Showing papers on "Compressive strength published in 1983"

The relation between porosity, microstructure and strength, and the approach to advanced cement-based materials

Abstract: A theory is formulated to connect the strength of cement paste with its porosity. The theory shows that bending strength is largely dictated by the length of the largest pores, as in the Griffith (1920) model, but there is also an influence of the volume of porosity, which affects toughness through changing elastic modulus and fracture energy. Verification of this theory was achieved by observing the large pores in cement, and then relating bending strength to the measured defect length, modulus and fracture energy. The argument was proved by developing processes to remove the large pores from cement pastes, thereby raising the bending strength to 70 MPa. Further removal of colloidal pores gave a bending strength of 150 MPa and compression strength up to 300 MPa with improved toughness. Re-introduction of controlled pores into these macro-defect-free (mdf) cements allowed Feret’s law (1897) to be explained.

Cohesive Material Erosion by Unidirectional Current

Abstract: The initiation of motion of consolidated cohesive sediments under a unidirectional flow of clear water was studied. Experiments were performed in a flume‐tunnel capable of providing a bed shear stress up to 26 Pa and a velocity of 3.5 m/s, 3 mm above the bed. Samples were prepared in a specially designed press using a carefully controlled consolidation procedure. Critical shear stress and velocity were found to increase with compressive strength, vane shear strength, plasticity index, clay content, and consolidation pressure.

A Study on the Tensile Strength of Ice as a Function of Grain Size

Abstract: : An analysis of ice fracture that incorporates dislocation mechanics and linear elastic fracture mechanics is discussed. The derived relationships predict a brittle to ductile transition in polycrystalline ice under tension with a Hall-Petch type dependence of brittle fracture strength on grain size. A uniaxial tensile testing technique, including specimen preparation and loading system design was developed and employed to verify the model. The tensile strength of ice in purely brittle fracture was found to vary with the square root of the reciprocal of grain size, supporting the relationship that the theory suggests. The inherent strength of the ice lattice and the Hall-Petch slope are evaluated and findings discussed in relation to previous results. Monitoring of acoustic emissions was incorporated in the tests, providing insights into the process of microfracture during ice deformation.

Effect of phosphorus doping on stress in silicon and polycrystalline silicon

Abstract: An investigation of the polysilicon stress properties as a function of film thicknesses and phosphorus doping showed that as‐deposited films are moderately compressive, and become less compressive with increasing film thickness. High temperature PBr3 diffusion in silicon produces wafer bending corresponding to a tensile stress in wafer. Following a PBr3 diffusion, polysilicon films, however, become less compressive. Subsequent oxidation introduces an additional compressive stress component of the order of 2−3×109 dyne/cm2 for oxidation temperatures between ∼900−1000 °C. The thermal expansion coefficients were similar for doped and undoped films (α∼2.9 ppm/°C) and slightly less than for 〈100〉 silicon, while the doped films were found to be less stiff than undoped ones but both were less stiff than 〈100〉 silicon. The observed changes in polysilicon stress due to film thickness and phosphorus doping have been interpreted in terms of a grain growth model wherein those factors which lead to enhanced grain grow...

Flexible inorganic films and coatings

Abstract: This paper describes a new family of materials derived from layer minerals such as phillosilicates and includes vermiculite, montmorillonite, etc. They are structurally analogous to the organic crystalline polyethylene in which the crystalline lamellae are replaced by inorganic lamellae of comparable dimensions. Flexible films can be produced with tensile strengths of 30 to 160 MN m−2, elongation of up to 6% and moduli of 14 G N m−2; they are stronger than organic films. Suspension of discrete lamellae in water can be used as coating for a variety of surfaces. The most interesting is the vermiculite-coated glass fibre which has unique properties. Finally, the suspension can be used to make a wholly inorganic foam which has similar properties to organic foams with good compressive strength.

Light-weight cementitious product

Abstract: A glass-fiber reinforced light-weight cementitious product having a density of less than 85 pounds per cubic foot, a high tensile strength and a high compressive strength, when cured, and hence, suitable for structural articles in which such properties are required. The product is formulated from a mixture in which the aggregate comprises substantially equal parts by weight of fly ash cenospheres and silica fume.

Geotechnical Characterization of Desiccated Clay

Abstract: Conventional testing procedures produce scatter and bias in indicated properties of soils, such as desiccated clays. This paper describes and compares several conventional and non-conventional methods for characterizing the engineering properties of such soils at a site in Houston, Texas. Properties considered include undrained shear strength, stress-deformation moduli, earth pressure coefficients, and compression indexes. Similarities and differences between soil preconsolidated by desiccation and by stress removal are noted.

