Showing papers on "Flexural strength published in 1969"

Strength of Concrete Filled Steel Tubular Columns

Abstract: The ultimate strength of axially and eccentrically loaded steel tubular columns covering a wide range of slenderness ratios was investigated. Hollow steel tubes were tested and compared with concrete filled steel tubes. It was found that the buckling load of the axially loaded long columns can be accurately predicted by summing the tangent modulus loads for the steel tube and the concrete core acting as independent columns. The effect of slenderness ratio on the lateral pressure exerted by the tube on the concrete was examined. Lateral pressure is exerted when the concrete commences to increase in volume at high strains and results in an increase in strength of the concrete. Buckling will occur before the longitudinal strain becomes sufficiently high to cause the concrete to increase in volume. For eccentrically loaded columns constructed from steel tubes infilled with concrete, it was found that a straight line interaction formula using the ultimate axial load and the ultimate flexural capacity of the sections predicted failing loads.

Fine structures and fracture processes in plastic/rubber two -phase polymer systems. I. Observation of fine structures under the electron microscope

Abstract: Detailed crazing behavior in several plastic/rubber twophase polymer systems was studied by means of direct observation of ultrathin sections under the electron microscope by employing osmium tetroxide staining and hardening procedure. Samples used are ABS polymer, high -impact polystyrene and several PVC/rubber blends. All of the systems investigated showed evidence of stress -crazing when under flexural stress. Relationships between the dispersed rubber particles and the crazing behaviors were studied, and the role of rubber particles in the toughening mechanism of plastics was discussed based on these observations.

Mechanical Properties of Polycrystalline β‐Sic

Abstract: The mechanical properties of chemically vapor-deposited β-Sic were measured in bending between room temperature and 1400°C. Material with grain diameters from less than 1 to 15 μm was tested. No grain-size dependence of the bend strength of dense (<99% of theoretical) Sic was observed at any test temperature. The fracture strength of dense Sic remained approximately constant between room temperature and about 900°C and then increased sharply up to the maximum test temperature of 1215° to 1400°C. This increase in fracture stress coincided with the onset of plastic yielding detectable in the stress-strain curves. The fracture mode of this material was transgranular cleavage at all test temperatures. The fracture stress of Sic of lower density, which was characterized by the presence of grain boundary flaws, decreased slightly at high temperature. The fracture mode of the low-density (3.17 g/cm3) β-Sic underwent a transition from predominantly transgranular at room temperature to predominantly intergranular at high temperature.

Strength, Fracture Mode, and Thermal Stress Resistance of HfB2 and ZrB2

Abstract: Zirconium diboride and hafnium diboride were fabricated by hot-pressing at 1800°C and 120,000 psi. Bend strengths were measured on the fully dense materials from 25° to 1400° C in an argon atmosphere. These diboride compounds do not exhibit any gross plastic flow in the temperature range studied. The bend strengths go through a maximum between 700° and 1000°C and vary from 39,000 to 68,000 psi for HfB2 and 30,000 to 56,000 psi for ZrB2. The maxima in strength correspond to maxima in the fraction of transgranular fracture. The bend strength and room-temperature elastic modulus measurements were combined with available thermal conductivity and expansion data to calculate thermal stress resistance parameters. Under steady-state heat flow conditions, the calculated thermal stress resistance parameters of the borides are higher than those calculated for other refractory compounds.

Thermoplastic resin blend of polyphenylene oxide with butadiene-containing polymers

Abstract: BLENDS OF THERMOPLASTIC POLYPHENYLENE OXIDE RESIN (WHICH OPTIONALLY CONTAINS AN ALKENYL AROMATIC POLYMER SUCH AS A STYRENE POLYMER) WITH BUTADIENE HOMOPOLYMERS AND COPOLYMERS ARE CHARACTERIZED BY AN UNUSUALLY USEFUL COMBINATION OF PROPERTIES, PARTICULARLY LOW TEMPERATURE MELT PROCESSABILITY IN COMBINATION WITH HIGH IMPACT STRENGTH AND FLEXURAL STRENGTH.

