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  • 1
    Electronic Resource
    Electronic Resource
    Continuum damage mechanics for softening of brittle materials (1992)
    Springer
    Acta mechanica 93 (1992), S. 133-143 
    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 Continuum damage theory is used to model the failure behaviour of brittle materials. In the constitutive equations a damage parameter is incorporated. A damage criterion is postulated such that large differences between tension and compression strength can be described. A damage growth law is quantified based on experimental data for concrete. For the elaboration of the mathematical formulation the finite element method is applied. Numerical results obtained for a plane strain example show the merits of the procedure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01182579
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  • 2
    Electronic Resource
    Electronic Resource
    Discrete ductile fracture modelling for the metal blanking process (2000)
    Springer
    Computational mechanics 26 (2000), S. 104-114 
    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  Design and realisation of a metal blanking process in current industrial practice are mainly based on empirical knowledge. For more sophisticated applications, involving high accuracy geometry specifications, or non-standard materials and product shapes, this empirical approach often fails. This paper presents a set of interrelated numerical techniques resulting in a finite element model of the metal blanking process, focusing on the prediction of the shape of the cut edge of a blanked product. The large, localised deformations are handled by an Operator Split Arbitrary Lagrange Euler (OS-ALE) method supplemented by full remeshing. Transport of the state variables between subsequent meshes for the OS-ALE and remeshing methods is accomplished by the Discontinous Galerkin (DG) method and an interpolation procedure, respectively. Ductile fracture is incorporated using a discrete cracking approach, which is shown to generate mesh independent results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004660000158
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  • 3
    Electronic Resource
    Electronic Resource
    A two-dimensional paving mesh generator for triangles with controllable aspect ratio and quadrilaterals with high quality (1998)
    Springer
    Engineering with computers 14 (1998), S. 248-259 
    Details
    ISSN: 1435-5663
    Keywords: Conversion ; High Aspect Ratio ; Mesh generation ; Paving ; Plastering ; Quadrilaterals ; Triangles
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract Certain classes of problems result in solution fields of which the characteristic length scales vary with the orientation. Often the orientation of these length scales is related to the orientation of the boundaries. Such solution fields can be captured by the finite element method, using a mesh that is refined in the direction of the short length scales and coarse in the other directions. These meshes contain elements with high aspect ratios in a predefined pattern. The mesh generator presented here can render triangles with high aspect ratios through a paving algorithm. The paving algorithm that is employed applies both triangles and quadrilaterals, combining the advantages of both to render a qualitatively good, oriented triangular mesh, with a concentration of elements in the direction where the internal length scales of the solution field are the shortest. The mesh generator produces triangles with one (almost) orthogonal corner. When low aspect ratio triangles are generated, these are well suited for conversion to quadrilateral elements. Test results indicate that quadrilateral meshes converted from the mesh generator introduced here have a considerably better quality than those converted from several other triangular mesh generators.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01215978
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  • 4
    Electronic Resource
    Electronic Resource
    Size effect predictions by fracture models for a refractory ceramic (1995)
    Springer
    International journal of fracture 75 (1995), S. 273-283 
    Details
    ISSN: 1573-2673
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Refractory ceramics used as kiln furniture are designed to operate at elevated temperatures with a high thermal shock resistance. In practice, however, the material fails due to thermal fatigue after a limited number of cycles. To predict this failure behaviour, it is generally not possible to use linear elastic fracture mechanics due to the fact that the coarse grained, porous material shows a dissipative mechanical behaviour. Differently sized specimens are tested to determine the size effect associated with this material. Four different finite element models widely used for concrete modelling are investigated on their ability to describe this nonlinear failure behaviour, in particular the associated size effect phenomenon. The results of the initially promising Nonlocal Continuum Damage Mechanics (CDM) model indicate that this approach cannot properly describe the observed size effect. The other three models (Adapted Local CDM, Fictitious Crack and Smeared Crack), however, give comparable results with a good description of the observed size effect phenomenon.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00037087
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  • 5
    Electronic Resource
    Electronic Resource
    Reduction of mesh sensitivity in continuum damage mechanics (1995)
    Springer
    Acta mechanica 110 (1995), S. 49-56 
    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 Continuum damage theories can be applied to simulate the failure behaviour of engineering constructions. In the constitutive equations of the material a damage parameter is incorporated. A damage criterion and a damage evolution law are postulated and quantified based on experimental data. The elaboration of the mathematical formulation is performed by common finite element techniques. Without special precautions the numerical results appear to be unacceptably dependent on the measure of the spatial discretization. It is shown that a simple but effective procedure leads to the conservation of objectivity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01215415
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  • 6
    Electronic Resource
    Electronic Resource
    Phenomenological nonlocal approaches based on implicit gradient-enhanced damage (2000)
    Springer
    Acta mechanica 144 (2000), S. 1-15 
    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 present paper focusses on five phenomenological approaches in gradient-enhanced damage, several of which have been proposed in the literature to simulate material degradation. These different gradient-damage based nonlocal models are examined with respect to their ability to describe crack initiation and crack propagation. The models are applied to identical mechanical benchmark tests, where the material damage evolution law is taken as good as possible equal for each model. Interesting differences between the different models arise, and it is shown that care must be taken in the interpretation and application of these models. One-dimensional results cannot be extrapolated in a straightforward fashion to two dimensions, and the physical relevance of some results is in some cases debatable. Furthermore, it is shown that the response of some models is strongly influenced by small differences in the applied damage evolution law. A discussion is made on the use of two different types of such evolution laws, which are frequently applied in the literature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01181824
