Showing papers on "Flexural strength published in 1972"

Reinforced concrete members with cyclic loading

Abstract: Theoretical moment-curvature relationships for reinforced concrete members with cyclic loading are derived using stress-strain curves for steel and concrete. The theoretical curves compare well with test results and illustrate the variation in flexural stiffness due to the Bauschinger effect of the steel and to the presence of open cracks in the compression zone of the concrete which may eventually close. These cracks mean that for large portions of the moment-curvature curves after the first yield excursion the moment of resistance is provided by a steel couple alone. During this part of the cyclic loading the main role of the concrete is to prevent buckling of the steel. For beams with a marked difference between the top and bottom steel areas and for columns the moment-curvature loops show a pinching in effect and the loop area is significantly smaller than that of the commonly used elastoplastic idealization.

The Strength and Fracture Toughness of Polycrystalline Magnesium Oxide Containing Metallic Particles and Fibres

Abstract: The transverse rupture strength of hot-pressed and annealed composites of magnesium oxide and dispersed metallic phases (nickel, iron, cobalt) increases with increasing volume fraction of metal and annealing temperature. The strengthening effect of the metal is attributed to an inhibition of grain growth while flaw healing occurs during the annealing of the composites.

The Deformations and Stresses in Floating Ice Plates

Abstract: In the past, the analyses of floating ice plates subjected to static or dynamic loads were based on the theory of a thin homogeneous plate, although in actual floating ice plates Young's modulus may vary strongly with depth. Recently,A. Assur concluded, on the basis of a heuristic argument, that the solutions obtained for homogeneous plates may be used for floating ice plates, if a modified flexural rigidity is used. The purpose of the present paper is to study this question, by establishing a mathematically consistent formulation for the dynamic plate equation, utilizing Hamilton's Principle in conjunction with the three dimensional theory of elasticity. It is proven that for a variable Young's modulus and a constant Poisson's ratio the resulting formulations for plates and beams are the same as those for the corresponding homogeneous problems, if a modified flexural ridigity is used; thus confirmingAssur's conclusion. It is shown that the stress distribution is not linear and that the stress formula\(\sigma _{\max } = M{{z_0 } \mathord{\left/ {\vphantom {{z_0 } I}} \right. \kern- ulldelimiterspace} I}\) used by a number of investigators for the determination of the carrying capacity of a floating ice plate, as well as for the computation of failure stresses from tests on floating ice beams, is not applicable. Correct formulas are derived, corresponding stress distributions are presented and the consequences of the findings discussed.

Flexural Fatigue Strength of Steel Fiber Reinforced Concrete Beams

Abstract: THE RESULTS OF FLEXURAL FATIGUE TESTING OF STEEL FIBER REINFORCED CONCRETE BEAMS ARE REPORTED. SEVERAL SIZES OF STEEL FIBERS WERE USED AS REINFORCEMENT IN CONCENTRATIONS OF 2.00 AND 2.98 PERCENT BY VOLUME OF CONCRETE. STATISTICAL ANALYSIS OF THE TEST DATA INDICATED FATIGUE STRENGTHS OF 73 AND 84 PERCENT OF THE FIRST CRACK STATIC FLEXURE STRENGTH OF 2 MILLION CYCLES OF COMPLETE REVERSAL AND NONREVERSAL OF LOADING, RESPECTIVELY. /AUTHOR/

Flexural strength in fiber-containing concrete

Abstract: A method of making a two-phase material comprising a mix of concrete and fibers of a material having a modulus of elasticity of at least about 20 million psi substantially uniformly distributed therein with an average spacing between fibers of up to about 0.3 inch. The flexural strengths are measured for a plurality of substantially different average bond areas of the fibers per unit area in planes normal to tensile stress in test specimens of the two-phase material, and the fibers are provided and distributed in such quantity in the bulk mix that the average bond area of the fibers intersecting planes normal to the stress at known regions of highest tensile stress is sufficient to provide at least a preselected flexural strength in such regions.

