Decrease In Shear Modulus Research Articles

Correlation between the elastic shear instability mechanism and empirical criteria for irradiation-induced amorphization

In an attempt to correlate the shear instability mechanism with empirical criteria for irradiation-induced amorphization, shear moduli of an A 3B-type fcc crystal were calculated as a function of the chemical long range order parameter S using a Morse potential. The shear moduli were found to decrease with decreasing S. When the depth and the curvature of the A-B potential were changed while keeping the A-A and B-B potentials constant, the magnitude of the decrease in shear moduli is greater for deeper and narrower A-B potentials. The present results indicate that a shear instability should occur more readily in compounds with larger ordering energy and larger elastic moduli. These results agree with the reported empirical criteria for irradiation-induced amorphization, therefore providing further support for the shear instability mechanism for solid-state amorphization.

Syntheses and properties of halato‐telechelic polyurethane‐ureas from divalent metal salts of p‐aminobenzoic acid, diamine, dialkylene glycols, and diisocyanate

AbstractHalato‐telechelic polyurethane‐ureas were synthesized from divalent metal salts of p‐aminobenzoic acid, 4,4′‐diaminodiphenylmethane (4,4′‐methylenedianiline, MDA), dialkylene glycols, and 2,4‐toluylene diisocyanate (TDI). As the divalent metal, Mg and Ca were used, and diethylene glycol and dipropylene glycol were the glycols used. The halatotelechelic polyurethane‐ureas obtained showed better solubilities in dimethylformamide (DMF) and dimethylsulfoxide (DMSO) than previously reported halato‐telechelic polyureas from the metal salts, MDA, and TDI. The reduced viscosities of the polyurethane‐ureas in DMF and DMSO were very low at very low concentrations but increased as the concentration increased. The increase was higher in DMF having lower dielectric constant, due to lower depression of ionic association. Introducing the metal into the urethane‐urea backbone resulted in a considerable decrease in decomposition temperature. In dynamic mechanical property measurements, they exhibited no sharp decrease in relative shear modulus and no peak of tan δ, probably due to aggregation of ionic groups in the polymer main chain.

A study on compressive strength of unidirectional graphite-epoxy composites

The shear moduli of the unidirectional graphite-epoxy composites and the matrix material 'epoxy' under compressive load were measured by torsion tests. The compressive failure tests were also carried out and the acoustic emission was measured. The shear modulus of epoxy did not decrease until a high compressive strain was applied. Therefore, the previous theories for the compressive strength which require the decrease of shear modulus of epoxy under the compressive stress should be questioned. Young's modulus and the shear modulus of composites suddenly decreased at a load about 10-20% lower than the compressive fracture load, and the numbers of events of acoustic emission rapidly increased. Scanning electron micrographs have shown that the section of the failed fiber is skewed and stepwise, (characteristics different from those of the tensile fracture). The stresses caused by the difference between Poisson's ratio of the fiber and that of the matrix under a compressive load and the thermal residual stres...

Analysis of nuclear explosion salmon free‐field ground motion data for nonlinear attenuation

In order to assess the existence and impact of mild nonlinear contributions to the attenuation of seismic signals from underground explosions, free‐field motion data from underground 5.3‐kt nuclear test Salmon have been examined. These data, which were taken in a salt dome at ranges from 166 to 660 m, show moderate strains (10−3 to 10−4) which may provide nonlinear attenuation. The attenuation over an order of magnitude in peak amplitude can be described approximately by an attenuation function Q of a bit less than 10; however, the calculated waveform using this constant Q is noticeably wider than the data. A linear but frequency dependent Q which decreases with decreasing frequency gives a reasonable fit to much of the waveform change as well as the peak amplitude decay with range. The higher‐speed precursor which precedes the main pulse in the data cannot be described by this linear Q. With a spherical finite difference calculation driven by the 166‐m Salmon pulse, it is found that a rapid shear modulus decrease at a 10−4 strain threshold can reproduce the observed precursor and other features of the pulses at greater ranges when a linear broad absorption band with Q ≈ 10 is also added. The attenuation of the Salmon pulse thus can be attributed in part to a nonlinear effect of material failure as well as to a conventional linear mechanism. There are reasons to believe that the attenuation is not linear, but the Salmon data alone cannot verify this view.

