Showing papers on "Flexural strength published in 1976"

Liquid crystal polymers. I. Preparation and properties of p-hydroxybenzoic acid copolyesters†

Abstract: High molecular weight copolyesters were prepared by the acidolysis of poly(ethylene terephthalate) with p-acetoxybenzoic acid and polycondensation through the acetate and carboxyl groups. The mechanical properties of the injection-molded copolyesters containing 40–90 mole-% p-hydroxybenzoic acid (PHB) were highly anisotropic and dependent upon the PHB content, polyester molecular weight, injection-molding temperature, and specimen thickness. As the injection-molding temperature increased and the specimen thickness decreased, the tensile strength, stiffness, and Izod impact strength increased when measured along the direction of flow of the polymer melt, and the coefficient of thermal expansion was zero. In some compositions these properties were superior to those of commercial glass fiber reinforced polyesters. Maximum tensile strengths, flexural moduli, notched Izod impact strengths, and minimum melt viscosities were obtained with polyesters containing 60–70 mole-% PHB. Higher oxygen indicies (39–40) and heat deflection temperatures (150–220°C) were obtained with 80–90 mole-% PHB.

Mechanical properties of bone cements containing large doses of antibiotic powders

Abstract: The addition of up to 10 g gentamicin sulfate antibiotic powder to 60 g units of Simplex-P acrylic bone cement caused gradual, proportional decreases in the bulk muchanical properties of compressive and diametral tensile strengths. Water leaching of the antibiotic from the cement did not significnatly decrease these strenghts. Scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDS) showed the antibiotic to reside in the acrylic matrix as discrete particles not usually associated with internal porosity. The surface-sensitive flexural strength of a proprietary bone cement was lowered immediately by small quantities of antibiotic powder, and continued to decrease as doses of up to 10 g/unit were admixed. Water leaching caused channeling as the antibiotic was removed from the surface, but it did not create further changes in flexural strength.

Fracture measurements on cement paste

Abstract: This paper describes an investigation into the fracture behaviour of hardened cement paste. Notched specimens of the material were tested to failure in flexure and tension. In the initial flexural tests on beams of fixed overall depth, the stress intensity factor at failure as calculated from linear-elastic fracture mechanics appeared to be a material constant. However, further investigation showed that this factor varied with specimen size, and suggested that linear-elastic fracture mechanics and the concept of fracture toughness are not readily applicable to hardened cement paste, which would appear to be a relatively notch insensitive material whose strength is not greatly reduced by the presence of flaws. A “tied crack” model explains semi-quantiatively the observed behaviour.

Shear strength of low-rise walls with boundary elements

Abstract: Results of tests on eight specimens representing low-rise shear walls with boundary elements are reported and analyzed. The principal variables included amount of flexural reinforcement, amount of horizontal wall reinformcement, amount of vertical wall reinforcement, and height-to-horizontal-length ratio. Flexural reinforcement was varied from 1.8% to 6.4% of the boundary element area; horizontal wall reinforcement and vertical wall reinforcement were varied from 0% to 0.5% of the wall area; and height-to-horizontal-lenght ratio was varied from 1:4 to 1:1. The test program was designed to determine the effect of load reversals. One specimen was repaired and retested. Results indicate that current design procedures underestimate the strength of lowrise shear walls, even when the walls are subjected to reversed load. A suggested design procedure is presented.

Flexural tests of steel-concrete-steel sandwiches

Abstract: Synopsis In order to reduce the weight of roadway slab on medium- and long-span composite bridges, a possible alternative in the form of a steel-concrete-steel sandwich has been appraised. This consists of a concrete core, precast or otherwise, to which is attached reinforcement in the form of flat steel plates by means of epoxy resin adhesive. Specimens of the order of 100 mm thick were tested statically over a span of 1·8 m, and carried loads equivalent to wheels of the HB vehicle with an adequate safety margin. Accepted design procedures gave reasonable prediction of the ultimate loads.

The effect of thermal exposure on the mechanical properties of aluminum-graphite composites

Abstract: The mechanical properties of aluminum-graphite composites were measured at room temperature in the as-received condition, after elevated temperature exposure and after thermal cycling. The composites were fabricated by solid-state diffusion bonding of liquid-phase Al-infiltrated Thornel 50 fibers. The results showed that the maximum longitudinal tensile strength of the as-received material was 80,000 psi, which corresponds well with the rule of mixture value. The composite strength was observed to vary widely, depending on the extent of wetting of the fibers by the aluminum. The strength of the composites in the transverse direction was generally very low, due to poor interfacial bonding. Aluminum carbide (Al4C3) formed at the surface of the fibers at temperatures greater than 500 C. Development of the carbide was shown to be diffusion-controlled and was dependent on the time and temperature used. It was shown that the tensile strength was virtually unaffected by heat-treatment up to 500 C; beyond that temperature a drastic degradation of tensile strength occurred. Thermal cycling of the composites below 500 C resulted in an observable degradation of the composite strength.

