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  • 1.
    Abiri, Olufunminiyi
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Qin, Hao
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Lindgren, Lars-Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Comparison of Multiresolution Continuum Theory and Nonlocal Dame model for use in Simulation of Manufacutring Processes2016In: International Journal for Multiscale Computational Engineering, ISSN 1543-1649, Vol. 14, no 1, p. 81-94Article in journal (Refereed)
    Abstract [en]

    Modelling and simulation of manufacturing processes may require the capability to account for localization behavior, often associated with damage/fracture. It may be unwanted localization indicating a failure in the process or, as in the case of machining and cutting, a wanted phenomenon to be controlled. The latter requires a higher accuracy regarding the modelling of the underlying physics, as well as the robustness of the simulation procedure. Two different approaches for achieving mesh-independent solutions are compared in this paper. They are the multiresolution continuum theory (MRCT) and nonlocal damage model. The MRCT theory is a general multilength-scale finite element formulation, while the nonlocal damage model is a specialized method using a weighted averaging of softening internal variables over a spatial neighborhood of the material point. Both approaches result in a converged finite element solution of the localization problem upon mesh refinement. This study compares the accuracy and robustness of their numerical schemes in implicit finite element codes for the plane strain shear deformation test case. Final remarks concerning ease of implementation of the methods in commercial finite element packages are also given.

  • 2.
    Lindgren, Lars-Erik
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Qin, Hao
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Liu, Wing Kam
    Northwestern University.
    Tang, Shan
    Northwestern University.
    Simplified multiscale resolution theory for elastic material with damage2011In: Computational plasticity XI : fundamentals and applications: proceedings of the XI International Conference on Computational Plasticity - fundamentals and applications held in Barcelona, Spain, 07 - 09 September 2011, Barcelona: CINME , 2011, p. 576-586Conference paper (Refereed)
    Abstract [en]

    The multiscale resolution continuum theory (MRCT) is a higher order continuum mechanics. A particle is represented by a point that is deformable. This enables the possibility to include the effect of microstructure features in the continuum model on the deformation behavior through additional nodal variables for the higher order scale. This reduces the need for a very fine mesh in order to resolve microstructure details. It is possible to further reduce the computational effort by keeping the additional degree of freedoms to a minimum by tailoring the theory to specific phenomena. The latter is illustrated in a simplified context for an elastic material with damage.

  • 3.
    Lindgren, Lars-Erik
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Qin, Hao
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Wedberg, Dan
    AB Sandvik Coromant, Metal Cutting Modeling, 811 81 Sandviken.
    Improved and simplified dislocation density based plasticity model for AISI 316 L2017In: Mechanics of materials (Print), ISSN 0167-6636, E-ISSN 1872-7743, Vol. 108, p. 68-76Article in journal (Refereed)
    Abstract [en]

    A previously published dislocation density based flow stress model has been refined and made more consistent with underlying physical assumptions. The previous model included many temperature dependent parameters that are taken as constant in the current work. The model has also been simplified with respect to dynamic strain aging. Additional contributions to flow stress from the Hall-Petch effect and solute hardening have now been explicitly included in the model. Furthermore, the dynamic recovery part of the model has been improved.

  • 4.
    Qin, Hao
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Multiresolution Continuum Theory and Dislocation Density Based Constitutive Relations2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In classical description, the mechanical state of a material point depends on the variables defined at this point solely. It can integrate and catch some aspects of the material’s microstructure by conventional homogenization method. The application of the conventional continuum assumption results in a simplified description of the system which makes the large scale simulation of the material more efficient but at the expense of a loss of information at small length scales. Localization is a phenomena where a large degree of deformation occurs in highly concentrated regions. The conventional continuum theory with strain softening can not give the convergent solution as the size of the localization zone is completely determined by the mesh discretization. The multiresolution continuum theory (MRCT) is a higher order continuum theory where additional kinematic variables supplementing the conventional macroscopic displacement field are added to account for deformations at several distinct length scales. The direct inclusion of the length scale parameters in the material’s constitutive equations remedies the convergence problem. In crystalline materials the initiation of plastic flow and subsequent permanent plastic deformation is attributed to the presence and movement of dislocations and also the interactions between the dislocation themselves and different kinds of obstacles, inclusions, second phase particles and grain boundaries etc. Some of these defects can alsolead to damage initiation in the materials. For example, the stresses developed at the dislocation pile-ups contribute to the initiation of the microvoids and microcracks. A dislocation density based damage model has been developed and combined with a physically based flow stress model. They are calibrated and validated for 316L stainless steel at different temperatures and strain rates. These models have been implemented into the macroscopic material description of the MRCT element.

