the presence of a residual fine porous phase The elastic modulus (E), flexural strength (MOR), and Vickers hardness (H v ) increase markedly with the amount of carbon in the oxycarbide glasses reaching the maximum values (E≃115 GPa, MOR≃550 MPa, and H v ≃9 GPa) for samples with the highest carbon content The experimental elastic modulus values of the silicon oxycarbide glasses compare well with the theoretical estimations obtained using the Voigt and Reuss models assuming the disordered network formed by the corresponding thermodynamic compositions
TL;DR: In this paper, the effect of several chemical treatments, viz. organotitanate, zirconate, silane, and N-substituted methacrylamide, on the properties of sisal fibers used as reinforcement in unsaturated polyester resin (∼50 vol%) was investigated.
Abstract: The effect of several chemical treatments, viz. organotitanate, zirconate, silane, and N-substituted methacrylamide, on the properties of sisal fibers used as reinforcement in unsaturated polyester resin (∼50 vol%) was investigated. An improvement in the properties was observed when sisal fibers were modified with surface treatments. Under humid conditions, a decrease of 30 to 44% in tensile and 50 to 70% in flexural strength has been noted. The strength retention of surface-treated composites (except silane) is high compared with untreated composites. It is observed that N-substituted methacrylamide-treated sisal composites exhibited better properties under dry as well as wet conditions. Fractographic evidence such as fiber breakage/splitting and matrix adherence on the pulled-out fiber surface explains such behavior.
TL;DR: In this article, the effect of reinforcement corrosion on the flexural strength of a uniformly loaded and simply supported one-way slab was investigated, where the authors used a calibration curve to establish a relationship between the duration of the impressed current and reinforcement corrosion.
Abstract: The effect of reinforcement corrosion on the flexural strength of a uniformly loaded and simply supported one-way slab was investigated. In addition to the flexural strength, the effect of different degrees of reinforcement corrosion on the deformational behavior, ductility, and the mode of failure of the slabs were also evaluated. The critical level of reinforcement corrosion that renders the strength contribution of steel negligible was evaluated by comparing the strengths of slabs with highly corroded reinforcement with the strengths of plain concrete slabs. In order to induce different levels of reinforcement corrosion, a calibration curve establishing a relationship between the duration of the impressed current and reinforcement corrosion was prepared. The magnitude of reinforcement corrosion was measured as gravimetric loss in weight of the steel bars. The results indicate a sharp reduction in the ultimate flexural strength of slabs with an up to a 29 reinforcement corrosion; thereafter, the strengt...
TL;DR: In this paper, a nonlinear elastic model for acoustic waves in a stressed medium is used to calculate tectonic stress-induced changes in borehole flexural dispersions, and a theoretical analysis shows that a horizontal uniaxial stress in the formation causes a crossover in flexural dispersion for the radial polarization aligned parallel and normal to the stress direction.
Abstract: A nonlinear elastic model for acoustic waves in a stressed medium is used to calculate tectonic stress-induced changes in borehole flexural dispersions. Our theoretical analysis shows that a horizontal uniaxial stress in the formation causes a crossover in flexural dispersions for the radial polarization aligned parallel and normal to the stress direction. This crossover in flexural dispersions is caused by stress-induced radial heterogeneities in acoustic wave velocities that are different in the two principal stress directions. Other sources of borehole flexural anisotropy caused by finely layered dipping beds, aligned fractures, or microstructures found in shales, exhibit neither such radial heterogeneities nor flexural dispersion crossovers. Consequently, a crossover in flexural dispersion can be used as an indicator of stress-induced anistropy. In this situation, the fast shear polarization direction coincides with the far-field uniaxial stress direction. The analysis also yields an expression for the largest shear stress parameter in terms of the fast and slow seismic shear-wave velocities with shear polarization parallel and perpendicular to the far-field stress direction.
TL;DR: In this article, the impact behavior of silver-powder-filled isotactic polypropylene composites was investigated in the composite composition range of 0-5.6 vol% of Ag.
Abstract: Mechanical properties, such as tensile and flexural properties, as well as impact behavior of silver-powder-filled isotactic polypropylene composites were investigated in the composite composition range of 0–5.6 vol% of Ag. Tensile modulus, strength, and elongation at break decreased with incorporation of silver and an increase in silver concentration. Analysis of tensile strength data indicated the introduction of stress concentration and discontinuity in the structure upon addition of Ag particles. Izod impact strength decreased sharply on addition of 0.43 vol % of Ag particles, beyond which the value decreased marginally. Both flexural modulus and strength increased with filler content due to an increase in rigidity. Surface treatment of filler marginally improved mechanical properties. © 1996 John Wiley & Sons, Inc.
TL;DR: In this article, the feasibility of using finely ground rubber in Portland-cement concrete was examined and the effects on the plastic and hardened properties of concrete were investigated, including compressive strength, split-cylinder strength, modulus of elasticity, and flexural strength.
