Showing papers on "Compressive strength published in 1979"

Statistical Descriptions of Strength of Concrete

Abstract: The variations in the compressive strength, splitting, and flexural-tension strengths, and the modulus of elasticity of concrete are reviewed, and representative probability distributions are suggested The effects of volume, rate of loading, and in-situ casting of concrete are included

Compressive Fatigue Limits of Composite Restorative Materials

Abstract: Compressive fatigue limits at 5,000 stress cycles have been measured for seven commercial composite restorative materials. The average of the ratios between fatigue limit and compressive strengths is 0.64.

Synthesis and fabrication of β-tricalcium phosphate (whitlockite) ceramics for potential prosthetic applications

Abstract: A novel process is described for preparing dense, polycrystalline tricalcium phosphates. Singleβ-phase compositional integrity is achieved by introducing catalytic amounts of sulphate ion and this pore free material has close to theoretical density. Preliminary mechanical properties include a compression strength of 687 MN m−2 and a tensile strength of 154 MN m−2. The relationship between processing variables and phase composition, microstructure, strength and translucence is described. The material has promise for bone implant applications.

Tensile strength of water

Abstract: THE measured tensile strength of water has long been known to be significantly less than theoretical predictions and the reduced strength is normally attributed to the presence of solid impurities that serve as nucleation sites for rupture of the liquid1. A favourite method of measuring tensile strength is through the dynamic stressing of a liquid by an acoustic field. At sufficiently large values of the peak negative acoustic-pressure amplitude the liquid ruptures and forms a rapidly growing vapour cavity that collapses violently during the positive portion of the cycle. This cavity collapse is normally violent enough to be observed easily with the unaided eye or ear. Such an event is termed the acoustic cavitation threshold and is a measure of the tensile strength of a liquid. Although some successes have been obtained in achieving measured values of the tensile strength comparable to theoretical predictions for extremely small samples2 or after extensive filtration3, I know of no current theory for the prediction of values of the dynamic tensile strength for ordinary distilled water. Using a modified version of a recent theory by Apfel4, an equation is presented here that correctly predicts the variation of the acoustic cavitation threshold of water with surface tension, dissolved gas content and temperature.

Estimating Strength of Sandstone Using Petrographic Thin-Section Data

Abstract: The determination of rock compressive strength is a major design requirement for underground openings in rock. However, determination of compressive strength by triaxial compression tests requires high quality core samples which are not always available from thin-bedded, fractured strata. This investigation shows that the compressive strength of calcareous sandstones can be estimated from critical petrographic properties observed in thin sections. For the sandstones from the Beehive Coal Mine, the significant petrographic properties are mean and median grain sizes, percent quartz grains, total percent quartz, sphericity, and percent intergrown and percent straight grain contacts. The accuracy of estimating compressive strength can be improved by increasing the number of petrologic properties used as estimators. A polynomial prediction equation utilizing three easily measured rock properties, percent quartz grains, total percent cement, and mean grain size, shows very good correlation between estimated and experimental compressive strengths.

Correlation of Fiber Composite Tensile Strength with the Ultrasonic Stress Wave Factor

Abstract: An acoustic-ultrasonic technique was used to indicate the strength variations of tensile specimens of a graphite/epoxy composite. A “stress wave factor” was determined and its value was found to depend on variations of the fiber-resin bonding as well as fiber orientation. The fiber orientations studied were 0 deg (longitudinal), 10 deg (off-axis), 90 deg (transverse), [0 deg/±45 deg/0 deg] symmetrical, and [±45 deg] symmetrical. Correlations indicated that the stress wave factor can predict variations of the tensile and shear strengths of composite materials. The method was also found to be sensitive to strength variations associated with microporosity and differences in fiber/resin ratio.

Effect of Impact Damage and Holes on the Compressive Strength of a Graphite/Epoxy Laminate

Abstract: An experimental investigation has been conducted to determine the effect of low-velocity impact damage and unloaded circular holes on the compressive strength of a 48-ply orthotropic graphite/epoxy flat laminate. Specimens were impacted by a 1.27-cm-diameter aluminum sphere with speeds from 52 to 101 m/x to simulate momenta typical of low-velocity impact hazards that can occur in commercial aircraft service. It is shown that low-velocity impact damage can significantly degrade the static compressive strength of the laminate. Specimens that fail at axial strains above 0.008 in the undamaged condition can fail at strains as low as 0.0031 when impacted at 100 m/s. Circular holes also reduce the static compressive strength of the laminate. The failure strain decreases as the hole diameter increases.