Apparent Flexural Modulus and Strength of Multimodulus Materials

Abstract: The ASTM flexure test is commonly used to measure the flexural modulus and flexural strength of materials other than the plastics for which it was originally developed. The officially designated equations for reporting the test results are applicable only to materials that are linear elastic to failure. However, the test is often used for carbon-carbon and other composite materials which have different (and sometimes nonlinear) stress-strain curves under tension loading than under compression loading. Such materials are called multimodulus materials. The influence of the multimodulus characteristic on the behavior of a test beam is evaluated for two representative carbon-carbon composite materials. The ASTM flexure test is found to be inapplicable to this class of materials because of the multimodulus characteristic and the nonlinear stress-strain behavior.

Structure and anisotropy of stiffness in glass fibre-reinforced thermoplastics

Abstract: Techniques which are readily available, and which may be considered suitable for the qualitative or quantitative assessment of fibre orientation distribution in short glass fibre-reinforced thermoplastics are reviewed. The results of using several of these techniques in structural studies on injection mouldings of glass fibre-reinforced grades of polypropylene and polyamide 66 are presented. Uniaxial tensile creep tests were carried out on specimens cut from the mouldings and the anisotropy of stiffness of each moulding is compared with that predicted from the structural studies. Certain of the structural techniques are considered to be unreliable or of restricted applicability and it is concluded that the technique of contact micro-radiography is the most versatile; being capable of yielding reliable qualitative or quantitative information on fibre orientation distribution. Detailed structural studies on edge-gated injection moulded discs, using the technique of contact micro-radiography, show that the fibre orientation distribution varies dramatically through the thickness of the mouldings, even in cases where uniaxial tensile creep tests suggest isotropy of stiffness in the plane of the moulding. Care must therefore be taken when seeking to relate flexural data to tensile data and strength data to stiffness data.

Analysis of Reinforced Fibrous Concrete Beams

Abstract: A method has been developed to predict the ultimate strength of concrete beams reinforced with a combination of steel bars and randomly distributed steel fibers. Strengths of three full-size beams were obtained experimentally to verify the analytical method. The method, which applies to beams using a cement-rich mortar mix with the steel fibers, shows good correlation with experimental results. A dynamic bond stress of 333 psi was assumed for the fibers. Fiber lengths were from 1-1/2 in. to 2-1/4 in. and the fiber amount was varied from 1.22% to 1.51% by volume. The test programs showed that: (1) Steel fibrous concrete increased the flexural load capacity of the reinforced beams by about 25%; (2) crack width and crack spacing were less than in a conventional reinforced beam; and (3) the post-cracking stiffness of the fibrous beams was greater than a conventional beam.

Fracture Analysis of Various Cracked Configurations in Sheet and Plate Materials

Abstract: A two-parameter fracture criterion has been derived which relates the linear-elastic stress-intensity factor at failure, the elastic nominal failure stress, and two material parameters. The fracture criterion was applied to center-crack tension, compact, and notch-bend fracture specimens made of steel, titanium, or aluminum alloy materials tested at room temperature. The fracture data included a wide range of crack lengths, specimen widths, and thicknesses. The materials analyzed had a wide range of tensile properties. Failure stresses calculated using the criterion agreed well (plus or minus 10 percent) with experimental failure stresses. The criterion was also found to correlate fracture data from different specimen types (such as center-crack tension and compact specimens), within plus or minus 10 percent for the same material, thickness, and test temperature.

Fracture‐Strength Anisotropy of Sapphire

Abstract: At 22°C, the bend strength of as-ground sapphire bars with different orientations of tensile surface and tensile axis varies from 4×104 to 12×104 psi as a result of the anisotropies of machining damage and fracture energy. Generally, the strength-controlling surface flaws caused by grinding are of constant size; failure from such flaws is affected by grinding-induced slip and twinning. Surface striations, which occur when there is negligible subsurface slip, can lead to stress concentrations, whereas twins can lead to increases in flaw size; each of these effects reduces strength. In addition, the large anisotropy in fracture strength, which is not predicted by the elastic anisotropy, is controlled by the anisotropic fracture energy. Approximation of the attractive forces across the fracture plane based on elastic moduli and interplanar distance can be used to understand the fracture energy anisotropy.