The response of asphalt pavements to low temperature climatic environments

Abstract: The response of asphalt pavements to environmental conditions is well recognized, but not easily quantified. Variations in temperature, particularly freezing conditions may result in non-traffic load associated distress. Analyses of several pavement systems in Western Canada where continuous temperature records were collected, has yielded specific information on temperature gradients and time variations at various depths throughout the pavement structures. To extend this information to other climatic areas, a computer program has been developed that utilizes a finite difference method to predict the thermal regime within pavement systems. The necessary input parameters for the program are the thermal properties of the component layers and readily available meteorological data. Comparisons of predicted and recorded temperatures have shown excellent agreement. Calculated temperatures throughout the asphalt concrete surface layer, together with laboratory evaluation of fracture strength have been used to predict the pavement susceptibility to thermally induced fracture. Results of field studies support the analysis technique described. /AUTHOR/

Hot pressed silicon nitride

Abstract: A hot pressed silicon nitride product is described, the product having high strength at room temperature as well as high strength at elevated temperature. The product has a flexural strength in excess of 100,000 psi at 20*C., in excess of 90,000 psi at 1,200*C., in excess of 35,000 psi at 1,375*C, and preferably above 45,000 psi at 1,375*C. A preferred form of the product includes between .25 and 2.0 mg in the form of complex silicate, which silicate also contains a limited amount of iron, aluminum and calcium. The complex silicate has a liquidus above 1,400*C. The product has a density between 3.1 and 3.3 g/cc, the total oxygen content of the product being less than 5%.

Sintered silicon carbide

Abstract: A DENSE SILICON CARBIDE PRODUCT IS DESCRIBED. THE PRODUCT HAS A FLEXURAL STRENGTH ABOVE 100,000 P.S.I. AT ROOM TEMPERATURE, ABOVE 80,000 P.S.I. AT 1200*C., ABOVE 60,000 P.S.I. AT 1375*C. AND ABOVE 45,000 P.S.I AT 1500*C. THE PRODUCT HAS A GRAIN SIZE OF LESS THAN 5 MICRONS AND ESENTIALLY ALL OF THE SILICON CARBIDE IS IN THE ALPHA FORM. THE PRODUCT HAS A DENSITY IN EXCESS OF 99% OF THEORETICAL DENSITY AND CONTAINS ABOUT .5% TO 5% ALUMINUM. A PREFERRED PROCESS FOR PREPARING THE PRODUCT IS ALSO DESCRIBED.

Factors affecting the flexural strength of steel fibrous concrete

Abstract: AN INVESTIGATION WAS MADE OF THE EFFECTS OF STEEL FIBER PARAMETERS AND CONCRETE MIX PARAMETERS ON THE FLEXURAL STRENGTH PROPERTIES OF STEEL FIBROUS CONCRETES AND MORTARS. COMPOSITIONS WERE EVALUATED IN WHICH THE STEEL FIBER CONTENT WAS AS HIGH AS 4.0 VOLUME PERCENT. DATA ARE PRESENTED WHICH SHOW THE RELATIONSHIP OF FIBER CONTENT AND FIBER SPACING ON THE ULTIMATE AND FIRST CRACK FLEXURAL STRENGTH OF A STANDARD MORTAR FORMULATION. THE EFFECT OF MIX WORKABILITY AS CONTROLLED BY THE MIX COMPOSITION ON THE FLEXURAL STRENGTH PROPERTIES IS DISCUSSED. THE EFFECT OF COARSE AGGREGATE ADDITIONS ON THE FLEXURAL STRENGTH OF A STEEL FIBROUS MORTAR IS ALSO DISCUSSED. THE USE OF STEEL WIRE FIBERS PROVIDES SIGNIFICANT IMPROVEMENTS IN THE FLEXURAL STRENGTH PROPERTIES OF CONCRETES AND MORTARS WHEN THE PROPER CONDITIONS OF MIX FORMULATION, BATCHING, AND PLACING ARE ACHIEVED. /ACI/

Strength of Fiber-Reinforced Concrete

Abstract: The results of experimental and analytical studies on the characteristics of concrete reinforced with uniformly distributed short wire pieces are presented. The experimental program includes tests on workability, modulus of rupture strength, and compressive strength of 75 batches of concrete; the major variables are water-cement ratio, percentage of steel, and gage and length of wire pieces. Despite the slight loss of workability, preparation of good wire reinforced concrete is quite feasible. Effective wire spacing has been formulated taking into consideration the bond deficiency and probable orientation of the wire pieces both within the interior concrete and near the exterior faces of the specimen. Based on experimental results, a correlation has been obtained between effective wire spacing and tensile strength ratio.

