Showing papers on "Flexural strength published in 1970"

Elastic Constants of Compression-Annealed Pyrolytic Graphite

Abstract: The elastic constants of pyrolytic graphite which has been highly ordered by annealing under compressive stress have been determined by ultrasonic, sonic resonance, and static test methods. Ultrasonic tests yielded the elastic constants c11, c12, c33, c44 = 1/s44, and the stress derivative of c33. The moduli 1/s11 and c44 were determined from the free flexural resonant vibrations of bars, and the shear modulus c44 also was determined from the fundamental torsional resonance of the bars and from the resonance of compound torsion oscillators composed of thin graphite disks with steel end pieces. Static tension, compression, and torsion tests on the pyrolytic graphite yielded a complete set of compliances (s11, s12, s13, s33, and s44). The following self‐consistent set of elastic constants (cij in units of 1011 dyn/cm2; sij in 10−11 cm2/dyn) has been deduced from the results: c11 = 106±2, c12 = 18±2, c33 = 3.65±0.10, c13 = 1.5±0.5, c44 = 0.018 to 0.035, 1/s11 = 102±3, 1/s33 = 3.65±0.10, s12 = −0.0016±0.0006,...

Finite element analysis of torsional and torsional–flexural stability problems

Abstract: Structure of flexural members, analyzing torsional and lateral stability by finite element method and matrix formulation

A review of parameters influencing some mechanical properties of tungsten carbide–cobalt alloys

Abstract: The paper reviews experimental results relating to the influence of composition, structure, and testing conditions on the hardness, compressive strength, and transverse rupture strength of sintered tungsten carbide–cobalt alloys.

Effect of a Reactive Environment on the Hertzian Strength of Brittle Solids

Abstract: Hertizan fracture theory, previously developed for ideal brittle solids fractured under essentially environment‐free conditions, is here modified to allow for an interaction between the growing cone crack and a reactive environment. Two alternative models, both of which account for the observed detrimental effect of an environment on the Hertzian strength but which predict slight differences in the growth of the cone crack, are offered. The first is based on a surface‐energy‐lowering concept and the second on a subcritical‐crack‐growth concept. The theoretical implications of these two models are examined in the light of Hertzian fracture experiments on abraded glass slabs in different test environments. Observations of the growth of the cone crack in fatigue experiments favor the second model for glass. The advantages of the Hertzian test as a tool for the study of environmental effects on the fracture strength of brittle solids in general are discussed in relation to more conventional fracture tests.

Glass Fibre Reinforced Cement and Gypsum Products

Abstract: Glass fibre reinforced cements and gypsum plaster provide examples of composite materials where both the components are brittle and the matrix phase fails at a much lower strain than the fibre. Porosities of the order of 30% or more are usually present in these matrices. The interfacial bond that develops between the fibre and the matrix is very discontinuous and irregular. The dispersion of glass fibre in the matrix is not easy. When chopped multifilament strands are distributed in the matrix by a spraying process, the tensile and flexural strength of the composite material produced from gypsum plaster reach maximum values around 10% by volume of fibre addition. Beyond the elastic limit, the composite material exhibits a quasi-plastic behaviour until it fails by fibre pull-out. Fire resistance and impact strength of plaster are greatly improved by fibre incorporation. Glass fibres now available commercially are not durable in the alkaline medium present in hydrating Portland cements. Experimental fibres produced from more alkali-resistant glasses are being studied for their suitability in reinforcing cements and concrete. It can be foreseen that given a durable glass, the composite material will have pronounced advantages over existing sheet materials in respect of impact strength and resistance to cracking, tensile and bending strength and fire resistance.

Hydraulic cementitious compositions reinforced with fibrillated plastic film

Abstract: CONCRETE, MORTAR, CEMENT OR PLASTER OF PARIS ARE REINFORCED TO PROVIDE PRODUCTS OF IMPROVED BENDING STRENGTH BY ADDITION OF UP TO 2% BY WEIGHT OF FIBRILLATED POLYPROPYLENE FILM TO THE MASS PRIOR TO OR DURING MIXING