Shear wave measurements for improved characterization of shock‐Induced phase transformations in Carrara marble

Shear waves have been measured in shock‐induced, high‐pressure phases of Carrara marble (polycrystalline calcite). The shear modulus decrease associated with the calcite‐CaCO3(II) transition is comparable to that observed under hydrostatic loading. Beyond this transition, the shear modulus in the shocked marble increases with compression, even with the occurrence of the CaCO3(II)‐CaCO3(III) transition. Longitudinal wave speeds over the entire compression range examined are in reasonable agreement with previous shock wave and hydrostatic measurements in polycrystalline CaCO3. A preliminary determination of the bulk modulus from the shear and longitudinal wave speeds in the shocked marble is in reasonable agreement with hydrostatic measurements on polycrystalline and single crystal calcite, suggesting that the transformation to CaCO3(III) may be complete during shock compression. The usefulness of shear wave measurements in studying shock‐induced phase transformations in solids is indicated.

Irradiation-Induced Amorphization and Elastic Shear Instability in Intermetallic Compounds

ABSTRACTPreviously we reported a substantial (∼ 50 %) decrease in shear modulus prior to amorphization in Kr irradiated Zr3Al, and proposed that amorphization is triggered when the crystalline lattice becomes unstable against shear stress. In the present work, the relation between amorphization and shear elastic instability has been investigated in two additional compounds (FeTi and NiAl) during room temperature irradiation with 1.7-MeV Kr+. A shear modulus was measured using Brillouin scattering; structural information was obtained in situ in a high voltage electron microscope interfaced to a tandem accelerator.During irradiation of FeTi, chemical disordering and a large (∼40 %) decrease of shear modulus were observed, and an amorphous phase developed subsequently. In contrast, NiAl remained crystalline and chemically ordered during irradiation, and exhibited only a ∼ 10 % decrease in shear modulus. Hence, these two results provide further support that a shear instability triggers irradiation-induced amorphization. The shear instability mechanism may also apply to other solid-state amorphization techniques, e.g. hydrogen charging and mechanical deformation.

Elasticity and failure of triorthogonally reinforced media. 2. shear

1. We worked out a theory of shear of triorthogonally reinforced media with interphase cracks in the structure of strands and on the interface between the strand and the matrix. 2. We discovered that the shear moduli decrease to a small fraction when the size and concentration of the cracks increase. 3. The experimental data and the theory are matched by comparing the calculations of the secant moduli with the experimentally measured tangents of the angles of slope of the diagram of the mechanical state of the medium.

Valence instability of samarium ions in phosphate glasses

Ultrasonic wave velocity, Raman spectra and electrical measurements have been made in samarium phosphate glasses. Both the bulk and the shear moduli decrease under hydrostatic pressure: these glasses show the extraordinary property of becoming easier to compress as pressure is increased. This is in marked contrast to the normal behaviour under pressure of other phosphate glasses. Raman spectroscopy shows that the structures of the samarium phosphate glasses are similar to those of other phosphate glasses. The unusual pressure-induced behaviour is consistent with valence instability of the samarium ions. The temperature dependence of the electrical conductivity is consistent with the small polaron mechanism.

Amorphization of Zr3Al by 1-MeV electron radiation

A crystalline to amorphous transition during high energy particle radiation has been reported in various intermetallic compounds. Chemical disordering is known to precede amorphization, which takes place only below a certain temperature. In Zr3A1, chemical disordering has been observed during 1-MeV electron radiation at temperatures between 130 and 375K but no amorphization has been reported. A large decrease in shear modulus was also observed during chemical disordering of Zr3Al by 1-MeV Kr ion irradiation at room temperature, followed by amorphization. In the present work, the possibility of amorphization of Zr3Al by electron radiation was examined, and the lattice softening due to chemical disordering was studied with electron diffraction.An alloy with a nominal composition of Zr-25at%Al was furnished by Chalk River National Laboratory. It was annealed at 925°C for 2 weeks and subsequently sliced and jet-polished. Specimen was irradiated and examined at 52K with 1-MeV electrons in the Argonne-HVEM.

A field method for the determination of rock-mass modulus

A field test for measuring rock modulus was developed and performed at the site of Darlington Generating Station in shaly limestone. The new method yields a value consistent with the rock-mass modulus evaluated from extensometer measurements in the tunnels.A complementary laboratory program to study the effect of specimen size on the elastic parameter was also performed by using compressional and shear wave velocity measurements. It was shown that beyond a threshold value of size, the Poisson's ratio increases, whereas both dynamic shear modulus and Young's modulus decrease with increasing volume of specimen towards the field value of static modulus. Key words: rock-mass modulus, field tests, shear wave velocity, size effect.

