Bulk Modulus (bulk + modulus)

Distribution by Scientific Domains


Selected Abstracts


Three-dimensional models of elastostatic deformation in heterogeneous media, with applications to the Eastern California Shear Zone

GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2009
Sylvain Barbot
SUMMARY We present a semi-analytic iterative procedure for evaluating the 3-D deformation due to faults in an arbitrarily heterogeneous elastic half-space. Spatially variable elastic properties are modelled with equivalent body forces and equivalent surface traction in a ,homogenized' elastic medium. The displacement field is obtained in the Fourier domain using a semi-analytic Green function. We apply this model to investigate the response of 3-D compliant zones (CZ) around major crustal faults to coseismic stressing by nearby earthquakes. We constrain the two elastic moduli, as well as the geometry of the fault zones by comparing the model predictions to Synthetic Aperture Radar inferferometric (InSAR) data. Our results confirm that the CZ models for the Rodman, Calico and Pinto Mountain faults in the Eastern California Shear Zone (ECSZ) can explain the coseismic InSAR data from both the Landers and the Hector Mine earthquakes. For the Pinto Mountain fault zone, InSAR data suggest a 50 per cent reduction in effective shear modulus and no significant change in Poisson's ratio compared to the ambient crust. The large wavelength of coseismic line-of-sight displacements around the Pinto Mountain fault requires a fairly wide (,1.9 km) CZ extending to a depth of at least 9 km. Best fit for the Calico CZ, north of Galway Dry Lake, is obtained for a 4 km deep structure, with a 60 per cent reduction in shear modulus, with no change in Poisson's ratio. We find that the required effective rigidity of the Calico fault zone south of Galway Dry Lake is not as low as that of the northern segment, suggesting along-strike variations of effective elastic moduli within the same fault zone. The ECSZ InSAR data is best explained by CZ models with reduction in both shear and bulk moduli. These observations suggest pervasive and widespread damage around active crustal faults. [source]


Experimental analysis of compaction of concrete and mortar

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 15 2001
Nicolas Burlion
Abstract Compaction of concrete is physically a collapse of the material porous microstructure. It produces plastic strains in the material and, at the same time, an increase of its bulk modulus. This paper presents two experimental techniques aimed at obtaining the hydrostatic response of concrete and mortar. The first one is a uniaxial confined compression test which is quite simple to implement and allows to reach hydrostatic pressures of about 600 MPa. The specimen size is large enough so that concrete with aggregate sizes up to 16 mm can be tested. The second one is a true hydrostatic test performed on smaller (mortar) specimens. Test results show that the hydrostatic response of the material is elasto-plastic with a stiffening effect on both the tangent and unloading bulk moduli. The magnitude of the irreversible volumetric strains depends on the initial porosity of the material. This porosity can be related in a first approximation to the water/cement ratio. A comparison of the hydrostatic responses obtained from the two testing techniques on the same material show that the hydrostatic response of cementitious materials cannot be uncoupled from the deviatoric response, as opposed to the standard assumption in constitutive relations for metal alloys. This feature should be taken into account in the development of constitutive relations for concrete subjected to high confinement pressures which are needed in the modelling of impact problems. Copyright © 2001 John Wiley & Sons, Ltd. [source]


Ultrasonic Velocity Technique for Nondestructive Quantification of Elastic Moduli Degradation during Creep in Silicon Nitride

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2003
Franti, ek Lofaj
The ultrasonic velocity technique was used for nondestructive quantification of creep damage during interrupted tensile creep tests at 1400°C in an advanced silicon nitride to investigate the possibilities of this technique for creep damage monitoring in ceramic components. The longitudinal and shear wave velocities, Poisson's ratio, and Young's, shear, and bulk moduli linearly decreased with strain. Precise density change measurements indicated a linear relationship with a coefficient of proportionality of 0.69 between the volume fraction of cavities and tensile strain. Cavitation was identified as the main creep mechanism in the studied silicon nitride and the reason for ultrasonic velocity and elastic moduli degradation. The measurement of just the longitudinal wave velocity changes was found to be sufficient for quantification of cavitation during creep. The capability of the ultrasonic velocity technique for simple, sensitive, and reliable nondestructive monitoring of creep damage during intermittent creep was demonstrated in silicon nitride. [source]


Prediction of electronic, structural and elastic properties of the hardest oxide: TiO2