Mechanical Properties of Glass and Steel Fiber Reinforced Mortar

Abstract: Tensile, flexural and compressive tests were conducted on mortar specimens reinforced with different lengths and volumes of steel and glass fibers. The tensile flexural strength of reinforced specimens was at most two to three times that of plain mortar while the corresponding strains or deflections were as much as ten times that of mortar. The stresses and strains at first cracking were not significantly different from those of plain mortar. The values of the modulus of elasticity and the extent of nonlinearity was observed to depend on the methods of deformation measurement. Extensive microcracking was observed on the surfaces of failed flexural specimens indicating a significant contribution of the matrix even after the first cracking. For steel fiber reinforced specimens, the peak loads and deformations appear to be linearly related to the fiber parameter: v f(L/D). After failure, steel fibers pulled out while most of the glass fibers broke.

Design and technique variables affecting fracture resistance of metal-ceramic restorations.

Abstract: An attempt was made in this study to make a clinically meaningful measure of fracture resistance in metal-ceramic restorations. Forty-four solid metal-ceramic crown forms were fabricated and subjected to compressive load testings. Variables included the presence or absence of a metal coating agent, the type of metal preparation (using stones of different abrasives), and three designs of the underlying metal. The following conclusions were arrived at: (1) The design of the underlying metal structure had a significant relation to the ultimate fracture strength. (2) A design with a definite acuteness of the underlying metal structure failed at significantly lower ultimate fracture strengths. (3) A metal conditioning agent did not decrease fracture resistance if applied properly. (4) Fracture strength was severely decreased when (a) improper thickness of the coating agent was used and (b) porcelain was fused to an unoxidized metal surface. (5) Bond strength, although a contributing factor, may not be as important as metal design and proper manipulation of materials during fabrication of the restoration.

Infinite dilution viscoelastic properties of poly(γ-benzyl-L-glutamate) in m-cresol

Abstract: The real and imaginary parts of complex viscosity, η′ and η″, are measured for dilute solutions of poly(γ-benzyl-L-glutamate) in m-cresol, a helicogenic solvent. The frequency range is 2.2–525 kHz; the concentration range 0.2–5 g/dl; the temperature 30°C, and the molecular weights Mr are 6.4 × 104–17 × 104. The dispersion curve of extrapolated intrinsic dynamic viscosity [η′] of samples with Mr > 105 is interpreted in terms of three mechanisms appearing from low to high frequencies: end-over-end rotation, flexural deformation, and side-chain motion. For a sample with Mr < 105, the flexural relaxation disappears and a plateau of [η′] is distinctly observed between rotational and side-chain relaxations. Rotational relaxation times of all the samples obey the Kirkwood–Auer theory. The strong concentration dependence of rotational relaxation time is explained by collisions of molecules rather than association. Flexural relaxation times calculated from a theory by assuming the persistence length as 1200 A are consistent with observed dispersion curves of [η′].

Shaped articles of hydraulic cement compositions with a glossy reflective surface and reinforced with fiber glass

Abstract: Shaped articles of hydraulic cement compositions reinforced with fiber glass fabric or with chopped fiber glass, and having a smooth, reflective surface, are produced by the admixture of "super" water reducers to the aqueous cementitious slurries followed by casting or spraying into synthetic polymer molds, or molds coated with such synthetic polymers which are water repellent and non-sticking to hydraulic cements, to yield cured articles of high flexural strength with at least one surface which is an exact reproduction of the surface of the synthetic polymer mold, such as high gloss and patterned design. A great variety of useful articles may be produced, such as building panels, curtain walls, hollow utility poles and pipes, "raised" flooring panels, roofing tiles, protective barriers, and other products requiring thin shell, high flexural strength products for decorative and utilitarian uses.

Strength of Slab-Column Connections with Shear and Unbalanced Flexure

Abstract: Tests were conducted on eight 1/2-scale models of reinforced concrete interior flat plate-column connections transferring shear and unbalanced moment from gravity and simulated seismic loading. The slab at the connection contained either no shear reinforcement or shear reinforcement in the form of either cranked bars, structural steel shearhead or closed vertical stirrups. The simulated seismic loading was statically applied, either monotonically or cyclically in the inelastic range. The strength and ductility of the connections, and the modes of failure, were compared. The connections without shear reinforcement failed suddenly in diagonal tension. The use of cranked bars as shear reinforcement increased the strength of the connection but did not increase the ductility. The use of a structural steel shearhead resulted in an increase in strength and in a limited increase in ductility. The use of closed vertical stirrups around the slab bars, which passed through the column, resulted in an increase in the strength and in a substantial increase in the ductility of the connection.