Effect of sample and grain size on the compressive strength of ice

Abstract: The effect of sample and grain size on the uni­ axial compressive strength of polycrystalline ice has been investigated at -10·C, at a strain-rate of 5.5 x 10- 4 S-1. The results show (a) that the sample size must be 12 or more times greater than the grain size for it to have no effect on the strength and (b) that there is no significant dependence of compressive strength on grain size, within the grain­ size range of 0.6 to 2.0 mm.

Failure characteristics of graphite-epoxy structural components loaded in compression

Abstract: Failure characteristics of compressively loaded graphite-epoxy components are described. Experimental results for both strength-critical laminates and structural components with postbuckling strength are presented. Effects of low speed impact damage and circular holes on compressive strength are discussed. Delamination and shear crippling failure mechanisms that limit the performance of strength-critical laminates are described. Transverse shear and skin-stiffener separation failure mechanisms that limit the performance of components with postbuckling strength are also described. The influence of matrix properties on compressive strength improvements for impact damaged laminates is discussed. Experimental data and results from a failure analysis for strength-critical laminates with cutouts are discussed and compared with impact damage results. Typical postbuckling test results are compared with analytical predictions.

Mechanical Properties, Durability, and Drying Shrinkage of Portland Cement Concrete Incorporating Silica Fume

Abstract: Portland cement is a highly energy intensive material, therefore, considerable effort is being made to find substitutes for partially replacing cement in concrete. Silica fume, a byproduct in the manufacture of ferrosilicon and silicon metal is one possible substitute. Results are given of a preliminary investigation to determine the strength, freezing and thawing characteristics, and drying shrinkage of concrete incorporating various percentages of silica fume. Eighteen 0.06-m3 air-entrained concrete mixes were made incorporating 0 to 30% silica fume as a partial replacement for cement. Some mixes were proportioned to have constant slump with water to cementitious materials ratio (W/C + S) ranging from 0.64 to 0.84 whereas others were proportioned to have a constant W/C + S of 0.40; the latter incorporated a superplasticizer. Cylinder and prism specimens were cast for determining the mechanical properties and durability of concrete. Test data indicate that silica fume when used in concrete as a partial replacement for cement performs as a highly efficient pozzolanic material. Notwithstanding the extreme fineness of silica fume (20 000 m2/kg) and, hence, its high water demand, the compressive strength of constant slump concrete incorporating up to 30% silica fume is comparable with or higher than the strength of control concrete. Superplasticized concrete mixes having a W/C + S maintained at 0.40 indicate some increase in compressive strength at all ages regardless of the percentage of silica fume. Concrete prisms incorporating 0 to 15% silica fume (W/C + S = 0.40) perform satisfactorily when subjected to 300 cycles of freezing and thawing; however, prisms incorporating 20 to 30% silica fume and large dosages of superplasticizer show excessive expansion and relatively low dynamic moduli after 300 cycles. The drying shrinkage of concrete incorporating silica fume is generally comparable with that of control concrete regardless of the W/C + S.

Comparative study of the temperature dependence of hardness and compressive strength in ceramics

Abstract: Hardness and compressive strength of several strong ceramics are measured from room temperature to 1000° C. Similarities in behaviour, and the results of microscopic examination, are interpreted in terms of the relative contributions of microplasticity and microfracture to material failure during compression testing and microhardness indentation. It is shown that microplasticity alone is an insufficient basis upon which to relate material response under the two test conditions, and that tensile microfracture is a significant contributor both to compressive failure and to subsurface indentation deformation, hence to hardness.

Compressive strength of tibial cancellous bone. Instron and osteopenetrometer measurements in an autopsy material.

Abstract: The topographic variation of proximal tibial cancellous bone strength was investigated in 12 knees from routine autopsies. Samples from eight knees were tested to compressive failure in an Instron® material testing machine, and four knees were tested with the osteopenetrometer, an instrument developed for intraoperative measurement of bone strength. Ultimate stress, elastic modulus and energy absorption of the bone were calculated from the Instron-curves. Mechanical properties varied considerably from knee to knee, but the topographic patterns were remarkably constant. The medial condyle showed the highest strength, the intercondylar area the lowest. On the medial side the bone was strongest at the front, while on the lateral side the reverse was true. The two horizontal levels tested did not differ significantly. The osteopenetrometer measurements closely modelled the pattern of ultimate stress.