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  • 1
    Electronic Resource
    Electronic Resource
    BIFURCATIONS AND INSTABILITIES IN FRACTURE OF COHESIVE-SOFTENING STRUCTURES: A BOUNDARY ELEMENT ANALYSIS (1992)
    Oxford, UK : Blackwell Publishing Ltd
    Fatigue & fracture of engineering materials & structures 15 (1992), S. 0 
    Details
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The “cohesive-crack model” is adopted, together with the hypotheses of small deformations and linear elasticity outside the process zone or “craze”, for the simulation of fracture processes in structures of concrete-like materials. A “direct”, collocation, multidomain boundary element method is employed and shown to be computationally effective in the considered situations, which are characterized by non-linearity on interfaces only. Iterative algorithms for the direction search and interface adjustment in propagation analysis and for the determination of the response to a craze-tip advancement are developed and numerically tested. Softening as an instabilizing factor embodied in the cohesive-crack model may give rise to path bifurcations (“equilibrium branching”), instability under load control and intrinsic (“snapback”) instability. These phenomena are analysed by the proposed boundary element procedure and discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1460-2695.1992.tb00066.x
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  • 2
    Electronic Resource
    Electronic Resource
    Static shakedown theorems in piecewise linearized poroplasticity (1998)
    Springer
    Archive of applied mechanics 68 (1998), S. 651-661 
    Details
    ISSN: 1432-0681
    Keywords: Key words poroplasticity ; shakedown ; limit analysis ; lower bound
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Summary A fully saturated two-phase solid or structure subjected to variable, in particular cyclic, external actions is described as a nonhardening poroelastoplastic material with piecewise linearized yield loci. With reference to a multifield finite element model, sufficient and necessary conditions for shakedown are established by the static Melan's approach. Shakedown analysis by linear programming is briefly discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004190050194
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  • 3
    Electronic Resource
    Electronic Resource
    Shakedown analysis of defective pressure vessels by a kinematic approach (1999)
    Springer
    Archive of applied mechanics 69 (1999), S. 751-764 
    Details
    ISSN: 1432-0681
    Keywords: Key words plasticity, shakedown, kinematic approach, pressure vessels, initial defect
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Summary In this paper, a kinematic approach and an iterative procedure, earlier proposed for limit analysis, are adopted for shakedown analysis under variable repeated loading. Reference is made to three-dimensional structures of engineering relevance, such as pressurized pipelines and vessels with fluctuating pressure and with slot damages due, e.g. to pitting corrosion. The numerical performance of the solution algorithm is investigated, and the cost-effectiveness of the proposed direct shakedown analysis method is assessed and compared to that of time-marching solutions by up-to-date codes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004190050254
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  • 4
    Electronic Resource
    Electronic Resource
    Calcium- und Knochenstoffwechsel nach Gastrektomie (1997)
    Springer
    Der Chirurg 68 (1997), S. 784-788 
    Details
    ISSN: 1433-0385
    Keywords: Key words: Calcium metabolism ; Bone metabolism ; Gastrectomy ; Therapy ; Review. ; Schlüsselwörter: Calciumstoffwechsel ; Knochenstoffwechsel ; Gastrektomie ; Therapie ; Übersicht.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Zusammenfassung. Nach Magenresektion oder Gastrektomie sind Störungen der Calcium- und Knochenstoffwechsels bekannt. Wahrscheinlich kommt es postoperativ aufgrund einer verminderten Calciumabsorption zu einem Abfall des Serumcalciums. Als Gegenregulation wird Parathormon ausgeschüttet und 1,25-(OH)2-Vitamin D neu gebildet, welche beide Calcium aus dem Knochen mobilisieren. Bei einem Teil der Patienten kommt es in der Folge zu einer Abnahme der Knochenmasse mit einem erhöhten Frakturrisiko. Bisher liegen keine anerkannten Behandlungsempfehlungen dieser Störungen vor, lediglich die Substitution von Vitamin D und Calcium wurde wiederholt empfohlen. Es wird eine Übersicht über die derzeitigen Vorstellungen zur Regulation des Calcium- und Knochenstoffwechsels nach Gastrektomie gegeben.