Effects of 2,3-diphosphoglycerate on the mechanical properties of erythrocyte membrane

Investigation by Schindler et al and Sheetz and Casaly have indicated that high (approximately 10 mmol/L) concentrations of 2,3- diphosphoglycerate (2,3-DPG) have a destabilizing effect on erythrocyte membrane and the membrane skeleton. We have investigated changes in the membrane mechanical properties that occur at elevated 2,3-DPG levels in both intact cells and ghosts. The membrane shear modulus, viscoelastic recovery time constant, critical force, “plastic” viscosity, and material relaxation time constant were measured by standard micropipette and flow channel techniques. Intact cells showed no change in properties at physiologic ionic strength and 2,3-DPG concentrations of about 20 mmol/L, except for an increase in membrane viscosity resulting from an increased cellular hemoglobin concentration that occurs when the 2,3-DPG concentration is elevated. At ionic strengths 20% below physiologic and 2,3-DPG concentrations of approximately 20 mmol/L, decreases in membrane shear modulus and membrane viscosity were observed. In ghosts, no changes in these properties were observed at a 2,3-DPG concentration of 10 mmol/L and ionic strengths as low as 25% below physiologic, but a decrease in the force required to form tethers (critical force) was observed at physiologic ionic strength. The decrease in membrane shear modulus and viscosity of intact cells and the reduced critical force in ghosts are consistent with the results of other investigators. However, the difference in the effects of 2,3-DPG on ghosts and intact cells indicates that the effects of 2,3-DPG depend strongly on the conditions of the experiment. It appears unlikely that 2,3-DPG affects erythrocyte membrane material properties under physiologic conditions.

Effects of 2,3-Diphosphoglycerate on the Mechanical Properties of Erythrocyte Membrane

Investigation by Schindler et al and Sheetz and Casaly have indicated that high (approximately 10 mmol/L) concentrations of 2,3-diphosphoglycerate (2,3-DPG) have a destabilizing effect on erythrocyte membrane and the membrane skeleton. We have investigated changes in the membrane mechanical properties that occur at elevated 2,3-DPG levels in both intact cells and ghosts. The membrane shear modulus, viscoelastic recovery time constant, critical force, "plastic" viscosity, and material relaxation time constant were measured by standard micropipette and flow channel techniques. Intact cells showed no change in properties at physiologic ionic strength and 2,3-DPG concentrations of about 20 mmol/L, except for an increase in membrane viscosity resulting from an increased cellular hemoglobin concentration that occurs when the 2,3-DPG concentration is elevated. At ionic strengths 20% below physiologic and 2,3-DPG concentrations of approximately 20 mmol/L, decreases in membrane shear modulus and membrane viscosity were observed. In ghosts, no changes in these properties were observed at a 2,3-DPG concentration of 10 mmol/L and ionic strengths as low as 25% below physiologic, but a decrease in the force required to form tethers (critical force) was observed at physiologic ionic strength. The decrease in membrane shear modulus and viscosity of intact cells and the reduced critical force in ghosts are consistent with the results of other investigators. However, the difference in the effects of 2,3-DPG on ghosts and intact cells indicates that the effects of 2,3-DPG depend strongly on the conditions of the experiment. It appears unlikely that 2,3-DPG affects erythrocyte membrane material properties under physiologic conditions.

ＣＦＲＰ一方向材の圧縮強度についての一考察

The shear moduli of the unidirectional graphite-epoxy composites and the matrix material “epoxy” under compressive load were measured by torsion test. The compressive failure tests of them were also carried out and the acoustic emission was measured. The shear modulus of epoxy did not decrease until a high compressive strain. Therefore the previous theories for the compressive strength which require the decrease of shear modulus of epoxy under the compressive stress should be denied. Young's modulus and the shear modulus of composites suddenly decreased at the load about 10% to 20% lower than the compressive failure load, and the numbers of events of acoustic emission rapidly increased. Photographs by the scanning electron-microscope have shown that the section of the failed fiber is skewed and stepwise, which is characteristics different from that of the tensile failure. The stresses caused by the difference between Poisson's ratio of the fiber and that of the matrix under a compressive load and the thermal residual stress produced in the process of curing have been analytically calculated on the assumption of the hexagonal array of fibers. The results have revealed that those two stresses cannot be the factors to determine the compressive strength of the composites. A formula to express the effect of compressive load on the torsional deformation has been obtained for the square section on the asssumption of no warping constraint.