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 3 2009
M. A. Caravaca
Abstract This work combines the theory of elasticity with first principles quantum mechanic calculations to predict the electronic, structural and elastic properties: elastic constants, bulk moduli of the TiO2 (Titania) in the Pnma phase. Band-structure shows a direct gap in , which increases its value under hydrostatic pressure. It has two regimes: in the range 0,50 GPa the band-gap has a negative second pressure derivative and changes its sign in the range 50,100 GPa. The band gap becomes indirect at pressures above 150 GPa. This phase improves its mechanical stability and insulator properties under extreme conditions of hydrostatic pressures. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Structural, electronic and optical calculations of Cu(In,Ga)Se2 ternary chalcopyrites

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 11 2004
M. Belhadj
Abstract In this work, we have investigated the structural, electronic and optical properties of the ternary I,III,VI2 chalcopyrite semiconductors ABX2 (A = Cu, B = In, Ga, X = Se) by means of a first-principles density-functional total-energy calculation with the local-density approximation (LDA), using the all-electron full-potential linear-augmented plane-wave method (FP-LAPW). The equilibrium lattice constants and the bulk moduli (a, c, c/a, u and B0) are compared with other theoretical calculations. The energy gap at ambient pressure is found to be direct and the nature of the gap crucially depends on the manner in which the d electrons of the A atoms are treated. We have also reported the optical properties of two chalcopyrite semiconductors CuInSe2 and CuGaSe2. Results on complex dielectric functions, refractive indices n, extinction coefficients k, and normal-incidence reflectivity R in the two crystals are given and compared with earlier data where available. We analyze in detail the structures of the dielectric function observed in the studied energy region. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Sorption behavior in polymers above Tg: Relations between mechanical properties and swelling in limonene

POLYMER ENGINEERING & SCIENCE, Issue 9 2005
J.E. Ritums
The sorption behavior of two highly swelling "rubbery" polymers, natural rubber and polyethylene, has been studied. The polymers are in many aspects very different. Yet, when the solute mass uptake, in this case limonene, is plotted as a function of the square root of time, both polymers show similar "sigmoidal"-types of curves. This triggered the research to determine what mechanisms were responsible for the observed similarities and if the degree in sigmoidal behavior and swelling anisotropy could be easily assessed explicitly by any mechanical parameter. It was found that their degrees of swelling anisotropy, described by a solute-surface-concentration relaxation time, could be explained by their relative bulk moduli. It was assumed that the ratio in bulk modulus at zero pressure, determined from compression measurements, could represent the ratio in expansion bulk modulus during swelling. However, the prediction in swelling anisotropy during sorption using the ratio in bulk modulus was slightly less successful when the swelling anisotropy was quantified as the relative ratio of sheet thickness to cross-sectional area side length. It should be noted that the ratio in uniaxial tensile modulus between polyethylene and natural rubber was several orders of magnitude higher than their ratio in swelling anisotropy. The natural rubber sheet became saddle-shaped during limonene sorption and collapsed into a flat shape when the saturation concentration was approached. During desorption, the sheet went from flat to cup-shaped and then flat again at the end of desorption. The saddle and cup shapes occurred in both square and round sheets. These shapes are believed to be a consequence of buckling and deformation due to instabilities in the stress state of the sheet. This was, in turn, explained by the normally existing local variation in cross-link density. POLYM. ENG. SCI., 45:1194,1202, 2005. © 2005 Society of Plastics Engineers [source]


Influence of pressure on the lengths of chemical bonds

ACTA CRYSTALLOGRAPHICA SECTION B, Issue 4 2003
I. David Brown
An expression to describe the force that a chemical bond exerts on its terminal atoms is proposed, and is used to derive expressions for the bond force constant and bond compressibility. The unknown parameter in this model, the effective charge on the atoms that form the bond, is determined by comparing the derived force constants with those obtained spectroscopically. The resultant bond compressibilities are shown to generally agree well with those determined from high-pressure structure determinations and from the bulk moduli of high-symmetry structures. Bond valences can be corrected for pressure by recognizing that the bond-valence parameter, R0, changes with pressure according to the equation [source]


Aplanarity of CO3 groups: a theoretical ­investigation

ACTA CRYSTALLOGRAPHICA SECTION B, Issue 4 2000
Björn Winkler
Density functional theory-based calculations have been used to demonstrate that the aplanarity of CO groups in some carbonates such as dolomite, CaMg(CO), aragonite, CaCO, and norsethite, BaMg(CO), is a ground-state property. This distortion stabilizes dolomite by ,500,J,mol. Up to at least 6,GPa, the aplanarity of CO groups in dolomite is independent of pressure. In aragonite the aplanarity increases slightly on increasing pressure, while a significant tilting of the CO groups occurs. The calculations do not support previous findings of anomalously low values for the pressure derivative of the bulk moduli, , of aragonite and dolomite. Instead, the computed pressure dependences of the unit-cell volumes correspond to = 5.0,(5) for aragonite and = 4,(1) for dolomite, when fitted with a third-order Birch,Murnaghan equation-of-state. [source]


