Showing papers on "Compressive strength published in 1976"

Hydroxylapatite synthesis and characterization in dense polycrystalline form

Abstract: A new process is described for preparing dense, polycrystalline hydroxylapatite. This material has close to theoretical density and is free of fine pores and second phases. The best material has an average compressive strength of 917 MN m−2 (133×103 psi), and polished samples have an average tensile strength of 196 MN m−2 (28.4×103 psi). The material is highly translucent, and the degree of translucence depends upon processing conditions. The relationship between processing variables and microstructure, strength, and translucence is described. This dense hydroxylapatite has good promise for bone implants and dental applications.

Bone compressive strength: the influence of density and strain rate

Abstract: The compressive strength of bone is proportional to the square of the apparent density and to the strain rate raised to the 0.06 power. This relationship is applicable to trabecular and compact bone, and provides clinical guidelines for predicting bone strength on the basis of x-ray and densitometric examination.

Development of a silicon carbide fibre with high tensile strength

Abstract: MUCH work has been done on preparing heat-resistant silicon carbide materials in fibrous form, since plastics or metals can be reinforced with them to obtain very heat-resistant material of great mechanical strength. SiC whiskers1 are, however, impractical because of their shortness (several mm), their non-uniform diameter and high cost of production. SiC-on-W (ref. 2) and SiC-on-C (ref. 3) filaments have been produced by chemical vapour methods. These coated filaments are more expensive, and the treatment for making such composite materials requires careful control. We report here on the synthesis of continuous β-SiC fibres by a new process: the conversion of organometallic polymers to inorganic substances. We have studied the transformation process and the structure and mechanical properties of these fibres.

Mechanical properties of dried defatted spongy bone.

Abstract: A study has been made of the compressive strength, compression at rupture, limit of proportionality, compression at the limit of proportionality and the modulus of elasticity of spongy bone from vertebrae and tibias. The specimens were obtained from autopsy subjects of both sexes aged 14 to 89 years. There was a qualitative deterioration of most of the strength parameters with age, and also differences between the sexes and between vertebrae and tibia. Spongy bone was found to have the unusual mechanical property that, despite rupture, its compressive strength often steadily increased; this was especially the case for vertebrae from young males.

Endochronic theory of inelasticity and failure of concrete

Abstract: A gradual accumulation of inelastic strain can be most conveniently described in terms of the so-called intrinsic time, whose increment depends on the time increment as well as the strain increments, and was previously developed for metals and is extended herein to concrete. It is demonstrated that the proposed model predicts quite closely: (1)Stress-strain diagrams for concretes of different strength; (2)uniaxial, biaxial, and triaxial stress-strain diagrams and failure envelopes; (3)failure envelopes for combined torsion and compression; (4)lateral strains and volume expansion in uniaxial and biaxial tests; (5)the behavior of spirally confined concrete; (6) hysteresis loops for repeated high compression; (7)cyclic creep up to 10 6 cycles; (8)the strain rate effect; (9)the decrease of long time strength; and (10)the increase of short-time strength due to low stress creep.

Shear transfer in lightweight reinforced concrete.

Abstract: A study is reported of the single direction shear transfer strength of lightweight aggregate concrete. Push-off tests were carried out on specimens made from sanded lightweight concrete, two types of all lightweight concrete, and sand and gravel concrete. Both initially uncracked specimens and specimens cracked in the shear plane before being subjected to shear, were tested. It was found that the shear transfer strength of lightweight concrete is less than that of sand and gravel concrete having the same compressive strength. The shear-friction provisions of Section 11.15 of ACI 318-71 may be used in the design of connections in lightweight concrete providing the value of the coefficients of friction, contained in Section 11.15.4, are multipled by the following factors (a) For all-lightweight concrete having a unit weight not less than 92 lb per cu ft (1488.43 kg per cu m), multiply the coefficient of friction by 0.75; and (b) For sanded lightweight concrete having a unit weight not less than 105 lb per cu ft (1698.75 kp per cu m), multiply the coefficient of friction by 0.85. /Author/

Tensile strength and fatigue of optical fibers

Abstract: A method is presented for analyzing laboratory measurements of tensile strength and fatigue failure rates of glass fibers. This method provides the physical basis for extrapolating laboratory data to the multikilometer lengths and long lifetimes which will be characteristic of field use of optical fibers in telecommunication systems.