The Effect of Duration of Load on the Bending Strength of Wood

Abstract: Despite differences in species, size, type, and moisture content of specimens, the results obtained by a number of research workers investigating the effect of duration of load on the bending strength of wood were generally consistent with each other. The combined values were fitted well by the following linear regression equation: SL-9I-5 —7log10T where SL = stress level = applied bending stress expressed as a percentage of the estimated standard test modulus of rupture for the specimen T = time to failure after application of maximum load plus time to apply the higher increments of load (hr) However, there was some indication that under rapid rates of loading green specimens showed larger proportional increases in strength than dry specimens. Also, specimens loaded to stress levels of about 90 % failed sooner than expected, possibly due to inertial effects. The variability of time to failure at particular stress levels was not much larger for the combined results than for the individual results of some investigations. For a given stress level, the time to failure covered a range of approximately 3 orders of magnitude. Conversely, a change of one order of magnitude would be expected on average for a change in stress level of 7 percentage points. No evidence was apparent for the existence of a threshold of stress below which failure is unlikely. Such a threshold, if it exists, would be below 50% of the standard test ultimate stress. Some increase in the multiplying factors for obtaining design stresses from the basic stresses for dead loads may be justified.

Stress prediction and low temperature fracture susceptibility of asphaltic concrete pavements

Abstract: FIVE DIFFERENT METHODS OF STRESS COMPUTATION WERE EMPLOYED TO EVALUATE THERMAL STRESSES IN A NUMBER OF DIFFERENT TEST SECTIONS INCORPORATED IN TWO TEST PROJECTS IN WESTERN CANADA. STRESSES WITHIN THE PARTICULAR ASPHALTIC CONCRETES WERE EVALUATED, USING STIFFNESS PROPERTIES DETERMINED BY INDIRECT MEANS, BY EMPLOYING NOMOGRAPHIC PROCEDURES. FRACTURE STRENGTH- TEMPERATURE RELATIONSHIPS WERE ESTABLISHED FOR ASPHALTIC CONCRETE CORES USING THE TENSILE SPLITTING TEST METHOD. OBSERVED CRACKING IN THE TEST PROJECTS WAS COMPARED TO THAT PREDICTED BY THE VARIOUS STRESS ANALYSES USING A POSTULATED FRACTURE CRITERION.

Simple equivalent network for the flexural mode of the ridge guide for acoustic surface waves

Abstract: A microwave-network approach is used to obtain an approximate but simple dispersion relation for the ‘flexural’ mode of the ridge waveguide. The propagation characteristics calculated from this relation compare well with experimental data over a wide frequency range.

Method of manufacturing bimetallic high-speed cutting tools

Abstract: A bimetallic high-speed cutting tool having a series of spaced teeth provided on one of its longitudinal edges is manufactured by providing each tooth at its forward top end with a cut-out portion on which a tip of super-hard material, molded before being sintered into a shape substantially equal to a desired final configuration, and having as cutting edges sharp square corners, is welded or brazed, so that the machining of said tip to said desired final configuration, after it has been welded or brazed to the tooth body is minimized, the super-hard materials constituting said tip being selected from those having such hardness and flexural strength as not to be affected by the heat applied thereto when the tip is welded or brazed firmly onto the tooth body.

Investigation of Ceramics for High-Temperature Turbine Vanes.

Abstract: : Large tubular crystals of alpha-SiC, which can become strength limiting, tend to grow during the hot-pressing boron containing beta-SiC powder. The exagerrated grain growth was controlled by several methods: Stabilization of beta-SiC by nitrogen; nucleation of alpha-SiC by seeding; and, decreasing the hot-pressing temperature by using SiC powders with increased sinterability. Nitrogen doping was achieved by the addition of either Si3N4 or BN and yields electrically conductive materials which are amenable to electro discharge machining. The hot-pressing of large billets of nitrogen-doped materials revealed that specimen thickness and the applied pressure are critical parameters which affect the final density. Pressure-less sintering was achieved in submicron beta-SiC powders by the addition of boron and carbon. Results of microstructural examination, room temperature and high temperature bend strength, creep and impact tests are presented. (Modified author abstract)