Pressure Effect Investigations on the Spin Crossover Systems{Fe[H2B(pz)2]2(bipy)} and {Fe[H2B(pz)2]2(phen)}

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 18 2006
Ana Galet
Abstract Pressure effect studies on the spin crossover behaviour of the mononuclear compounds {Fe[H2B(pz)2]2(bipy)}(1) and {Fe[H2B(pz)2]2(phen)}(2) have been performed in the range of 105 Pa,1.02 GPa at variable temperatures (100,310 K). Continuous spin transitions and displacement of its characteristic temperature has been observed for 1 with increasing pressure. Meanwhile the response of 2 under applied pressures is quite unexpected, and can only be understood in terms of a crystallographic phase transition or change in the bulk modulus of the compound. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]


Elastic properties of dry clay mineral aggregates, suspensions and sandstones

GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2003
Tiziana Vanorio
SUMMARY The presence of clay minerals can alter the elastic behaviour of rocks significantly. Although clay minerals are common in sedimentary formations and seismic measurements are our main tools for studying subsurface lithologies, measurements of elastic properties of clay minerals have proven difficult. Theoretical values for the bulk modulus of clay are reported between 20 and 50 GPa. The only published experimental measurement of Young's modulus in a clay mineral using atomic force acoustic microscopy (AFAM) gave a much lower value of 6.2 GPa. This study has concentrated on using independent experimental methods to measure the elastic moduli of clay minerals as functions of pressure and saturation. First, ultrasonic P - and S -wave velocities were measured as functions of hydrostatic pressure in cold-pressed clay aggregates with porosity and grain density ranging from 4 to 43 per cent and 2.13 to 2.83 g cm,3, respectively. In the second experiment, P - and S -wave velocities in clay powders were measured under uniaxial stresses compaction. In the third experiment, P -wave velocity and attenuation in a kaolinite,water suspension with clay concentrations between 0 and 60 per cent were measured at ambient conditions. Our elastic moduli measurements of kaolinite, montmorillonite and smectite are consistent for all experiments and with reported AFAM measurements on a nanometre scale. The bulk modulus values of the solid clay phase (Ks) lie between 6 and 12 GPa and shear (,s) modulus values vary between 4 and 6 GPa. A comparison is made between the accuracy of velocity prediction in shaley sandstones and clay,water and clay,sand mixtures using the values measured in this study and those from theoretical models. Using Ks= 12 GPa and ,s= 6 GPa from this study, the models give a much better prediction both of experimental velocity reduction due to increase in clay content in sandstones and velocity measurements in a kaolinite,water suspension. [source]


Lithology and hydrocarbon mapping from multicomponent seismic data

GEOPHYSICAL PROSPECTING, Issue 2 2010
Hüseyin Özdemir
ABSTRACT Elastic rock properties can be estimated from prestack seismic data using amplitude variation with offset analysis. P-wave, S-wave and density ,reflectivities', or contrasts, can be inverted from angle-band stacks. The ,reflectivities' are then inverted to absolute acoustic impedance, shear impedance and density. These rock properties can be used to map reservoir parameters through all stages of field development and production. When P-wave contrast is small, or gas clouds obscure reservoir zones, multicomponent ocean-bottom recording of converted-waves (P to S or Ps) data provides reliable mapping of reservoir boundaries. Angle-band stacks of multicomponent P-wave (Pz) and Ps data can also be inverted jointly. In this paper Aki-Richards equations are used without simplifications to invert angle-band stacks to ,reflectivities'. This enables the use of reflection seismic data beyond 30° of incident angles compared to the conventional amplitude variation with offset analysis. It, in turn, provides better shear impedance and density estimates. An important input to amplitude variation with offset analysis is the Vs/Vp ratio. Conventional methods use a constant or a time-varying Vs/Vp model. Here, a time- and space-varying model is used during the computation of the ,reflectivities'. The Vs/Vp model is generated using well log data and picked horizons. For multicomponent data applications, the latter model can also be generated from processing Vs/Vp models and available well data. Reservoir rock properties such as ,,, ,,, Poisson's ratio and bulk modulus can be computed from acoustic impedance, shear impedance and density for pore fill and lithology identification. , and , are the Lamé constants and , is density. These estimations can also be used for a more efficient log property mapping. Vp/Vs ratio or Poisson's ratio, ,, and weighted stacks, such as the one computed from ,, and ,/,, are good gas/oil and oil/water contact indicators, i.e., pore fill indicators, while ,, mainly indicates lithology. ,, is also affected by pressure changes. Results from a multicomponent data set are used to illustrate mapping of gas, oil and water saturation and lithology in a Tertiary sand/shale setting. Whilst initial log crossplot analysis suggested that pore fill discrimination may be possible, the inversion was not successful in revealing fluid effects. However, rock properties computed from acoustic impedance, shear impedance and density estimates provided good lithology indicators; pore fill identification was less successful. Neural network analysis using computed rock properties provided good indication of sand/shale distribution away from the existing wells and complemented the results depicted from individual rock property inversions. [source]