Viscoelastic behaviour of polycarbonate plasticized with stilbene

New parameters are introduced, permitting characterization of the effects of plasticization and antiplasticization of polymers. It was found that by the introduction of the same amount of stilbene into PK, in the range of rubber elasticity the dynamical shear modulus decreases by the same amount, by which it increases in the glassy state. The mechanical loss maximum preceding the glass transition, increases with increasing concentration of the plasticizer. It is assumed that this loss maximum corresponds to the melting of segmental mobility of the non-cooperative type.

High temperature experiments on the elastic and anelastic behaviour of magmatic rocks

Measurements of the complex shear modulus have been performed on various ultrabasic and basic rocks (dunite, peridotite, gabbro, and basalts) and a synthetic forsterite at temperatures between 600 and 1500°C (depending on the sample material) and in the frequency range from 0.003 to 30 Hz under forced torsional oscillations. The maximum shear stress was 0.3 MPa and the strains were of the order 5 · 10 −6 to 5 · 10 −5. Measurements of the electrical resistivity as a function of temperature have been carried out together with the mechanical experiments to indicate the beginning of partial melting. The absolute values of the shear modulus below T m are comparable with the results of other authors. The onset of melting shows up in a rapid decrease of both shear modulus and electrical resistivity. At high temperatures ( T > 0.8 · T m) the absorption factor Q −1 follows a power law Q −1∈ ω − α exp(− A′/ RT) with α = 0.15−0.30 and A′ between 100 and 200 kJ mol −1. Towards lower temperatures this “High Temperature Background” is superimposed by a flat absorption peak which shifts from high to low frequencies with falling temperature. This peak can often be described by a lognormal distribution of simple relaxation processes with a standard deviation of about three and a mean relaxation time τ ∼ exp( A/ RT) with A ≈ 400–600 kJ mol −1. Above T m a third contribution to Q −1 is observed that can be regarded as independent of frequency between 1 and 30 Hz. This last component which contributes < 50% to the total absorption is attributed to the melt phase in the samples. An explanation for the high temperature background and the peak is proposed which is based on the relaxation of pinned dislocation lines. By some coupling mechanism via the reorganisation of the stress field with increasing deformation this process may be responsible for both features. At very high temperatures and low frequencies a small influence of steady state flow on Q −1 is observed and below T = 0.6 T m thermal cracking or thermoelastic losses may contribute to Q −1. The influence of lithostatic pressure on Q −1 is estimated and the extrapolation of the experimental data to the p, T conditions of the uppermost mantle are in good agreement with published Earth models. An attempt is made to establish a general Q− T relationship from the experimental data.

Analysis and simulation of calendering process of non-newtonian polymeric fluids

Maxwellian fluid flow between asymmetric calenders was analyzed by the numerical solution to the simplified equations of motion and energy equation. The solution techniques combined the power-law weighted upwind difference method for the energy equation with the analytical solution of the momentum equations. The calculated results provided not only pressure and temperature distributions of the flow field, but also the power consumption and the roll separating force of the calendering processes. The decrease in the elastic shear modulus led to the reduction in the temperature profile as well as in the power requirement. The asymmetry in the roll speeds generated higher temperature field throughout the whole flow region due to the higher viscous heating, compared with the case of the symmetry in the roll speeds.

The effects of extensional creep and creep recovery on the dynamic properties of an unfilled and filled crosslinked polyester resin

Changes in the dynamic properties of unfilled and filled cured polyester resins during extensional creep were measured with the aid of a modified torsion pendulum. Glass beads were used as filler. The decrease in the real shear modulus during creep is attributed mainly to a debonding process. Dewetting-rewetting processes reflected by modulus changes, were discussed on the basis of a theory of Takahashiet al. Voigt-Kelvin rheological models were used to characterize the modulus and the creep compliance recoveries after load release.