High strength ophthalmic lens

Abstract: An ophthalmic glass lens has an internal zone in which the tensile stress is less than three kg./mm.2 and a compressively stressed, ion-exchanged surface zone that is at least four mils in depth and in which the compressive stresses generate a modulus of rupture greater than 35,000 psi. The lens is molded from a preferably lime-free, alkali silicate glass containing, by weight on the oxide basis, 12-20% Na2O plus K2O, 10-20% ZnO plus MgO plus TiO2, and 1-5% Al2O3, and is chemically strengthened by an exchange of potassium ions for sodium ions in the surface layer of the lens at a temperature below the strain point of the glass. A surface abraded lens will withstand fracture from the impact of a 5/8 inch diameter steel ball dropped from a height of 50 inches, but if broken by a point impact, has a breakage pattern of a few large pieces.

Flexure fatigue tests on asphalt paving mixtures

Abstract: A REPEATED FLEXURE APPARATUS WHICH HAS BEEN USED FOR MUCH OF THE RECENT RESEARCH ON FATIGUE BEHAVIOR OF ASPHALT PAVING WAS MODIFIED TO ACCOMMODATE 15-IN.-LONG BEAM SPECIMENS WITH 3-IN. INSTEAD OF 1 1/2-IN. WIDTHS AND DEPTHS. CONTROLLED STRESS FLEXURAL FATIGUE STUDIES WERE CONDUCTED FOR 10 DIFFERENT PAVING MIXES USING THE LARGER CROSS SECTION SPECIMENS IN AN EFFORT TO REDUCE TEST VARIABILITY, AND IN SO DOING REDUCE TIME AND COST FOR DETERMING THE FATIGUE BEHAVIOR OF A PAVING MIXTURE. BASED ON RESULTS OF THE STUDIES AND ON PUBLISHED WORK OF OTHERS, IT WAS FOUND THAT VARIABILITY OF FLEXURAL FATIGUE TESTS WAS REDUCED WHEN 3-IN. INSTEAD OF 1 1/2-IN. WIDTH AND DEPTH SPECIMENS WERE USED. CORRELATION COEFFICIENTS RANGING FROM 0.91 TO 0.99 WERE OBTAINED FOR STRESS-FRACTURE LIFE AND STRAIN-FRACTURE LIFE REGRESSION LINES WHEN FROM 6 TO 9 SPECIMENS WITH 3-IN. WIDTHS AND DEPTHS WERE TESTED AT 70 F. FLEXURAL FATIGUE BEHAVIOR DETERMINED FOR 8 OR 9 SPECIMENS WITH 3-IN. WIDTHS AND DEPTHS APPEARS TO BE THE SAME AS DETERMINED FOR 2 OR MORE TIMES AS MANY SPECIMENS WITH 1 1/2-IN. WIDTHS AND DEPTHS. /ASTM/

Computation of Residual Stresses in Quenched Al2O3

Abstract: A method of computing the residual stress profile in quenched A12O3 rods was developed. For these calculations, certain material parameters must be determined. Thus, strain rate was measured as a function of stress for 96% A12O3 at 1300° to 1500°C, and the heat-transfer rates of cylindrical samples quenched in several media were determined. Using calculated temperature distributions and measured strain rates, plastic strains were computed for the entire quenching period, and these strains were converted to a profile of residual room-temperature stresses. The substantial increases in flexural strength observed in Al2O3 after it is quenched (thermally conditioned) are considered to originate in the residual compressive surface layers.

Filamentary sapphire: Part 2 Fracture strength in tension

Abstract: The fracture strength in tension of nominally 0.026 cm diameter c-axis sapphire filament grown from the melt using the “edge-defined, Film-fed Growth” technique is presented. The strength is found to be a function of filament diameter, decreasing with decreasing diameter. This relationship is explained on the basis of the particular characteristics of the melt growth preparation method. A melt temperature controlling device, dependent on the infra-red emitted from the melt area at which the filament is withdrawn, was developed and used to grow filament of constant diameter in the growth rate range 2.5 to 7.5 cm/min. With this device strength is not found to vary significantly with growth rate. Average strengths in tension of 2.75×109 N/m2 (400×103 lb f/in.2) are reported using this temperature controlling method compared with 2.5×109 N/m2 (360×103 lb f/in.2) for similar diameter material grown using a constant power mode system.