Diametral Compressive Testing Method

Abstract: A new approach of diametral compressive testing with circular anvils is proposed. The circular anvils are used to select a suitable contact width or to avoid the collapse of the specimen in the contact edge. Furthermore, the statistical corrections on the diametral compressive strength for the effects of the size and stress distribution are explained by the application of Weibull’s statistical theory. The experimental results of the diametral compressive testing are compared with the uniaxial tensile strengths for some kinds of graphite and marble, and the discrepancies between the two strengths are discussed. According to our macroscopic brittle fracture criterion under biaxial stress state, which was proposed recently, the tensile strength can be deduced from the diametral compressive strength σHC* and the uniaxial compressive strength σC as follows, σt* = KICKIIC 12 σCσHC*(1+σx/σH)+σC {σHC*(1−σx/σH)−σC}+σC2 where σt* is the deduced tensile strength, σx /σH is the ratio of maximum and minimum principal stresses at the center of the disk, and KIC and KIIC are the values of Mode I and Mode II fracture toughness. The deduced values σt* are ascertained experimentally to agree very well with the uniaxial tensile strength in wide range of brittle materials, such as graphite and marble.

Size Effect in Model Concretes

Abstract: The paper reviews current research on the effect of specimen size on compressive, indirect tensile and flexural tensile strengths, the stress-strain characteristics, and related quantities. The measured compressive and tensile strengths were observed to increase with a decrease in specimen size in all investigations. The nondimensional stress-strain curves in compression tests were noted to be homologous for prototype and model concretes. A higher tensile-compressive strength ratio is observed in smaller specimens. The effects of duration and conditions of curing compactions, shape of specimen, and other factors are reported. Techniques are suggested to select the cylinder size to evaluate the concrete compressive strength in a model specimen. To assist with the determination of size effects and standardization, the ACI Committee 444 on Models of Concrete Structures has recommended that model investigations should include compression tests on 2-in.x4-in. (50-mmx100-mm) cylinders along with any other cylinder sizes used.

Brittle interface layers and the tensile strength of metal matrix-fibre composites

Abstract: The influence of brittle layers on the ultimate tensile strength of metal matrix composites is discussed. An equation has been derived to calculate the first critical thickness of the layer. The brittle layers have two effects on the fracture of the fibre, one of which is the value of the local stress near the tip of the crack, situated at the fibre-layer interface. Methods have been developed for the theoretical calculation of the critical stress intensity factor, KIC, of brittle materials. Experimental results with B-SiC fibres have shown that their tensile strength is reduced with increasing thickness of the SiC layer. The critical thickness of the layer, tl*,for B-SiC fibres is about 1.0 to 7.5 μm, which coincides well with the theoretical value of tl*.

Method of enhancing the compressive strength of hydraulic cement composition

Abstract: The compressive strength of a hydrated hydraulic cement composition such as Portland cement concrete is enhanced by the addition of a very small amount of certain select synthetic non-ionic surface active agents to the compositions.

Fluid Cushion Truly Triaxial or Multiaxial Testing Device

Abstract: The derivation of the constitutive relations of soils requires a testing facility that can apply a homogeneous and nearly ideal set of controlled boundary conditions to a specimen. A new multiaxial cubical test apparatus is described. It uses fluid or pneumatically pressurized flexible cushions to transmit a three-dimensional, independently controlled, and compressive stress state to a 102-mm (4-in.) specimen of geologic material. The deformations in three orthogonal directions are detected by a set of linear variable differential transformers. Flexible cushions allow nearly unrestrained deformations in the specimen. The deformations are uniform even at large strains. The specimen preparation and apparatus assembly procedures are straightforward. The simplicity of the multiaxial cubical cell and its easy operating procedures are emphasized. Typical stress-strain curves for straight-line stress paths are discussed. The apparatus appears to operate especially well at low stress levels.

Effects of applied stress on the magnetic properties of high permeability silicon-iron

Abstract: It is well known that magnetic properties of Goss-oriented silicon-iron are dependent upon external mechanical stress. This paper describes some of the recent work carried out in the UK on the effects of high compressive stress, combined longitudinal and transverse stresses, and also the effects of elevated temperature on the power loss and magnetostriction of silicon-iron. Results show that,when compressive stress greater than about 15 MPa is applied along the rolling direction the power loss generally is double the zero stress level, the permeability drops linearly, and the B-H loop becomes constricted. The loss does not rise so rapidly in higher permeability material, but the magnetostriction reaches a higher final level. These effects are explained using a simple domain model. Measurements of magnetostriction under combined longitudinal and transverse stress before and after coating removal are shown. At elevated temperature,the effect of stress is found to be more pronounced, and the benefit of the coating on high permeability material is reduced. The extent to which stress may degrade the performance of laminated cores is discussed, and it is hinted that perhaps the effects of stress might only partly account for the building loss in high permeability cores.

The compressive strength of lumbar vertebrae.