Abstract: Because used tires represent an increasingly serious environmental problem in the United States, this study was undertaken to examine the feasibility of using finely ground rubber in Portland-cement concrete. Various percentages of rubber, by weight of cement, were added to a control mix and the effects on the plastic and hardened properties of concrete were investigated. Workability of the mixes was affected, but it was controllable. For hardened concretes, the tests were conducted for compressive strength, split-cylinder strength, modulus of elasticity, and flexural strength. Stress-strain response was also investigated. The strength and stiffness characteristics were markedly reduced for rubcrete mixtures.
TL;DR: In this article, a set of ultra-high-strength concretes reinforced with steel fibers was studied with respect to compressive strength and two-point loading strength to define its mechanical behavior.
Abstract: Reactive Powder Concretes (RPC) are a set of ultrahigh-strength concretes reinforced with steel fibers. Their compressive strength is between 200 and 800MPa, and their flexural strength can reach 140MPa.RPC200 has been studied with respect to compressive strength and two-point loading strength to define its mechanical behavior.RPC800, which has been mostly studied from the point of view of compressive strength, displays hardening elastic non-linear behavior at low stress. This behavior is similar to that of some natural rocks. The critical stress intensity factorKIc, and the average fracture energy,\(\bar G_F \), ofRPC200 andRPC800 have been studied experimentally by applying the theory of linear fracture mechanics (compliance method). The fracture energy, which is a measurement of ductility, can reach 40,000 J/m2 forRPC200, as compared to 100 to 150 J/m2 for ordinary concretes. Fracture energy depends on the volume of fibers added to the concrete. The optimum content is between 2 and 3% by volume.
TL;DR: In this article, a finite element model of microcantilever beams was analyzed using ABAQUS, and the resulting model stiffness correlated well with the experimental data, and fracture types were divided into two categories, {111} and {110}, according to the type of silicon crystalline plane along which fracture occurred.
Abstract: A custom experimental system was developed to fracture silicon microcantilever beams in side loading (i.e., the load was applied in the noncompliant direction), and the resulting force/deflection (stiffness) characteristics were obtained. A finite element model of these structures was analyzed using ABAQUS, and the resulting model stiffness correlated well with the experimental data. Fracture types were divided into two categories, {111} and {110}, according to the type of silicon crystalline plane along which fracture occurred. The initiation location of each fracture type was identified. The fracture stress (strength) in the beam was obtained from the stress produced in the model at the fracture initiation site for a load equivalent to the experimental fracture force. Numerous beams were tested, and the statistical results were compiled. The distributions and statistical data from each of the fracture types were compared to each other and to previously acquired results from front/back loading (i.e., loading in the compliant direction) of these same structures. Side-loading results indicated that the {110} fracture type had a greater fracture strength than the {111} type. Based on a comparison of the side loading data with the front/back loading data, it was concluded that side wall roughness and especially the edge roughness greatly affected the fracture strength of the silicon micromechanical structures.
TL;DR: In this paper, aqueous blends of microcrystalline cellulose (MCC) or methyl cellulose and corn starch with or without polyols were extruded, hot pressed and studied, after their conditioning at different relative humidities, in terms of their thermal, mechanical and water and gas permeability properties.
TL;DR: Although fiber reinforced composites may have the potential to replace metals in many clinical situations, additional research is needed to ensure a satisfying life-span.
Abstract: The aim of this study was to compare the mechanical properties of a prefabricated root canal post made of carbon fiber reinforced composites (CFRC) with metal posts and to assess the cytotoxic effects elicited. Flexural modulus and ultimate flexural strength was determined by 3 point loading after CRFC posts had been stored either dry or in water. The bending test was carried out with and without preceding thermocycling of the CFRC posts. The cytotoxicity was evaluated by an agar overlay method after dry and wet storage. The values of flexural modulus and ultimate flexural strength were for dry stored CFRC post 82±6 GPa and 1154±65 MPa respectively. The flexural values decreased significantly after water storage and after thermocycling. No cytotoxic effects were observed adjacent to any CFRC post. Although fiber reinforced composites may have the potential to replace metals in many clinical situations, additional research is needed to ensure a satisfying life-span.
Journal Article•
TL;DR: The Procera AllCeram had a consistently higher failure stress than the other two materials and was also subjected to Weibull analysis.
Abstract: The failure stresses in flexural tests of a densely sintered high-purity alumina (Procera AllCeram) were evaluated using three-point bend, ring-on-ring, and piston-on-three-ball tests. Glass-infiltrated presintered alumina (In-Ceram) and leucite-reinforced porcelain (IPS Empress) disks with the same dimensions were also tested using ring-on-ring and piston-on-three-ball tests. The failure stresses for all materials were substantially different (up to 50%) with different testing methods, and cannot be directly compared. However, by considering the effective specimen area under the maximum tensile stress, these failure stress data could be compared. The results emphasize the importance of knowing the test method and the method of calculation when comparing data. These three testing methods were also subjected to Weibull analysis. The Procera AllCeram had a consistently higher failure stress than the other two materials.
TL;DR: In this paper, the authors examined published works related to surface/subsurface damage and the fracture strength of ground structural ceramics over the last 20 years and highlighted several issues such as non-uniformity of the grinding interface, crack measurement, thermal effects and microstructural features.
