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  • 1
    Electronic Resource
    Electronic Resource
    Optimal prestress of structures with frictional unilateral contact interfaces (1995)
    Springer
    Archive of applied mechanics 66 (1995), S. 71-81 
    Details
    ISSN: 1432-0681
    Keywords: Key words Elastic structure ; frictional contact ; optimal control ; nonconvex variational inequality
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Summary  The problem of optimal prestress stabilization of elastic structures with frictional contact interfaces subject to static loads is studied in this paper. A linear elastic structure with given unilateral contact at frictional interfaces is considered. The prestressing control is modelled by the pin-load method. The static problem is formulated as a nonsymmetric variational inequality. The goal of the optimal control design is closing of the unilateral contact joints as well as minimization of the friction induced slips with a minimum effort. The resulting optimal control problem is nonsmooth and nonconvex, as it concerns the control of structures governed by variational inequalities. Appropriate techniques of nonsmooth analysis are used for its numerical solution. Effective computer realization and integration into existing finite element software is facilitated by appropriate static condensation techniques, which are outlined in the paper. Numerical examples illustrate the theory.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00786690
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    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    New models for a class of adhesive grippers. The hemivariational inequality approach (1996)
    Springer
    Archive of applied mechanics 67 (1996), S. 50-61 
    Details
    ISSN: 1432-0681
    Keywords: Key words robotics ; grippers ; hemivariational inequalities ; contact problems
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Summary A hemivariational inequality model for adhesive grasping problems is proposed and studied in this paper. The unilateral frictionless and frictional contact effects between the fingertips and the grasping object that lead to linear complementarity problems with singular matrices for the study of static equilibrium of the gripper-object system are generalized here to cover adhesive multifingered grippers. Adhesive effects are modelled by appropriately defined, generally nonconvex, yield sets in the space of contact stresses, friction stresses, gaps or frictional slips and their combinations. The hemivariational inequality problem that arises may involve copositive plus, symmetric matrices and nonempty closed sets for the frictionless gripper problem and copositive plus, nonsymmetric matrices with starshaped sets for the frictional case. Solvability conditions that guarantee the existence of a solution to the gripper problem are given. They specify the conditions which are required to hold between external forces, fingertip mechanical behavior and finger placement in order to solve the gripper problem.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004190050098
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    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Optimal prestress of structures with frictional unilateral contact interfaces (1995)
    Springer
    Archive of applied mechanics 66 (1995), S. 71-81 
    Details
    ISSN: 1432-0681
    Keywords: Elastic structure ; frictional contact ; optimal control ; nonconvex variational inequality
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Summary The problem of optimal prestress stabilization of elastic structures with frictional contact interfaces subject to static loads is studied in this paper. A linear elastic structure with given unilateral contact at frictional interfaces is considered. The prestressing control is modelled by the pin-load method. The static problem is formulated as a nonsymmetric variational inequality. The goal of the optimal control design is closing of the unilateral contact joints as well as minimization of the friction induced slips with a minimum effort. The resulting optimal control problem is nonsmooth and nonconvex, as it concerns the control of structures governed by variational inequalities. Appropriate techniques of nonsmooth analysis are used for its numerical solution. Effective computer realization and integration into existing finite element software is facilitated by appropriate static condensation techniques, which are outlined in the paper. Numerical examples illustrate the theory.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00786690
    Library Location Call Number Volume/Issue/Year Availability
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    Paper (German National Licenses)
    Fulltext
  • 4
    Electronic Resource
    Electronic Resource
    New models for a class of adhesive grippers. The hemivariational inequality approach (1996)
    Springer
    Archive of applied mechanics 67 (1996), S. 50-61 
    Details
    ISSN: 1432-0681
    Keywords: robotics ; grippers ; hemivariational inequalities ; contact problems
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Summary A hemivariational inequality model for adhesive grasping problems is proposed and studied in this paper. The unilateral frictionless and frictional contact effects between the fingertips and the grasping object that lead to linear complementarity problems with singular matrices for the study of static equilibrium of the gripper-object system are generalized here to cover adhesive multifingered grippers. Adhesive effects are modelled by appropriately defined, generally nonconvex, yield sets in the space of contact stresses, friction stresses, gaps or frictional slips and their combinations. The hemivariational inequality problem that arises may involve copositive plus, symmetric matrices and nonempty closed sets for the frictionless gripper problem and copositive plus, nonsymmetric matrices with starshaped sets for the frictional case. Solvability conditions that guarantee the existence of a solution to the gripper problem are given. They specify the conditions which are required to hold between external forces, fingertip mechanical behavior and finger placement in order to solve the gripper problem.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00787139
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    Paper (German National Licenses)
    Fulltext
  • 5
    Electronic Resource
    Electronic Resource
    The homogenization method for the study of variation of Poisson's ratio in fiber composites (1998)
    Springer
    Archive of applied mechanics 68 (1998), S. 281-295 
    Details
    ISSN: 1432-0681
    Keywords: Key words Homogenization method ; Poisson's ratios ; fiber composites
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Summary Materials with specific microstructural characteristics and composite structures are able to exhibit negative Poisson's ratio. This fact has been shown to be valid for certain mechanisms, composites with voids and frameworks and has recently been verified for microstructures optimally designed by the homogenization approach. For microstructures composed of beams, it has been postulated that nonconvex shapes (with reentrant corners) are responsible for this effect. In this paper, it is numerically shown that mainly the shape, but also the ratio of shear-to-bending rigidity of the beams do influence the apparent (phenomenological) Poisson's ratio. The same is valid for continua with voids, or for composites with irregular shapes of inclusions, even if the constituents are quite usual materials, provided that their porosity is strongly manifested. Elements of the numerical homogenization theory and first attempts towards an optimal design theory are presented in this paper and applied for a numerical investigation of such types of materials.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004190050165
