Showing papers on "Compressive strength published in 1989"

Prediction of the compressive strength of human lumbar vertebrae.

Abstract: The compressive strength of 98 specimens of motion segments of human thoracolumbar spines was measured. In addition, the density of the trabecular bone in the midplane of the vertebrae was assessed by quantitative computed tomography (QCT); the size of the vertebral endplates was measured by CT as w

Transparent silica gel–PMMA composites

Abstract: Transparent silica gel–polymer composites have been prepared by the impregnation of porous gels with organic monomer and polymerization in situ. The relative amount of each phase was adjusted by varying the porosity of the silica gel prior to impregnation. These materials constitute a new class of transparent composites. Properties, such as density, refractive index, modulus of rupture, compressive strength, abrasion rate, and Vickers hardness, have been measured over the compositional range of 100% silica to 100% polymethyl methacrylate (PMMA).

Cementation Effects in Frictional Materials

Abstract: Cementation effects are studied on the basis of three series of drained triaxial compression tests on compacted soil, soil‐cement, and mortar. The frictional materials have the same gradation curve and the same water content, and the specimens are produced using the same compactive effort and have nearly the same initial, total density. The only difference between the three sets of specimens is the amount of cement exchanged with inert rock flour. Increasing cement contents produces increasing cohesion and tensile strength as well as increasing friction angle at low confining pressures. The curvature of the failure envelopes increases with cementation, and the failure envelopes are parallel at medium confining pressures. At high confining pressures, they cross each other such that the compacted soil becomes stronger than the two cemented soils. Analyses of the strengths show that this behavior can be explained in terms of the different compressibilities and different rates of dilation observed for the thr...

Properties and microstructures of Lanxide Al2O3-Al ceramic composite materials

Abstract: A study has been made of four Al2O3-Al composite materials fabricated by the directed oxidation of molten aluminium alloys. Their microstructures are described and measurements of density, coefficient of thermal expansion, thermal conductivity, hardness, elastic constants, compressive strength, flexural strength, fracture toughness, work of fracture, and thermal shock resistance are reported. Compared to a typical dense sintered Al2O3, such as Durafrax® 1542, which is somewhat harder, stiffer, and stronger in compression, the new composites can be stronger in flexure, particularly at high temperatures, far tougher, and considerably more resistant to thermal shock. Attempts are made to relate their differences in properties to microstructure.

On the estimation of the tensile strength of carbon fibres at short lengths

Abstract: Generally, to determine the fibre-matrix interfacial properties in fibre reinforced plastics, it is necessary to know the tensile strength of the fibre at very short lengths, for which direct measurements are not possible. Accordingly, in this study, the determination of the tensile strength of high strength carbon fibres and their gauge length dependence are analysed by means of the Weibull model. The influence of the estimator chosen and of the sample size on the calculated value of the tensile strength of the fibre are first determined. Secondly, the accuracy of the three- and the two-parameter Weibull distributions is examined. Finally, it is shown that the most appropriate extrapolation at short length is performed by means of a linear logarithmic dependence on gauge length of the tensile strength. This method seems to be valid for untreated as well as for surface-treated high strength carbon fibres.

Regional variations in the compressive properties of lumbar vertebral trabeculae. Effects of disc degeneration.

Abstract: The compressive mechanical properties of human lumbar vertebral trabeculae were examined on the basis of anatomic origin, bone density, and intervertebral disc properties. Trabecular bone compressive strength and stiffness increased with increasing bone density, the latter proportional to strength and stiffness to the one-half power. Regional variations within each segment were found, the most prevalent differences occurring in regions of bone overlying the disc nucleus in comparison with bone overlying the disc anulus. For normal discs, the ratio of strength of bone overlying the disc nucleus to bone overlying the disc anulus was 1.25, decreasing to 1.0 for moderately degenerated discs. These results suggest that an interdependency of trabecular bone properties and intervertebral disc properties may exist.

