The Experts below are selected from a list of 78 Experts worldwide ranked by ideXlab platform

Robert Levy - One of the best experts on this subject based on the ideXlab platform.

  • Geometrically nonlinear analysis of shell structures using a flat triangular shell finite element
    Archives of Computational Methods in Engineering, 2006
    Co-Authors: Robert Levy
    Abstract:

    This paper presents a state of the art review on geometrically nonlinear analysis of shell structures that is limited to the co-rotational approach and to flat triangular shell finite elements. These shell elements are built up from flat triangular membranes and plates. We propose an element comprised of the Constant Strain Triangle (CST) membrane element and the discrete Kirchhoff (DKT) plate element and describe its formulation while stressing two main issues: the derivation of the geometric stiffness matrix and the isolation of the rigid body motion from the total deformations. We further use it to solve a broad class of problems from the literature to validate its use.

Peter Noe Poulsen - One of the best experts on this subject based on the ideXlab platform.

  • An Enhanced Cohesive Crack Element for XFEM using a Double Enriched Displacement Field
    2020
    Co-Authors: Jens Falkenskov Mougaard, Peter Noe Poulsen, Leif Otto Nielsen
    Abstract:

    Applying the principles of the eXtended Finite Element Method a partly cracked cohesive element is developed. The element is based on a double enrichment of the standard displacement field, which allows the element to model equal stresses at the both sides of the crack in the crack-tip element. The formulation is implemented for the 3 node Constant Strain Triangle. A general stress calculation in the cracked elements is presented, the principle is based on an area weighting of the stresses in the cracked elements, which gives a continuous transition to the uncracked respectively the fully cracked element. The performance of the developed element is tested in a Three Point beam Bending Test, where the partly cracked element gives a good over all structural response. Furthermore the partly cracked element gives results without the often seen zigzag behavior on the load-deflection curve.

  • an embedded crack in a Constant Strain Triangle utilizing extended finite element concepts
    Computers & Structures, 2013
    Co-Authors: John Forbes Olesen, Peter Noe Poulsen
    Abstract:

    This paper revisits the formulation of the CST element with an embedded discrete crack taking advantage of the direct formulations developed within the framework of the extended finite element method, XFEM. The result is a simple element for modeling cohesive fracture processes in quasi-brittle materials. The element is easily fitted a standard FEM code, and as such it is an alternative to more cumbersome XFEM elements which require special d.o.f.'s and extra administration. The crack description is embedded, in the sense that extra d.o.f.'s controlling the crack opening are eliminated at the element level. The cracked element is stress-compatible in the sense that stresses are continuous across the crack. A special shape function is introduced to allow for the discontinuous displacements without eradicating the stress compatibility. The simplicity of the element comes at the cost of inter-element discontinuity of displacements. The formulation is based on a variational principle of virtual work involving only the interpolation of displacements. The good performance of the element is demonstrated through the comparison with three benchmark tests in which a single crack is propagated: The center cracked sheet in uni-axial tension, the three-point bending test and the four-point shear beam test.

  • a consistent partly cracked xfem element for cohesive crack growth
    International Journal for Numerical Methods in Engineering, 2007
    Co-Authors: Jesper L. Asferg, Peter Noe Poulsen, Leif Otto Nielsen
    Abstract:

    Present extended finite element method (XFEM) elements for cohesive crack growth may often not be able to model equal stresses on both sides of the discontinuity when acting as a crack-tip element. The authors have developed a new partly cracked XFEM element for cohesive crack growth with extra enrichments to the cracked elements. The extra enrichments are element side local and were developed by superposition of the standard nodal shape functions for the element and standard nodal shape functions for a sub-Triangle of the cracked element. With the extra enrichments, the crack-tip element becomes capable of modelling variations in the discontinuous displacement field on both sides of the crack and hence also capable of modelling the case where equal stresses are present on each side of the crack. The enrichment was implemented for the 3-node Constant Strain Triangle (CST) and a standard algorithm was used to solve the non-linear equations. The performance of the element is illustrated by modelling fracture mechanical benchmark tests. Investigations were carried out on the performance of the element for different crack lengths within one element. The results are compared with previously obtained XFEM results applying fully cracked XFEM elements, with computational results achieved using standard cohesive interface elements in a commercial code, and with experimental results. The suggested element performed well in the tests. Copyright © 2007 John Wiley & Sons, Ltd.

