Showing papers on "Compressive strength published in 1975"

The compression strength of unidirectional carbon fibre reinforced plastic

Abstract: A simple compression test, suitable for quality control measurements on unidirectional carbon fibre composite, is described. The specimen, a plane bar, with aluminium end tabs attached, is compressed by applying shear forces over the ends. With either type 1 or type 2 treated fibre the failure mode is one of shear over a plane at approximately 45° to the fibre axis. With untreated type 1 material failure is due to delamination. The variation of the compression strength of treated material with fibre volume loading is linear, the values being considerably below those predicted by buckling theory. Increasing void content causes a steady decrease in compression strength, and off-axis strength values are above those given by the maximum work criterion. The present work supports the recently proposed view that the compression strength of unidirectional carbon fibre composites at room temperature is not governed by fibre buckling but is related to the ultimate strength of the fibre.

Axial compression fracture in carbon fibres

Abstract: Axial compression fracture of carbon fibres was studied by embedding single fibres in epoxy resin and compressing the specimens parallel to the fibre axis. By careful optical monitoring of the fibre surface the earliest stages of fracture were identified leading to estimates of the fibre axial compression failure strengths. Compression strength decreases markedly from about 2.2 GN m−2 for moderately oriented fibres to <1 GN m−2 for highest modulus filaments. The trend towards decreasing compression strength with increasing anisotropy is explained on the basis of an increasing fibre microfibrillar nature. However fracture morphology studies show that the unduly rapid strength decrease results from an increasing degree of fibre outer layer ordering which accompanies increasing axial anisotropy in carbon fibres since cracking occurs first on the more highly aligned filament surfaces. It is suggested that fibre compression fracture changes from a shear to a microbuckling or kinking mode with increasing fibre anisotropy, where the latter initiates in individual, well-aligned but uncoupled microfibrils. The similarity of fine axial compression fractures in oriented carbon fibres to those found in elastica loop experiments is noted as are the possible implications which the low strain-to-failure in compression of very high modulus fibres might have for practical composites.

Multiple Failure State and Strain Controlled Triaxial tests

Abstract: In this paper new methods are reported for the determination of the triaxial compressive strength of rocks. The “Multiple Failure State Test” with several single failure states in the same specimen, represents an extension of the classical testing procedure. The “Strain Controlled Test” is based, however, on a new concept and permits the determination of the failure envelope for a single test specimen. This type of test yields in addition useful information concerning the influence of changing lateral pressures and the influence of plastic deformations on the ultimate strength. A large number of tests with the different experimental methods and on several types of rock show good agreement in the results for the peak strength of intact rock as well as for the residual strength in the broken condition.

Metallurgical aspects in cold rolled high strength steel sheets

Abstract: Cold rolled high strength steel sheets with yield strength from 300 to 500 N/mm2 have been developed by using conventional equipment for producing commercial cold rolled steel sheet, that is, cold rolling, box annealing, and temper rolling. Effective alloying elements for strengthening are carbon, silicon, manganese, phosphorus, niobium, etc. The sheets up to 400 N/mm2 yield strength grade are easily produced by selecting appropriate chemical compositions. The sheets with higher yield strength grade than 450 N/mm2 are obtained by introducing the new idea that the steel with more than 2 pct manganese is annealed between A1 and A3 transformation temperatures, and moderately temper rolled. Increase of tensile strength does not affect deep drawability while it deteriorates stretch-forming and stretch-flanging properties. As for electric resistance spot welding, shear tension strength increases in proportion to tensile strength, but cross tension strength hardly increases or tends to decrease. These sheets have been applied to door beams and bumper reinforcements.

Effect of Various Accelerating Chemical Admixtures on Setting and Strength Development of Concrete

Abstract: A study of the rate of hardening of concretes which contain inorganic accelerators demonstrates the superior performance of calcium chloride. However, there are significant changes in the compressive strength of concretes at various ages when accelerators are employed. Calorimetric studies of cement mortars show the advantages as an accelerator that calcium chloride maintains over other inorganic salts. Also, calorimetric tests demonstrate what appears to be different mechanisms of acceleration between different kinds of accelerators. Differential thermal analysis (DTA) techniques were applied to a study of the effect of calcium chloride and calcium formate on the early stages of hydration of a cement. DTA patterns show definite differences between the function of the accelerators.

Compressive Strength of Fiber-Reinforced Composite Materials

Abstract: Results of an experimental and analytical investigation of the compressive strength of unidirectional boron-epoxy composite material are presented. Observation of fiber coordinates in a boron-epoxy composite indicates that the fibers contain initial curvature. Combined axial compression and torsion tests were conducted on boron-epoxy tubes and it was shown that the shear modulus is a function of axial compressive stress. An analytical model which includes initial curvature in the fibers and permits an estimate of the effect of curvature on compressive strength is proposed. Two modes of failure which may result from the application of axial compressive stress are analyzed - delamination and shear instability. Based on tests and analysis, failure of boron-epoxy under axial compressive load is due to shear instability.

