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Roland W. Lewis - One of the best experts on this subject based on the ideXlab platform.

  • h adaptive finite element analysis for localization phenomena with reference to Metal Powder Forming
    Finite Elements in Analysis and Design, 2002
    Co-Authors: Amir R. Khoei, Roland W. Lewis
    Abstract:

    Standard finite element models, i.e. finite element methods that use standard constitutive models, suffer from excessive mesh dependence when strain-softening models are used in numerical analyses and cannot reproduce the size effect commonly observed in quasi-brittle failure. In this paper, an h-adaptive analysis for the mixed finite element solution of solid mechanics problems is presented with special reference to Metal Powder Forming involving localization due to material instability. A remeshing strategy is employed to compute the distribution of required element size using the estimated error distribution. The numerical results are obtained for a Von-Mises yield criterion applied to a multi-level component, at the final stage of compaction. It shows how adaptive remeshing techniques can be applied to improve the definition of the shear band, using a non-local constitutive model to avoid loss of mesh objectivity.

  • a plasticity model for Metal Powder Forming processes
    International Journal of Plasticity, 2001
    Co-Authors: Roland W. Lewis, Amir R. Khoei
    Abstract:

    Abstract In this paper, a double-surface plasticity model, based on a combination of a convex yield surface consisting of a failure envelope, such as a Mohr–Coulomb yield surface and, a hardening cap model, is developed for the nonlinear behaviour of Powder materials in the concept of a generalized plasticity formulation for the description of cyclic loading. This model reflects the yielding, frictional and densification characteristics of Powder along with strain and geometrical hardening which occur during the compaction process. The solution yields details on the Powder displacement from which it is possible to establish the stress state in the Powder and the densification is derived from consideration of the elemental volumetric strain. A hardening rule is used to define the dependence of the yield surface on the degree of plastic straining. Finally, an adaptive finite element model (FEM) analysis is employed by the updated Lagrangian formulation to simulate the compaction of a set of complex Powder Forming processes.

  • numerical modelling of large deformation in Metal Powder Forming
    Computer Methods in Applied Mechanics and Engineering, 1998
    Co-Authors: Roland W. Lewis, Amir R. Khoei
    Abstract:

    Abstract In this paper, the transient dynamic analysis of Metal Powder during the cold compaction process is simulated by the finite element method based on a ‘Total’ and ‘Updated’ Lagrangian formulation. Since the compaction process involves a very large reduction in volume, the behaviour of the Powders is assumed to be that of a rate-independent elasto-plastic material. The process is therefore described by a large displacement finite element formulation for the spatial discretization. A generalized Newmark scheme is used for the time domain discretization and then the final nonlinear equations are solved by a Newton-Raphson procedure. A combination of a Mohr-Coulomb and elliptical cap yield model is utilised as a constitutive model to describe the nonlinear behaviour of Powder materials. An incremental elasto-plastic material model is used to simulate the compaction process and a plasticity theory for friction is employed in the treatment of the Powder-tooling interface. The interfacial behaviour between the die and Powder is modelled by using an ‘interface’ element mesh. Finally, the Powder behaviour during the compaction of a plane bush, a cutting tool and a rotational flanged component is analysed numerically. The predictive compaction forces at different displacements, the variation with time of the displacement, relative density and stress contours are obtained. It is shown that the proposed large displacement elasto-plastic finite element approach is capable of simulating the Metal Powder during compaction.

  • Finite element simulation for dynamic large elastoplastic deformation in Metal Powder Forming
    Finite Elements in Analysis and Design, 1998
    Co-Authors: Amir R. Khoei, Roland W. Lewis
    Abstract:

    Abstract In this paper, a transient dynamic analysis of the Powder compaction process is simulated by a large displacement finite element method based on a total and updated Lagrangian formulation. A combination of the Mohr–Coulomb and elliptical yield cap model, which reflects the stress state and degree of densification, is applied to describe the constitutive model of Powder materials. A Coulomb friction law and a plasticity theory of friction in the context of an interface element formulation are employed in the constitutive modelling of the frictional behaviour between the die and Powder. Finally, the Powder behaviour during the compaction of a plain bush, a rotational flanged and a shaped tip component are analysed numerically. It is shown that the updated Lagrangian formulation, using a combination of the Mohr–Coulomb and elliptical cap model, can be effective in simulating Metal Powder compaction.