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    Paper (German National Licenses)
    Fulltext
  • 6
    Electronic Resource
    Electronic Resource
    Negative Poisson's ratios in composites with star-shaped inclusions: a numerical homogenization approach (1997)
    Springer
    Archive of applied mechanics 67 (1997), S. 274-286 
    Details
    ISSN: 1432-0681
    Keywords: Key words negative Poisson's ratio ; mechanics and design of composites ; numerical homogenization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Summary Materials with specific microstructural characteristics and composite structures are able to exhibit negative Poisson's ratio. This result has been proved for continuum materials by analytical methods in previous works of the first author, among others [1]. Furthermore, it also has been shown to be valid for certain mechanisms involving beams or rigid levers, springs or sliding collars frameworks and, in general, composites with voids having a nonconvex microstructure.Recently microstructures optimally designed by the homogenization approach have been verified. For microstructures composed of beams, it has been postulated that nonconvex shapes with re-entrant corners are responsible for this effect [2]. In this paper, it is numerically shown that mainly the shape of the re-entrant corner of a non-convex, star-shaped, microstructure influences the apparent (phenomenological) Poisson's ratio. The same is valid for continua with voids or for composities with irregular shapes of inclusions, even if the individual constituents are quite usual materials. Elements of the numerical homogenization theory are reviewed and used for the numerical investigation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004190050117
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    Paper (German National Licenses)
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  • 7
    Electronic Resource
    Electronic Resource
    Numerical treatment of hemivariational inequalities in mechanics: two methods based on the solution of convex subproblems (1995)
    Springer
    Computational mechanics 16 (1995), S. 406-416 
    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 Hemivariational inequality problems describe equilibrium points (solutions) for structural systems in mechanics where nonmonotone, possibly multivalued laws or boundary conditions are involved. In the case of problems which admit a potential function this is a nonconvex, nondifferentiable one. In order to avoid the difficulties that arise during the calculation of equilibria for such mechanical systems, methods based on sequential convex approximations have recently been proposed and tested by the authors. The first method is based on ideas developed in the fields of quasidifferential and difference convex (d.c.) optimization and transforms the hemivariational inequality problem into a system of convex variational inequalities, which in turn leads to a multilevel (two-field) approximation technique for the numerical solution. The second method transforms the problem into a sequence of variational inequalities which approximates the nonmonotone problem by an iteratively defined sequence of monotone ones. Both methods lead to convex analysis subproblems and allow for treatment of large-scale nonconvex structural analysis applications. The two methods are compared in this paper with respect to both their theoretical assumptions and implications and their numerical implementation. The comparison is extended to a number of numerical examples which have been solved by both methods.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00370562
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    Paper (German National Licenses)
    Fulltext
  • 8
    Electronic Resource
    Electronic Resource
    Numerical treatment of hemivariational inequalities in mechanics: two methods based on the solution of convex subproblems (1995)
    Springer
    Computational mechanics 16 (1995), S. 406-416 
    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.  Hemivariational inequality problems describe equilibrium points (solutions) for structural systems in mechanics where nonmonotone, possibly multivalued laws or boundary conditions are involved. In the case of problems which admit a potential function this is a nonconvex, nondifferentiable one. In order to avoid the difficulties that arise during the calculation of equilibria for such mechanical systems, methods based on sequential convex approximations have recently been proposed and tested by the authors. The first method is based on ideas developed in the fields of quasidifferential and difference convex (d.c.) optimization and transforms the hemivariational inequality problem into a system of convex variational inequalities, which in turn leads to a multilevel (two-field) approximation technique for the numerical solution. The second method transforms the problem into a sequence of variational inequalities which approximates the nonmonotone problem by an iteratively defined sequence of monotone ones. Both methods lead to convex analysis subproblems and allow for treatment of large-scale nonconvex structural analysis applications. The two methods are compared in this paper with respect to both their theoretical assumptions and implications and their numerical implementation. The comparison is extended to a number of numerical examples which have been solved by both methods.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004660050083
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    Paper (German National Licenses)
    Fulltext
  • 9
    Electronic Resource
    Electronic Resource
    Nondestructive elastostatic identification of unilateral cracks through BEM and neural networks (1997)
    Springer
    Computational mechanics 20 (1997), S. 439-451 
    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 An inverse problem in nonlinear elastostatics is considered which concerns the identification of unilateral contact cracks by means of boundary measurements for given static loadings. Highly nonlinear structural behaviour like closed cracks can hardly be identified. In this case, the analysis of more than one loading cases is proposed and tested in this paper. The direct problem is modelled by using a direct multiregion boundary element formulation. The arising linear complementarity problem is solved explicitly by a pivoting (Lemke) technique. In view of the complexity of the inverse problem, a neural network based identification approach is adopted which uses feed-forward multilayer neural networks trained by back-propagation, error-driven supervised training. The applicability of the method is demonstrated by some numerical examples.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004660050264
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    Paper (German National Licenses)
    Fulltext
  • 10
    Electronic Resource
    Electronic Resource
    Nonsmooth and nonconvex structural analysis algorithms based on difference convex optimization techniques (1996)
    Springer
    Structural and multidisciplinary optimization 12 (1996), S. 167-176 
    Details
    ISSN: 1615-1488
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The impact of difference convex optimization techniques on structural analysis algorithms for nonsmooth and non-convex problems is investigated in this paper. Algorithms for the numerical solutions are proposed and studied. The relation to more general optimization techniques and to computational mechanics algorithms is also discussed. The theory is illustrated by a composite beam delamination example.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01196953
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    Paper (German National Licenses)
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