Analysis of RC Shear Panels under Cyclic Loading

Abstract: A nonlinear constitutive model for plain concrete subjected to cyclic biaxial stresses is described in brief. The model takes account of the compressive softening of concrete prior to reaching maximum compressive stress. Two reinforced concrete shear wall structures, one loaded monotonically and the second subjected to large cyclic load reversals are analyzed and compared with test data. Simulation of cyclic loading response is greatly improved compared to previous elastoplastic models. In addition to the improved material characterization in compression, the treatment of tensile cracking is felt to be a significant factor in the good match obtained with experimental data.

Factors affecting textural characteristics of cooked comminuted fish muscle

Abstract: Factors affecting textural characteristics of cooked comminuted fish muscle were investigated. These factors included: time of comminution, presence of NaCl or NaCl and polyphosphates, effect of mechanical deboning, temperature of cooking, and type of heating medium used. Textural characteristics were evaluated objectively using as an index: compressive strength, modulus of elasticity, resilience, and shear strength. The change in the physical state of the protein-water system was determined from the quantity of fluid (expressible fluid) that can be expressed from the specimen subjected to a fixed compression force. With extensive chopping, mechanical strength diminished as the concentration of extractable myosin in the muscle homogenates decreased. Changes in expressible fluid followed changes in physical properties. Formulations with higher moisture contents were more susceptible to adverse changes brought about by mechanical treatments such as chopping. Mechanical strength of the cooked comminuted muscle progressed in the order of increasing strength as follows: no additives, with NaCl, with NaCl and polyphosphates. The presence of polyphosphates allowed increased solubilization of muscle protein and improved water binding. The variation in textural strength of products receiving different preheating treatments appeared to be related to the changes in water binding as shown by the inverse relationship of mechanical strength to the quantity expressible fluid. The textural strength of cooked muscle homogenates decreased in the order of: steamed, water cooked, and smoke-house cooked.

Mechanical Properties of Glass and Steel Fiber Reinforced Mortar

Abstract: Tensile, flexural and compressive tests were conducted on mortar specimens reinforced with different lengths and volumes of steel and glass fibers. The tensile flexural strength of reinforced specimens was at most two to three times that of plain mortar while the corresponding strains or deflections were as much as ten times that of mortar. The stresses and strains at first cracking were not significantly different from those of plain mortar. The values of the modulus of elasticity and the extent of nonlinearity was observed to depend on the methods of deformation measurement. Extensive microcracking was observed on the surfaces of failed flexural specimens indicating a significant contribution of the matrix even after the first cracking. For steel fiber reinforced specimens, the peak loads and deformations appear to be linearly related to the fiber parameter: v f(L/D). After failure, steel fibers pulled out while most of the glass fibers broke.

Longitudinal shear strength of Douglas-fir

Abstract: Weibull's theory of brittle fracture is applied to the determination of strength of Douglas-fir wood in longitudinal shear. Ultimate stresses, at a given survival probability, are derived for beams...

Marine floating concrete made with polystyrene expanded beads

Abstract: Synopsis The performance of concrete containing expanded polystyrene beads was studied in the context of marine floating structures and compared with that of concrete containing perlite, the latter being an ultra-lightweight aggregate used for marine applications. It was found that, for an equal density of about 80% that of sea water, polystyrene concrete has a compressive strength that is 50% higher, a modulus of elasticity 100% higher, and a modulus of rupture 25% higher than those of perlite concrete. Furthermore, polystyrene concrete is much more resistant to sulphate solutions than perlite concrete even though it is less resistant than normal-weight concrete.