Quantitative detection of fluid distribution using time-lapse seismic

GEOPHYSICAL PROSPECTING, Issue 2 2007
Futoshi Tsuneyama
ABSTRACT Although previous seismic monitoring studies have revealed several relationships between seismic responses and changes in reservoir rock properties, the quantitative evaluation of time-lapse seismic data remains a challenge. In most cases of time-lapse seismic analysis, fluid and/or pressure changes are detected qualitatively by changes in amplitude strength, traveltime and/or Poisson's ratio. We present the steps for time-lapse seismic analysis, considering the pressure effect and the saturation scale of fluids. We then demonstrate a deterministic workflow for computing the fluid saturation in a reservoir in order to evaluate time-lapse seismic data. In this approach, we derive the physical properties of the water-saturated sandstone reservoir, based on the following inputs: VP, VS, , and the shale volume from seismic analysis, the average properties of sand grains, and formation-water properties. Next, by comparing the in-situ fluid-saturated properties with the 100% formation-water-saturated reservoir properties, we determine the bulk modulus and density of the in-situ fluid. Solving three simultaneous equations (relating the saturations of water, oil and gas in terms of the bulk modulus, density and the total saturation), we compute the saturation of each fluid. We use a real time-lapse seismic data set from an oilfield in the North Sea for a case study. [source]


An approach to combined rock physics and seismic modelling of fluid substitution effects

GEOPHYSICAL PROSPECTING, Issue 2 2002
Tor Arne Johansen
ABSTRACT The aim of seismic reservoir monitoring is to map the spatial and temporal distributions and contact interfaces of various hydrocarbon fluids and water within a reservoir rock. During the production of hydrocarbons, the fluids produced are generally displaced by an injection fluid. We discuss possible seismic effects which may occur when the pore volume contains two or more fluids. In particular, we investigate the effect of immiscible pore fluids, i.e. when the pore fluids occupy different parts of the pore volume. The modelling of seismic velocities is performed using a differential effective-medium theory in which the various pore fluids are allowed to occupy the pore space in different ways. The P-wave velocity is seen to depend strongly on the bulk modulus of the pore fluids in the most compliant (low aspect ratio) pores. Various scenarios of the microscopic fluid distribution across a gas,oil contact (GOC) zone have been designed, and the corresponding seismic properties modelled. Such GOC transition zones generally give diffuse reflection regions instead of the typical distinct GOC interface. Hence, such transition zones generally should be modelled by finite-difference or finite-element techniques. We have combined rock physics modelling and seismic modelling to simulate the seismic responses of some gas,oil zones, applying various fluid-distribution models. The seismic responses may vary both in the reflection time, amplitude and phase characteristics. Our results indicate that when performing a reservoir monitoring experiment, erroneous conclusions about a GOC movement may be drawn if the microscopic fluid-distribution effects are neglected. [source]


Experimental analysis of compaction of concrete and mortar

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 15 2001
Nicolas Burlion
Abstract Compaction of concrete is physically a collapse of the material porous microstructure. It produces plastic strains in the material and, at the same time, an increase of its bulk modulus. This paper presents two experimental techniques aimed at obtaining the hydrostatic response of concrete and mortar. The first one is a uniaxial confined compression test which is quite simple to implement and allows to reach hydrostatic pressures of about 600 MPa. The specimen size is large enough so that concrete with aggregate sizes up to 16 mm can be tested. The second one is a true hydrostatic test performed on smaller (mortar) specimens. Test results show that the hydrostatic response of the material is elasto-plastic with a stiffening effect on both the tangent and unloading bulk moduli. The magnitude of the irreversible volumetric strains depends on the initial porosity of the material. This porosity can be related in a first approximation to the water/cement ratio. A comparison of the hydrostatic responses obtained from the two testing techniques on the same material show that the hydrostatic response of cementitious materials cannot be uncoupled from the deviatoric response, as opposed to the standard assumption in constitutive relations for metal alloys. This feature should be taken into account in the development of constitutive relations for concrete subjected to high confinement pressures which are needed in the modelling of impact problems. Copyright © 2001 John Wiley & Sons, Ltd. [source]


