Showing papers on "Young's modulus published in 1988"

Technical note: relation between static and dynamic young's moduli of rocks

Abstract: The objective of this paper was to establish a relationship between static and dynamic Young's moduli of rocks. Compilation and analysis of data on static and seismically determined Young's moduli of rock revealed that the correspondence between the two moduli was rather low. A better estimate of the static Young's modulus was obtained from an empirical relation between the logarithm of static Young's modulus and the logarithm of the product of dynamic Young's modulus and density, with a coefficient of correlation equal to 0.96.

Structure of skin layer in injection‐molded polypropylene

Abstract: The structure of skin layer in injection-molded polypropylen which displayed a clear two-phase structure of skin and core has been studied by means of wide-angle x-ray diffraction, small-angle x-ray scattering, melting behavior, density, dynamic viscoelasticity, and tensile test. In skin layer, the c-axis and a*-axis were highly oriented to the machine direction (MD), and the plane of the lamellar structure of about 160 A in thickness was in normal to MD. The density was about 0.907 g/cm3, which was nearly the same as that of core layer. Although the majority of crystallites melted in the same temperature range as in that of the core layer, there was about 5.3% higher temperature melting structure (Tm = 182°C). The dynamic tensile modulus E′ in MD decreased more slowly with increasing temperature than that of the core layer and held high modulus in the range of ca. 30°C, just above the temperature at which E′ of the core layer suddenly dropped. E′ in MD was higher than that in TD in the temperature range below 33°C, which was slightly higher than the primary absorption temperature, and the order reversed above 33°C. The tensile yield stress in MD was 1.5 times higher than that of the core layer. The skin layer in MD ruptured just after yielding and did not show necking. The tensile yield stress in TD was about half of that in MD about 0.7 times that of the core layer. The necking stress in TD was about 0.6 times that of the core layer. In general, a polypropylene melt crystallizes under a high shear stress in injection molding. From these facts, it was concluded that the skin layer is composed of so-called “shishkebab”-like main skeleton structures, whose axis is parallel to MD, piled epitaxially with a*-axis-oriented imperfect lamellar substructure.

Factors Affecting Bond Between New and Old Concrete

Abstract: When new concrete is placed next to old concrete, attempts are usually made to bond the two concretes together: ofen a cement paste or mortar joint is used, as in masonry. The service stress states in bonds can vary tremendously so no single test method can replicate all these states. A method of test for bond should reflect a typical in-service stress state yet also be sensitive to variation in the strength of the bond. Four tests were evaluated, and a slant shear test was found to be the most appropriate. The effects of various parameters were evaluated theoretically with the finite element and/or experimentally. A bond material with a modulus of elasticity similar to the adjacent concrete was found to be desirable, as was consistency in the bond material properties. Thick bond layers were found to reduce bond strength considerably and copolymer polyvinyl acetate was found to be a poor bonding agent over a wide range of curing conditions and mortar mix designs.

Elastic Anisotropy in Zirconia Single Crystals

Abstract: Results are presented for the measured single-crystal elastic constants of yttria-stabilized zirconia, for yttria contents of 1.7 to 20 mol%. The results cover a range of materials which vary from a mixture of monoclinic, tetragonal, and cubic to those which are fully cubic. These single-crystal measurements are used to calculate the bounds on the elastic moduli for polycrystalline materials. Comments are made on the elastic anisotropy of zirconia relative to a number of other single-crystal ceramics, with graphical comparisons of the anisotropy of Young's moduli of these ceramics.

Composite technology for total hip arthroplasty.

Abstract: Composite materials, which can be very strong while having a low modulus of elasticity, are being studied because such materials have potential to be made into isoelastic hip prostheses. Composites intended for medical applications incorporate carbon or polyamide as a fiber component, while polysulfone, polyetheretherketone, or polyethylene is used as a matrix component. Mechanical properties (especially the modulus of elasticity) are emphasized because of the desire to match those properties of the proximal femur. Many of the variables that affect the mechanical properties of these materials are explained. The application of stress to different fiber orientations demonstrates the mechanical properties of the composite, and this is proved mathematically. It is shown that in composites with fibers oriented in the same direction, the modulus of elasticity in the direction of the fibers generally approaches that of the fibers as the amount of matrix decreases. Perpendicular to the fibers, the modulus of elasticity of the composite is only slightly greater than that of the matrix material. For isotropic chopped-fiber composites, the modulus of elasticity approaches that of the matrix as the fiber content decreases; at high-fiber content, the modulus is significantly less than that of oriented long-fiber composites. In general, the modulus of elasticity and fiber content have a linear relationship. Composites have fatigue properties that vary with direction and approach ultimate strength in tension but are lower in compression. The fatigue properties of proposed composites are discussed. Abrasion as a cause of stress concentration sites and wear particles is considered.