Effect of Low Velocity Impact Damage on the Compressive Strength of Graphite/Epoxy Hat-Stiffened Panels

Abstract: Low velocity impact damage on the compressive strength of graphite/epoxy hat stiffened panels is studied. Fourteen panels, representative of minimum-mass designs for two compression load levels were tested. Eight panels were damaged by impact and the effect on compressive strength was evaluated by comparing the results with data for undamaged panels. The impact tests consisted of firing 1.27 cm diameter aluminum projectiles normal to the plane of the panel at a velocity of approximately 55 m/sec to simulate impact from runway debris. The results of this investigation indicate that impact damage in the panels designed for 0.53 MN/m was contained locally and the damaged panels were capable of carrying the design load. The panels designed for 1.58 MN/m failed between 50 and 58 percent of the design load due to impact damage in the high axial stiffness region. The extent of damage in the high axial stiffness region of both panel designs increased with the magnitude of applied axial load. Damage in this region was the most significant factor in reducing panel strength. Limited damage that was not visually detectable reduced ultimate strength as much as extensive visible damage.

Determination of Biaxial Compressive Strength of a Sintered Alumina Ceramic

Abstract: The compressive strength of commercial high-density alumina was measured in several compressive biaxial stress states. The compressive strength was only slightly affected by the magnitude of the intermediate principal stress. The average value of the compressive strengths measured in all stress states, excluding the equibiaxial and the near-uniaxial compressive stress states, was 528 ksi. The average of the coefficients of variation was 3%. The tensile strength measured for the material indicates that the ratio of compressive strength to tensile strength is ∼ 18.

Modulus of elasticity and strength properties of dental cements

Abstract: The modulus of elasticity, compressive strength, and tensile strength of six dental cements of primary consistency, four cements of secondary consistency, and two liners were evaluated. Several commercial dental cements were tested. A zinc phosphate cement had the highest values for compressive strength and modulus of elasticity, but a zinc polyacrylate cement had the highest tensile strength. The calcium hydroxide liner showed higher values than the zinc oxide-eugenol liner. The modulus of elasticity, compressive strength, and tensile strength of commercial dental cements of primary and secondary consistency were evaluatedt 24 hours after mixing. Among the cements with a primary consistency tested, a zinc phosphate cement had the highest values of compressive strength (117 MN/m 2 ) and modulus (13,700 MN/m 2 ); however, a zinc polyacrylate cement had the highest tensile strength (12.6 MN/m 2 ). Among the cements with a secondary consistency, zinc phosphate cement had the highest values of compressive strength (161 MN/m 2 ) and modulus (22,−400MN/m 2 ). A calcium hydroxide liner had higher values of strength and modulus than a zinc oxide-eugenol liner.

Characteristics of akwara as a reinforcing fibre

Abstract: Synopsis Some relevant physical characteristics of akwara and akwara-reinforced concrete (akwaracrete) are discussed. Akwara is a natural vegetable stem fibre, dark brown in colour when mature, and has a hard smooth sheath enclosing a cellular core. Akwara is brittle and lighter than water. It is dimensionally stable in water, durable in a cement matrix environment, and has a low modulus of elasticity. Mixes containing akwara have lower mobility and compactibility than their plain counterpart. The fibre improves the impact resistance of concrete, but appears to have no effect upon uniaxial compressive strength or modulus of rupture.

Mechanical Properties and Density of Bone in a Case of Severe Endemic Fluorosis

Abstract: Mechanical properties of 25 standardized specimens of compact bone from a 45-year-old man with extreme endemic fluorosis were compared with similar specimens of nonfluorotic bone. Data from dry and wet tested specimens were compared. Tensile strength, strain, energy absorbed to failure, and modulus of elasticity were reduced in fluorotic specimens while compressive strength, strain and energy were increased in both wet and dry specimens. Compressive properties exceeded tensile properties. Drying increased tensile and compressive strength and modulus but decreased tensile and compressive strength and energy absorbed. Dry specimens tended to follow Hooke's Law but wet specimens exhibited visco-elastic behavior. Wet fluorotic specimens had lower tensile properties but higher compressive properties and were more dense than fresh human compact bone.