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  • 7
    Electronic Resource
    Electronic Resource
    Predictive modelling of the properties and toughness of polymeric materials Part I Why is polystyrene brittle and polycarbonate tough? (2000)
    Springer
    Journal of materials science 35 (2000), S. 2855-2867 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The brittleness of polystyrene (PS) and the toughness but notch sensitivity of polycarbonate (PC) have been studied by the detailed finite element analyses of the stress and strain fields in a notched tensile bar with a minor defect. The defect represented a flaw or imperfection, generated during the test specimen production. The large-strain mechanical responses of both materials were approximated by an accurate elasto-viscoplastic constitutive model with appropriate material parameters. It was assumed that failure occurs instantaneously once the dilative stress exceeds a certain critical craze-initiation stress. The analyses show that the unstable post-yield mechanical response of both materials results in localisation of stresses and strains near the defect at a very low macroscopic strain (0.16%). As a result, a strong dilative stress concentration is formed just below the surface of the defect. For the polystyrene specimen, the critical stress is reached at the defect. For the polycarbonate, however, the effect of the stress concentrating defect was counteracted by a higher craze-initiation stress and stronger strain hardening. The PC craze-initiation resistance, however, did not suffice to overcome the dilative stress concentration raised by the notch tip.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004711622159
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  • 8
    Electronic Resource
    Electronic Resource
    Predictive modelling of the properties and toughness of polymeric materials Part II Effect of microstructural properties on the macroscopic response of rubber-modified polymers (2000)
    Springer
    Journal of materials science 35 (2000), S. 2869-2879 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The influence of microstructural properties on the macroscopic mechanical behaviour has been studied by finite element predictions of the response of different microstructures of polystyrene (PS) or polycarbonate (PC) containing voids or rubbery particles, subjected to unidirectional extension. The voids represent a low-modulus non-adhering dispersed phase. The rubbery inclusions, which are assumed to be pre-cavitated and perfectly adhering, idealise core-shell particles with a hard rubber shell and a soft non-adhering or pre-cavitated core. The predictions show that the inclusion properties strongly affect the averaged post-yield response of the heterogeneous systems. Especially the post-yield strain softening can be eliminated by the introduction of voids in PC or rubbery particles in PS. Since macroscopic strain softening is believed to be the main cause of catastrophical stress or strain localisations, the softening elimination is believed to be primarily responsible for toughness enhancement of the polystyrene or polycarbonate systems. The results and experiences are extrapolated in order to explain the influence of the absolute length scale of a sub-micron sized morphology on the macroscopic behaviour, especially toughness. Two potential sources of particle-size effects are presented that may result in a stabilised, and thus tougher, macroscopic mechanical response, i.e. the yield stress reduction near a surface or interface because of a locally enhanced mobility of the polymer segments, and the temporary excessive hardening because of a sufficiently small size of the yield zones which results in a reduced effective entanglement distance. The paper concludes with a discussion on the extension of this knowledge to all other, for the moment amorphous, polymers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004763606229
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  • 9
    Electronic Resource
    Electronic Resource
    Predictive modelling of the properties and toughness of polymeric materials Part III Simultaneous prediction of micro- and macrostructural deformation of rubber-modified polymers (2000)
    Springer
    Journal of materials science 35 (2000), S. 2881-2892 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The deformation behaviour of heterogeneous tensile bars is investigated by using the recently developed multi-level finite element method (MLFEM) that allows for a numerical coupling between the microscopic and macroscopic stress-strain behaviour, combined with an accurate elasto-viscoplastic constitutive model (single-mode compressible Leonov model) and a detailed finite element model of the microstructure. The method is used to predict the influence of the microstructure on localisation phenomena in plane strain notched and hour-glass-shaped polycarbonate and polystyrene tensile specimen with different volume fractions of non-adhering or adhering rubbery particles. In Part I and II of this series it was already suggested that elimination of the unstable post-yield strain softening behaviour of a polymeric material by appropriate microstructural modifications may be essential for toughening. The results of the multi-level analyses presented in this paper confirm this statement. It is shown that a stable post-yield response, resulting from microstructural adaptations, is indeed a prerequisite for the distribution of plastic strains over the whole macro- and microstructure: massive shearing is promoted by the introduction of voids in the polycarbonate or load bearing pre-cavitated rubbery particles in the polystyrene. Furthermore, it is shown that the voids indeed reduce the macroscopic dilative stresses to safe values. The results suggest that localisations of strain and stress will always occur on a macro and/or micro level. Catastrophic failure, however, can be postponed by stabilisation of the post-yield behaviour of the material and reduction of the macroscopic dilative stresses through appropriate microstructural adjustments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004715707138
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  • 10
    Electronic Resource
    Electronic Resource
    An Eulerian approach for die compaction processes (1991)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 31 (1991), S. 509-524 
    Details
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: For the analysis of deformation processes the Eulerian approach is usually formulated in material velocities. To describe the die compaction of compressible media, this paper presents an Eulerian simulation method, basically expressed in displacements. The material behaviour is modelled by the theory of elastoplasticity. Frictional interaction with the surroundings is included. As a spatially fixed finite element mesh is applied, rezoning is governed by the process specification and not, as in the Lagrangian approach, by the mesh distortion. The solution scheme, using a Newton-Raphson algorithm, is considered in detail. A consistent iteration procedure is derived. Examples demonstrate the merits of the method developed.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/nme.1620310307
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