Showing papers on "Young's modulus published in 1995"

Relationships between Hysteresis Measurements and the Constituent Properties of Ceramic Matrix Composites: I, Theory

Abstract: A methodology for assessing constituent properties of ceramic matrix composites (CMCs) from stress/strain curves is developed. The procedures demonstrate how the properties of the interface and the misfit strain can be related to the unload/reload hysteresis and the permanent strain. The approach is illustrated in companion papers by obtaining experimental measurements on two CMCs. The results demonstrate why differences in the sliding stress and the debond energy of the interfaces result in substantial changes in the shape of the stress/strain curve.

Full strength compacts by extrusion of glassy metal powder at the supercooled liquid state

Abstract: We report the production of full strength compacts of metallic glass by warm extrusion of powders at the supercooled liquid state just above the glass transition temperature. The alloy used was Zr65Al10Ni10Cu15 (at. %) which has the lowest viscosity among Zr‐based metallic glasses with large supercooled liquid region. The tensile strength and Young’s modulus of the glassy powder compacts were 1520 MPa and 80 GPa, respectively, which are similar to that obtained in the as‐cast bulk alloy and melt‐spun ribbon. This opens up possibilities of producing high strength amorphous alloys with complex shapes.

The Young's modulus of feather keratin

Abstract: The flexural stiffness of the rachis varies along the length of a primary feather, between primaries and between species; the possible contribution of variations in the longitudinal Young's modulus of feather keratin to this was assessed. Tensile tests on compact keratin from eight species of birds belonging to different orders showed similar moduli (mean E=2.50 GPa) in all species apart from the grey heron (E=1.78 GPa). No significant differences were seen in the modulus of keratin from primaries 7­10 in any species. There was a systematic increase in the modulus distally along the length of the rachis from swan primary feathers. Dynamic bending tests on swan primary feather rachises also showed that the longitudinal elastic modulus increases with increasing frequency of bending over the range 0.1­10 Hz and decreases monotonically with increasing temperature over the range -50 to +50 °C. The position-, frequency- and temperature-dependent variations in the modulus are, however, relatively small. It is concluded that, in the species studied, the flexural stiffness of the whole rachis is principally controlled by its cross-sectional morphology rather than by the material properties of the keratin.

Laboratory Investigation of Compacted No-Fines Concrete for Paving Materials

Abstract: In this study the physical and engineering characteristics of various no-fines concrete mixtures are investigated. No-fines concrete mixtures subjected to impact compaction are studied under unconfined compression, indirect tension, and static modulus of elasticity; and the results are interpreted as functions of mixture proportions. The effect of impact-compaction energies, consolidation techniques, mixture proportions, curing types, and testing conditions on physical and engineering properties are presented. The abrasion characteristics and resistance to freezing and thawing of no-fines concrete are also discussed. It was found that the strength of no-fines concrete is strongly related to its mixture proportion and compaction energy. A sealed compressive strength of 20.7 MPa (3,000 psi) can readily be achieved with an aggregate cement ratio of 4.5:1 or less and a minimum compaction energy of 165 J/m 3 (4,303 ft-lb/cu ft). The splitting tensile-compressive relationship followed a pattern similar to that ...

Al-B-C Phase Development and Effects on Mechanical Properties of B4C/Al-Derived Composites

Abstract: B4C/A1 offers a family of engineering materials in which a range of properties can be developed by postdensiflcation heat treatment. In applications where hardness and high modulus are required, heat treatment above 600°C provides a multiphase ceramic material containing only a small amount of residual metal. Heat treatment between 600° and 700°C produces mainly A1B2; 700° and 900°C results in a mixture of A1B2 and A14BC; 900° and 980°C produces primarily A14BC; and 1000° to 1050°C results in A1B24C4 with small amounts of A14C3 if the heating does not exceed 5 h. Deleterious A14C3 is avoided by processing below 1000°C. All of these phases tend to form large clusters of grains and result in lower strength regardless of which phase forms. Toughness is also reduced; the least determinal phase is A1B2. The highest hardness (88 Rockwell A) and Young's modulus (310 GPa) are obtained in Al4BC-rich samples. AlB2-containing samples exhibit lower hardness and Young's modulus but higher fracture toughness. While the modulus, Poisson's ratio, and hardness of multiphase B4C/A1 composites containing 5–10 vol% free metal are comparable to ceramics, the unique advantage of this family of materials is low density (>2.7 g/cm3) and higher than 7 MPa-m1/2 fracture toughness.