Engineering Properties of Concrete Affected by Alkali-Silica Reaction

Abstract: A detailed study of the effects of alkali-silica reaction (ASR) on the engineering properties of concrete such as compressive and tensile strength, elastic modulus, and pulse velocity is presented. Two types of reactive aggregate - a naturally occurring Beltane opal and synthetic fused silica - were used. The tests wee carried out at 20 C and 96 percent relative humidity (RH). The results showed that losses in engineering properties do not all occur at the same rate or in proportion to the expansion undergone by the ASR-affected concrete. The two major properties affected by ASR were flexural strength and dynamic modulus of elasticity. Compressive strength was not a good indicator of ASR, but the flexural strength proved to be a reliable and sensitve test for mointoring ASR. Nondestructive tests like dynamic modulus and pulse velocity were also able to identify deterioration of concrete by ASR. The data indicate that critical expansion limits due to ASR would vary depending on the type and use of a concrete structure.

Mechanical properties of SiO2 aerogels

Abstract: Ultrasonic and static compression experiments were performed in the frequency range 50 kHz to 1 MHz in order to investigate the mechanical behaviour of silica aerogels as a function of internal gas pressure pG and external stress Pext The measurement of longitudinal and transverse sound velocities allows the Young's modulus and the Poisson's ratio for aerogels of different densities to be determined upon variation of pG and Pext For low-density aerogels ( rho approximately=100 kgm-3) the authors found a decrease in sound velocity upon evacuation Surprisingly, the sound velocity decreases upon uniaxial compression with small loads The most important finding from the static compression experiments is that low-density aerogels display creeping with a time constant of about 45 min

Physical and mechanical properties of YBa2Cu3O7-δ superconductors

Abstract: The physical and mechanical properties of YBa2Cu3O7−° superconductors are examined. These properties are related to powder preparation method, powder characteristics, sintering behaviour and sintered microstructure. The sintering atmosphere and sintering schedules affect the final microstructure very strongly and determine, in conjunction with starting powder characteristics, the sintered density. The mechanical properties such as Young's modulus, bend strength and critical stress intensity factor (fracture toughness) are measured and related to microstructure as determined by electron microscopy. Control of microstructure by careful powder selection and sintering schedule is seen as key to optimizing the physical and mechanical properties of the material. Finally attention is drawn to fabrication techniques and how these must be optimized in order to realize the mechanical properties which are necessary if these are to be useful as engineering materials. Comparisons between fabrication techniques show that uniaxial powder pressing suffers from limitations in terms of specimen complexity and densification whereas the favoured route, termed viscous processing, gives a more homogeneous microstructure, higher strength and allows near theoretical density to be achieved.

Composite Parameters and Mechanical Compatibility of Material Joints

Abstract: The elastic behaviour of a bimaterial interface with interfacial cracks, misfit dislocations and interfacial thermal stresses can be described in a simple manner by using the com posite parameters α and β, and the effective modulus of elasticity E*, assuming a plane deformation of ideally bonded isotropic materials. A coefficient KT for the thermally in duced stress intensity at the interface serves as a measure of the mechanical compatibility of two bonded materials. An examination of these parameters for many composite materials shows that the values of the composite parameters α and β are limited to a nar row range and that the material transition can be classified into six groups with regard to their mechanical compatibility.

Dynamic moduli and damping ratios for cemented sands at low strains

Abstract: This paper advances the present understanding of the beneficial effects of cementation of sands on their dynamic behavior at low strain amplitudes. The influence of important parameters such as cem...