Hydrostatic low-range pressure applications of the Paris,Edinburgh cell utilizing polymer gaskets for diffuse X-ray scattering measurements

JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 1 2007
Karena W. Chapman
The use of a polymeric Torlon (polyamide,imide) gasket material in a Paris,Edinburgh pressure cell for in situ high-pressure X-ray scattering measurements is demonstrated. The relatively low bulk modulus of the gasket allows for fine control of the sample pressure over the range 0.01,0.42,GPa. The quality of the data obtained in this way is suitable for Bragg and pair distribution function analysis. [source]


High-pressure neutron powder diffraction study of the Im phase of ReO3

JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 6 2004
J.-E. Jřrgensen
The structure of ReO3 has been studied over the pressure range from 1.27 to 8.01,GPa by neutron powder time-of-flight diffraction as well as by X-ray diffraction up to 41,GPa using Fluorinert as the pressure-transmitting medium. The cubic phase was found to be stable in the pressure range 0.5 to 13.2,GPa and to be highly compressible with a zero-pressure bulk modulus of Bo = 43,(1),GPa. The neutron data were used in least-squares refinements, showing that the ReO6 octahedra remain almost undistorted, while the Re,O,Re bond angle decreases from 166.5,(1) to 146.4,(3)° within the investigated pressure range of 1.27 to 8.01,GPa. The compression mechanism is also described in terms of sphere-packing models of the oxygen anions. [source]


Chemical Crosslinking of PVA and Prediction of Material Properties by Means of Fully Atomistic MD Simulations

MACROMOLECULAR THEORY AND SIMULATIONS, Issue 4-5 2009
Javier Sacristan Bermejo
Abstract A method has been developed for building fully atomistic models of chemically crosslinked PVA. It combines a dynamic crosslinking approach followed by a high-temperature annealing procedure. The crosslinking procedure allows to control both crosslinking density and the amount of free crosslinking sites. It also takes into account some network defects, such as dangling tails and wasted loops, which have been experimentally observed on chemically crosslinked polymer networks. This procedure is applied to PVA which is chemically crosslinked with two different linear polyols. Several material properties such as glass transition temperature, Young's, shear and bulk modulus were predicted from the equilibrated structures and found to agree well with available experimental data. [source]


Elasticity, electronic structure, and dielectric property of cubic SrHfO3 from first-principles

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2009
Z. F. Hou
Abstract Recently, SrHfO3 compound was proposed as a potential gate dielectric to fabricate metal,oxide,semiconductor field-effect transistors (MOSFET) with equivalent oxide thickness (EOT) below 1 nm. Here we report the elasticity, electronic structure, and dielectric property of cubic SrHfO3 from first-principle study based on the plane-wave pseudopotential method within the local density approximation (LDA). The independent elastic constants of cubic SrHfO3 are derived from the derivative of total energy as a function of lattice strain. The elastic modulus is predicted from Voight-Hill bounds. The Born effective charges, electronic dielectric tensors, long wavelength phonon frequencies, and LO,TO splitting of cubic SrHfO3 are computed by linear response with density functional perturbation theory (DFPT). The calculated lattice constant and bulk modulus of cubic SrHfO3 are in good agreement with the available experimental data and other theoretical results. Our results show cubic SrHfO3 is a ductile insulator with an indirect band gap of 3.74 eV (LDA value) and electric dielectric tensor of 4.43, Hf 5d states and O 2p states exhibit a strong hybridization, and cubic SrHfO3 can be mechanically stable. In addition, the phonon frequency of ,soft mode' at zone-center also agrees well with previous theoretical value. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Error propagation in multiscale approaches to the elasticity of polycrystals

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 12 2008
Martin Friák
Abstract The error propagation properties of the Voigt, Reuss, Voigt,Reuss,Hill,Gilvarry, and Hershey schemes for the determination of the integral elastic response of texture free polycrystalline aggregates with cubic structure were studied. The sensitivity of the homogenized polycrystalline shear modulus was tested (i) analytically on the partial derivatives of the shear modulus with respect to the individual elastic constants within extremal Voigt and Reuss schemes, and (ii) numerically for all four methods. The sensitivity of the Hershey shear modulus on the input parameters, the single crystalline elastic constants B, C ,, C44, is shown to be within the limiting values found for the Voigt and Reuss schemes. This conclusion is illustrated numerically on a set of five cubic materials with very different physical properties. The influence of the bulk modulus was found to be approximately two orders of magnitude smaller than that of C , and C44. The Hershey modulus was also found to be non-linear, asymmetric, and strongly dependent on the level of the elastic anisotropy of the studied system. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Truss-type systems exhibiting negative compressibility