Stress-strain response of the human vocal ligament.

Abstract: The longitudinal elastic properties of the human vocal ligament were quantified by stress-strain measurements and by modeling the response mathematically. Human ligaments were obtained from surgery and autopsy cases. They were dissected, mounted, and stretched with a dual-servo ergometer to measure force versus elongation and to convert the results into stress and strain. To calculate a longitudinal Young's modulus, the stress-strain curves were fitted with polynomial and exponential functions and differentiated. Young's modulus was separately defined in the low- and high-strain regions. The mean Young's modulus for the low-strain region was 33.1 ± 10.4 kilopascals. In the high-strain region, A and B parameters for an exponential fit were 1.4 ± 1.0 and 9.6 ± 1.2 kilopascals, respectively. The stress-strain and Young's modulus curves showed the typical hysteresis and nonlinearity seen previously in other vocal fold tissues (muscle and mucosa), but the nonlinearity was most profound for the vocal ligament.

Elastic constants of single crystal γ – TiAl

Abstract: The six independent second-order elastic stiffness coefficients of a Ti{sub 44}Al{sub 56} single crystal ({ital L}1{sub 0} structure) have been measured at room temperature for the first time using a resonant ultrasonic spectroscopy (RUS) technique. These data were used to calculate the orientation dependence of Young`s modulus and the shear modulus. The Young`s modulus is found to reach a maximum near a [111] direction, close to the normal to the most densely packed planes. The elastic moduli and the Poisson`s ratio for polycrystalline materials, calculated by the averaging scheme proposed by Hill, are in good agreement with experimental data and theoretical calculations.

Strength and Young's Modulus Behavior of a Partially Sintered Porous Alumina

Abstract: The strength of alumina materials that had been subjected to varying degrees of densification was determined. Significant increases in strength were obtained for these materials even when there was minimal densification. For the most porous materials, the Weibull modulus values were similar but showed a significant increase for materials that were close to the theoretical density. Young's modulus data were found to be similar to previous work, in that significant increases occur during the initial stage of sintering, showing a strong correlation with the strength data. A simple modi fication to a previous theory allowed the Young's modulus data to be fitted with excellent accuracy.

Young's modulus of nanocrystalline Fe measured by nanoindentation

Abstract: Nanoindentation techniques were used to measure Young's modulus for nanocrystalline Fe samples produced by inert-gas condensation and warm consolidation. The samples had grain sizes of 4–20 nm and residual porosity of 2–30% calculated relative to conventional Fe. Values of Young's modulus for the nanocrystalline Fe are reduced relative to that of conventional, fully dense Fe. A review of Young's modulus for other nanocrystalline materials showed similar trends. Published results for porous conventional Fe showed similar reductions in Young's modulus for samples with comparable porosity levels. The observed reductions in Young's modulus for both the nanocrystalline and the conventional porous Fe can be described adequately by several theories utilizing spheroidal porosity.

Microstructural modelling of auxetic microporous polymers

Abstract: A simple two-dimensional model for the deformation of auxetic microporous polymers (those with a negative Poisson's ratio) has been developed. This model network of rectangular nodules interconnected by fibrils has been further developed to include the possibilities of fibril hinging, flexure and stretching. Expressions for strain-dependent Poisson's ratio and Young's modulus have been derived and compared with experimental results on microporous PTFE and UHMWPE. A combination of the hinging mode followed by the stretching mode of deformation can be used to explain the general features of the experimental data for these auxetic polymers. The force coefficients governing the different modes of deformation are dependent on fibril dimensions and intrinsic material properties. By varying the geometry of the network, the model can be used to predict different combinations of Poisson's ratio with modulus, from large positive through to large negative values.

