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  • 1
    Digitale Medien
    Digitale Medien
    Instability phenomena in plasticity: Modelling and computation (1995)
    Springer
    Computational mechanics 17 (1995), S. 74-87 
    Details
    ISSN: 1432-0924
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00356480
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  • 2
    Digitale Medien
    Digitale Medien
    Comparison of different finite deformation inelastic damage models within multiplicative elastoplasticity for ductile materials (1994)
    Springer
    Computational mechanics 13 (1994), S. 458-474 
    Details
    ISSN: 1432-0924
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00374241
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  • 3
    Digitale Medien
    Digitale Medien
    Instability phenomena in plasticity: Modelling and computation (1995)
    Springer
    Computational mechanics 17 (1995), S. 74-87 
    Details
    ISSN: 1432-0924
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00356480
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  • 4
    Digitale Medien
    Digitale Medien
    Fission of highly excited fragments from collisions of 750 A.MeV 238U-ions on 208Pb (1998)
    Springer
    The European physical journal 2 (1998), S. 179-191 
    Details
    ISSN: 1434-601X
    Schlagwort(e): PACS:25.85.-w Fission reactions – 25.75.-q Relativistic heavy-ion collosions
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract: Fragments of relativistic 750 A.MeV U-projectiles were investigated by using the fragment separator FRS for magnetic selection of reaction products including ray-tracing and ΔE-ToF techniques. For elements between Ge and Sb, measurements of isotopic yield distributions and velocities revealed three processes: fragmentation, low-energy fission, and high-energy fission. The last of these regimes is presently reported. First and second moments of distributions of mass numbers, atomic numbers and velocities of the corresponding fragments allowed us to identify 101 43Tc56 as the most probable fragment of a high energy symmetric fission reaction. Moreover, we could deduce a hypothetical mean fissioning fragmentation product 208Rn and its highly excited pre-fragmentation parent 227Ra produced in a primary abrasion reaction at an excitation energy of about 290 MeV.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s100500050107
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  • 5
    Digitale Medien
    Digitale Medien
    Low-energy fission investigated in reactions of 750 AMeV 238U-ions on 208Pb. II: Isotopic distributions (1998)
    Springer
    The European physical journal 1 (1998), S. 407-426 
    Details
    ISSN: 1434-601X
    Schlagwort(e): PACS:25.85.-W Fission reactions
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s100500050076
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  • 6
    Digitale Medien
    Digitale Medien
    Post-critical discontinuous localization analysis of small-strain softening elastoplastic solids (1994)
    Springer
    Archive of applied mechanics 64 (1994), S. 267-285 
    Details
    ISSN: 1432-0681
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Beschreibung / Inhaltsverzeichnis: 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.
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00789125
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  • 7
    Digitale Medien
    Digitale Medien
    A theory of large-strain isotropic thermoplasticity based on metric transformation tensors (1995)
    Springer
    Archive of applied mechanics 66 (1995), S. 45-64 
    Details
    ISSN: 1432-0681
    Schlagwort(e): finite elastoplasticity ; thermoplasticity ; becking ; plastic localization ; coupled problems ; finite element method
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Summary A formulation of isotropic thermoplasticity for arbitrary large elastic and plastic strains is presented. The underlying concept is the introduction of a metric transformation tensor which maps a locally defined six-dimensional plastic metric onto the metric of the current configuration. This mixed-variant tensor field provides a basis for the definition of a local isotropic hyperelastic stress response in the thermoplastic solid. Following this fundamental assumption, we derive a consistent internal variable formulation of thermoplasticity in a Lagrangian as well as a Eulerian geometric setting. On the numerical side, we discuss in detail an objective integration algorithm for the mixed-variant plastic flow rule. The special feature here is a new representation of the stress return and the algorithmic elastoplastic moduli in the eigenvalue space of the Eulerian plastic metric for plane problems. Furthermore, an algorithm for the solution of the coupled problem is formulated based on an operator split of the global field equations of thermoplasticity. The paper concludes with two representative numerical simulations of thermoplastic deformation processes.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00786688
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  • 8
    Digitale Medien
    Digitale Medien
    A theory of large - strain isotropic thermoplasticity based on metric transformation tensors (1995)
    Springer
    Archive of applied mechanics 66 (1995), S. 45-64 
    Details
    ISSN: 1432-0681
    Schlagwort(e): Key words finite elastoplasticity ; thermoplasticity ; becking ; plastic localization ; coupled problems ; finite element method
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Summary  A formulation of isotropic thermoplasticity for arbitrary large elastic and plastic strains is presented. The underlying concept is the introduction of a metric transformation tensor which maps a locally defined six - dimensional plastic metric onto the metric of the current configuration. This mixed-variant tensor field provides a basis for the definition of a local isotropic hyperelastic stress response in the thermoplastic solid. Following this fundamental assumption, we derive a consistent internal variable formulation of thermoplasticity in a Lagrangian as well as a Eulerian geometric setting. On the numerical side, we discuss in detail an objective integration algorithm for the mixed-variant plastic flow rule. The special feature here is a new representation of the stress return and the algorithmic elastoplastic moduli in the eigenvalue space of the Eulerian plastic metric for plane problems. Furthermore, an algorithm for the solution of the coupled problem is formulated based on an operator split of the global field equations of thermoplasticity. The paper concludes with two representative numerical simulations of thermoplastic deformation processes.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00786688
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  • 9
    Digitale Medien
    Digitale Medien
    β-decay half-lives of very neutron-rich isotopes of elements from Ti to Ni (1998)
    Springer
    The European physical journal 1 (1998), S. 275-283 
    Details
    ISSN: 1434-601X
    Schlagwort(e): PACS:23.40.-s β decay, double β decay, electron and muon capture – 27.30.+t 20 ≤ A ≤ 38 – 27.50.+e 59 ≤ A ≤ 89
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract: The unknown β-decay half-lives of 22 isotopes far off stability (5 〈 T Z 〈 10) in the region from Ti to Ni were measured at GSI, Darmstadt. The nuclei were produced in a fragmentation reaction of 500 A.MeV 86Kr-projectile impinging on a thick Be target. The isotopes of interest were separated and identified with the fragment separator, FRS, by a combination of Bρ,Z, and ToF techniques. An additional range separation was performed by a selective implantation into granular detectors. The spatial and time correlations of the implant with the consecutively detected β-particles were used to determine the unknown half-lives. For nuclei far off stability, β-decay chains were measured and analyzed as well, leading to an even more reliable evaluation of the lifetimes. The large discrepancies found between the measured and the theoretical values emphasize that most recent theoretical work is not an improvement over calculations made almost a decade ago.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s100500050062
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  • 10
    Digitale Medien
    Digitale Medien
    Two non-associated isotropic elastoplastic hardening models for frictional materials (1999)
    Springer
    Acta mechanica 135 (1999), S. 73-90 
    Details
    ISSN: 1619-6937
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01179047
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