Abstract: Values for the compressive breaking load of lumbar vertebrae at physiological strain rates show enormous scatter across the population, ranging from 0.8 kN to nearly 16 kN. Increase in strength was found at faster strain rates, but differences in compressive strength between upper and lower lumbar vertebrae were not significant. Hydraulic strengthening does not appear to contribute to the compressive strength at the strain rates studied.

An investigation of tensile strength of dental solder joints

Abstract: Tensile specimens of dental solder joints were tested to determine the effect of gap distance on the strength of solder joints. Two dental alloys were used; a Type III gold alloy and a gold-palladium (Au-Pd) alloy. The Type III alloy was joined with the recommended gold solder. The Au-Pd alloy was joined using preceramic and postceramic application soldering techniques. Gap distances of 0.13 mm, 0.5 mm, and 1 mm were used with each soldering technique. All solder specimens were machined to a uniform diameter and then tested for tensile strength. It was concluded that: 1. There was a significant increase in strength for the Type III gold as the gap distance was increased. 2. The trend toward stronger joints at narrow gap distances for Au-Pd alloy joined with presolder was not statistically significant. 3. The trend toward stronger joints at wide gap distances for the Au-Pd alloy joined with the postsolder was not statistically significant. 4. The postsolder joints were statistically stronger than the presolder joints. 5. The trends observed could be partially explained in terms of competing effects of yield strength (triaxially), wettability, and void or inclusion content at the various gap distances.

Method and apparatus for nondestructive testing of cement

Abstract: Methods and apparatus for the nondestructive testing of cement slurry samples as a function of time are disclosed. A sample placed in a temperature and pressure controlled autoclave is coupled to transducer means under computer control. Ultrasonic energy is propagated through the sample and the transit time is measured. A predetermined relationship relating transit time to compressive strength is employed and enables the determination of compressive strength. The measurements are repetitively performed on up to eight samples simultaneously and the time history of the development of compressive strength is recorded.

The Effect of Temperature on Tensile and Compressive Strengths and Young's Modulus of Oil Shale

Abstract: The analysis of underground oil-shale recovery processes requires knowledge of the mechanical properties of oil shale at various temperatures The tensile strength, compressive strength, and Young's modulus are of special importance The variation of these properties with temperature is important in assessing the strength of underground columns and confining walls for process cavities This work presents the results of an experimental study to quantify this temperature dependence It was found that both tensile and compressive strength of oil shale show a marked decrease in strength as temperature is increased, for a given richness At a given temperature, both the tensile and compressive strengths decrease as richness increases, although the rate of decrease diminishes at richnesses of about 42 gal/ton and above Equations have been developed to permit estimates of the various paramters involved The Young's moduli estimated show a considerable decrease with temperature At 400/sup 0/F, the modulus is reduced to 60% of its room temperature value for 192-gal/ton shale in tension (23 refs)

The hardness of Al-Si eutectic alloys

Abstract: The Vickers hardness values of Al-Si eutectic alloys, solidified unidirectionally at rates ranging from 2.8×10−5 to 1 cm sec−1, have been determined. These are compared with associated tensile and compressive properties. It is shown that there is no close correlation of hardness and strength over the entire range of growth rates although similar trends are seen between hardness and compressive yield strength. It is concluded that caution should be exercised when inferring strength from hardness data.

Compositions of vermiculite lamellae and solid particulate materials

Abstract: A composition comprising vermiculite lamellae (delaminated vermiculite) and one or more solid particulate materials which have a basic reaction in water, especially magnesium oxide These particulate additives improve the physical properties of vermiculite articles especially the compressive strength and stability to water of foam

Polyethylene blend foams having improved compressive strength

Abstract: Low density foams from polyethylene blends having substantially closed cell structure and improved compressive strength are prepared using gel-forming extrusion technology. The polyethylene blend comprises from about 35 to about 60 weight percent of low density branched polyethylene in admixture with from about 40 to about 65 weight percent of intermediate density linear polyethylene. An exemplary blowing agent is 1,2-dichlorotetrafluoroethane, there being up to about 0.12 gram-mole of such blowing agent per 100 grams of resin blend in the flowable gel.

Shear Strength of Concrete Masonry Joints

Abstract: The experimental results of 46 shear tests of ungrouted and grouted concrete block masonry are reported. The shear specimens were tested under shear along the bed joints. The influence of mortar type, grout strength, bed-joint reinforcement, and the level of compressive stress normal to the bed joints were studied. The results indicate that the mortar joint's strength characteristics do not have a major effect on the resistance of masonry joints to shear-slip failure. The grout strength and the normal compressive stress are the most significant parameters influencing the joint capacity. The relative contribution of grouting towards increasing the joint shear strength decreases as the level of precompression increases. A strong correlation between the shear strength and the normal compressive stress is shown to exist for both ungrouted and grouted masonry under low levels of precompression.