Mechanical properties of glass fibre-reinforced gypsum

Abstract: Gypsum plaster, like other inorganic cements, is strong in compression but weak in tension exhibiting brittle behaviour. Commercialy available E glass fibres can be used to reinforce the gypsum plaster matrix and produce a strong composite material having improved tensile and impact properties. This paper describes the effect of glass content on the flexural, tensile, compressive and impact strength of this glass fibre plaster composite which is made by a simple spray/suction technique.

Diagonal Tension Cracking in Concrete Beams with Axial Forces

Abstract: Study made of available data on diagonal tension cracking in reinforced concrete beams with and without axial load. Increment of shear between calculated flexural cracking and observed diagonal tension cracking was found to be a function of flexural reinforcement ratio, p , and modular ratio, n . In the study, 31 reinforced concrete beams were tested under combined transverse load and axial load, including both tension and compression. Results obtained confirm the conclusions reached as result of study of previously available test data. Two modified forms of Equation 26-12 of the ACI Building Code, AC1 318-63, are proposed as applicable to both prestressed concrete and reinforced concrete with or without axial load.

Strength ‐Composition relationships of random short glass fiber ‐thermoplastics composites

Abstract: Twelve polymers and copolymers reinforced with random short glass fibers are used for the study of the strength -composition relationship. Six of these reinforced systems are new and have not been reported elsewhere. The effect of fiber volume fraction on tensile and flexural strengths is related to the Kelly and Tyson equation. For each composition the strengthening factor, F, is calculated and discussed with respect to the structure of the polymer. One factor pertaining to the actual performance of fiber glass, fiber efficiency, K, has been extrapolated for the fiber glass used for this study. The effects of fibers on toughness and the Izod notched impact strength are discussed. It is the impact strength ratio and not the toughness which is used to describe the net result of reinforcement. The deviations between the wet and the dry strengths are used to illustrate the effect of the fiber -matrix interfacial bond. A new parameter, Δθ, is introduced to describe the effect of structure on the fiber -matrix interface. The effect of water at the fiber -matrix interface is further demonstrated through the determination of dielectric constant and dissipation factor of the composite before and after water immersion. The rule of mixtures was found to apply to dry electrical properties of composites.

Torsional-Flexural Buckling of Thin-Walled Sections Under Eccentric Load

Abstract: A detailed analysis of the behavior of thin-walled open sections under eccentric loading is presented, with emphasis on singly-symmetric sections loaded in the plane of symmetry. It is shown that for a given shape, depending on eccentricity and slenderness, a variety of behavior modes is possible: continuous purely flexural beam-column behavior, flexural instability, torsional-flexural instability and, in exceptional cases, purely torsional instability. The purpose of this paper is the development of accurate design methods and procedures. For most practically important open shapes yielding by simple flexural beam-column action governs when the load is applied on the side of the shear center opposite from that of the centroid. If the load is applied on the open side of the section, or between shear center and centroid, failure can be by torsional-flexural instability, by yielding in the beam-column mode, or by flexural instability. Experimental investigation is in very satisfactory agreement with theory.

Plane strain fracture toughness.

Abstract: The general concept of the K I c plane strain fracture toughness, due to G. R. Irwin, is reviewed, and the current (tentative) standard procedure for determination of K I c with crack-notched bend specimens is discussed in detail. The standard procedure constitutes an operational definition of K I c which is somewhat arbitrary, but no more so than is the definition of offset yield strength. Experimental data for high-strength steels, titanium, and aluminum alloys validate the standard procedure for determination of K I c , and confirm that it is reasonable to regard K I c as an inherent material property which controls fracture under conditions of sufficiently high constraint. However, the required specimen dimensions increase in proportion to the square of the ratio of K I c to yield strength, and impractically large specimens may be required for tough, low-strength materials. The standard test procedure for bend specimens can be adapted to other types of specimens with the aid of information given in an appendix.