Texture of cooked potatoes: Relationship between the compressive strength of cooked potato disks and release of pectic substances

Abstract: In experiments where the interaction of starch and cell size were kept to a minimum by taking identical material for each experiment (disks from the same tuber), the loss of compressive strength of potato tissue on cooking was found to be related to the release of pectic substances into the cooking liquor. This relationship was found to hold true whether large differences in compressive strength were produced by cooking the disks in water for varying lengths of time or by cooking disks in solutions of calcium or potassium chloride for fixed times. The release of starch into the cooking liquor was not related to loss of compressive strength when the results of a number of experiments from disks from the same tuber were compared. Increased cooking time, or the presence of potassium chloride in the cooking solution, reduced compressive strength and increased the amount of pectic substances released. The presence of calcium chloride had the reverse effect. It was not clear whether the effects of calcium chloride were due to calcium per se or the pH of the solutions after cooking, which were inversely related to calcium chloride concentration.

Deformation and microstructure of extended‐chain polydiacetylene crystals

Abstract: The mechanical properties (Young's modulus, ultimate tensile strength, deformation processes) of extended-chain polydiacetylene crystals are investigated. The properties observed are similar to those of metal and ceramic whiskers. The elastic modulus is strain-dependent and the ultimate tensile strength increases with decreasing crystal size. The maximum tensile strength observed was 1700 Nmm−2. The ultimate tensile strength seems to be controlled by the presence of a small number of defects near the surface at which fracture nucleates. Irreversible deformation of the crystals was observed to occur by crack propagation normal and parallel to the direction of the macromolecules. The observed mechanical behavior corresponds to exceptionally high per-chain properties. The per-chain modulus obtained for these crystals is nearly as high as that of diamond. A chain-aligned polyethylene fiber with the same per-chain mechanical properties would have an ultimate strength as high as 0.9 × 104 Nmm−2.

Influence of Crystallographic Texture on the Strength and Toughness of the Controlled Rolled High Tensile Strength Steel

Abstract: The effect of crystallographic texture on the anisotropies of strength and toughness of the controlrolled high tensile steels was quantitatively investigated . The effect of the textures on the anisotro.bies of yield and tensile strees could be accurately evaluated with Hosford and B ackofen's method, if fine de tails of textures were properly taken in to account. The anisotropies of toughness were found to be qualitatively related with the dis tribution of { 100} cleavage plane. 1 t was f urther found that among the main components of the textures of tlzese steels, {3 1J }<01J> orientations not only enhanced the difference in stmlgth between L (OO) and C(900) directions, but also reduced the toughness at 45° direction, whereas {332}< 113> orientations gave rise to a weak anisotropy and better average strength and toughness . T hus, f urther im/Jrovemen t in strength and toughness might be eX/Jected,ij /Jreferential development of {332}< 113> orientations was to be achieved .

Tensile properties of ultradrawn polyethylene

Abstract: : High density polyethylene filaments, prepared by a solid-state deformation in an Instron Capillary Rheometer, show unusually high crystal orientation, chain extension, axial modulus and ultimate tensile strength. The Young's modulus and ultimate tensile strength have been determined from stress-strain curves. Gripping of this high modulus polyethylene has been a problem heretofore. Nevertheless, the measurement of ultimate tensile strength has become feasible by a special gripping procedure reported in this study. Tensile moduli show an increase with sample preparation temperature and pressure. The effect of strain rate and frequency on modulus has also been evaluated by a combination of stress-strain data and dynamic tension plus sonic measurements over nine decades of time.

Texture of cooked potatoes: The effect of ions and ph on the compressive strength of cooked potatoes

Abstract: It was shown from experiments on disks cooked in solutions of calcium chloride and calcium acetate, and in buffered solutions of calcium chloride at various pHs (sodium concentration constant) and from experiments where the ratios of disks to calcium chloride were varied, that the effect of calcium in increasing the compressive strength of the disks was small compared to the effect of reduced pH. The interaction of sodium and calcium was investigated at pH 6 (≈ the pH of cooked potato tissue). The effect of sodium in reducing compressive strength of the disks outweighed the effect of calcium in increasing compressive strength. Sodium and potassium chloride had a similar effect on loss of compressive strength on cooking. Increased compressive strength due to pH or the presence of calcium was overcome by extending the length of cooking. It is suggested that transelimination, ion exchange and hydrogen bond breakage may be more important factors than the chelation of calcium by naturally occurring phytin, in the breakdown of pectic substances and loss of intercellular adhesion during normal cooking of toes.