Irreversible property changes of small loblolly pine specimens heated in air, nitrogen, or oxygen

Abstract: The objective of this research was to characterize the roles played by atmospheric oxygen and wood moisture in the thermal degradation of loblolly pine as measured by selected physical and mechanical properties. These two factors relate, respectively, to the oxidation and hydrolysis reactions that comprise the total degradation reaction. Small clear specimens were individually heated at 150 C from 1 to 16 hours in airtight cylinders, which were flushed with oxygen, nitrogen, or air prior to being to sealed. Measured properties were rellectance, specific gravity, hygroscopicity, and the moduli of rupture and elasticity in bending. Property values generally exhibited a decrease with increasing exposure time. The properties can be ranked from most-to-least degraded as follows: relfectance, modulus of rupture, hygroscopicity, modulus of elasticity, and specific gravity. The degradation of these properties was not adequately described by first-order reaction kinetics, Instead, a nonlinear equation was used, which accurately described the data and still reflected a rate controlled process. The rate of property loss was accelerated by the presence of wood moisture, with the exception of residual hygroscopicity. The greatest decrease in property due to the presence of wood moisture occurred with reflectance. The degradation of modulus of rupture and modulus of elasticity was directly related to the amount of wood moisture present. The apparent role of oxygen in total thermal degradation depended on specimen moisture content. The influence of oxygen on the the degradation process was apparent for specimens heated in the oven-dry condition. When moist specimens were heated, however, losses caused by hydrolysis overshadowed oxygen-dependent degradation. Oxygen-dependent degradation was most visible for moduli of rupture and elasticity, and, to a lesser degree for reflectivity. No effect due to the presence of oxygen could be discerned for residual specific gravity and hygroscopicity.

Mechanical properties of fine grained polysilicon-the repeatability issue

Abstract: Calculation and measurements of Young's modulus, Poisson's ratio, shear modulus, and internal strain for fine-grained polysilicon as a function of processing conditions are presented. Calculations are based on appropriate averaging of single-crystal silicon properties, taking into account the film morphology. Experimental data are taken from strain diagnostic and resonant beam structures. It is found that polysilicon films can be in tension and that the intrinsic quality factor is approaching 75000. >

Mechanical properties of concrete at low temperature

Abstract: Laboratory studies were conducted on concrete compressive and splitting tensile strength, modulus of elasticity, and Poisson's ratio and on the local bond strength between concrete and steel under ...

Experimental verification of a microbuckling model for the axial compressive failure of high performance polymer fibres

Abstract: A previously derived theoretical compressive strength for fibres composed of uniaxially oriented and extended polymer chains was compared with the measured strengths of several high performance fibres. For failure initiated by elastic microbuckling of polymer chains or fibrils, the maximum fibre strength is predicted to be equal to the minimum longitudinal shear modulus of the fibre. An excellent linear correlation between measured strengths and torsion moduli was obtained for four liquid-crystalline polymer fibres and high modulus graphite fibres. The correlation shows that measured strengths are 30% of the corresponding torsion moduli for all these fibres. A high modulus, high strength polyethylene fibre exhibited a compressive strength-torsion modulus ratio that was lower than the value 0.3 obtained for the other fibres examined in this study.

Dynamic Testing and Reinforcement of Rubber

Abstract: A series of experiments have been run to determine which mechanisms dominate carbon black reinforcement of rubber. A broad range of compounds using oil-extended and non-oil-extended rubbers and carbon blacks covering the spectrum of tread blacks have been tested. The results for measurements made in an all-SBR formulation are reported here. The primary experiment consisted of measurement of the dynamic modulus and hysteresis of the cured and uncured compounds over a broad range of frequencies, temperatures, and strains. Ternperatures ranged from −70°C to +90°C; frequencies varied from 0.01 to 10 Hz; double strain amplitudes varied from 0.5% to 35%. From a discussion of the literature and evaluation of the experimental results, two mechanisms have been found to control the primary effects of carbon black on rubber reinforcement, where reinforcement refers to a general enhancement of properties, such as modulus, as well as the tensile strength of the compound. Hydrodynamic interaction, which is the...

Mechanical properties of trabecular bone by a non-destructive compression testing approach.

Abstract: In order to optimize non-destructive mechanical testing of trabecular bone specimens, different techniques were analysed, and correlations were established between properties derived from such non-destructive testings and those derived from destructive testing. Non-destructive testing to a fixed percentage of predicted ultimate stress was hampered by inaccuracy of this prediction. Simulation of non-destructive testing conducted to the linear' part of the compression curve using a drop of the increase of the stiffness (slope of the compression curve) below a certain value as stop criterion revealed strong correlations (r: 0.97–0.99) between the stiffness at the stop point and modulus of elasticity derived from destructive testing. However, trabecular damage will probably occur during such testing because high strain values were obtained. Testing to a fixed strain (0.6 per cent) also revealed strong correlation between the stiffness at the 0.6 per cent strain level and modulus of elasticity (r = 0.96) deriv...