  • A direct XFEM formulation for modeling of cohesive crack growth in concrete
    Computers and Concrete, 2007
    Co-Authors: Jesper L. Asferg, Peter Noe Poulsen, Leif Otto Nielsen
    Abstract:

    Applying a direct formulation for the enrichment of the displacement field an extended finite element (XFEM) scheme for modeling of cohesive crack growth is developed. Only elements cut by the crack is enriched and the scheme fits within the framework of standard FEM code. The scheme is implemented for the 3-node Constant Strain Triangle (CST) and the 6-node linear Strain Triangle (LST). Modeling of standard concrete test cases such as fracture in the notched three point beam bending test (TPBT) and in the four point shear beam test (FPSB) illustrates the performance. The XFEM results show good agreement with results obtained by applying standard interface elements in FEM and with experimental results. In conjunction with criteria for crack growth local versus nonlocal computation of the crack growth direction is discussed.

John Forbes Olesen - One of the best experts on this subject based on the ideXlab platform.

  • an embedded crack in a Constant Strain Triangle utilizing extended finite element concepts
    Computers & Structures, 2013
    Co-Authors: John Forbes Olesen, Peter Noe Poulsen
    Abstract:

    This paper revisits the formulation of the CST element with an embedded discrete crack taking advantage of the direct formulations developed within the framework of the extended finite element method, XFEM. The result is a simple element for modeling cohesive fracture processes in quasi-brittle materials. The element is easily fitted a standard FEM code, and as such it is an alternative to more cumbersome XFEM elements which require special d.o.f.'s and extra administration. The crack description is embedded, in the sense that extra d.o.f.'s controlling the crack opening are eliminated at the element level. The cracked element is stress-compatible in the sense that stresses are continuous across the crack. A special shape function is introduced to allow for the discontinuous displacements without eradicating the stress compatibility. The simplicity of the element comes at the cost of inter-element discontinuity of displacements. The formulation is based on a variational principle of virtual work involving only the interpolation of displacements. The good performance of the element is demonstrated through the comparison with three benchmark tests in which a single crack is propagated: The center cracked sheet in uni-axial tension, the three-point bending test and the four-point shear beam test.

Leif Otto Nielsen - One of the best experts on this subject based on the ideXlab platform.

  • An Enhanced Cohesive Crack Element for XFEM using a Double Enriched Displacement Field
    2020
    Co-Authors: Jens Falkenskov Mougaard, Peter Noe Poulsen, Leif Otto Nielsen
    Abstract:

    Applying the principles of the eXtended Finite Element Method a partly cracked cohesive element is developed. The element is based on a double enrichment of the standard displacement field, which allows the element to model equal stresses at the both sides of the crack in the crack-tip element. The formulation is implemented for the 3 node Constant Strain Triangle. A general stress calculation in the cracked elements is presented, the principle is based on an area weighting of the stresses in the cracked elements, which gives a continuous transition to the uncracked respectively the fully cracked element. The performance of the developed element is tested in a Three Point beam Bending Test, where the partly cracked element gives a good over all structural response. Furthermore the partly cracked element gives results without the often seen zigzag behavior on the load-deflection curve.

