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  • 1
    Electronic Resource
    Electronic Resource
    A theory of ferroelectric hysteresis with a superimposed stress (2002)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 91 (2002), S. 3806-3815 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Based on the mechanism of domain switch, a micromechanics-based model is developed to calculate the hysteresis loop of ferroelectric ceramics under combined electromechanical loading. The development makes use of an extension of the Eshelby-type elastic inclusion problem to a heterogeneous electromechanically coupled ferroelectric medium with distribution of eigenstrain and eigenpolarization generated by domain switch. The ferroelectric ceramic at a generic state is considered to consist of the parent domain and the switched domains whose volume fraction fp, continues to evolve under an increasing electromechanical load. At a given level of applied stress and electric field, the volume fraction of the new domain is determined from a kinetic equation that is derived from consideration of the thermodynamic driving force caused by the reduction of Gibbs free energy and the resistance force associated with the domain wall movement. The theory developed is used first to simulate the hysteresis behavior of a PZT-51 without any superimposed stress, and then with the derived material constants, to independently predict the influence of a superimposed compression. It is found that, consistent with experimental observations, the hysteresis loops flatten out under the axial compression, but that the loops elongate under a transverse compression. Both the remanent polarization and coercive field also tend to decrease with the compressive force regardless of how the compression is applied. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1448397
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  • 2
    Electronic Resource
    Electronic Resource
    Micromechanics simulation of spontaneous polarization in ferroelectric crystals (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 2484-2491 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Based on a modified equivalent inclusion method and a thermodynamic theory, a micromechanics model is developed to predict the evolution of internal stress and the effects of microstructural features (i.e., new domain concentration and porosity) and the external hydrostatic pressure on the transition temperature for single crystal ferroelectric ceramics upon cooling. During the cubic-to-tetragonal transition the material is a composite, with an internal stress due to phase transformation. Consideration of the thermodynamic driving force and resistance force leads to a kinetic equation that provides the volume concentration of new domains at a given level of temperature and applied stress. This new domain concentration results in an increase of overall electric polarization. Numerical calculations using the properties of BaTiO3 indicate that internal stress in the parent cubic phase continues to develop during spontaneous polarization, and that increased porosity greatly facilitates the transition process. Hydrostatic pressure provides an additional contribution to the Gibbs free energy of the system and also can increase the transition temperature. Its effect generally follows the Clausius-Clapeyron equation, but weak nonlinearity is found at very high pressure. This departure is attributed to the change in heat capacity during the cubic–tetragonal transition. A comparison with some observed data for the evolution of overall polarization of a BaTiO3 crystal serves to support the rationality of the model. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1388567
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  • 3
    Electronic Resource
    Electronic Resource
    Determination of notch-tip plasticity by X-ray diffraction and comparison to continuum mechanics analysis (1982)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 15 (1982), S. 594-601 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Dislocation-free silicon crystals of ({\bar 2 \bar 1 \bar 1}) orientation with a hyperbolic notch, subjected to tensile deformation at 1073 K, were used as model material for the analysis of the induced plastic zone. The results obtained by X-ray topography and X-ray rocking-curve measurements were compared to theoretical calculations and predictions based on continuum mechanics. Good agreement between experiment and theory was obtained regarding the shape of the plastic zone, the contribution of the active slip systems to the size of the plastic zone and the direction of the maximum plastic strain trajectory in the zone. Discrepancies between experiment and theory regarding the symmetry relation of the plastic zone lobes and the dislocation density near the notch tip were attributed to the interactions and resulting work-hardening. These aspects were not taken into account in calculations of continuum mechanics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889882012746
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  • 4
    Electronic Resource
    Electronic Resource
    Determination of strain concentration by microfluorescent densitometry of X-ray topography: A bridge between microfracture and continuum mechanics (1980)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 290-296 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The strain distribution in the vicinity of the notches of a double-notched, elastically bent silicon crystal was determined by measuring the diffracted X-ray intensities. The measurements were carried out on traverse-oscillation topographs of a crystal section extending through both notches. Strain distributions were determined by measuring the local densities of silver deposits (measurements of `opacities') with a scanning electron microscope. It was shown that both the density range and spatial resolution of X-ray densitometry were larger by an order of magnitude than those of optical densitometry. The strain concentration factors associated with the notches were measured experimentally and calculated by continuum mechanics. The results were in satisfactory agreement. Also, the experimentally found rise of strains, to a maximum in the critical area adjacent to the notch root, followed the trend predicted by continuum mechanics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889880012083
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  • 5
    Electronic Resource
    Electronic Resource
    Determination of the strain concentration factors around holes and inclusions in crystals by X-ray topography (1982)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 15 (1982), S. 423-429 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Long-range, elastic strains emanating from stress raisers, such as holes and inclusions, were investigated in bent silicon crystals which functioned as a model material. The strains and strain interactions were characterized by X-ray Pendellösung fringe topography and were quantitatively evaluated by X-ray intensity measurements of transverse-oscillation topographs. Improvement of strain measurements were obtained by considering the contribution of anomalous transmission to the intensity measurements and by deposition of an appropriate metal film on the developed topograph to heighten the fluorescence of the silver grains in the emulsion. The strain gradient emanating from a bent specimen containing a hole was experimentally determined and the results were compared to calculations based on continuum mechanics having closed-form solution. Good agreement between experiment and theory was obtained. The dependence of strain interaction on interflaw distance was experimentally demonstrated for specimens containing two holes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889882012308