Mechanical effects in peel adhesion test

Abstract: —Mechanical effects in the peel strength of a thin film have been studied both experimentally and theoretically. It has been found that the adhesion strength measured by the peel test is a practical adhesion (an engineering strength per unit width) and does not represent the true interface adhesion strength. The measured value may represent a multiplication of the true interface adhesion and other work expended in the plastic deformation of the thin film. The contribution of the latter to the peel strength is found to be, sometimes, of the order of 100 times higher than the former. It is found that the major controlling factors in the peel strength are the thickness, Young's modulus, the yield strength, the strain hardening coefficient of the film, and the compliance of the substrate as well as the interface adhesion strength. Even though the true interface adhesion strength is the same, a higher peel strength is obtained if the film is thinner or more ductile under the test conditions reported in this pa...

Set retarded cement compositions and methods for well cementing

Abstract: Set retarded cement compositions for cementing across a zone or zones in a well having enhanced compressive strength and rapid gel strength development after placement. The cement compositions are comprised of hydraulic cement, sufficient fresh water to form a pumpable slurry, a set retarder comprising a copolymer of 2-acrylamido, 2-methylpropane sulfonic acid and acrylic acid having an average molecular weight below about 5000 and any other desired additives. Methods of cementing utilizing the cement composition also are provided.

Tensile stress-strain Properties of SIFCON,

Abstract: Slurry-infiltrated fiber concrete (SIFCON) composites differ from conventional fiber reinforced concrete in at least two aspects: they contain a much larger volume fraction of fibers, and they use a matrix consisting of very fine particles. As such, they could be made simultaneously to exhibit outstanding strength and ductility properties. This research deals with the tensile stress-strain properties of SIFCON and comprises an experimental and an analytical program. Parameters investigated include the matrix composition and the fiber type where length, aspect ratio, surface characteristics, and overall fiber geometry vary. It is shown that SIFCON composites can exhibit tensile strength up to 4 ksi (28 MPa) at peak strains ranging from 1 to 2 %. A model is proposed to predict the ascending branch of the stress-strain curves of SIFCON from its compressive strength and its fiber-reinforcing parameters.

Bond effects in high-strength silica-fume concretes

Abstract: The strengthening effects in high-strength silica-fume concretes were evaluated in terms of water-reducing effect associated with the reduction in water requirement in the silica fume system and in terms of an inherent effect that reflects the increase in strength of the silica-fume concrete over a similar water/cement ratio concrete without silica fume. The inherent effect was found to be as important as the water-reducing effect, and it is suggested that its origin is in the improved aggregate-matrix bond. This enhanced bonding is associated with the formation of a dense microstructure in the transition zone of the silica-fume concrete.

Mechanical properties of BIS-GMA resin short glass fiber composites.

Abstract: The use of short glass fibers as a filler for dental restorations or cement resins have not been examined extensively. The mechanical properties and untreated glass fibers (5 microns dia x 25 microns) in Bis-phenol A glycidyl methacrylate (BIS-GMA) diluted with triethylene-glycol dimethacrylate (TEGDMA) resin were investigated for possible use as a restorative dental composite or bone cement. Compression, uniaxial tension and fracture toughness tests were conducted for each filler composite mixtures of 40, 50, 60 and 70%. Set time and maximum temperature of polymerization were determined. The results show that the elastic modulus, tensile strength and compressive strength are dependent on the percent of filler content. Elastic modulus and compressive yield (0.2%) strength of silane treated glass fibers filled composite increased from 2.26 to 4.59 GPa and 43.3 to 66.6 MPa, respectively, wtih increasing the filler content while the tensile strength decreased from 26.7 to 18.6 MPa. The elastic modulus of the untreated composite was less than that of the silane treated fiber composite. The tensile strength and compressive strengths were 20 to 50% lower than those of silane treated composites. The fracture toughness of the silane treated glass fiber additions were not significantly different from the untreated additions. The highest fracture toughness was obtained at 50% filler content with 1.65 MPa m.5. Set time increased from 3.5 to 7.7 minutes with increased filler content and peak temperature dropped from 68.3 to 34 degrees C. The results of this study indicate that the addition of silane coated glass fiber to BIS-GMA resin increased the elastic modulus, tensile and compressive strengths compared with non-treated fibers. The addition of either treated or non-treated fibers increased the set time of the material and decreased the maximum temperature.

Concrete Over the Top--Or, is there Life After Peak?