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 11 2008
Joseph N. Grima
Abstract We propose novel two- and three-dimensional truss structures made from rods of different materials connected together through pin-joints to form triangular units which can exhibit anomalous compressibility properties. In particular, we show that these systems may be made to exhibit negative linear compressibility along certain directions or compressibilities that are even more positive than any of the component materials, i.e. the end product is a system with tunable compressibility properties that can be tailor made for particular practical applications. We also show that in specific cases, these systems can exhibit an overall negative area compressibility and sometimes even negative volumetric compressibility (i.e. negative bulk modulus) thus confirming that this property can indeed exist. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Preface: phys. stat. sol. (b) 245/3

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 3 2008
Christopher W. Smith
This is the third Special Issue of physica status solidi (b) focusing on materials with a negative Poisson's ratio or other ,anomalous' physical properties. This issue contains selected papers from the First International Conference on Auxetics and Anomalous Systems held at the University of Exeter, UK, on 4,6 September 2006. Around 50 participants from all over the world as well as from a wide range of scientific and engineering disciplines contributed to what was a highly successful conference. This conference follows in the footsteps of two previous workshops held at the Mathematical Research and Conference Centre in B,dlewo near Pozna,, Poland, in 2004 and 2005 [1, 2]. The papers selected for this issue publish recent results obtained for ,anomalous systems' in experiment, theory and computer simulations. In the following we summarize very briefly their contents. Alderson and Coenen compare the performance of auxetic composites to similar systems with conventional positive Poisson's ratios. They find that there are indeed differences which appear to arise from the change of the overall Poisson's ratio of the composite, some beneficial like a rise in impact tolerance at low impact rates, and others deleterious such as the reduced tolerance at higher impact rates. This is one of the first investigations of possible applications for auxetic materials. The two papers by Gaspar and Koenders both examine the effects of disorder upon anomalous properties, especially negative Poisson's ratio. In the first one Gaspar demonstrates how a mean strain estimate fails to predict negative values of Poisson's ratio because of an inability to account for local fluctuations in elastic properties. For instance it is shown that the volume fraction of auxetic regions in an globally auxetic material (measured experimentally) are smaller than a mean strain homogenisation would require. Koenders and Gaspar explore the elastic properties, and especially Poisson's ratio, of a heterogeneous 2D network of bending beams. They predict auxetic behaviour arising from localised disorder in the packing, and therefore effective locally aggregated elastic properties of the beams. In the three articles by Gatt et al. and Grima et al. models based on simple geometry are used to explain the behaviour of seemingly disparate systems, i.e. 2D honeycombs systems and zeolite SiO2 networks. Two papers concerning honeycombs demonstrate relationships between elastic properties and structure and the bounds for auxetic behaviour. The paper concerning the zeolite Natrolite uses numerical force field based energy minimisation methods to simulate the response of this particular zeolite to applied forces and then simplifies the predicted properties even further by considering structural units as rigid 2D polyhedra linked by flexible hinges. In a similar vein, though using a different approach and concerning a very different form of matter, Heyes shows how the heterogeneity in an assembly of particles in a liquid can affect the elastic properties of a liquid and notably the infinite frequency Poisson's ratio. Heyes uses the Molecular Dynamics approach to simulate a Lennard,Jones fluid under various pressures, notably comparing behaviour under positive and negative pressures. In their first paper Jasiukiewicz and co-authors derive elastic constants of 2D crystals for all four classes of 2D crystalline solids: hexagonal (isotropic), quadratic, rectangular, and oblique systems. In their second paper they demonstrate conditions required for auxetic behaviour of 2D crystals. Auxetic solids are further divided into those with some negative Poisson's ratios (auxetic), all negative Poisson's ratios (completely auxetic) and no negative Poisson's ratios (non-auxetic). Lakes and Wojciechowski consider counterintuitive properties of matter, like negative compressibility, negative Poisson's ratio, negative thermal expansion, negative specific heat, and negative pressure. They present and interpret experimental observations of negative bulk modulus in pre-strained foams. They propose also a constrained microscopic model which exhibits negative compressibility. Finally, they solve a very simple thermodynamic model with negative thermal expansion. Martin et al. take a long stride toward a real world application of auxetic materials with a wide ranging study starting with numerical modelling of a wingbox section to experimental testing in a wind tunnel. They show that an auxetic core in a wing box section can allow a passive aero-elastic response which can be tailored by careful design of the core so that camber, and thus drag, is reduced with increasing airspeed but without sacrificing structural integrity. Miller et al. consider another anomalous physical property, negative thermal expansivity, and its application in the form of particulate composites for amelioration of stresses arising from thermal mismatch. They show via experiments that particles with a negative coefficient of thermal expansion may be used as a composite reinforcer to reduce overall thermal expansion and behave according to the standard volume fraction based models. Narojczyk and Wojciechowski examine the effects of disorder upon the bulk elastic properties of 3D fcc soft sphere systems in terms of particle size. Systems, such as colloids, can be thought of in such terms. The study shows that higher order moments of probability distribution do not influence the bulk elastic properties much, but that lower moments such as the standard deviation of particle size influence the elastic properties greatly. The "hardness" of the particle interaction potential is also important in this context. In general, it is shown that the effect of increasing polydispersity is to increase the Poisson's ratio, except the [110] [10] directions. Scarpa and Malischewsky in their paper on Rayleigh waves in auxetic materials show how the Rayleigh wave speed is affected by the Poisson's ratio. The behaviour is complex and depends upon the homogeneity within the material, for instance slowing with decreasing Poisson's ratio in isotropic solids, but showing the reverse trend and increased sensitivity to Poisson's ratio in laminate composites. Scarpa et al. explore the buckling behaviour of auxetic tubes via three types of model, a simple beam mechanics and Eulerian buckling model, a 3D linear elastic FE model and a bespoke non-linear continuum model. The more sophisticated models provide increasing insight into the buckling behaviour though the simple beam model predicts reasonably well in the pre-buckling linear region. Some unexpected and interesting behaviour is predicted by the continuum model as the Poisson's ratio approaches the isotropic limit of ,1, including increasing sensitivity to Poisson's ratio and rapid mode jumping between integer wave numbers. The paper by Shilko et al. presents an analysis of a particular kind of friction joint, a double lap joint, and explores the effects of altering the elastic properties of one component, in particular it's Poisson's ratio. The manuscript introduces the evolution of smart materials from monolithic materials, and the classification of composites exhibiting negative Poisson's ratios. The paper then presents the case of a double lap joint and performs a sensitivity type study, via a 2D FE model, of the effects of changing the elastic properties and degree of anisotropy of one section of the model on various parameters defining the limits of functionality of the joint. The main finding is that an enhanced shear modulus, via a negative Poisson's ratio, can endow such a friction joint with superior performance. Manufacturing of auxetic materials on a commercial scale has proved to be the largest obstacle to their fuller exploitation. The paper by Simkins et al. explores one route for post processing of auxetic polymers fibres produced by a conventional melt extrusion route. Simkins et al. showed that a post process thermal annealing treatment, with carefully optimised parameters, was able to even out otherwise inhomogenous auxetic properties, and moreover improve other elastic and fracture properties often sacrificed for auxetic behaviour. We gratefully acknowledge the support given by the sponsors of the conference, namely the EPSRC of the UK and Auxetic Technologies Ltd. (UK). We also thank the Scientific Committee, the Organising Committee, and all the participants of the conference. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Ab-initio investigation of structural, electronic and optical properties for three phases of ZnO compound