The cohesion of previously fractured Fcc metals in ultrahigh vacuum

Abstract: The cohesion of clean surfaces of the fcc metals Ag, Al, Cu, and Ni was investigated using the technique of cold welding specimens previously fractured in an ultrahigh vacuum The cohesive strength of the weld increased with compressive load, all data falling on a single curve with slight positive curvature when the cohesive strength and compression load were normalized through the initial fracture strength of each metal The cohesion coefficients ranged from 062 to 115 and were in accord with those obtained using more elaborate techniques of surface preparation and testing It is proposed that the essentially constant cohesion coefficient obtained for all the unalloyed fcc metals resides in the fact that the area of contact produced by a given compressive load is inversely proportional to the fracture stress of the metal and the cohesive strength is directly proportional to this fracture stress A lowered cohesion coefficient was observed for copper specimens which had recrystallized in the vicinity of the interface either during the cold welding or as the result of a subsequent heat treatment

Transient Flexural Vibrations of Ship-Like Structures Exposed to Underwater Explosions

Abstract: The flexural vibrations of ship‐like structures are easily excited by underwater explosions, particularly if the explosion bubble period approximately synchronizes with a period of flexural vibration. A summary of the theoretical analysis shows how the transient motions are related to the principal vibration modes of the structure, and to the distribution and history of the applied pressures. The latter depend on the size, depth, and relative position of the explosive. Experiments on small idealized ship and submarine models are described which vary the weight, depth, and position of the explosive, and which measure the instantaneous deformations of the structure with strain gauges connected into special bridge circuits to yield the normal coordinates associated with the principal flexural vibration modes. Comparison of the theory and experiments verify the theory as applied to the fundamental flexural mode, and with less precision, as applied to the higher flexural modes. The principal mode patterns and the history of the explosion bubble are verified by independent experiments.

Design of composite beams with formed metal deck

Abstract: THE AISC SPECIFICATION FOR BUILDINGS DOES NOT PROVIDE FOR COMPOSITE BEAMS WITH A FORMED METAL DECK BETWEEN THE STEEL AND CONCRETE SLAB. WHEN THE METAL DECK CORRUGATIONS ARE PARALLEL TO THE BEAM, THEY DO NOT INTERFERE WITH THE STEEL-CONCRETE INTERACTION AND THE CONDITION IS SIMILAR TO A HAUNCHED SLAB FOR WHICH THE SPECIFICATION PROVISIONS ARE APPLICABLE. HOWEVER, WHEN THE METAL DECK IS PLACED PERPENDICULAR TO THE STEEL BEAMS AND SHEAR CONNECTORS ARE PLACED IN THE RIBS OF THE CORRUGATIONS, THE BEHAVIOR OF THE COMPOSITE SYSTEM MAY DIFFER SUBSTANTIALLY FROM THE EXPECTED BEHAVIOR. STUDIES INDICATE THAT ALL CORRUGATIONS HAVE LITTLE OR NO INFLUENCE ON BEAM BEHAVIOR AND THAT BEAMS COULD BE DESIGNED AS THOUGH THE SLABS WERE SOLID. TESTS ON COMPOSITE BEAMS WITH RIBS UP TO 1 AND 1/2 INCH, ARE SUMMARIZED IN THE FIGURE. WITH INCREASING RIB HEIGHT, THE FLEXURAL CAPACITY OF THE BEAMS WAS DECREASED AS A RESULT OF THE REDUCTION IN SHEAR CONNECTION STRENGTH. THE REDUCTION IN FLEXURAL CAPACITY IS ANALOGOUS TO THE REDUCTION OBSERVED IN CONVENTIONAL COMPOSITE BEAMS WHEN PARTIAL SHEAR CONNECTION IS AVAILABLE. THIS REDUCED FLEXURAL CAPACITY CAN BE DETERMINED WHEN THE STRENGTH OF THE SHEAR CONNECTION IS KNOWN. THE SLAB WIDTH AND CONNECTOR SIZE AFFECT THE CONNECTORS STRENGTH. THE FLEXIBILITY OF THE SHEAR CONNECTOR HAS SOME EFFECT ON THE BEHAVIOR OF THE RIB AND ITS ABILITY TO RESIST SHEAR. TENTATIVE DESIGN RECOMMENDATIONS ARE PRESENTED FOR COMPOSITE BEAMS WITH FORMED METAL DECK UP TO 3 IN. HIGH.

Effect of Surface Finish on Structural Ceramic Failure

Abstract: The relation between fracture strength and surface finish of brittle nonmetallic materials was examined and related to surface-crack theory. Specimens used in an experimental illustration were made of a commercially available 96%-pure alumina with an average grain size of 3.8 μm and a porosity of about 6%. Several groups of specimens, each having a different surface finish, were used in a biaxial ball-and-ring

Fractographic analysis of the low energy fracture of an aluminum alloy

Abstract: A study of the fracture process in a high strength aluminum alloy, 2014T6, was undertaken to identify the void nucleating particles in this material, to determine their composition, and to suggest means by which they might be eliminated without loss of strength.