  • a consistent partly cracked xfem element for cohesive crack growth
    International Journal for Numerical Methods in Engineering, 2007
    Co-Authors: Jesper L. Asferg, Peter Noe Poulsen, Leif Otto Nielsen
    Abstract:

    Present extended finite element method (XFEM) elements for cohesive crack growth may often not be able to model equal stresses on both sides of the discontinuity when acting as a crack-tip element. The authors have developed a new partly cracked XFEM element for cohesive crack growth with extra enrichments to the cracked elements. The extra enrichments are element side local and were developed by superposition of the standard nodal shape functions for the element and standard nodal shape functions for a sub-Triangle of the cracked element. With the extra enrichments, the crack-tip element becomes capable of modelling variations in the discontinuous displacement field on both sides of the crack and hence also capable of modelling the case where equal stresses are present on each side of the crack. The enrichment was implemented for the 3-node Constant Strain Triangle (CST) and a standard algorithm was used to solve the non-linear equations. The performance of the element is illustrated by modelling fracture mechanical benchmark tests. Investigations were carried out on the performance of the element for different crack lengths within one element. The results are compared with previously obtained XFEM results applying fully cracked XFEM elements, with computational results achieved using standard cohesive interface elements in a commercial code, and with experimental results. The suggested element performed well in the tests. Copyright © 2007 John Wiley & Sons, Ltd.

  • A direct XFEM formulation for modeling of cohesive crack growth in concrete
    Computers and Concrete, 2007
    Co-Authors: Jesper L. Asferg, Peter Noe Poulsen, Leif Otto Nielsen
    Abstract:

    Applying a direct formulation for the enrichment of the displacement field an extended finite element (XFEM) scheme for modeling of cohesive crack growth is developed. Only elements cut by the crack is enriched and the scheme fits within the framework of standard FEM code. The scheme is implemented for the 3-node Constant Strain Triangle (CST) and the 6-node linear Strain Triangle (LST). Modeling of standard concrete test cases such as fracture in the notched three point beam bending test (TPBT) and in the four point shear beam test (FPSB) illustrates the performance. The XFEM results show good agreement with results obtained by applying standard interface elements in FEM and with experimental results. In conjunction with criteria for crack growth local versus nonlocal computation of the crack growth direction is discussed.

Jesper L. Asferg - One of the best experts on this subject based on the ideXlab platform.

  • a consistent partly cracked xfem element for cohesive crack growth
    International Journal for Numerical Methods in Engineering, 2007
    Co-Authors: Jesper L. Asferg, Peter Noe Poulsen, Leif Otto Nielsen
    Abstract:

    Present extended finite element method (XFEM) elements for cohesive crack growth may often not be able to model equal stresses on both sides of the discontinuity when acting as a crack-tip element. The authors have developed a new partly cracked XFEM element for cohesive crack growth with extra enrichments to the cracked elements. The extra enrichments are element side local and were developed by superposition of the standard nodal shape functions for the element and standard nodal shape functions for a sub-Triangle of the cracked element. With the extra enrichments, the crack-tip element becomes capable of modelling variations in the discontinuous displacement field on both sides of the crack and hence also capable of modelling the case where equal stresses are present on each side of the crack. The enrichment was implemented for the 3-node Constant Strain Triangle (CST) and a standard algorithm was used to solve the non-linear equations. The performance of the element is illustrated by modelling fracture mechanical benchmark tests. Investigations were carried out on the performance of the element for different crack lengths within one element. The results are compared with previously obtained XFEM results applying fully cracked XFEM elements, with computational results achieved using standard cohesive interface elements in a commercial code, and with experimental results. The suggested element performed well in the tests. Copyright © 2007 John Wiley & Sons, Ltd.

  • A direct XFEM formulation for modeling of cohesive crack growth in concrete
    Computers and Concrete, 2007
    Co-Authors: Jesper L. Asferg, Peter Noe Poulsen, Leif Otto Nielsen
    Abstract:

    Applying a direct formulation for the enrichment of the displacement field an extended finite element (XFEM) scheme for modeling of cohesive crack growth is developed. Only elements cut by the crack is enriched and the scheme fits within the framework of standard FEM code. The scheme is implemented for the 3-node Constant Strain Triangle (CST) and the 6-node linear Strain Triangle (LST). Modeling of standard concrete test cases such as fracture in the notched three point beam bending test (TPBT) and in the four point shear beam test (FPSB) illustrates the performance. The XFEM results show good agreement with results obtained by applying standard interface elements in FEM and with experimental results. In conjunction with criteria for crack growth local versus nonlocal computation of the crack growth direction is discussed.