Amir R. Khoei - One of the best experts on this subject based on the ideXlab platform.

  • h adaptive finite element analysis for localization phenomena with reference to Metal Powder Forming
    Finite Elements in Analysis and Design, 2002
    Co-Authors: Amir R. Khoei, Roland W. Lewis
    Abstract:

    Standard finite element models, i.e. finite element methods that use standard constitutive models, suffer from excessive mesh dependence when strain-softening models are used in numerical analyses and cannot reproduce the size effect commonly observed in quasi-brittle failure. In this paper, an h-adaptive analysis for the mixed finite element solution of solid mechanics problems is presented with special reference to Metal Powder Forming involving localization due to material instability. A remeshing strategy is employed to compute the distribution of required element size using the estimated error distribution. The numerical results are obtained for a Von-Mises yield criterion applied to a multi-level component, at the final stage of compaction. It shows how adaptive remeshing techniques can be applied to improve the definition of the shear band, using a non-local constitutive model to avoid loss of mesh objectivity.

  • a plasticity model for Metal Powder Forming processes
    International Journal of Plasticity, 2001
    Co-Authors: Roland W. Lewis, Amir R. Khoei
    Abstract:

    Abstract In this paper, a double-surface plasticity model, based on a combination of a convex yield surface consisting of a failure envelope, such as a Mohr–Coulomb yield surface and, a hardening cap model, is developed for the nonlinear behaviour of Powder materials in the concept of a generalized plasticity formulation for the description of cyclic loading. This model reflects the yielding, frictional and densification characteristics of Powder along with strain and geometrical hardening which occur during the compaction process. The solution yields details on the Powder displacement from which it is possible to establish the stress state in the Powder and the densification is derived from consideration of the elemental volumetric strain. A hardening rule is used to define the dependence of the yield surface on the degree of plastic straining. Finally, an adaptive finite element model (FEM) analysis is employed by the updated Lagrangian formulation to simulate the compaction of a set of complex Powder Forming processes.

  • numerical modelling of large deformation in Metal Powder Forming
    Computer Methods in Applied Mechanics and Engineering, 1998
    Co-Authors: Roland W. Lewis, Amir R. Khoei
    Abstract:

    Abstract In this paper, the transient dynamic analysis of Metal Powder during the cold compaction process is simulated by the finite element method based on a ‘Total’ and ‘Updated’ Lagrangian formulation. Since the compaction process involves a very large reduction in volume, the behaviour of the Powders is assumed to be that of a rate-independent elasto-plastic material. The process is therefore described by a large displacement finite element formulation for the spatial discretization. A generalized Newmark scheme is used for the time domain discretization and then the final nonlinear equations are solved by a Newton-Raphson procedure. A combination of a Mohr-Coulomb and elliptical cap yield model is utilised as a constitutive model to describe the nonlinear behaviour of Powder materials. An incremental elasto-plastic material model is used to simulate the compaction process and a plasticity theory for friction is employed in the treatment of the Powder-tooling interface. The interfacial behaviour between the die and Powder is modelled by using an ‘interface’ element mesh. Finally, the Powder behaviour during the compaction of a plane bush, a cutting tool and a rotational flanged component is analysed numerically. The predictive compaction forces at different displacements, the variation with time of the displacement, relative density and stress contours are obtained. It is shown that the proposed large displacement elasto-plastic finite element approach is capable of simulating the Metal Powder during compaction.

  • Finite element simulation for dynamic large elastoplastic deformation in Metal Powder Forming
    Finite Elements in Analysis and Design, 1998
    Co-Authors: Amir R. Khoei, Roland W. Lewis
    Abstract:

    Abstract In this paper, a transient dynamic analysis of the Powder compaction process is simulated by a large displacement finite element method based on a total and updated Lagrangian formulation. A combination of the Mohr–Coulomb and elliptical yield cap model, which reflects the stress state and degree of densification, is applied to describe the constitutive model of Powder materials. A Coulomb friction law and a plasticity theory of friction in the context of an interface element formulation are employed in the constitutive modelling of the frictional behaviour between the die and Powder. Finally, the Powder behaviour during the compaction of a plain bush, a rotational flanged and a shaped tip component are analysed numerically. It is shown that the updated Lagrangian formulation, using a combination of the Mohr–Coulomb and elliptical cap model, can be effective in simulating Metal Powder compaction.