    Notes: Summary. Disturbances in calcium and bone metabolism after gastrectomy have long been recognized. It has been suggested that due to impaired calcium absorption after gastrectomy, serum calcium is decreased, being counterregulated by parathyroid hormone release and 1,25-(OH)2-vitamin D formation. Both parathyroid hormone and 1,25-(OH)2-vitamin D are known to release calcium from bone, resulting in bone mass loss and increased fracture risk in some of the gastrectomized patients. No therapy is currently generally agreed on, although supplementation of vitamin D and calcium has been suggested repeatedly. A review on the current understanding of calcium and bone metabolism after gastrectomy is given.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001040050270
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  • 5
    Electronic Resource
    Electronic Resource
    Symmetric Galerkin boundary element method in plasticity and gradient plasticity (1995)
    Springer
    Computational mechanics 17 (1995), S. 115-129 
    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: Abstract A boundary integral equation (BIE) formulation and a boundary element (BE) method which confer symmetry to key operators are concisely described with reference to quasi-static plasticity. This formulation is based on the combined use of static and kinematic sources, on Galerkin weighted residual enforcement of integral equations for displacements and tractions along the boundary and for stresses in the potentially yielding domain and on space discretizations in terms of generalized variables in Prager's sense. Typical theoretical results of computational interest not available in conventional nonsymmetric BE methods are surveyed. The subjectivity (mesh-dependence) implied by material instability is illustrated by examples. As a remedy, a symmetric BIE-BE formulation for nonlocal, gradient-dependent plasticity is developed and discussed on the basis of its variationally consistent discretization.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00356484
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    Paper (German National Licenses)
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  • 6
    Electronic Resource
    Electronic Resource
    Symmetric Galerkin boundary element method for quasi-brittle-fracture and frictional contact problems (1993)
    Springer
    Computational mechanics 13 (1993), S. 74-89 
    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: Abstract The analysis of elastic quasi-brittle structures containing cohesive cracks and contacts with friction is given a unitary formulation in the framework of incremental plasticity. Integral equations for displacements and tractions are enforced by a weighted-residual Galerkin approach so that symmetry is preserved in the key operators (in contrast to collocation BE approaches) and cracks (either internal or edge cracks) can be dealt with by a single-domain BE formulation. The space-discrete problem in rates is expressed as a linear complementarity problem centered on a symmetric matrix or, equivalently, as a quadratic programming problem in variables pertaining to the displacement discontinuity locus only. Criteria for overall instabilities and bifurcations are derived from this formulation. The BE approach proposed and implemented by a suitable time-stepping technique, is comparatively tested by numerical solutions of cohesive-crack propagation problems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00350704
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  • 7
    Electronic Resource
    Electronic Resource
    A symmetric boundary integral approach to transient poroelastic analysis (1997)
    Springer
    Computational mechanics 19 (1997), S. 169-178 
    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: Abstract  The problem of the transient quasi-static analysis of a poroelastic body subjected to a history of external actions is formulated in terms of four boundary integral equations, using time-dependent Green's functions of the “free” poroelastic space. Some of these Green's functions, not available in the literature are derived “ad hoc”. The boundary integral operator constructed is shown to be symmetric with respect to a time-convolutive bilinear form so that the boundary solution is characterized by a variational property and its approximation preserving symmetry can be achieved by a Galerkin boundary element procedure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004660050166
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    Paper (German National Licenses)
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  • 8
    Electronic Resource
    Electronic Resource
    On multiplicity of solutions in quasi-brittle fracture computations (1997)
    Springer
    Computational mechanics 19 (1997), S. 511-516 
    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: Abstract The analysis of quasi-brittle fracture processes is formulated as a linear complementarity problem either in finite increments or in rates. Some time-stepping solution procedures and mathematical programming algorithms are discussed as for their ability to capture the whole set of possible alternative equilibrium paths. Potentialities and limitations of the proposed approach and of the relevant procedures are pointed out also by means of a numerical example.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004660050201
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    Paper (German National Licenses)
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  • 9
    Electronic Resource
    Electronic Resource
    Symmetric Galerkin boundary element method in plasticity and gradient plasticity (1995)
    Springer
    Computational mechanics 17 (1995), S. 115-129 
    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: Abstract  A boundary integral equation (BIE) formulation and a boundary element (BE) method which confer symmetry to key operators are concisely described with reference to quasi-static plasticity. This formulation is based on the combined use of static and kinematic sources, on Galerkin weighted residual enforcement of integral equations for displacements and tractions along the boundary and for stresses in the potentially yielding domain and on space discretizations in terms of generalized variables in Prager’s sense. Typical theoretical results of computational interest not available in conventional nonsymmetric BE methods are surveyed. The subjectivity (mesh-dependence) implied by material instability is illustrated by examples. As a remedy, a symmetric BIE-BE formulation for nonlocal, gradient-dependent plasticity is developed and discussed on the basis of its variationally consistent discretization.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00356484
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    Paper (German National Licenses)
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  • 10
    Electronic Resource
    Electronic Resource
    Boundary integral equation analysis in linear viscoelasticity: variational and saddle point formulations (1991)
    Springer
    Computational mechanics 8 (1991), S. 87-98 
    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: Abstract This paper presents a symmetric, double integration boundary integral equation (BIE) approach to linear viscoelastic analysis. The time evolution of the boundary unknowns is shown to be characterized by a variational theorem over an arbitrary time interval and by a min-max theorem from the time origin to infinite (minimum for displacements, maximum for tractions). Boundary element (BE) discretization in space and time leads to algebraic equations with symmetric coefficient matrix.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00350613
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