Glass-ceramics with random and oriented microstructures

Abstract: The variation of a number of physical properties of a glass-ceramic composition as a function of the crystallization heat-treatment temperature are reported. The properties studied include mechanical strength, modulus of elasticity, electrical properties and linear coefficient of thermal expansion. It is shown that several of the properties are dependent on microstructural effects. This dependence is especially marked for modulus of rupture and is also apparent for electrical properties such as conductivity and loss tangent. For the latter, however, compositional changes in the residual glass phase also exert a significant influence. For other properties, such as indentation hardness, the microstructural dependence is less well defined.

Fabrication and flexural strength of ultrafine-grained yttria-stabilized zirconia

Abstract: Ultrafine powders of yttria-stabilized zirconia were fabricated into specimens by die pressing, extrusion and slip casting. Gross pores present in unfired specimens varied with fabrication procedure and persisted in the fired microstructures. Pressure-cast specimens with no apparent internal pores larger than grain size and with as-fabricated surfaces containing surface pores approximately 2 ..mu..m exhibited mean flexural strengths as high as 129 kpsi. The ultimate flexural strength of extruded and pressed specimens appeared to be limited by residual coarse pores near the surface, and flexural strengths ranged as low as 16 kpsi.

Optimal Design of Flexural Systems: Beams, Grillages, Slabs, Plates and Shells

Abstract: Well, someone can decide by themselves what they want to do and need to do but sometimes, that kind of person will need some optimal design of flexural systems beams grillages slabs plates and shells references. People with open minded will always try to seek for the new things and information from many sources. On the contrary, people with closed mind will always think that they can do it by their principals. So, what kind of person are you?

Characteristics of akwara as a reinforcing fibre

Abstract: Synopsis Some relevant physical characteristics of akwara and akwara-reinforced concrete (akwaracrete) are discussed. Akwara is a natural vegetable stem fibre, dark brown in colour when mature, and has a hard smooth sheath enclosing a cellular core. Akwara is brittle and lighter than water. It is dimensionally stable in water, durable in a cement matrix environment, and has a low modulus of elasticity. Mixes containing akwara have lower mobility and compactibility than their plain counterpart. The fibre improves the impact resistance of concrete, but appears to have no effect upon uniaxial compressive strength or modulus of rupture.

On the relation of J sub I to work done per unit uncracked area: Total, or component 'due to crack'

Abstract: The direct evaluation of Rice's JI as a function of displacement, from the load-displacement record of a test of a single precracked specimen, was discussed. Special attention was given to the general form of the underlying relation.

Silicon carbide sintered moldings and a method for producing the same

Abstract: of the Disclosure Silicon carbide sintered moldings having a high flexural strength and various excellent properties are produced by mixing SiC powders or SiC fibers with a binder of organosilicon low molecular weight compounds or organo-silicon high molecular weight compounds, molding the mixture into a desired shape and heating the molded mixture at a high temperature.

The Unit Strength Concept in the Interpretation of Beam Test Results for Brittle Materials

Abstract: SYNOPSISBrittle materials are usually characterised in terms of the “modulus of rupture” obtained from the results of fracture tests on beam specimens. This is not a fundamental quantity. Alternative quantities (the mean strength of unit volume and of unit area) are introduced which are independent of the size of the specimen and the form of test, which allow the correlation of results from different tests, and which may be validly used in design calculations. After an outline of the necessary theory, the derivation of the two “unit strengths” and their use in correlating test results are illustrated using fracture data from a series of reaction-bonded silicon nitride beams. Minimum values obtained are:- mean uniaxial fracture stress of unit volume, 140 N/mm2 per cm3; mean uniaxial fracture stress of unit surface area, 180 N/mm2 per cm2.A means of allowing for the effects of contact friction in the analysis of beam fracture test data is presented. The ignoring of these effects may result in a significant ...

SiC sintered bodies with three-dimensional polycarbosilane as binder

Abstract: As is well known, silicon carbide is a practical heat-resisting material, because it has high strength and excellent oxidation, corrosion and thermal shock resistance. It is, however, difficult to obtain it as a sintered body because of its poor sintering characteristics. The usual method1 for obtaining SiC with high flexural strength are to add a sintering promoter to fine SiC powder followed by hot pressing. The process is complicated and not suitable for obtaining large products. We here report the synthesis of high purity SiC mouldings with high mechanical strength by low temperature (1,000−1,400 °C) sintering of SiC powders bond with three-dimensional polycarbosilanes. The method is based on the conversion of an organosilicon polymer to the inorganic compound by heat treatment2–5.