The Experts below are selected from a list of 26349 Experts worldwide ranked by ideXlab platform

I Vardoulakis - One of the best experts on this subject based on the ideXlab platform.

  • modelling of localisation and scale effect in thick walled cylinders with gradient elastoplasticity
    International Journal of Solids and Structures, 2001
    Co-Authors: A Zervos, Panos Papanastasiou, I Vardoulakis
    Abstract:

    We model the progressive localisation of deformation which causes failure around thick-walled cylinders under external radial pressure. The study is based on a second-gradient elastoplastic model developed to regularise the ill-posedness caused by material strain-softening behaviour. The stress increment is related to both the strain increment and its Laplacian. The gradient terms introduce an internal length scale to the material allowing robust modelling of its post-peak behaviour. The numerical implementation is based on a C-1 finite element Displacement Formulation. Mesh insensitivity in terms of load-Displacement and failure mechanism is demonstrated. The internal length in the constitutive equations enables modelling of the scale effect in thick-walled cylinders, according to which the load required to induce failure appears to be much larger for small holes than for large holes.

  • a finite element Displacement Formulation for gradient elastoplasticity
    International Journal for Numerical Methods in Engineering, 2001
    Co-Authors: A Zervos, Panos Papanastasiou, I Vardoulakis
    Abstract:

    We present a second gradient elastoplastic model for strain-softening materials based entirely on a finite element Displacement Formulation. The stress increment is related to both the strain increment and its Laplacian. The Displacement field is the only field needed to be discretized using a C-1 continuity element. The required higher-order boundary conditions arise naturally from the Displacement field. The model is developed to regularize the ill-posedness caused by strain-softening material behaviour. The gradient terms in the constitutive equations introduce an extra material parameter with dimensions of length allowing robust modelling of the post-peak material behaviour leading to localization of deformation. Mesh insensitivity is demonstrated by modelling localization of deformation in biaxial tests. It is shown that both the thickness and inclination of the shear-band zone are insensitive to the mesh directionality and refinement and agree with the expected theoretical and experimental values.

E C Aifantis - One of the best experts on this subject based on the ideXlab platform.

  • nanomechanics of a screw dislocation in a functionally graded material using the theory of gradient elasticity
    Journal of the mechanical behavior of materials, 2013
    Co-Authors: Kamyar M Davoudi, Hossein Davoudi, E C Aifantis
    Abstract:

    The modest aim of this short article is to provide some new results for a screw dislocation in a functionally graded material within the theory of gradient elasticity. These results, based on a Displacement Formulation and the Fourier transform technique, completes earlier findings obtained with the stress function method and extends them to the case of the second strain gradient elasticity. Rigorous and easy-to-use analytical expressions for the Displacements, the strains and the stresses are obtained which are free from singularities at the dislocation line. keywords: Screw dislocation; Functionally graded material; Second strain gradient elasticity

  • nanomechanics of a screw dislocation in a functionally graded material using the theory of gradient elasticity
    arXiv: Materials Science, 2010
    Co-Authors: Kamyar M Davoudi, Hossein Davoudi, E C Aifantis
    Abstract:

    The modest aim of this short article is to provide some new results for a screw dislocation in a functionally graded material within the theory of gradient elasticity. These results, based on a Displacement Formulation and the Fourier transform technique, extends earlier findings (Lazar, M., 2007. On a screw dislocation in a functionally graded material, Mech. Res. Comm. 34, 305-311) obtained by the stress function method, to the case of the second gradient elasticity. Rigorous and easy-to-use analytical expressions for the Displacements, the strains and the stresses are obtained which are free from singularities at the dislocation line.

A Zervos - One of the best experts on this subject based on the ideXlab platform.