Tensile strength of butt-joined epoxy-aluminum plates

Abstract: Tensile tests conducted on butt joined epoxy-aluminum plates containing single cracks along the bond surfaces showed that there exists a characteristic crack length below which the fracture strength of the composite is mainly influenced by the stress concentrations at the bond edges. For specimens with cracks longer than the characteristic length the fracture of the composite is entirely controlled by the stress concentrations at crack tips. In the latter case the stress intensity factors defined by Sih and Rice, and Erdogan appeared to agree reasonably well with test results.

Fatigue Tests on Prestressed Concrete I-Beams

Abstract: Six fatigue tests of prestressed concrete I-beams containing web reinforcement are reported. Each beam was initially subjected to a high overload, and then subjected to 2,000,000 cycles of a design equivalent repeated loading. The beams failed by either flexural or shear fatigue. The flexural fatigue life of the test beams was less than expected from available information on the fatigue strength of strand. The tests demonstrated that prestressed concrete beams have a remarkable shear fatigue resistance. Prestressed beams, with enough web reinforcement to develop their flexural capacity, can be subjected to overloads which cause extensive cracking without subsequent danger of a shear fatigue failure under design loads. Shear fatigue failures do not occur suddenly. There is considerable warning, as indicated by increasing deflection and increasing inclined crack width, before failure occurs. In these and other tests, shear fatigue failures did not occur when the range in inclined crack width was less than 0.006 in. under application of repeated loads.

Theory of Brittle Fracture Applied to Soil Cement

Abstract: The cracking in a soil-cement base is examined using Griffith’s theory of brittle fracture Flexural tests are performed on soil-cement beams with crack-simulating notches to determine the critical strain energy-release-rate, \IG\dc\N, associated with the rapid extension of the crack Model studies are made to evaluate the crack propagation in a soil-cement pavement base The variations of critical strain energy release-rate according to soil texture, clay mineral present, and the time rate of loading, as well as its independence of the notch geometry indicate that \IG\dc\N is a physical property of the cement-treated soil Fracture toughnes, \IK\dc\N, a function of the stress intensity factor \iK and the crack extension force \iG, in accord with fracture mechanics concepts, exhibits an inverse relation with the rate of crack propagation In addition, the crack patterns observed in the model slabs are in keeping with the fundamental postulate of Griffith In simple and symmetrical cases, the cement base upon cracking tends to form a pattern of hexagons; but when the material is more brittle, the cracks form rather poorly defined “irregular random orthogonal polygons”, with the various cracks meeting primarily in three-way nodes

An engineering analysis of ductile fractures

Abstract: A critical strain at a small distance from a crack tip is proposed as a ductile fracture criterion. Surface strain in double edge cracked specimen made of 2024-0 aluminum alloy was measured using the moire method. The strain along the crack line and near a crack tip is proportional to the cracked-section-elongation, the latter is used as a measurable quantity to characterize ductile fractures. The effect of specimen size on fracture strength and energy absorption by the specimen were analyzed. The proposed ductile fracture analysis agrees qualitatively with fracture tests on fully annealed 4340 steel and 2024-T351 aluminum.

Research and Development of Refractory Oxidation-Resistant Diborides. Part II, Volume IV: Mechanical Properties.

Abstract: : Hot pressed diboride compositions of ZrB2 or HfB2 with additions of SiC and/or C were employed to produce materials with a range of compositions and microstructural variations of porosity and grain size for mechanical property evaluations which included ben strength and elastic modulus from room temperature to 1800 and 2100C, respectively; deformation characteristics from 1800 to 2200C, short time compressive creep from 1000 to 1800C and a limited stress-rupture time data at 1040C All data except the stress-rupture tests were obtained from measurements in either vacuum or inert atmosphere; the stress-rupture tests were conducted in air Bend strengths were consistent for a specific microstructure and composition; values ranged from 45,000 to 90,000 psi at temperatures up to 800C; 20,000 to 40,000 psi up to 1900C Bend strength data were analyzed for effects of residual elastic strain, grain size and porosity Macroscopic deformation was observed above 1600C for a dense 4 micron grain size ZrB2 composition containing C and SiC additives Creep rates are inversely proportional to grain size and flow stresses are proportional to strain rate to the 04 power Strain hardening was observed at elevated temperatures for several diboride materials containing SiC and/or C (Author)

Propagation of flexural waves in infinite, damped rib-skin structures.