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 9 2007
Z. Charifi
Abstract The complex density-functional theory (DFT) calculations of structural, electronic and optical properties for the three phases: wurtzite (B4), zincblende (B3) and rocksalt (B1) of ZnO compound have been reported using the full-potential linearized-augmented plane-wave (FP-LAPW) method as implemented in the WIEN2k code. We employed both the local-density approximation (LDA) and the generalized-gradient approximation (GGA), which is based on exchange,correlation energy optimization to calculate the total energy. Also, we have used the Engel,Vosko GGA formalism, which optimizes the corresponding potential for band-structure calculations. The 3d orbitals of the Zn atom were treated as the valence band. The calculated structural properties (equilibrium lattice constant, bulk modulus, etc.) of the wurtzite and rocksalt phases are in good agreement with experiment. The B4 structure of ZnO is found to transform to the B1 structure with a large volume collapse of about 17%. The phase transition pressure obtained by using LDA is about 9.93 in good agreement with the experimental data. B1-ZnO is shown to be an indirect bandgap semiconductor with a bandgap of 1.47 eV, which is significantly smaller than the experimental value (2.45 ± 0.15 eV). While B3 and B1 phases have direct bandgap semiconductors with bandgaps 1.46 and 1.57 eV, respectively. Also, we have presented the results of the effective masses. We present calculations of the frequency-dependent complex dielectric function , (,) and it zero-frequency limit ,1(0). The optical properties of B4 phase show considerable anisotropic between the two components. The reflectivity spectra has been calculated and compared with the available experimental data. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Mechanical and optical properties of AIIBIVC2V and AIBIIIC2VI semiconductors

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 12 2006
A. S. Verma
Abstract A simple method based on a plasma oscillations theory of solids is proposed for the calculation of mechanical and optical properties such as microhardness (H), bulk modulus (B), dielectric constant (,), polarizability (,), electronic susceptibility (,) of AIIBIVC2V and AIBIIIC2VI semiconductors. Our calculated values are in excellent agreement with the values reported by earlier researchers. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


How do electronic properties of conventional III,V semiconductors hold for the III,V boron bismuth BBi compound?