TL;DR: In this article, the Strombus gigas conch shell has a crossed-lamellar micro-architecture, which is layered at five distinct length scales and can be considered a form of ceramic "plywood".
Abstract: Flexural strength, crack-density evolution, work of fracture, and critical strain energy release rates were measured for wet and dry specimens of the Strombus gigas conch shell. This shell has a crossed-lamellar microarchitecture, which is layered at five distinct length scales and can be considered a form of ceramic “plywood”. The shell has a particularly high ceramic (mineral) content (99.9 wt%), yet achieves unusually good mechanical performance. Even though the strengths are modest (of the order 100 MPa), the laminated structure has a large strain to fracture, and a correspondingly large work of fracture, up to 13 kJ m−2. The large fracture resistance is correlated to the extensive microcracking that occurs along the numerous interfaces within the shell microstructure. Implications of this impressive work of fracture for design of brittle laminates are considered.
TL;DR: The new pin design allows application of light interfragmentary compression, thus reducing the risk of pin loosening, and an X-ray marker is provided, and the relatively slow strength loss rate of the Polypin potentially extends the application of resorbable devices to slow-healing fractures.
TL;DR: In this article, a finite element model of silicon microcantilever beams is created, and ABAQUS is used to calculate the displacements and stresses produced by an applied load force.
Abstract: Silicon microcantilever beams are fractured and characterized. The specially designed beams, etched into two wafers, are loaded to fracture in bending using a unique measurement system. A finite element model of the beams is created, and ABAQUS is used to calculate the displacements and stresses produced by an applied load force. A special testing scheme is devised to obtain certain model parameters: E〈110〉, the Young’s modulus along the length of the beam and Lforce, the position of the applied force. With these parameters defined, the model is well correlated with that of the experimental data. The fracture stress (strength) of the beam is obtained from the stress produced in the model at the fracture location by a load equivalent to the experimental fracture force. This fracture stress can be used as a design parameter for silicon micromechanical structures. Numerous beams are fractured from both the front and back sides of the wafer, and statistical fracture strength results are compiled for each of t...
TL;DR: In this article, the effect of reinforced concrete rectangular beams with epoxy bonded carbon fiber reinforced plastic (CFRP) laminate is experimentally investigated, and the results generally indicate that the flexural strength of strengthened beams is significantly increased.
Abstract: Flexural behavior of reinforced concrete rectangular beams with epoxy bonded carbon fiber reinforced plastic (CFRP) laminate is experimentally investigated. Comprehensive test data are presented on the effect of CFRP laminates, bonded to the soffit of a beam, on the first crack load, cracking behavior, deflections, serviceability loads, ultimate strength and failure modes. The increase in strength and stiffness provided by the bonded laminates is assessed by varying the number of laminates. The results generally indicate that the flexural strength of strengthened beams is significantly increased. Theoretical analysis using a specially developed computer software is presented to predict the ultimate strength and moment deflection behavior of the beams. The comparison of the experimental results with theoretical values is presented, along with an investigation of the failure nodes.
TL;DR: In this article, a commercially procured fiber reinforced plastic (FRP) composite indeed produced cracks on prolonged thermal cycling between 50°C (122°F) and -60°C (-76°F), but a specially manufactured woven glass reinforced FRP did not produce any visual cracks for two and half times more thermal cycling in the same temperature range.
Abstract: Low temperature produces internal stresses in composites of polymeric materials. The polymeric matrix phase becomes stiffer, and may suffer from damage-inducing stresses resulting from thermal coefficient mismatch of fibers and resins. These influences have been studied by subjecting two types of FRP composites to flexural tests. A commercially procured fiber reinforced plastic (FRP) composite indeed produced cracks on prolonged thermal cycling between 50°C (122°F) and -60°C (-76°F) temperature. But a specially manufactured woven glass reinforced FRP did not produce any visual cracks for two and half times more thermal cycling in the same temperature range. It is suspected that the resin type and the curing process control the thermal cycle response and ultimate durability of such FRP composites in extreme temperature environments.
Journal Article•
TL;DR: The hybrid resin composite exhibited the lowest resistance to wear caused by brushing and the strength properties of the tested resin-modified glass-ionomer materials and the polyacid-modified resin composite materials were inferior to those of the hybrids.
Abstract: The objective of the study was to evaluate the physical properties of four resin-modified glass-ionomer cements (Fuji II LC, Ionosit Fil, Vitremer, Photac-Fil) and two polyacid-modified resin composite materials (Dyract and Variglass VLC)). They were compared with a hybrid resin composite (blend-a-lux) and a chemically cured glass-ionomer cement (ChemFil Superior). The compressive strength, flexural strength, modulus of elasticity, and surface microhardness of the resin-modified glass-ionomer materials and the polyacid-modified resin-composite materials were inferior to those of the hybrid resin composite and similar to those of the conventional glass-ionomer cement. The hybrid resin composite exhibited the lowest resistance to wear caused by brushing. Some of the materials showed a marked decrease in hardness at depths exceeding 2.0 mm. Generally, the strength properties of the tested resin-modified glass-ionomer materials and the polyacid-modified resin composite materials were inferior to those of the hybrid resin composite.