Abstract: Test results are presented that show the postpack response of concretes of 3 different strengths under triaxial stress states These test results clearly show the transition from brittle to ductile behavior under increasing confinement, the residual strength, and the strain behavior at and after peak Some evidence that indicates that Drucker's postulate may be relaxed for concrete is presented also Concrete of different strengths behave similarly, with increasing brittleness for higher strength concretes

Effect of metal fillers on some physical properties of acrylic resin.

Abstract: Thermal conductivity of poly(methylmethacrylate) is low. Fillers of silver, aluminum, and copper particles at 25% concentration, increased thermal conductivity of poly(methylmethacrylate) by 4.53, 4.43, and 4.04 times, respectively. Although the compressive strength of poly(methylmethacrylate) increased with the addition of these fillers, tensile strength decreased. Silver and copper particles made the material radiopaque. Advantages of metal-filled acrylic resin denture bases are described.

Compression strength and fracture properties of model particulate food composites in relation to their microstructure and particle‐matrix interaction

Abstract: Foods containing particles in a matrix were modelled by setting glass spheres, varying in size and surface chemistry, and oil droplets in heat-denatured whey protein gels. Composites containing particles with hydrophilic surfaces were much stronger in compression, the strength being dependent on particle surface area, than those with hydrophobia surfaces. The relationship between strength and particle size was compared with existing rheological and composite theories. SEM examination of fracture surfaces, resulting from compression, showed that particles with an hydrophilic surface were an integral part of the composite, failure occurring within the protein matrix. Gels made from particles with an hydrophobic surface fractured adjacent to the particle surface, indicating little or no interaction between particle and matrix.

Enhancement of physical properties of resin restorative materials by laser polymerization

Abstract: A study was conducted to compare the compressive strength, diametral tensile strength, transverse flexural strength, and flexural modulus of a microfilled and a small particle composite resin restorative material following argon laser and conventional visible light polymerization techniques. All physical properties examined in this study were enhanced by laser polymerization. The diametral tensile strength of both types of restorative materials was significantly greater following laser polymerization, as were the transverse flexural strength and the flexural modulus of the microfilled resin restorative material. Additionally, these results were obtained with a laser polymerization time that was one-fourth that used for visible light activation. It was concluded that the argon laser is a potentially advantageous means of initiating the polymerization of dental composite resin restorations.

Effect of martensite strength on the tensile strength of dual phase steels

Abstract: Fe-2% Si-1.5% Mn steels with three levels of carbon content (0.10, 0.14 and 0.19 wt%) were intercritically annealed followed by water quenching to obtain dual phase (martensite plus ferrite) structure. It is found that the ultimate tensile strength of dual phase steels increased with increasing the volume fraction as well as the tensile strength of martensite. The tensile strength of dual phase steel can be predicted using the law of mixtures although the predicted tensile strength is slightly higher than the experimental one. It is suggested that martensite never reaches its ultimate tensile strength when the necking of dual phase steels occurs.

High-Strength Concrete Containing Large Quantities of Fly Ash

Abstract: The paper presents research performed to indentify and recommend mix designs for high fly ash content 3000 and 4000 psi (21 and 28 MPa) structural grade concrete utilizing Class C fly ash. The fly ash was produced at Wisconsin Electric Power Plant.

Compressive strength of municipal sludge ash mortars

Abstract: Sludge ashes produced by the incineration of municipal sewage wastes are becoming increasingly difficult to dispose of in landfills, and there is a resulting increase of interest in disposal by inorporation in building materials. In the present study, a comprehensive test program was developed to examine the potential for using the ash as a fine aggregate in mortar. The strength characteristics of mortars prepared from sludge ash with addition of fly ashes (both Classes C and F) and varying amounts of cement and lime were cured under standard laboratory conditions for periods of 1, 3, 7, 14, and 28 days before testing for compressive strength. The results indicate that the addition of sludge ash adversely affects the strength behavior of mortars. Although partial substitution of sludge ash with fly ash gave improved results, strengths were always less than those obtained from control mortars using sand. Addition of fly ashes also improves mortar workability. The addition of lime in place of cement reduces strength.