Mechanical properties of a new class of metallic glasses based on aluminum

Abstract: The mechanical properties (i.e., tensile fracture strength and Young’s modulus) of eight different alloys of a new class of metallic glasses containing up to 90 at. % aluminum are reported along with crystallization temperatures of these alloys. The Al90Fe5Ce5 material has a tensile fracture strength of 940 MPa (1 MPa=145 psi), while two others (Al87Fe8.7Gd4.3 and Al87Ni8.7Y4.3) exceed 800 MPa. Young’s modulus measurements for three of these exceed 60 GPa with a high value of 66 GPa for the Al90Fe5Ce5 glass. These unusually high strengths of the aluminum glasses can be of significant importance in obtaining high‐strength, low‐density materials.

Mechanical properties of polycrystalline diamonds

Abstract: The room temperature mechanical properties of polycrystalline diamonds, i.e. tensile strength, transverse rupture strength, compressive strength, impact strength, fracture toughness, and elastic constants, have been determined. The applied test techniques are described and the results compared with those obtained by other authors. The fracture mode under the present experimental conditions was primarily transgranular. A grain size dependence, where strength increases with decreasing grain size, has been found. Fracture toughness was found to go through a maximum for grain sizes between 10 to 30 μm. The modulus of elasticity increases with increasing grain size. An influence of cobalt content on strength and modulus of elasticity has been found, while no significant influence on toughness could be determined. Increasing the cobalt content increases strength, but has the inverse effect on the modulus of elasticity. The results of strength, toughness, and elastic constants measurements are discussed ...

High strength, low modulus, ductile, biopcompatible titanium alloy

Abstract: A high strength, low modulus, ductile, biocompatible titanium base alloy containing one or more isomorphous beta stabilizers, eutectoid beta stabilizers and optional alpha stabilizers, characterized by a modulus of elasticity not exceeding 100 GPa; a method for the preparation of said alloy and prostheses made from said alloy.

Properties of steel fiber reinforced concrete under cyclic loading

Abstract: An experimental investigation of the behavior of steel fiber reinforced concrete under cyclic compressive loading is presented. Cylindrical specimens were cast using normal- and high-strength concrete mixes, four types of steel fiber, and three different volume fractions. Stress-strain responses were obtained for three cyclic loading regimes as well as for monotonic loading. The envelope curve is shown to govern cyclic response. Toughness under cyclic loading is found to be at least as great as that under monotonic loading. The behavior of fiber reinforced concrete under cyclic loading, when normalized by its monotonic behavior, is very similar to that of plain concrete or concrete confined by steel spirals, indicating that the fibers primarily influence the envelope curve.

Effect of Fiber Waviness on the Nonlinear Elastic Behavior of Flexible Composites

Abstract: The effect of fiber waviness on the elastic moduli of flexible composites is investigated theoretically and experimentally. The flexible composites examined are composed of con tinuous fibers with sinusoidal waviness in an elastomeric matrix. Both iso-phase and random-phase fiber arrangements are used for this study. The constitutive relations for the longitudinal and transverse tensile behavior have been developed for these models. Tensile tests have been conducted to verify the constitutive relations. Carbon fiber and silicone elastomer were used for the experiments. Techniques for specimen fabrication as well as photoelastic tests are also presented. Experimental results show good agreement with the theoretical predictions.

Cavitation in model elastomeric composites

Abstract: Layers of transparent silicone rubber were bonded between two steel spheres or between two parallel steel cylinders, to make simple mechanical models of particle-filled and fibre reinforced elastomers. When the steel end-pieces were pulled apart, visible cavities appeared suddenly in the rubber layer between them, at well-defined tensile loads and displacements. The critical conditions for cavity formation are shown to be in good agreement with a theoretical criterion for the unbounded elastic expansion of a microscopic precursor void within the rubber: that the local triaxial tensile stress attains a value of 5E/6, whereE is Young's modulus for the rubber. When the rubber layer was extremely thin, however, less than about 5% of the steel end-piece diameter, then the stress required to form a cavity was greater than this, and it increased rapidly as the rubber thickness was reduced further.