Variations in Young's modulus and intrinsic stress of LPCVD-polysilicon due to high-temperature annealing

Abstract: The effect of high-temperature annealing on Young's modulus E and the intrinsic stress sigma of thin films made of LPCVD-polysilicon was investigated. The films were annealed for 2 hours in a nitrogen atmosphere at temperatures between 600 degrees C and 1100 degrees C. Then Young's modulus and the intrinsic stress were determined by the membrane deflection method. An extended analytical theory for the membrane deflection was developed and the results correspond well with FEM analysis of Pan J.Y. et al. (1990 Technical Digest, IEEE Solid-State Sensor and Actuator Workshop, Hilton Head Island, SC, USA p 70). LPCVD-polysilicon was produced with a SiH4 flow rate of 70 sccm and a total pressure of 100 mTorr at 620 degrees C. The film thickness was 460 nm. For the as deposited films the method of membrane deflection yields a Young's modulus of 151+or-6 GPa and an intrinsic stress of -350+or-12 MPa. After annealing at temperatures higher than the deposition temperature the compressive stress started to decrease with increasing annealing temperature. It relaxed nearly completely after annealing at 1100 degrees C. Young's modulus seems to increase a little with increasing annealing temperature up to 162+or-8 GPa at 1100 degrees C. The values for E and sigma obtained with the membrane deflection method were compared with the values obtained by the method of ultrasonic surface waves. The method of ultrasonic surface waves yields systematically higher values for E. The discrepancy can be explained by the uncertainty of Poisson's ratio of polysilicon.

Weibull modelling of particle cracking in metal matrix composites

Abstract: An investigation into the occurrence of reinforcement cracking within a particulate ZrO 2 /2618 Al alloy metal matrix composite under tensile plastic straining has been carried out, special attention being paid to the dependence of fracture on particle size and shape. The probability of particle cracking has been modelled using a Weibull approach, giving good agreement with the experimental data. Values for the Weibull modulus and the stress required to crack the particles were found to be within the range expected for the cracking of ceramic particles. Additional information regarding the fracture behaviour of the particles was provided by in situ neutron diffraction monitoring of the internal strains, measurement of the variation in the composite Young's modulus with straining and by direct observation of the cracked particles. The values of the particle stress required for the initiation of particle cracking deduced from these supplementary experiments were found to be in good agreement with each other and with the results from the Weibull analysis. Further, it is shown that while both the current experiments, as well as the previous work of others, can be well described by the Weibull approach, the exact values of the Weibull parameters so deduced are very sensitive to the approximations and the assumptions made in constructing the model.

Structure and property development in poly(p‐phenylene terephthalamide) during heat treatment under tension

Abstract: The evolution of several structural characteristics during isothermal heat treatment of poly(p-phenylene terephthalamide) was studied In this work, heat treatment was interrupted after different treatment times, with the specimens immediately quenched to room temperature These specimens were then characterized by tensile testing, wide- and small-angle x-ray scattering, and optical microscopy Structural parameters obtained from these measurements relate to crystal perfection (via the paracrystalline axial distortion parameter), axial crystallite size, transverse crystallite size, degree of chain misorientation, and degree of pleating Structural and mechanical parameters were then plotted against heat-treatment time to obtain kinetic isotherms for each parameter The kinetics of the removal of chain misorientation parallels that of tensile modulus increase under all conditions Of the other structural parameters, only the kinetics of pleat removal mimics that of modulus change, indicating that pleat removal is the effective cause of increased chain alignment and thereby of increased axial stiffness ©1995 John Wiley & Sons, Inc

Method for the continuous production of a polyethylene material having high strength and high modulus of elasticity

Abstract: Disclosed is a method for the continuous production of a polyethylene material having high strength and high modulus of elasticity by rolling an ultra-high-molecular-weight polyethylene film or film like material and then drawing the rolled material, wherein a thermoplastic resin film having incorporated therein at least one additive selected from the group consisting of a coloring agent, a weathering stabilizer, an antistatic agent, a hydrophilicity-imparting agent, an adhesion promoter and a dyeability-imparting agent is laminated to the film material in the rolling step and the resulting polyethylene material is further slit or split as required. This method makes it easy to color the polyethylene material having high strength and high modulus of elasticity and to impart weather resistance and other desirable properties thereto.

Fracture energy and tension properties of high-strength concrete

Abstract: A test setup and adequate instrumentation were developed to record the tension properties of high-strength concrete, including the postpeak softening response. The direct uniaxial tension tests were performed under a strain-controlled mode through a close-loop testing machine. The splitting tensile strength and modulus of rupture were also recorded conforming to standard ASTM test procedures. Test results revealed that high-strength concrete exhibits a more brittle and stiffer behavior with a large initial modulus of elasticity and a more sharply descending branch of the stress-deformation curve beyond the peak load. The unique softening behavior and the more brittle nature of high-strength concrete were expressed in terms of a stress-displacement (crack width) diagram and fracture energy. The fracture energy of high-strength concrete is estimated to be about five times the area under the ascending portion of the stress-deformation curve, compared to a corresponding value of 10 estimated for normal-strength concrete. Based on the test results, a constitutive relationship is recommended for the behavior of high-strength concrete in tension, including postpeak softening response.