  • 5.
    Qin, Hao
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Multiresolution Continuum Theory Finite Element For Implicit Time Stepping Methods2014Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The multiresolution continuum theory is a higher order continuum theory where additional kinematic variables are added to account for the microstructural inhomogeneities at several distinct length scales. This can be particularly important for localization problems. The strength of this theory is that it can account for details in the microstructure of a material without using an extremely fine mesh. The thesis focuses on implementation and verification of a 3D elastic-plastic multiresolution element based on an implicit time stepping algorithm. It is implemented in the general purpose finite element program FEAP. The mesh independence associated with the length scale parameter is examined and the convergence rate of the element is also evaluated.

  • 6.
    Qin, Hao
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Lindgren, Lars-Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    MRCT Element With A Dislocation Based Plasticity Model2015In: Computational Plasticity XIII: Fundamentals and Applications - Proceedings of the 13th International Conference on Computational Plasticity - Fundamentals and Applications,held in Barcelona, Spain, 1-3 September 2015 / [ed] E. Oñate; D.R.J. Owen; D. Peric; M. Chiumenti, Barcelona: International Center for Numerical Methods in Engineering (CIMNE), 2015, p. 366-377Conference paper (Refereed)
    Abstract [en]

    The multiresolution continuum theory (MRCT) [1] has been established to link the material's macroscopic behaviour with its microstructural inhomogeneities. Additional kinematic variables in addition to the conventional macroscopic displacement field are added to account for microstructural deformations at multiple microscales. Metal plasticity is associated with interaction of motion of dislocations and microstructures. A Dislocation density based material model [2] calibrated and validated for AISI 316L at different temperatures and strain rates is used as the macroscopic constitutive equation of the MRCT element. We investigated particularly how the changing property of the microdomain with changing temperature affects the macroscopic behaviours of the material

  • 7.
    Qin, Hao
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Lindgren, Lars-Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Liu, Wing Kam
    Northwestern University, Department of Mechanical Engineering, Evanston, IL.
    Smith, Jacob
    Northwestern University, Evanston.
    Implicit finite element formulation of multiresolution continuum theory2015In: Computer Methods in Applied Mechanics and Engineering, ISSN 0045-7825, E-ISSN 1879-2138, Vol. 293, p. 114-130Article in journal (Refereed)
    Abstract [en]

    The multiresolution continuum theory is a higher order continuum theory where additional kinematic variables account for microstructural inhomogeneities at several distinct length scales. This can be particularly important for localization problems. The strength of this theory is that it can account for details in the microstructure of a material without using an extremely fine mesh. The present paper describes the implementation and verification of a 3D elastic–plastic multiresolution element based on an implicit time stepping algorithm. It is implemented in the general purpose finite element program FEAP. The mesh independency associated with the length scale parameter is examined and the convergence rate of the element is also evaluated.

  • 8.
    Qin, Hao
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Lindgren, Lars-Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Liu, Wingkam
    Northwestern University, Evanston.
    Tang, Shan
    College of Material Science and Engineering, Chongqing University.
    Multiscale resolution continuum theory for elastic plastic material with damage, an implicit 3D implementation2013In: Computational Plasticity XII: Fundamentals and Applications - Proceedings of the 12th International Conference on Computational Plasticity - Fundamentals and Applications, COMPLAS 2013, Barcelona, 2013, p. 1448-1457Conference paper (Refereed)
    Abstract [en]

    The multiscale resolution continuum theory (MRCT) [1] is a higher order continuum theory in which additional kinematic variables are added to account for the size effect at several distinct length scales. This remedies the deficiency of the conventional continuum approach when predicting both strain softening and strain hardening materials and resolves the microstructure details without extremely fine mesh in the localization zone, however additional nodal degrees of freedom are needed and the requirement of element size at the length scale somewhat adds to the computational burden. This paper is an extension of the simplified 1D multiscale implementation presented in Complas XI 2011 [14]. A 3D elastic-plastic multiscale element, with one additional subscale in which the damage is applied, is implemented implicitly in the general purpose finite element analysis program FEAP.

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