Method of producing high strength steel pipe

Abstract: A method of treating steel pipe made by forming and welding a mother plate. The pipe is shrunk in the radial direction by applying compressive radial pressure to the outside surface of the pipe to reduce the pipe diameter by at least about 1%. The shrinking of the pipe increases the circumferential compressive yield strength and decreases the circumferential tensile yield strength. The pipe is then heated to a temperature below the transformation temperature of the steel but high enough to increase the circumferential tensile yield strength of the pipe, preferably at least about 15% above the tensile yield strength of the mother plate. The heating step does not significantly decrease the high circumferential compressive yield strength of the pipe. The pipe is preferably heated to a temperature within the range of from about 500° F to about 1000° F, and the preferred heating technique is induction heating.

The composite resin dowel and core

Abstract: T o d a y ' s elnphasis on the maintenance and preservation of the natural dentition, combined with the success of endodontically treated teeth, has resulted in a variety of procedures to restore pulpless teeth. Unfortunately, the exact minimal mechanical and physical properties required for a dowel and core have not yet been defined. Until controlled clinical investigations provide suet1 guidelines, many materials must be tried and evaluated. Alternatives to the cast gold dowel and core include prefabricated steel dowels and numerous techniques employing pins, amalgam, and resin. ~j Although pins have been popular in recent years, they have only been shown to increase retention. They do not increase the compressive strength of a material and actually decrease tensile strength. '~ Since pins tend to weaken the remaining tooth structure, they may result in further damage to the tooth. The purpose of this study was to determine, through clinical and laboratory studies, the possibility of utilizing composite resin in the construction of dowels and cores. The technique, which will be described, requires only one visit for the patient, few instruments, and no aid from a dental laboratory.

High early strength cement

Abstract: A high early strength cement composition is disclosed which is capable of providing sufficient compressive strength within 2 to 24 hours to enable one to use it in highway or airport runway patching. The cement also exhibits satisfactory ultimate strength, that is, strength after 28 or more days of curing. The high early strength cement comprises a mixture of portland cement, calcium aluminate, and calcium sulfate in certain specified proportions.

Manufacture of sulfur concrete

Abstract: Sulfur concrete which exhibits improved compressive strength and flexural strength, and improved corrosion characteristics, is manufactured by mixing sulfur, dicyclopentadiene and aggregate at from 120° to 160° C. The period for which the sulfur and dicyclopentadiene interact should not exceed certain limits.

Fifty year properties of concrete

Abstract: Compressive strength, unit weight, and volume changes of concrete for ages up to 50 years have been determined. Variables included are types of cement and coarse aggregate, mix proportions, consistency, methods of placement, and storage conditions. Over 2500 concrete cylinders, 132 concrete expansion prisms, and several thousand mortar cylinders and briquets were made in 1910, 1923, and 1937 for this program. Earlier reports on these tests were published in 1931, 1943, and 1961. Under outdoor storage in Madison the compressive strength of concrete made with coarsely ground cements having high C2S contents generally increased as the log cf the age out to 50 years, but concrete made with finer cements having relatively low C2S contents appeared to reach maximum strength at ages between 10 to 25 years and showed some retrogression thereafter.

Strain rate effect on the strength of frozen silt

Abstract: Uniaxial compression and tension tests were conducted on frozen Fairbanks silt at a temperature of -10 degrees C. A relatively stiff testing machine was operated at a constant displacement rate for each test. The tests showed that compressive strength is very sensitive to strain rate and that tensile strength is relatively insensitive to it. The compressive strength increased ten times over a strain rate range of 1.2 x 10 to the -4 power s to the -1 power to 2.9 s to the -1 power. As was found in other investigations, tangent moduli increased slightly with greater strain rates. The specific energy increased at higher strain rates for compression tests and decreased slightly for tension tests. For increased strain rates, uniaxial compression strength showed no tendency to plateau; nor did the specific energy reach a minimum during uniaxial tensile testing.

Lamination residual stresses in fiber composites

Abstract: An experimental investigation was conducted to determine the magnitude of lamination residual stresses in angle-ply composites and to evaluate their effects on composite structural integrity. The materials investigated were boron/epoxy, boron/polyimide, graphite/low modulus epoxy, graphite/high modulus epoxy, graphite/polyimide and s-glass/epoxy. These materials were fully characterized. Static properties of laminates were also determined. Experimental techniques using embedded strain gages were developed and used to measure residual strains during curing. The extent of relaxation of lamination residual stresses was investigated. It was concluded that the degree of such relaxation is low. The behavior of angle-ply laminates subjected to thermal cycling, tensile load cycling, and combined thermal cycling with tensile load was investigated. In most cases these cycling programs did not have any measurable influence on residual strength and stiffness of the laminates. In the tensile load cycling tests, the graphite/polyimide shows the highest endurance with 10 million cycle runouts at loads up to 90 percent of the static strength.