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  • 11
    Electronic Resource
    Electronic Resource
    Springer
    Archive of applied mechanics 64 (1994), S. 267-285 
    ISSN: 1432-0681
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Übersicht Die Arbeit stellt Aspekte der Formulierung und numerischen Implementation von Lokalisierungsphänomenen in elastoplastischen Festkörpern im Rahmen kleiner Verzerrungen dar. Zunächst diskutieren wir die theoretischen Grundlagen und die algorithmische Implementation einer lokalen begleitendenprä-kritischen Lokalisierungsanalysis zur Aufdeckung von kritischen Zonen wie Scherbändern, die den Verlust der globalen Strukturstabilität bewirken können. Der zeiite Teil schlägt einen besonderen Zugang zu einerpost-kritischen Lokalisierungsanalysis vor zur Verfolgung postkritischer lokalisierter Gleichgewichtspfade von Strukturen mit einer globalen Verschiebungsdiskontinuität. In diesem Zusammenhang untersuchen wir zwei allgemeine konstitutive Zugänge zur Modellierung der Verschiebungsdiskontinuität und entwickeln eine Finite-Elemente-Formulierung zu ihrer numerischen Implementation.
    Notes: Summary The paper presents some aspects of the formulation and numerical implementation of localization phenomena in elastoplastic solids at small strains. At first we point out the theoretical foundation and algorithmic implementation of a localpre-critical localization analysis for the detection of critical zones which may cause a loss of global structural stability, e.g. shear-bands. The second part proposes a particular approach to thepost-critical localization analysis in order to trace post-critical localized equilibrium branches of solids with a global displacement-discontinuity surface. Within this context we investigate two general constitutive approaches to the modelling of the displacement discontinuity and develop a finite-element formulation for its numerical implementation.
    Type of Medium: Electronic Resource
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  • 12
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Journal of the Mechanics and Physics of Solids 42 (1994), S. 1969-1994 
    ISSN: 0022-5096
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Type of Medium: Electronic Resource
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  • 13
    Electronic Resource
    Electronic Resource
    Springer
    Computational mechanics 17 (1995), S. 74-87 
    ISSN: 1432-0924
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Summary We presented aspects and results related to the broad field of strain localization with special focus on large strain elastoplastic response. Therefore, we first re-examined issues related to the classification of discontinuities and the classical description of localization with a particular emphasis on an Eulerian geometric representation. We touched the problem of mesh objectivity and discussed results of a particular regularization method, namely the micropolar approach. Generally, regularization has to preserve ellipticity and to reflect the underlying physics. For example ductile materials have to be modelled including viscous effects whereas geomaterials are adequately described by the micropolar approach. Then we considered localization phenomena within solids undergoing large strain elastoplastic deformations. Here, we documented the influence of isotropic damage on the failure analysis. Next, the interesting influence of an orthotropic yield condition on the spatial orientation of localized zones has been studied. Finally, we investigated the localization condition for an algorithmic model of finite strain single crystal plasticity.
    Type of Medium: Electronic Resource
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  • 14
    ISSN: 1432-0924
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The new contribution of this study is to formulate two wellknown isotropic elastoplastic damage concepts for ductile materials in the framework of ‘geometrically exact’ finite multiplicative elastoplasticity. For the model originally proposed by Lemaitre the damage evolution follows from a dissipation potential and the hypothesis of general associativity. In contrast, the Gurson model takes into account the balance of mass separately to formulate damage evolution. In this contribution both formulations are based on logarithmic Hencky strains leading to a simple application of the so called ‘exponential map’ stress integrator which is the algorithmic counterpart of the multiplicative elastoplastic formulation adopted. Special emphasis is directed towards the numerical implementation of these models within the framework of finite element analysis of inelastic boundary value problems. To compare the results of numerical computations several standard examples within finite elastoplasticity are analysed with both damage models and the results are contrasted to the outcome of an analysis with the classical v. Mises model. thereby, the dramatic influence of damage on the behaviour within necking and localization computations is highlighted. The different behaviour of the two models considered within compression dominated problems is appreciated.