Abstract: : Equations for the propagation constants of free flexural waves in rib-skin type structures are first developed in terms of the edge receptance of the ribs and skin elements. It is shown that two complex propagation constants exist for each frequency, and corresponding to each of these is a distinct 'natural wave' of flexural motion in the skins. A particular rib-skin structure with thin ribs is then studied in detail, and the variation of the propagation constants with frequency is observed. Free, unattenuated propagation of the waves is only possible in certain frequency ranges which, for each of the two natural waves, may overlap. The influence of the ribs on these ranges is investigated. (Author)

Effect of Loading Sequence on Notch Strength of Warm Prestressed Alloy Steel

Abstract: An experimental study of the effects of warm prestressing on the fracture strength of notched and fatigue-cracked bend bars of a Ni-Cr-Mo, low-alloy forging-grade steel was conducted. The steel was tested in four heat treatment conditions simulating four thickness fractions of a 23-1/2 -in-thick forging. Three load-temperature paths were investigated: (1) preload-cool-fracture, (2) preload-cool-unload-fracture, (3) preload-unload-cool-fracture. The fracture strengths of the prestressed bars were compared with the fracture strengths of unprestressed bars. The benefits of prestressing for each load-temperature path decreased in the order listed, although prestressing was always beneficial. The benefits also decreased with decreasing fracture-test temperature relative to the 50-percent FATT.

Fracture strength of relatively brittle structures and materials

Abstract: In the case of relatively brittle structural materials, linear fracture mechanics provides an analysis basis for testing and control of fracture strength. Standardized methods of crack toughness testing are available only for metals which can be pre-cracked by fatigue. Hence, further work on this topic is needed for glassy and polymeric solids. Proper use of surface residual compressive stress is a primary method of fracture control for such materials, and environment-assisted stable crack extension is often a significant factor. In the case of layered or parallel-fiber stiffened composites, the single crack fracture mechanics viewpoint usually applies to individual separations, but the aggregate effect of the expected distribution of cracks must be taken into account. Often the proof test is the main safeguard against strength-type failures in service, and the efficiency with which proof testing is employed is important.

Determination of the modulus of elasticity of bone by a vibration method.

Abstract: Specimens of bone cut from tibiae of older beef cattle have been subjected to sinusoidal vibration in flexural and longitudinal modes. From the known dimensions and density of the specimens the modulus of elasticity of each specimen was calculated following its observed resonance. The calculation was based on the small-deflection linear beam theory, the degree of validity of which was shown by finding the ratio of frequencies of the consecutive modes and the position of the nodes. A mean value of the modulus of 3·4×106 lbf/in2(23·4×109 N/m2) was obtained for the 10 specimens tested.

Comments on the long-term tensile strength of plain concrete

Abstract: Synopsis The variation of the tensile strength of concrete with age, and the relationship between the compressive and the tensile strength during the period of hardening, are investigated. Some fac...

Graphite Fiber Reinforced Polyimide Composites

Abstract: Comparatively low-void content, high strength and modulus graphite fiber reinforced polyimide composites were fabricated. Utilizing matrices of Monsanto's Skybond 700 polyimide resin and TRW's P13N polyimide resin and reinforcements of ozone-treated Thornel 40 and 50 graphite fibers, these composites exhibited flexural strengths in excess of 100,000 psi, short-beam shear values in excess of 5000 psi, and void contents as low as 5%. Flexural strength versus time at 600°F is presented for composites of P13N and graphite, Skybond 700 and graphite; P13N and glass; Skybond 700 and glass; and P13N and Morganite II. Short-beam shear strength versus time at 600°F is plotted for a composite of P13N and Morga nite II. The best isothermal heat-aging data was obtained with Sky bond 700 and Thornel 50 (ozone treated) composites. These mate rials showed no short-term loss of flexural strength and demonstrated a 76% retention of the initial room temperature flexural strength after 500 hours at 600°F.

Diisocyanate coupling of oxymethylene polymer and polybutylene terephthalate

Abstract: Disclosed herein is a modified oxymethylene polymer having an improved balance of physical properties such as tensile strength, tensile modulus, flexural strength and impact strength. The modified oxymethylene polymer is prepared by the coupling reaction of an oxymethylene polymer and polybutylene terephthalate with an isocyanate or isothiocyanate.