Mechanical properties and structural aspects of binary phosphate glass fibers

Glass fibers of binary lithium phosphate glasses with Li/P ratios of 1 2 and 2 3 were investigated with respect to tensile strength, Youngs modulus and shear modulus. The fibers were prepared by a nozzle drawing process with variation of the following drawing parameters: nozzle temperature, mass flow, fiber diameter, and drawing speed. The tensile strength of the fibers - when related to the fiber diameter - shows the well known behaviour only for relatively large diameters: increasing in strength with decreasing diameter. However, for thin fibers (diameter <20 μm) the relationship between strength and diameter was found to be the opposite, which can be explained by the drawing stress acting during the drawing process. With increasing stress an increasing orientation of the chains in the fiber will be produced. For diameters less than 20 μm the drawing stress exceeds 3 MPa and gives rise to mechanically induced defects in the glass network as a result of which the tensile strength will be reduced. The elastic constants of the fibers are mainly dependent on two parameters: fictive temperature (itself dependent on cooling rate and nozzle temperature) and drawing stress. Both, Youngs modulus and shear modulus decrease as these parameters increase due to the frozen-in open structure of these glasses. With respect to the drawing stress the decrease of Youngs modulus is less than that of the shear modulus. This shows that the structural units of these fibers are considerably orientable: a preferred orientation parallel to the fiber axis for that part of the glasses with chain molecules (chains of tetrahedra). The fictive Poisson ratio μ ∗, calculated from the Youngs and shear modulus, exhibits both smaller and larger values than the bulk glass. Especially for thin fibers, which are produced by high drawing stresses, μ ∗ exceeds 0.5, which again shows the dominant influence of the orientation.

Machine foundatios on deposits of soft clay overlain by a weathered crust

Currently available methods to design machine foundations against excessive dynamic displacements assume that the stiffness of the supporting soil is either constant or increases with depth. But frequently, soft normally consolidated clay deposits have stiffer upper crusts due to desiccation and weathering; in such crusts shear modulus and strength decrease sharply with depth. The Paper presents a theoretical study of the coupled horizontal-rotational and vertical vibrations of long massive foundations that carry rotating machinery and are supported by such weathered clay deposits. A key step in the analysis is the determination of the dynamic foundation impedances appropriate for the range of anticipated operational frequencies of the machinery. By utilizing a rational analytical procedure, extensive parametric studies were carried out and are reported in the form of graphs relating normalized impedance functions to crucial non-dimensional factors influencing the response. Particular emphasis is accorded to the effects of the degree and depth of weathering and a numerical example illustrates the direct practical applicability of the graphs. Les méthodes dont on dispose actuellement pour calculer des fondations de machines sans déplacements dynamiques excessifs admettent que la rigidité du sol support est constante ou qu'elle augmente avec la profondeur. Mais bien souvent, less croûtes supérieures des dépôts d'argile molle normalement consolidée sont plus rigides en raison de la dessiccation et de l'altération; dans le cas de telles croûtes, le module de cisaillement et la résistance à la rupture au cisaillement diminuent brusquement en fonction de la profondeur. L'article présente une étude théorique des vibrations verticales et horizontales-circulaires associées auxquelles sont soumises de longues fondations massives qui portent des machines rotatives et reposent sur de tels dépôts d'argile 'altéré'. L'étape-cléf de l'analyse réside dans la détermination des 'impédances' dynamiques de fondations convenant à la gamme de fréquences opérationnelles prévues pour les machines. A l'aide d'une méthode analytique rationnelle, d'importantes études paramétriques ont été effectuées; les résultats de ces études sont présentés sous forme de graphiques qui représentent les fonctions d'impédances normalisées par rapport aux facteurs critiques adimensionnels qui influencent la réponse. Une importance particulière est accordée aux effets du degré et de la profondeur de l'altération, et l'application pratique directe des graphiques présentés est illustrée à l'aide d'un exemple numérique.

Estimation of the size of earthquake preparation zones

During the earthquake preparation a zone of cracked rocks is formed in the region of a future earthquake focal zone under the influence of tectonic stresses. In the study of the surrounding medium this region may be considered as a solid inclusion with altered moduli. The inclusion appearance causes a redistribution of the stresses accompanied by corresponding deformations. This paper deals with the study of deformations at the Earth's surface, resulting from the appearance of a soft inclusion. The Appendix contains an approximate solution of the problem for a soft elastic inclusion in an elastic half-space. It is assumed that the moduli of the inclusion differ slightly from those of the surrounding medium (by no more than 30%). The solution permits us to calculate the deformations at the Earth's surface for the inclusion with an arbitrary heterogeneity and anisotropy. The problem is solved by the small perturbation method. The calculation is made for a special case of a homogeneous isotropic inclusion where only the shear modulus decreases. The shear stresses act at infinity. The equations are deduced for the estimation of deformations and tilts at the Earth's surface as a function of the magnitude of the preparing earthquake and the distance from the epicentre. Comparison has shown a satisfactory agreement between the theoretical and field results. Let us assume that the zone of effective manifestation of the precursor deformations is a circle with the centre in the epicentre of the preparing earthquake. The radius of this circle called ‘strain radius’ may be calculated from the equation $$\rho = 10^{0.43M} km,$$ where M is the magnitude. It was shown that the precursors of other physical nature fall into this circle.