    Type of Medium: Electronic Resource
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  • 15
    Electronic Resource
    Electronic Resource
    Springer
    Computational mechanics 17 (1995), S. 74-87 
    ISSN: 1432-0924
    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
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  • 16
    Electronic Resource
    Electronic Resource
    Springer
    Acta mechanica 135 (1999), S. 73-90 
    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 paper proposes two new elastoplastic constitutive models for the description of deformation mechanisms of frictional materials which are suitable for a wide range of applications in soil mechanics. The first model provides an extension of the classical Drucker-Prager-type function in order to overcome numerical difficulties in the tensile stress range. The key idea here is the introduction of a constantperturbation-type parameter which yields aC 2-differentiable smoothing-out of the peak of the Drucker-Prager cone. We then extend this formulation to a closed single-surface model based on a decoupled description of the deviatoric and the mean stress response. Both models are equipped with a saturation-type hardening mechanism. They have proved to be very robust and successful in numerical implementations.
    Type of Medium: Electronic Resource
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  • 17
    ISSN: 1434-601X
    Keywords: PACS:25.85.-W Fission reactions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: Projectile fission of 750 AMeV 238U-ions interacting with a Pb target was studied by means of the spectrometer FRS, GSI-Darmstadt. One of the two fission fragments was detected with a transmission of few percent and identified in mass and charge. Low-energy fission (E* 〈 25 MeV) events were selected by their magnetic rigidity. Whereas the production of asymmetric fission events is dominated by the GDR excitation, very asymmetric fission and symmetric fission take place after a GQR or DGDR excitation or after a nuclear interaction. Cross sections of more than 250 isotopes were measured. Isotopic distributions of low-energy fission were reconstructed for elements from Se to Te. The fission modes SI, SII and SL were clearly shown in these distributions and in the mass and TKE distributions. Charge polarization and mass dispersion were deduced for each fission mode. Finally, the characteristics of the low-energy fission process explain the production rates of neutron-rich species.
    Type of Medium: Electronic Resource
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  • 18
    Electronic Resource
    Electronic Resource
    Springer
    Hyperfine interactions 129 (2000), S. 83-96 
    ISSN: 1572-9540
    Keywords: N=Z line ; β-decay ; charged-particle emission ; mirror symmetry ; rp-process ; ion sources ; spallation reaction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The spectroscopy in the vicinity of the N=Z line at ISOLDE is reviewed. New data on the Gamow–Teller strength properties in the A=60–80 region have been obtained. These data provide an insight to nuclear deformation, level densities and mirror β-decay, and can be used to model and test astrophysical predictions in the region of the expected termination of the rp-process.
    Type of Medium: Electronic Resource
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  • 19
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 9 (1993), S. 889-896 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: An explicit formulation and a procedure for the computation of isotropic tensor-valued tensor functions is discussed. The formulation is based on a spectral decomposition in terms of second-order eigenvalue bases, which avoids the costly computation of eigenvectors. As an important result a compact structure of the fourth-order derivatives of general second-order isotropic tensor functions is presented.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 20
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996), S. 3367-3390 
    ISSN: 0029-5981
    Keywords: finite plasticity ; single crystals ; multisurface plasticity ; active set search ; exponential map ; stress update algorithm ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: This paper presents a new stress update algorithm for large-strain rate-independent single-crystal plasticity. The theoretical frame is the well-established continuum slip theory based on the multiplicative decomposition of the deformation gradient into elastic and plastic parts. A distinct feature of the present formulation is the introduction and computational exploitation of a particularly simple hyperelastic stress response function based on a further multiplicative decomposition of the elastic deformation gradient into spherical and unimodular parts, resulting in a very convenient representation of the Schmid resolved shear stresses on the crystallographic slip systems in terms of a simple inner product of Eulerian vectors. The key contribution of this paper is an algorithmic formulation of the exponential map exp: sl(3) → SL(3) for updating the special linear group SL(3) of unimodular plastic deformation maps. This update preserves exactly the plastic incompressibility condition of the anisotropic plasticity model under consideration. The resulting fully implicit stress update algorithm treats the possibly redundant constraints of single-crystal plasticity by means of an active set search. It exploits intrinsically the simple representation of the Schmid stresses by formulating the return algorithm and the associated consistent elastoplastic moduli in terms of Eulerian vectors updates. The performance of the proposed algorithm is demonstrated by means of a representative numerical example.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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