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  • 6
    Electronic Resource
    Electronic Resource
    Effective electrostrictive coefficients of polycrystalline ceramics (2000)
    Springer
    Journal of materials science 19 (2000), S. 291-293 
    Details
    ISSN: 1573-4811
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006798210633
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  • 7
    Electronic Resource
    Electronic Resource
    Theoretical calculation of creep and relaxation of polycrystals, and stress redistribution among constituent grains (1987)
    Springer
    Journal of materials science 22 (1987), S. 1390-1396 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Taking into account both transient and steady creep of slip systems in the grain, a theoretical method is developed to determine the overall creep and relaxation behaviour of polycrystals and, by which, the accompanying stress and strain distribution among the constituent grains can also be evaluated. This method extends the incremental self-consistent relation for grain interactions to the total form, and is further complemented with an iterative computational process. It is primarily intended for the calculation of creep under a constant stress, relaxation under a constant strain, and a combination of both. While maintaining almost the same degree of accuracy, this new method, as compared to the incremental one, is far more effective. Its theoretical predictions on the creep and relaxation of a 2618-T61 aluminium are shown to be in good accord with experiments. The heterogeneous nature of creep deformation and stress distribution among the constituent grains are also displayed for several selected grain orientations. Finally some implications and limitations of the model are assessed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01233139
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  • 8
    Electronic Resource
    Electronic Resource
    Dislocation theories of work hardening and yield surfaces of single crystals (1980)
    Springer
    Acta mechanica 37 (1980), S. 217-230 
    Details
    ISSN: 1619-6937
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Description / Table of Contents: Zusammenfassung Es werden die Eigenschaften vorhandener Versetzungsverfestigungstheorien untersucht. Diese Analyse zeigt, daß die Verfestigungsmechanismen in zwei Gruppen eingeteilt werden können; nämlich isotrope und kinematische. Als Folge davon wird ein allgemeines, physikalisches Verfestigungsgesetz vorgeschlagen, welches die Begriffe des Grades der Isotropie und der Arbeitsverfestigung vereinigt. Die dazugehörigen Bewegungen der Fließfläche werden sowohl im Spannungs-als auch im Verzerrungsraum auf der Basis dieses allgemeinen Verfestigungsgesetzes und seiner beiden extremen Fälle, der isotropen und der kinematischen Verfestigung, untersucht.
    Notes: Summary The nature of existing dislocation hardening mechanisms are analyzed. This analysis shows that the hardening mechanisms can be classified into two categories: isotropic and kinematic; consequently a general physical hardening law, which incorporates the concept of the degree of isotropy in work hardening, is proposed. The corresponding motions of yield surface in both stress and strain space are examined on the basis of this general hardening law and its two extreme cases: isotropic and kinematic hardening.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01202945
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  • 9
    Electronic Resource
    Electronic Resource
    Elastic moduli of heterogeneous solids with ellipsoidal inclusions and elliptic cracks (1995)
    Springer
    Acta mechanica 110 (1995), S. 73-94 
    Details
    ISSN: 1619-6937
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary The influence of ellipsoidal inclusions and elliptic cracks on the overall effective moduli of a two-phase composite and of a cracked body, respectively, is investigated by means of Mori-Tanaka's theory for three types of inclusion and four types of crack arrangements: monotonically aligned, 2-D randomly oriented (two kinds for cracks), and 3-D randomly oriented. The effective moduli of the composite in the aligned case are known to coincide with Willis' orthotropic lower (or upper) bounds with a two-point ellipsoidal correlation function if the matrix is the softer (or harder) phase. With 2-D randomly oriented inclusions, the effective moduli are examined under Willis' transversely isotropic bounds with a two-point spheroidal correlation function, and it is found that, as the cross-sectional aspect ratio of the ellipsoidal inclusions flattens from circular shape to disc-shape, the two effective shear moduli and the plane-strain bulk modulus all lie on or within the bounds. The effective bulk and shear moduli of an isotropic composite containing randomly oriented ellipsoidal inclusions also fall on or within Hashin-Shtrikman's bounds as the shape of the ellipsoids changes. The obtained moduli are then extended to a cracked body containing elliptic cracks, which are generated by compressing the thickness of ellipsoidal voids to zero. It is found that only selected components of the effective moduli are dependent upon the crack density parameter η. Their dependence on η and the crack shape γ are explicitly established.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01215417
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  • 10
    Electronic Resource
    Electronic Resource
    Influence of random bridging on the elastic and elastoplastic properties of fiber-reinforced composites (1996)
    Springer
    Acta mechanica 116 (1996), S. 29-44 
    Details
    ISSN: 1619-6937
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary The overall elastic moduli and elastoplastic stress-strain relations of a fiber-reinforced composite containing either aligned or randomly oriented spheroidal voids are derived explicitly. The results are given in terms of the void shape and concentration, and for the elastic moduli the void shape is further pushed to the limit for cracked bodies. The present theory also corresponds to the condition of “random bridging”, with a longitudinal Young's modulus and axial shear modulus lying between those of “full bridging” and “no bridging”. Numerical results further indicate that both elastic and elastoplastic strength of the fiber-reinforced composite can be significantly weakened by the presence of both types of distribution, but the extent of stiffness or strength reduction is highly dependent upon the void shape and loading direction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01171418
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