The effect of time and temperature on the mechanical behavior of a 'plasticized' epoxy resin under different loading modes

Abstract: Epoxy–Versamid specimens were loaded in tension, compression, and flexure at different strain rates and temperatures to determine mode of failure, yield stress and strain, and tangent and relaxation moduli. Stress-strain curves were used to define brittle, ductile, ductile-rubbery, and rubbery modes of behavior which prevailed in different temperature-strain rate regions. The time-temperature superposition principle was applied to yield stress, initial tangent moduli, and relaxation moduli data for all three types of loading. The transition regions, tangent and relaxation moduli, and shift factors were the same in tension, compression, and flexure. Thus the most convenient mode of loading can be used to determine the general time-temperature dependence. The ratio of compressive-to-tensile yield stress was almost constant over the entire ductile region. Flexural yielding data were used to predict yield stress in tension and compression, and stress relaxation master curves were shown to be related to elastic modulus vs. strain rate curves. The yielding phenomenon was interpreted using Eyring's theory of non-Newtonian viscoplastic flow. The apparent activation energy and activation volume were larger for tension than compression. A theory is offered to explain why yielding can occur in a cross-linked system.

Effect of porosity on the strength of concrete

Abstract: AN EXPONENTIAL FUNCTION IS RECOMMENDED FOR THE COMPRESSIVE STRENGTH VERSUS AIR CONTENT RELATIONSHIP. EXPERIMENTAL EVIDENCE SHOWS THAT A CHANGE IN THE AIR CONTENT AFFECTS THE COMPRESSIVE STRENGTH OF A CONCRETE MORE THAN ITS FLEXURAL OR TENSILE STRENGTHS. EXPERIMENTAL RESULTS ALSO INDICATE HIGHER SENSITIVITY OF THE COMPRESSIVE STRENGTH WHEN THE CHANGE IN POROSITY IS CAUSED BY A CHANGE IN THE WATER-CEMENT RATIO OR AGE. AN APPROXIMATE FORMULA IS PRESENTED WHICH PROVIDES THE EFFECT OF WATER-CEMENT RATIO ON THE RATIO OF FLEXURAL STRENGTH TO COMPRESSIVE STRENGTH OF COMPARABLE CONCRETES. APPROXIMATE FORMULAS ARE PRESENTED WHICH ARE OBTAINED FROM THE PROPOSITION THAT A CHANGE IN THE WATER-CEMENT RATIO AFFECTS THE CONCRETE STRENGTH THROUGH A CHANGE IN POROSITY OF THE HARDENED PASTE. ONE OF THESE FORMULAS PROVIDES A FAMILY OF CONVERGING STRAIGHT LINES IN THE STRENGTH VERSUS LOG (WATER-CEMENT RATIO) SYSTEM FOR COMPARABLE CONCRETES OF VARIOUS AGES AS WELL AS FOR COMPARABLE COMPRESSIVE, FLEXURAL, AND TENSILE STRENGTHS. POSSIBILITIES FOR THE REFINEMENT OF THIS FORMULA ARE DISCUSSED. /AUTHOR/

Strengthening Sapphire by Compressive Surface Layers

Abstract: Compressive surface layers were formed on sapphire rods. The methods included glazing and quenching, formation of Al2O3–Cr2O3 solid solution surface layers, and formation of mullite and calcium aluminate surface layers. The presence of the compressive stresses was demonstrated by slotted rod tests. Substantial improvements in flexural strength and thermal shock resistance were observed. The highest average flexural strength was obtained by glazing and quenching and was 340 000 psi. The strengths were measured in the ``as‐treated'' and ``as‐treated and abraded'' conditions. The abraded samples retain a substantial portion of the improved strength.