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

  • numerical analysis of strain localization in Metal Powder Forming processes
    International Journal for Numerical Methods in Engineering, 2001
    Co-Authors: R W Lewis, A R Khoei
    Abstract:

    It is well known that strain localization and indeed displacement discontinuity can arise in materials exhibiting plastic behaviour. Indeed such localization is almost certain to occur if strain softening or non-associated behaviour exists, though it can be triggered even when ideal plasticity is assumed. This study is concerned mainly with the manner in which the numerical discretization process has to be devised so as to capture the localization phenomenon. In this paper, a method is presented for applying the mixed formulation to study the prediction of localization phenomenon in Powder-Forming processes. This study is focused on the performance of mixed u−π triangular elements to study their efficiency in indicating localization for various mesh refinements. An adaptive analysis using element elongation is applied in the modelling of strain localization. The numerical results are obtained for a Von Mises yield criterion applied to a multi-level component, at the final stage of compaction. It is shown that if a correct approximation is used then both the uniform and non-uniform mesh refinements will converge to the correct answer and clearly indicate the localization phenomenon. It is also observed that an adaptive analysis using element elongation can be effective in the modelling of such phenomena. Copyright © 2001 John Wiley & Sons, Ltd.

R W Lewis - One of the best experts on this subject based on the ideXlab platform.

  • numerical analysis of strain localization in Metal Powder Forming processes
    International Journal for Numerical Methods in Engineering, 2001
    Co-Authors: R W Lewis, A R Khoei
    Abstract:

    It is well known that strain localization and indeed displacement discontinuity can arise in materials exhibiting plastic behaviour. Indeed such localization is almost certain to occur if strain softening or non-associated behaviour exists, though it can be triggered even when ideal plasticity is assumed. This study is concerned mainly with the manner in which the numerical discretization process has to be devised so as to capture the localization phenomenon. In this paper, a method is presented for applying the mixed formulation to study the prediction of localization phenomenon in Powder-Forming processes. This study is focused on the performance of mixed u−π triangular elements to study their efficiency in indicating localization for various mesh refinements. An adaptive analysis using element elongation is applied in the modelling of strain localization. The numerical results are obtained for a Von Mises yield criterion applied to a multi-level component, at the final stage of compaction. It is shown that if a correct approximation is used then both the uniform and non-uniform mesh refinements will converge to the correct answer and clearly indicate the localization phenomenon. It is also observed that an adaptive analysis using element elongation can be effective in the modelling of such phenomena. Copyright © 2001 John Wiley & Sons, Ltd.

S.s.m. Nor - One of the best experts on this subject based on the ideXlab platform.

  • Numerical simulation and experimentation of warm Metal Powder compaction process
    Key Engineering Materials, 2011
    Co-Authors: Mujibur Rahman, A K Ariffin, Faris Tarlochan, Ramesh Singh, S.s.m. Nor
    Abstract:

    Powder compaction at elevated temperature or known as warm compaction is a process of producing green compacts from Metal Powder, which is generally conducted between the ambient and the recrystalization temperature of the main Powder constituent. Even though, warm compaction was initiated at around 1998, not a lot of information can be found in the literature especially on the numerical simulation of the process. Therefore, this paper presents the simulation of warm Metal Powder Forming process by using the developed computer code. The Elliptical Cap yield model has been used to represent the deformation behaviour of the Powder mass during the Forming process at above ambient temperature. The material properties of Powder mass, i. e., friction coefficient, elastic index, and plastic index, at different Forming temperature, are established through warm compaction experiment. The simulation was conducted to generate a green compact of a plain bush component. Some numerical simulation results were validated through experimentation, where a good agreement was found between the numerical simulation and the experimental results.