Strength and stiffness of lightweight concrete corners

Abstract: THIS PAPER PRESENTS RESULTS OF TESTS ON 54 REINFORCED LIGHTWEIGHT CONCRETE CORNERS SUBJECTED TO LOADS OPENING THE CORNER (I.E., PRODUCING TENSION ON THE INSIDE) ARE REPORTED. THE EFFECTS OF 28 TYPES OF REINFORCEMENT DETAILS ON ULTIMATE FLEXURAL STRENGTH, STIFFNESS, AND CRACKING WERE STUDIED, AND IT WAS FOUND THAT THE USE OF TWO SETS OF MUTUALLY PERPENDICULAR DIAGONAL REINFORCEMENTS SHOWED PROMISE. /AUTHOR/

Properties of laterite aggregate concrete

Abstract: The paper presents the results of tests conducted on fresh and hardened concrete using laterite as aggregate. Several mixes of laterite aggregate concrete were made with varying watercement and aggregate-cement ratios to study the properties like workability, compressive, flexural, tensile strength and Modulus of elasticity. The tests indicate that the workability decreases with increasing aggregate-water ratio. The compressive strength of laterite aggregate concrete is considerably lower than that of gravel or crushed granite aggregate concrete, while the average ratio of cylinder to cube strength compared favourably with that for normal aggregate concrete, for the range of aggregate and water-cement ratios covered in this investigation.

Mercury embrittlement of age-hardened cu-1.9wt Pct cobalt and Cu-3.6 wt Pct Titanium

Abstract: The embrittlement of age-hardened Cu-1.9 wt pct Co and Cu-3.6 wt pct Ti by mercury was investigated at room temperature. The embrittlement effect on alloys subjected to different aging conditions is correlated with slip mode and precipitate morphology. Copper-cobalt failures in mercury occurred at a stress above conventional yield strength, but below the ultimate tensile strength. The solution-treated condition exhibited the greatest loss in fracture strength. Here, the slip lines were distinct and heterogeneous, while in aged samples, they were diffuse and homogeneous. Heterogeneous slip results in large stress concentrations which can account for the greater embrittlement in the solution-treated structure. In copper-titanium, all failures in mercury occurred in a relatively narrow stress band of 52 to 66 ksi, independent of the state of aging. The yield strength attainable in air ranged from 40 to 98 ksi. In those samples which were aged to form coherent precipitates, failure in mercury occurred below the conventional yield stress. It is thus concluded that the mode of slip and yield strength do not appear to influence significantly the fracture characteristics of copper-titanium in a liquid mercury environment.

Flexural mode of ridge guides for elastic surface waves

Abstract: An analysis procedure developed for the thick overlay type of elastic waveguides is shown to give, within experimental error, the dispersion curves of the recently reported flexural mode for ridge guides. Displacement patterns are shown for representative propagation conditions.

Microstructural aspects of the fracture of two-phase alloys

Abstract: This chapter is concerned with the fracture of two-phase alloys consisting of hard and relatively brittle particles embedded in a soft and relatively ductile matrix. In dilute alloys, the particles act as inclusions which alter the homogeneity of the internal stress field, causing stress concentration and residual stresses. Crack initiation takes place at the particles but, generally, only after the onset of overall plastic deformation, as shown in detail by a quantitative study of the fracture of silicon particles in aluminium-silicon alloys. The presence of brittle particles reduces the ductility of metals, the extent depending mainly on the volume fraction of the particles. An attempt to relate analytically the elongation at rupture to the volume concentration of rigid particles is discussed. The fracture behavior of alloys with high concentrations of a hard phase is described on the basis of two cermet-type systems one, a so-called heavy metal, W-Ni-Fe; the other, a cemented carbide, WC-Co. In both alloy systems, the fracture studies indicate that, as the hard particle content is increased, the fracture initiation site changes from matrix to particle or particle interface, and the fracture propagation path also changes from matrix to matrix and particles. The fracture strength first increases with particle concentration, but the change from a ductile to a brittle fracture mode eventually leads to lower fracture strengths at high particle concentrations.