Strength of concrete filled steel columns

Abstract: THE ULTIMATE STRENGTH OF AXIALLY AND ECCENTRICALLY LOADED STEEL TUBULAR COLUMNS COVERING A WIDE RANGE OF SLENDERNESS RATIOS WAS INVESTIGATED. HOLLOW STEEL TUBES WERE TESTED AND COMPARED WITH CONCRETE FILLED STEEL TUBES. IT WAS FOUND THAT THE BUCKLING LOAD OF THE AXIALLY LOADED LONG COLUMNS CAN BE ACCURATELY PREDICTED BY SUMMING THE TANGENT MODULUS LOADS FOR THE STEEL TUBE AND THE CONCRETE CORE ACTING AS INDEPENDENT COLUMNS. THE EFFECT OF SLENDERNESS RATIO ON THE LATERAL PRESSURE EXERTED BY THE TUBE ON THE CONCRETE WAS EXAMINED. LATERAL PRESSURE IS EXERTED WHEN THE CONCRETE COMMENCES TO INCREASE IN VOLUME AT HIGH STRAINS AND RESULTS IN AN INCREASE IN STRENGTH OF THE CONCRETE. BUCKLING WILL OCCUR BEFORE THE LONGITUDINAL STRAIN BECOMES SUFFICIENTLY HIGH TO CAUSE THE CONCRETE TO INCREASE IN VOLUME. FOR ECCENTRICALLY LOADED COLUMNS CONSTRUCTED FROM STEEL TUBES INFILLED WITH CONCRETE, IT WAS FOUND THAT A STRAIGHT LINE INTERACTION FORMULA USING THE ULTIMATE AXIAL LOAD AND THE ULTIMATE FLEXURAL CAPACITY OF THE SECTIONS PREDICTED FAILING LOADS. /ASCE/

Thermoplastic resin blend of polysulfone resin and an ethylenepropylene terpolymer or graft derivative thereof

Abstract: BLENDS OF THERMOPLASTIC POLYSULFONE RESIN AND ETHYLENEPROPYLENE TERPOLYMERS AND GRAFT DERIVATIVES THEREOF ARE CHARACTERIZED BY AN UNUSUALLY USEFUL COMBINATION OF PROPERTIES, PARTICULARLY LOW TEMPERATURE MELT PORCESSABILITY IN COMBINATION WITH HIGH IMPACT STRENGTH AND FLEXURAL STRENGTH.

Moment-rotation characteristics of shear connections

Abstract: A STANDARD SHEAR CONNECTION IS A PAIR OF ANGLES FASTENED TO THE WEB BY WELDS AND FIELD BOLTED OR WELDED TO THE SUPPORTING GIRDER OR COLUMN. THIS TYPE OF CONNECTION HAS PROVED RELIABLE AND HAS AS ADVANTAGES: (1) THE LONGITUDINAL POSITION OF THE ANGLES CAN BE ADJUSTED SLIGHTLY TO ALLOW FOR OVER- OR UNDER-CUT IN THE LENGTH OF THE BEAM, AND (2) THE PROJECTION OF THE ANGLES BEYOND THE END OF THE BEAM PROVIDE FOR SOME CLEARANCE FOR ERECTION. A SIMPLER SHEAR CONNECTION CONSISTS SOLELY OF A VERTICAL END PLATE WELDED TO THE END OF THE WEB THAT TRANSFERS TO THE BEAM. THE BEHAVIOR IS ANALYZED OF THESE END PLATE SHEAR CONNECTIONS TO DETERMINE THE MOMENT-ROTATION CHARACTERISTICS. COMPARATIVE TESTS WERE CONDUCTED ON ANGLE CONNECTIONS OF COMPARABLE GEOMETRY. BY COMPARING SETS OF CURVES, IT WAS POSSIBLE TO DETERMINE, WITHIN THE LIMITS OF THE EXPERIMENTS, THE EFFECT OF VARIATION OF EACH PARTICULAR PARAMETER ON THE MOMENT-ROTATION CURVE. THE ADEQUACY OF THE SHEAR CONNECTIONS FOR USE DEPENDS ON WHETHER OR NOT THEY CAN DEVELOP THE REQUIRED SHEAR CAPACITY AND WHETHER THE ROTATIONS REACHED EXCEED THOSE WHEN THE BEAM HAS ITSELF REACHED ITS ULTIMATE LOAD. TWO METHODS OF ANALYSIS ARE SUGGESTED BY THE BEHAVIOR OF THE CONNECTION PLATES: FLEXURAL ANALYSIS AND MEMBRANE ANALYSIS. THESE ANALYSES SHOW THAT: (1) END PLATE CONNECTIONS CAN PROVIDE ADEQUATE SHEAR CONNECTIONS WHEN DESIGNED FOR SHEAR ONLY, (2) END PLATE CONNECTIONS DISPLAY MOMENT ROTATION CHARACTERISTICS SIMILAR TO THOSE OF ANGLE CONNECTIONS, (3) END PLATE CONNECTIONS CAN BE DESIGNED FOR A WIDE RANGE OF FLEXIBILITIES, (4) IN DEEP CONNECTIONS THE POSSIBILITY OF BOLT FRACTURE SHOULD BE INVESTIGATED, (5) END PLATE CONNECTIONS SHOULD PROVIDE A ROTATION IN EXCESS OF THE BEAM LINE WHEN COLUMN BEARING OCCURS, (6) A TWO-PHASE BEAM LINE IS REQUIRED TO REPRESENT THE ATTAINMENT OF SOME SPECIFIED STRESS LEVEL IN THE BEAM, AND (7) A COMBINED FLEXURAL MEMBRANE ANALYSIS CAN BE USED TO PREDICT THE MOMENT AND ROTATION AT COLUMN BEARING.

