Home About us Contact
|
Home About us Contact | ||
|
|
||
Material Constants (material + constant)
Selected AbstractsA density-dependent elastoplastic hydro-mechanical model for unsaturated compacted soilsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 11 2007D. A. Sun Abstract This paper presents a three-dimensional elastoplastic constitutive model for predicting the hydraulic and mechanical behaviour of unsaturated soils. It is based on experimental results obtained from a series of controlled-suction triaxial tests on unsaturated compacted clay with different initial densities. Hydraulic hysteresis in the water-retention behaviour is modelled as an elastoplastic process, with the elastic part modelled by a series of scanning curves and the elastoplastic part modelled by the main drying and wetting curves. The effect of void ratio on the water-retention behaviour is studied using data obtained from controlled-suction wetting,drying cyclic tests on unsaturated compacted clay with different initial densities. The effect of the degree of saturation on the stress,strain-strength behaviour and the effect of void ratio on the water-retention behaviour are considered in the model, as is the effect of suction on the hydraulic and mechanical behaviour. The initial density dependency of the compacted soil behaviour is modelled by experimental relationships between the initial density and the corresponding yield stress and, thereby, between the initial density and the normal compression line. The model is generalized to three-dimensional stress states by assuming that the shapes of the failure and yield surfaces in the deviatoric stress plane are given by the Matsuoka,Nakai criterion. Model predictions of the stress,strain and water-retention behaviour are compared with those obtained from triaxial tests with different initial densities under isotropic compression, triaxial compression and triaxial extension, with or without variation in suction. The comparisons indicate that the model accurately predicts the hydraulic and mechanical behaviour of unsaturated compacted soils with different initial densities using the same material constant. Copyright © 2006 John Wiley & Sons, Ltd. [source] High-Energy Density Ceramic Composition in the System Pb(Zr,Ti)O3,Pb[(Zn,Ni)1/3Nb2/3]O3JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2006Rashed Adnan Islam This study reports a high-energy density piezoelectric polycrystalline ceramic composition in the system Pb(Zr1,xTix)O3,Pb[(Zn1,yNiy)1/3Nb2/3]O3 (PZT,PZNN). Two different Zr/Ti ratios in the PZT system were investigated: 52/48 corresponding to morphotropic phase boundary (MPB) and 56/44 corresponding to the tetragonal phase. The compositions investigated in this study are represented as: 0.9Pb(Zr0.52Ti0.48)O3,0.1Pb(Zn1/3Nb2/3)O3 [0.9PZT (52:48),0.1PZN]+y wt% MnCO3, where y varies from 0 to 0.9 wt% and 0.9Pb(Zr0.56Ti0.44)O3,0.1Pb[(Zn0.8Ni0.2)1/3Nb2/3]O3 [0.9PZT (56:44),0.1PZNN] +y mol% MnO2, where y varies from 1 to 3 mol%. A high-energy density material is characterized by the large magnitude of the product of the piezoelectric voltage constant (g) and the piezoelectric strain constant (d) given as (dg). The condition for obtaining large magnitude of dg was derived to be as |d|=,n, where , is the permittivity of the material and n is a material constant having a lower limit of 0.5. The d33.g33 value of the samples having composition 0.9 PZT (56:44),0.1 PZNN+2 mol% MnO2 (sintered in two steps at 1100°,1000°C) was found to be 18456.2 × 10,15 m2/N, which, to the knowledge of the authors, is the highest value reported for polycrystalline ceramics. This composition was also found to exhibit a high magnitude of g33 as 83.1 V·(m·N),1, corresponding to the magnitude of n as 1.126. [source] A fatigue criterion for general multiaxial loadingFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 1 2000Jiang An incremental fatigue damage model is proposed. The model incorporates the critical plane concept in multiaxial fatigue, plastic strain energy and material memory in cyclic plasticity. With an incremental form the model does not require a cycle counting method for variable amplitude loading. The model is designed to consider mean stress and loading sequence effects. Features of the new model are discussed and the determination of material constants is detailed. Verification of the model is achieved by comparing the predictions obtained by using the new model and experimental data of four materials under different loading