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 14 2005
D. Madouri
Abstract We have performed ab-initio self-consistent calculations using the full potential linear augmented plane wave method to investigate the structural and the electronic properties of the boron bismuth III,V compound BBi. Our calculations provide the first available information about the structural and electronic ground-state properties of BBi. Total energy calculations of the cubic zinc-blende, wurtzite, rock-salt, cesium chloride and orthorhombic Cmcm phases are made. The zinc-blende structure is found to be the ground-state phase of BBi; within the generalized gradient approximation (local density approximation), we found a lattice constant of 5.529 Ĺ (5.416 Ĺ) and a bulk modulus of 72.20 GPa (86.27 GPa). We found that, contrary to other boron compounds, the band gap of BBi is direct at the , point. The relativistic contraction of the 6s orbital of Bi has a strong influence on the bands and bonds of BBi. Consequently, the electronic properties of BBi are shown to differ considerably from those of common group III,V semiconductors (e.g. GaAs); in particular, we found an unusually strong p,p mixing of the valence-band maximum relative to most of the other III,V compounds. Furthermore, the calculated valence charge density shows an anomalous behavior, characterized by a charge transfer towards the ,cation' B atom, further illustrating the rich behavior of boron bismuth compounds. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


First principles simulations of F centers in cubic SrTiO3

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2005
J. Carrasco
Abstract Atomic and electronic structure of regular and O-deficient SrTiO3 have been studied. Several types of first principles atomistic simulations: Hartree-Fock method, Density Functional Theory, and hybrid HF-DFT functionals, have been applied to periodic models that consider supercells of different sizes (ranging between 40 and 240 atoms). We confirm the ionic character of the Sr-O bonds and the high covalency of the Ti-O2 substructure. For the stoichiometric cubic crystal; the lattice constant and bulk modulus correctly reproduce the experimental data whereas the band gap is only properly obtained by the B3PW functional. The relaxed geometry around the F center shows a large expansion of the two nearest Ti ions. Moreover, the vacancy formation energy is extremely sensitive to the size and the shape of the supercell as well as the calculation method. The electronic density map indicates the redistribution of two electrons of the missing O atom between the vacancy and 3d atomic orbitals of the two nearest Ti ions, in contrast to the F centers in ionic oxides where the charge centroid does not change. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Sorption behavior in polymers above Tg: Relations between mechanical properties and swelling in limonene

POLYMER ENGINEERING & SCIENCE, Issue 9 2005
J.E. Ritums
The sorption behavior of two highly swelling "rubbery" polymers, natural rubber and polyethylene, has been studied. The polymers are in many aspects very different. Yet, when the solute mass uptake, in this case limonene, is plotted as a function of the square root of time, both polymers show similar "sigmoidal"-types of curves. This triggered the research to determine what mechanisms were responsible for the observed similarities and if the degree in sigmoidal behavior and swelling anisotropy could be easily assessed explicitly by any mechanical parameter. It was found that their degrees of swelling anisotropy, described by a solute-surface-concentration relaxation time, could be explained by their relative bulk moduli. It was assumed that the ratio in bulk modulus at zero pressure, determined from compression measurements, could represent the ratio in expansion bulk modulus during swelling. However, the prediction in swelling anisotropy during sorption using the ratio in bulk modulus was slightly less successful when the swelling anisotropy was quantified as the relative ratio of sheet thickness to cross-sectional area side length. It should be noted that the ratio in uniaxial tensile modulus between polyethylene and natural rubber was several orders of magnitude higher than their ratio in swelling anisotropy. The natural rubber sheet became saddle-shaped during limonene sorption and collapsed into a flat shape when the saturation concentration was approached. During desorption, the sheet went from flat to cup-shaped and then flat again at the end of desorption. The saddle and cup shapes occurred in both square and round sheets. These shapes are believed to be a consequence of buckling and deformation due to instabilities in the stress state of the sheet. This was, in turn, explained by the normally existing local variation in cross-link density. POLYM. ENG. SCI., 45:1194,1202, 2005. © 2005 Society of Plastics Engineers [source]