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  • 1
    Electronic Resource
    Electronic Resource
    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
    Keywords: PACS:25.85.-w Fission reactions – 25.75.-q Relativistic heavy-ion collosions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100500050107
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  • 2
    Electronic Resource
    Electronic Resource
    Instability phenomena in plasticity: Modelling and computation (1995)
    Springer
    Computational mechanics 17 (1995), S. 74-87 
    Details
    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
    URL: http://dx.doi.org/10.1007/BF00356480
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  • 3
    Electronic Resource
    Electronic Resource
    Instability phenomena in plasticity: Modelling and computation (1995)
    Springer
    Computational mechanics 17 (1995), S. 74-87 
    Details
    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
    URL: http://dx.doi.org/10.1007/BF00356480
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  • 4
    Electronic Resource
    Electronic Resource
    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
    Keywords: finite elastoplasticity ; thermoplasticity ; becking ; plastic localization ; coupled problems ; finite element method
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00786688
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  • 5
    Electronic Resource
    Electronic Resource
    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
    Keywords: Key words finite elastoplasticity ; thermoplasticity ; becking ; plastic localization ; coupled problems ; finite element method
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00786688
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  • 6
    Electronic Resource
    Electronic Resource
    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
    Keywords: 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
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100500050062
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  • 7
    Electronic Resource
    Electronic Resource
    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
    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
    URL: http://dx.doi.org/10.1007/s100500050076
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  • 8
    Electronic Resource
    Electronic Resource
    Two non-associated isotropic elastoplastic hardening models for frictional materials (1999)
    Springer
    Acta mechanica 135 (1999), S. 73-90 
    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 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
    URL: http://dx.doi.org/10.1007/BF01179047
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  • 9
    Electronic Resource
    Electronic Resource
    EXPONENTIAL MAP ALGORITHM FOR STRESS UPDATES IN ANISOTROPIC MULTIPLICATIVE ELASTOPLASTICITY FOR SINGLE CRYSTALS (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996), S. 3367-3390 
    Details
    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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