  • modelling of localisation and scale effect in thick walled cylinders with gradient elastoplasticity
    International Journal of Solids and Structures, 2001
    Co-Authors: A Zervos, Panos Papanastasiou, I Vardoulakis
    Abstract:

    We model the progressive localisation of deformation which causes failure around thick-walled cylinders under external radial pressure. The study is based on a second-gradient elastoplastic model developed to regularise the ill-posedness caused by material strain-softening behaviour. The stress increment is related to both the strain increment and its Laplacian. The gradient terms introduce an internal length scale to the material allowing robust modelling of its post-peak behaviour. The numerical implementation is based on a C-1 finite element Displacement Formulation. Mesh insensitivity in terms of load-Displacement and failure mechanism is demonstrated. The internal length in the constitutive equations enables modelling of the scale effect in thick-walled cylinders, according to which the load required to induce failure appears to be much larger for small holes than for large holes.

  • a finite element Displacement Formulation for gradient elastoplasticity
    International Journal for Numerical Methods in Engineering, 2001
    Co-Authors: A Zervos, Panos Papanastasiou, I Vardoulakis
    Abstract:

    We present a second gradient elastoplastic model for strain-softening materials based entirely on a finite element Displacement Formulation. The stress increment is related to both the strain increment and its Laplacian. The Displacement field is the only field needed to be discretized using a C-1 continuity element. The required higher-order boundary conditions arise naturally from the Displacement field. The model is developed to regularize the ill-posedness caused by strain-softening material behaviour. The gradient terms in the constitutive equations introduce an extra material parameter with dimensions of length allowing robust modelling of the post-peak material behaviour leading to localization of deformation. Mesh insensitivity is demonstrated by modelling localization of deformation in biaxial tests. It is shown that both the thickness and inclination of the shear-band zone are insensitive to the mesh directionality and refinement and agree with the expected theoretical and experimental values.

Yang Yeh Hisen - One of the best experts on this subject based on the ideXlab platform.

Filip C Filippou - One of the best experts on this subject based on the ideXlab platform.

  • mixed Formulation of nonlinear steel concrete composite beam element
    Journal of Structural Engineering-asce, 2000
    Co-Authors: Ashraf Ayoub, Filip C Filippou
    Abstract:

    This paper presents an inelastic beam element for the analysis of steel-concrete girders with partial composite action under monotonic and cyclic loads. The element is derived from a two-field mixed Formulation with independent approximation of internal forces and transverse Displacements. The nonlinear response of the steel and concrete component of the girder is based on the section discretization into fibers with uniaxial hysteretic material models for the constituent materials. The partial interaction between concrete deck and steel girder through shear connectors is accounted for by an interface model with distributed force transfer charac- teristics. A direct state determination algorithm for the implementation of the composite element in a general purpose nonlinear analysis program is presented, and the stability characteristics of the algorithm are discussed in conjunction with the selection of appropriate force and Displacement interpolation functions. The validity of the model is established by correlation of analytical results with experimental evidence. Numerical studies are used to compare the model with the classical Displacement Formulation. These studies confirm the superiority of the proposed model in modeling composite girders under monotonic and cyclic loads that induce stiffness deterioration and strength softening.

  • mixed Formulation of bond slip problems under cyclic loads
    Journal of Structural Engineering-asce, 1999
    Co-Authors: Ashraf Ayoub, Filip C Filippou
    Abstract:

    The stress transfer mechanism between reinforcing steel and surrounding concrete through bond and the resulting slip plays an important role in the hysteretic behavior of reinforced concrete structures. Earlier models of the stress transfer problem were based on a Displacement Formulation. Recent models, however, have demonstrated the significant advantages of a flexibility Formulation on account of its accuracy and numerical stability under large inelastic strains in the reinforcing steel and bond damage in the surrounding concrete. This paper presents a critical evaluation of existing anchored reinforcing bar models and proposes a new model based on a two-field mixed Formulation in which independent interpolation functions are used for the relative slip and the reinforcing steel forces. The advantages of this approach over existing models are assessed by numerical studies of anchored reinforcing bars under monotonic loads. The accuracy of the proposed model is established by correlation of analytical results with experimental data of an anchored reinforcing bar under severe cyclic loading.