Dynamic Strength of Oil Shale

Abstract: In-situ retorting of oil shale requires explosive loading under overburden pressure to break up rock masses. Therefore, a study of the dynamic, confined failure strength under compressive loading was carried out for shale ranging in kerogen content from 11 to 45 gal/ton. It was found that the envelope of ultimate strength could be described by a first-order failure criterion that expands uniformly in principal stress space about the hydrostatic axis as the strain rate increases. The strength/log-strain-rate dependence was found to be nonlinear, with the strength doubling over seven orders of magnitude in strain rate. In these laboratory tests, considerable ductility at failure was encountered, with the strain at failure ranging from 2 to 35 percent. Failure strength was ordered consistently with respect to kerogen content, but the strength-reducing presence of large calcite inclusions in the leanest grade of shale overcame the effect of lower kerogen content to the extent that specimens of intermediate richness exhibited the highest strength.

Split-cylinder test and double-punch test for tensile strength of concrete

Abstract: This paper investigates the load strain behavior and ultimate tensile strength for both plain and polymer impregnated concrete cylinders subjected to split-cylinder load method and double-punch load method. These two testing techniques have been used frequently in practice for the determination of tensile strength of concrete materials. Behavior and strength variations in the two tests are described.

Short Fibers Rubber Composites: the Comparative Properties of Treated and Discontinuous Cellulose Fibers

Abstract: Composites produced by dispersion of selected short cellu lose fibers in elastomeric matrices are useful engineering materials. These fibers are pre-treated to provide dispersion in conventional mixing equip ment while minimizing fiber damage, and to give bonding to utilize the rubber reinforcing ability of the fiber. In the uncured composite, the fibers contribute higher green tensile strength, and almost no die swell on extru sion. The vulcanized composites show a monotonic increase in Young's Modulus and a decrease in ultimate elongation with increasing fiber load ing. As with many composites, the tensile strength is less than the matrix strength at very low fiber loading, but at higher fiber levels the matrix is reinforced and the composite tensile strength exceeds the matrix strength. The stiffening action of the fibers provides a harder material with greatly reduced solvent swelling characteristics compared to the matrix rubber. Finally, the tensile properties of the composite are precisely related ...

The determination of tensile properties from hardness measurements for Al-Zn-Mg alloys

Abstract: The correlations between tensile properties (yield strength, ultimate tensile strength and uniform strain) and indentation hardness are studied for two types of Al-Zn-Mg alloys. The reasons why Tabor's equations do not well fit the experimental data when the strain-hardening coefficient is larger than 0.3 are discussed. New equations for the determination of tensile properties from hardness measurements are theoretically derived and found to be in excellent agreement with the experimental data for Al-Zn-Mg alloys. The equations areT u=(H v/c 2)[4.6(m−2)] m−2 and σy=(H v/C 2)1-(3−m> ) +25 (m−2), whereT u andσ y are ultimate tensile strength and yield strength,H v is Vicker's hardness number,m is Meyer's hardness coefficient,E is Young's modulus,c 2 is a constant about 2.9 in magnitude. In these equationsT u,σ y,H v andE are all expressed in kg mm−2.

Hard Object Impact Damage of Metal Matrix Composites

Abstract: The paper presents results on the damage mechanisms in hard object impact and their effect on the residual tensile strength of unidirectional Boron/Aluminum and Borsic/Titanium composites. The ballistic tests were carried out with 0.177" steel spheres impacting at the center of centilever plates over a velocity range of 50 to 4000 ft/sec. The induced ballistic damage and the different failure modes are examined by radiography and SEM, and the post impact residual tensile strength and residual velocity after perforation are studied for both materials.The damage induced in Boron/Aluminum consists mainly of lateral and axial cracks causing large strength degradation, up to 50 percent of the initial strength. Borsic/Titanium, on the other hand, shows much better impact resistance and the ballistic damage consists of localized plastic de formation and formation of a sheared plug causing strength degradation of 20 percent of the initial strength, as is the case with homogeneous titan ium.An analytical model bas...