Effect of multiaxial stresses on the fracture strength of silicon carbide

Abstract: This work describes the fracture behaviour of silicon-carbide tubular specimens under multi-axial stresses at room temperature. A method of obtaining combinations of stresses in the form of torsion, hoop, axial tension, and compression is described and failure envelopes for silicon carbide are included from the data obtained.Failure theories are reviewed and the results from the work show that the available theories are inadequate to describe both the tension-tension and tension-compression quadrants.For practical purposes a straight-line relation can be used joining axial and hoop tensile strengths and the axial compression strength.

THERMAL PROPERTIES OF β-SILICON CARBIDE FROM 20 TO 2000°C

Abstract: Thermal and mechanical properties have been measured on chemical vapor deposited, polycrystal β-SiC. Density was measured from 20°C (3.166 gm/cm3) to 2000°C (3.075). Linear thermal expansion, measured between 20 and 2000°C, showed a total differential expansion of less than 1%. Enthalpy and specific heat were characterized between 0 and 2000°C and thermal diffusivity and thermal conductivity from 200 to 2000°C. Hardness and flexural strength were measured to 1500°C. Maximum strength is at 1000°C, dropping to 2/3 of its room temperature value at 1500°C.

The Role of Bond Strength in the Fracture of Advanced Filament Reinforced Composites

Abstract: Longitudinal strength characteristics of filament reinforced composites, discussing bond strength effect on filament fracture

Composite beam incorporating cellular steel decking

Abstract: RESULTS OF A TEST ON A COMPOSITE STEEL AND CONCRETE BEAM INCORPORATING A CELLULAR STEEL DECK ARE REPORTED. GOOD AGREEMENT BETWEEN MEASURED AND COMPUTED VALUES OF STRAIN AND DEFLECTION IS INDICATED PRIOR TO FIRST YIELDING. THE BEAM BEHAVED IN ACCORDANCE WITH THE ELASTIC THEORY FOR COMPOSITE BEAMS WITH INCOMPLETE INTERACTION. THE LOAD-SLIP CHARACTERISTICS FOR THE END CONNECTIONS WAS DETERMINED FROM THE BEAM TEST RESULTS. THE MAXIMUM STRENGTH OF A CONNECTION COMPUTED FROM THE MEASURED LOAD AND END SLIPS IN THE ELASTIC RANGE HAS BEEN USED TO ESTIMATE THE ULTIMATE STRENGTH OF THE BEAM. ELASTIC THEORY PREDICTION OF MAJOR BREAKDOWN OF INTERACTION UNDER THE LOAD-POINTS OF A BEAM WITH SYMMETRICAL TWO POINT LOAD SYSTEM WAS CONFIRMED IN THE TEST WHEN THE EXTREME FIBER STRAINS IN THE STEEL AND CONCRETE AT THE LOAD POINTS EXCEEDED THOSE AT MID-SPAN IN THE ELASTIC RANGE. AT MAXIMUM LOAD TWO HINGES FORMED AT THE LOAD POINTS. IT IS SHOWN HOW EFFICIENCY FACTORS FOR FLEXURAL STRESS AND DEFLECTION CAN BE DERIVED. /ASCE/