conditions. [source] A small-strain overlay modelINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 1 2009T. Benz Abstract The paper begins with a discussion of the phenomenon of small-strain stiffness and presents the small-strain overlay model, a simple model that takes into account the non-linear stiffness of soils at small strains. The new model can enhance already established elastoplastic formulations for non-linear stiffness variation at small strains in a similar way that intergranular strain enhances the hypoplastic model. The overlay model is driven by the material's strain history and only two additional material constants, both with clear physical meaning. Therefore, the proposed model is a step towards the incorporation of small-strain stiffness into routine design. In this paper, the new small-strain overlay model is formulated. Its ability to take into account the influence of various strain histories on soil stiffness is illustrated in several examples. Copyright © 2008 John Wiley & Sons, Ltd. [source] Hyperfine structure of hydrogen and geoniumLASER PHYSICS LETTERS, Issue 2 2004A.V. Andreev Abstract The self-consistent theory of hyperfine atomic structure is developed. The theory is based on Lorentz and gauge invariant equation for action of spin 1/2 particle. The specific feature of proposed equation for action (or Lagrangian) is that it is enable to introduce the three material constants: mass m0, charge q, and magneton (i.e. magnitude of magnetic moment) ,. The analytically tractable solutions of the wave equation for the electron motion in Coulomb field and electron motion in uniform magnetic field are found. In both cases the calculated spectra include the hyperfine splitting that is agreed well with the experimentally observed spectra. The calculated frequencies of 8(12)d3/2 , 8(12)d5/2 transitions in hydrogen atom are compared with the results of experimental measurements by the highprecision spectroscopy methods. It is shown that the results of calculations are in good agreement with the experimentally measured data. (© 2004 by HMS Consultants. Inc. Published exclusively by WILEY-VCH Verlag GmbH & Co.KGaA) [source] Theoretical and experimental analysis of plastic response of isotropic circular plates subjected to underwater explosion loadingMATERIALWISSENSCHAFT UND WERKSTOFFTECHNIK, Issue 2 2008J. Z. Ashani Abstract Dynamic response analysis of structures subjected to underwater explosion (UndEx) loading has been always an interesting field of study for ship designers and metal forming specialists. Understanding the deformation and rupture mechanism of simple structures plays an important role in successful designing of a reliable structure under this kind of loading. In this paper, first the major parameters of the UndEx phenomenon (peak overpressure, impulse per unit area, dimensionless damage parameter ,, etc.) are discussed and determined by means of available experimental relations mostly offered by R. Cole. After that, the maximum deflection of a fully clamped circular plate has been calculated using a theoretical procedure assuming two different conditions: (1) neglecting the effect of strain rate, (2) considering the strain rate sensitivity of the material. Some experiments have been conducted on 5010 aluminum circular plates, using C4 as explosive. In order to simulate reality, a fixture was designed so that the plates are loaded in air-backed condition. Plates were fixed on top of the fixture, so the fully clamped condition which was assumed as the boundary condition was achieved. The test specimens were measured, not only their maximum deflection but also their thickness at different radii were determined. The results are compared to experimental-based predictions offered by Nurick and Rajendran who has conducted similar experiments. The results show reasonable agreement with theoretical predictions, especially when strain rate effects are considered. In addition, two new material constants (D, q) for this special aluminum alloy are introduced. Theoretische und experimentelle Analyse der plastischen Umformung isotroper kreisförmiger Platten bei Unterwasser-Explosionsbelastung Die Analyse der dynamischen Reaktion einer Struktur bei einer Explosionsbelastung unter dem Wasser ist für die Konstrukteure von Schiffen und Umformspezialisten eine interessante Forschungsaufgabe. Das Verständnis der Umformung und der Bruchmechanismen einfacher Strukturen spielt eine wichtige Rolle im erfolgreichen Konstruieren einer festen