Constitutive Models for Healing of Materials with Application to Compaction of Crushed Rock Salt

Abstract: Certain materials exhibit a capability to heal with time. Healing implies that microcracks and microvoids reduce in size, with a corresponding increase in stiffness and strength, features that are exactly the opposite of those normally associated with continuum damage mechanics. A continuum healing mechanics model is proposed within a framework that automatically meets the restrictions of thermodynamics. Rate-independent and rate-dependent formulations are both given. Specific evolution equations are given for a scalar isotropic assumption and comparisons with a limited amount of experimental data on crushed rock salt are given. Good correlations are shown for changes in time of Young's modulus and inelastic strain. The preliminary results provide a good foundation for other examples of healing such as the curing of concrete, the sintering of ceramics and the compaction of cohesive sands and clays.

Thermal residual stresses in ceramic matrix composites—I. Axisymmetrical model and finite element analysis

Abstract: The residual stresses induced in composites when cooling down from the processing temperature were determined using a cylinder model and using a finite element computer program. Various specimen geometries were examined: microcomposites, unidirectional composites and flat substrates coated with one or two layers. Various combinations were investigated involving MoSi2 as an interphase, SiC as a fiber, a matrix, a substrate or an external coating layer and C as a fiber, a substrate, an interphase or an intermediate coating layer. The influence of factors such as interphase thickness and uncertainty in interphase properties (including Young's modulus and coefficient of thermal expansion) was analyzed. It was shown that trends in distribution of thermal residual stresses (TRS) prevailing in 1D composites can be satisfactorily predicted using the analytical cylinder model. The presence of a MoSi2 interphase induces the highest interfacial stresses but it relieves stresses in the matrix. The presence of a C interphase essentially reduces the interfacial stresses.

Mapping the local Young's modulus by analysis of the elastic deformations occurring in atomic force microscopy

Abstract: The atomic force microscope (AFM) is used to map the local elastic properties of substrates by analysis of the force versus tip motion curves. Measurements are presented, which show that gold islands on a rough polypropylene substrate can be distinguished from the surrounding polymer. Quantitative calculations of the elastic deformations of the tip and of the sample, as induced by the AFM, were performed. Surprisingly, the tip deformation is predominant over the sample deformation in a wide regime of forces and of tip radii; which are commonly used in AFM. This fact limits the capability of the AFM to measure local elastic properties. However, with our experimental set-up one can induce a total deformation dominated by the sample deformations.

Relationship between compressive strength and modulus of elasticity of high strength concrete

Abstract: Modulus of elasticity of concrete is frequently expressed in terms of compressive strength. While many empirical equations for predicting modulus of elasticity have been proposed by many investigators, few equations are considered to cover the whole data. The reason is considered to be that the mechanical properties of concrete are highly dependent on the properties and proportions of binders and aggregates. This investigation was carried out as a part of the work of the Research Committee on High-strength Concrete of the Architectural Institute of Japan (AlJ) and National Research and Development Project, called New RC Project, sponsored by the Ministry of Construction. More than 3,000 data, obtained by many investigators using various materials, on the relationship between compressive strengths and modulus of elasticity were collected and analyzed statistically. The compressive strength of investigated concretes ranged from 20 to 160 MPa. As a result, a practical and universal equation is proposed, which takes into consideration types of coarse aggregates and types of mineral additions.

Residual stress, strain and faults in nanocrystalline palladium and copper

Abstract: Nanocrystalline Pd and Cu, prepared by inert-gas condensation and warm compaction, were studied using X-ray diffraction techniques. A sample of Cu with submicrometer grain size produced by severe plastic deformation was also examined. The Warren-Averbach technique was used to separate the line broadening due to grain size, t.m.s. strain and faults. Peak shifts and asymmetry were used to determine the long-range surface stresses, stacking-fault probability and twin probability. Young's modulus for a Pd sample was determined by an ultrasonic technique and compared with the coarse-grained, fully dense value.