Resins and reinforced plastic laminates for continuous use at 650°f—II

Abstract: This paper is the third in a series describing work done under Air Force sponsorship to develop high temperature polyimide laminates for radomes and other parts for supersonic aircraft. Twelve resin compositions are described and evaluated. Most were prepared from benzophenonetetracarboxylic dianhydride and one or more aromatic diamines. Modifying linkages such as amide, ether, benzimidazole, and oxadiazole were present in some cases. A variety of precure and pressing conditions were studied, best results being obtained with a fully cured prepreg pressed at about 700°F and 200–1000 psi. Most of the laminates were made with E glass cloth, but some work was done also with S glass, Refrasil, and carbon cloth. Initial flexural strengths on E glass of 35–60,000 psi at room temperature, and 20–40,000 psi at 600°F were observed for the better resins. On S glass, slightly higher strengths were observed together with values of about 10,000 psi at 700–1000°F. Aging data on E glass laminates show retention of at least 10,000 psi flexural strength at temperature for about 250 hrs. at 650°F, 1000 hrs. at 600°F, 5000 hrs. at 527°F, and 30,000 hrs. at 482°F. Dielectric constant and dissipation factor at 10 Gc were found to be nearly constant at 3.5–4.4 and 0.005–0.01, respectively, for temperatures up to 662°F and for aging up to 1000 hrs. at 600°F. At frequencies of 60 c and 1 Kc, an increase of dissipation factor with temperature was found and was used as a measure of Tg.

Thermoplastic resin blends of polysulfone and a graft derivative of a butadiene containing polymer spine

Abstract: BLENDS OF THERMOPLASTIC POLYSULFONE RESIN AND A GRAFT DERIVATIVE OF A BUTADINE CONTAINING POLYMER SPINE ARE CHARACTREIZED BY UNUSUALLY USEFGUL COMBINATION OF PROPERTIES, PARTICULARLY LOW TEMPERTURE MELT PROCESSABILITY IN COMBINATION WITH HIGH IMPACT STRENGTH AND FLEXURAL STRENGTH.

Acid resistant polyester resins

Abstract: THE ACID RESISTANCE AND FLEXURAL STRENGTH OF CROSS-LINKED POLYESTER RESINS IS INCREASED BY USING SMALL AMOUNTS OF GLYCIDYL METHACRYLATE OR GLYCIDYL ACRYLATE IN THEIR PREPARATION.

Bonded Wood-Concrete T-Beams

Abstract: Timber-concrete composite T-beams were fabricated and tested to destruction. Unreinforced precast concrete slabs were glued to timber beams using an epoxy compound resulting in a T-section with the concrete serving as the flange and the timber serving as the web. Using an equivalent all wood transformed section gave good experimental agreement for the neutral axis position and curvature in the test beams but poor agreement for deflection. Four beams failed in sliding shear at the high shear region while one beam reached the full flexural strength of the composite section. It was shown that wood-concrete bonded T-beams may carry substantial loads and function as true composite beams.

Method of strengthening ceramic bodies and strengthened ceramic bodies produced thereby

Abstract: A METHOD OF INCREASING THE BENDING STRENGTH AND THERMAL SHOCK CHARACTERISTICS OF SINGLE CRYSTAL AND POLYCRYSTALLINE CERAMIC BODIES AND STRENGTHENED CERAMIC BODIES PRODUCED THEREBY. THE BODIES ARE STRENGTHENED BY FORMING AT LEAST ON ONE SURFACE THEREOF AT AN ELEVEATED TEMPERATURE A LAYER OF LOW EXPANSION MATERIAL WHICH IS A MATERIAL COMPOSEED AT LEAST PARTLY OF THE MATERIAL WHICH IS THE BODY AND WHICH AT THE LEAST HAS A COEFFICIENT OF EXPANSION WHICH IS LESS THAN THAT OF THE MATERIAL OF THE BODY. THE MATERIAL CAN ALSO HAVE AN INCREASED VOLUME, AND CAN BE A SOLID SOLUTION OR THE MATERIAL OF THE BODY IN A CHANGED PHASE. THE BODY IS THEN COOLED SO AS TO PRODUCE ON THE SURFACE OF THE BODY A LAYER WHICH IS UNDER COMPRESSION RELATIVE TO THE BODY.