Struktur gegen diese Belastungsart. In diesem Beitrag werden erstens die Hauptparameter der Explosionserscheinung unter Wasser (maximaler Druck, Impulse per Flächeneinheit, dimensionsloser zerstörender Parameter usw.) dargestellt und zweitens durch die vorhandenen Methoden, die überwiegend von R. Cole vorliegen, berechnet. Danach ist die maximale Durchbiegung einer ganz gespannten kreisförmigen Platte durch eine analytische Methode in zwei Formen bestimmt worden: (1) Vernachlässigung der Dehnungsgeschwindigkeit, (2) Berücksichtigung der Dehnungsgeschwindigkeitsempfindlichkeit des Werkstoffes. Einige Untersuchungen wurden an kreisförmigen Platten aus Aluminium 5010 mittels Sprengstoff C4 durchgeführt. Zur Praxissimulation wurde die Spannvorrichtung so konstruiert, so dass die Platten Luft-gepuffert belastet wurden. Die Platten wurden oben auf der Spannvorrichtung vollständig eingespannt, um Grenzbedingungen zu erhalten. Bei den Proben wurde nicht nur die maximale Durchbiegung sondern auch die Dicke in verschiedenen Radien ermittelt. Die Ergebnisse wurden mit den experimentellen Abschätzungen von Nurick und Rajendran, die ähnliche Versuche durchgeführt haben, verglichen. Die Ergebnisse zeigen eine gute Übereinstimmung mit den theoretischen Abschätzungen, insbesondere bei Betrachtung der Dehngeschwindigkeit. Zusätzlich wurden für diese spezielle Aluminiumlegierung zwei neue Materialkonstanten (D, q) eingeführt. [source] Transmission problems for Maxwell's equations with weakly Lipschitz interfacesMATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 6 2006Andreas Axelsson Abstract We prove sufficient conditions on material constants, frequency and Lipschitz regularity of interface for well posedness of a generalized Maxwell transmission problem in finite energy norms. This is done by embedding Maxwell's equations in an elliptic Dirac equation, by constructing the natural trace space for the transmission problem and using Hodge decompositions for operators d and , on weakly Lipschitz domains to prove stability. We also obtain results for boundary value problems and transmission problems for the Hodge,Dirac equation and prove spectral estimates for boundary singular integral operators related to double layer potentials. Copyright © 2005 John Wiley & Sons, Ltd. [source] Minimal regularity of the solutions of some transmission problemsMATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 4 2003D. Mercier We consider some transmission problems for the Laplace operator in two-dimensional domains. Our goal is to give minimal regularity of the solutions, better than H1, with or without conditions on the (positive) material constants. Under a monotonicity or quasi-monotonicity condition on the constants (or on the inverses according to the boundary conditions), we study the behaviour of the solution near vertex and near interior nodes and show in each case that the given regularity is sharp. Without condition we prove that the regularity near a corner is of the form H1+,, where , is a given bound depending on the material constants. Numerical examples are presented which confirm the sharpness of our lower bounds. Copyright © 2003 John Wiley & Sons, Ltd. [source] Acoustic phonons in InSb probed by time-resolved X-ray diffractionPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 12 2006A. Morak Abstract Acoustical phonons in InSb were induced with femtosecond light pulses and probed by diffraction of ultrashort X-ray pulses in the crystal lattice. The time dependent transient X-ray diffraction signal due to elastic lattice deformation was measured with subpicosecond resolution. The elastic lattice deformation depends on the temporal evolution of the energy transfer from excited electrons in the semiconductor into the lattice. As already shown in previous investigation a conventional thermoelastic model is not sufficient to describe this coupling process. Here a complex simulation including a two temperature model of the electron and lattice as well as the microscopic behavior of the electron plasma is applied to explain important effects like thermal carrier diffusion and band gap deformation found in the lattice deformation experiments. When this model is used, with realistic values for both pump laser fluences and bulk material constants, excellent agreement between the experimentally observed time dependent lattice deformation and calculated values is obtained throughout the observation period. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | |||||||||||||