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  • 1. Alberg, Henrik
    et al.
    Berglund, Daniel
    Comparison of plastic, viscoplastic, and creep models when modelling welding and stress relief heat treatment2003In: Computer Methods in Applied Mechanics and Engineering, ISSN 0045-7825, E-ISSN 1879-2138, Vol. 192, no 49-50, p. 5189-5208Article in journal (Refereed)
    Abstract [en]

    A major concern when carrying out welding and heat treatment simulations is to accurately model material behaviour as it varies with temperature and composition. Early in the product development process, a less sophisticated material model may be suitable to compare different concepts where less accuracy in deformation and residual stress is acceptable. At later stages in the product development process, more sophisticated models may be used to obtain more accurate predictions of deformations and residual stresses. This paper presents a comparison of five different material models applied to the simulation of a combined welding and heat treatment process for a fabricated martensitic stainless steel component.

  • 2. Alberg, Henrik
    et al.
    Berglund, Daniel
    Corrigendum to: "Comparison of plastic, viscoplastic, and creep models when modelling welding and stress relief heat treatment"2004In: Computer Methods in Applied Mechanics and Engineering, ISSN 0045-7825, E-ISSN 1879-2138, Vol. 193, no 45-47, p. 5063-5067Article in journal (Other academic)
  • 3.
    Chowdhury, K.A.
    et al.
    Department of Aerospace Engineering, Texas A&M University.
    Benzerga, Ahmed Amine
    Department of Aerospace Engineering, Texas A&M University.
    Talreja, Ramesh
    A computational framework for analyzing the dynamic response of glassy polymers2008In: Computer Methods in Applied Mechanics and Engineering, ISSN 0045-7825, E-ISSN 1879-2138, Vol. 197, no 49-50, p. 4485-4502Article in journal (Refereed)
    Abstract [en]

    A framework is presented for analyzing the low temperature inelastic behavior of amorphous glassy polymers with full account taken of finite deformations and inertial effects. Two classes of viscoplastic constitutive equations are explored: rate-sensitive Drucker-Prager type models and an elaborate macromolecular model. These constitutive equations are integrated using a forward gradient time integration scheme. The capabilities of the framework are illustrated by finite element solutions of initial/boundary-value problems under plane-strain conditions. The discretized equations of motion are integrated using a Newmark algorithm. Three illustrative benchmark problems are used to evaluate the proposed implementation: dynamic shear band formation and propagation in a polymer under compression, dynamic response of a polymer under impact and quasi-static response of a polymer composite plate with a hole under uniaxial tension along fibers

  • 4.
    Häggblad, Hans-åke
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Li, Wen-Bin
    Luleå tekniska universitet.
    A micro mechanical based constitutive model for finite element simulation of hot isostatic pressing of powder1995In: Computer Methods in Applied Mechanics and Engineering, ISSN 0045-7825, E-ISSN 1879-2138, Vol. 128, no 1-2, p. 191-198Article in journal (Refereed)
    Abstract [en]

    Hot isostatic pressing (HIP) facilitates new designs and product shaping, for example by direct manufacture of composite products with differing materials in the various parts (compound). The specific material characteristics are thus created at the manufacturing stage (consolidation), and these in themselves often give good possibilities regarding shape, so-called NS (Net Shape)-or NNS (Near Net Shape)-manufacture. The HIP-technique is used economically in the low series production of complex-shaped steel parts. In order to achieve quality products, an integration of material, design and manufacturing technology is necessary, since the function and cost of the final component depends to a large extent on the development of production technology and its integration with design technology. Simulation of the hot isostatic pressing process is required to reduce the need for expensive and time-consuming experimental design. The use of finite element techniques in analyses of the highly non-linear process is preferable, especially for complex-shaped components. In this work, a micro-mechanical based continuum mechanics model for finite element analysis is presented. The model is used in the finite element simulation of hot isostatic pressing of two components. The results from the analyses correspond well with the experimental results.

  • 5.
    Lindgren, Lars-Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Numerical modelling of welding2006In: Computer Methods in Applied Mechanics and Engineering, ISSN 0045-7825, E-ISSN 1879-2138, Vol. 195, no 48-49, p. 6710-6736Article in journal (Refereed)
    Abstract [en]

    The paper describes the application of the finite element method to predict the thermal, material and mechanical effects of welding; Computational Welding Mechanics (CWM). The most common numerical approach used in CWM is only described shortly. The paper focuses on different modelling aspects. The most important modelling issues are the models for heat input and material behaviour. Finally, some recent applications are reviewed and future developments are discussed.

  • 6.
    Lindgren, Lars-Erik
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Häggblad, Hans-åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    McDill, J.M.J.
    Carleton University, Ottawa.
    Oddy, Alan S.
    Oddy/McDIll Numerical Investigations Sciences, Inc..
    Automatic remeshing for three-dimensional finite element simulation of welding1997In: Computer Methods in Applied Mechanics and Engineering, ISSN 0045-7825, E-ISSN 1879-2138, Vol. 147, no 3-4, p. 401-409Article in journal (Refereed)
    Abstract [en]

    Three-dimensional finite element simulation of electron beam welding of a large copper canister has been performed. The use of an automatic remeshing algorithm, based on a graded hexahedral element was found to be effective. With this algorithm the strongly nonlinear thermomechanical effects locally close to the moving heat source can accurately be modelled using a dense element mesh that follows the heat source.

  • 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.
    Runnemalm, H.
    et al.
    Volvo Aero Corporation, Trollhättan.
    Hyun, Seokjeong
    Luleå tekniska universitet.
    Three-dimensional welding analysis using an adaptive mesh scheme2000In: Computer Methods in Applied Mechanics and Engineering, ISSN 0045-7825, E-ISSN 1879-2138, Vol. 189, no 2, p. 515-523Article in journal (Refereed)
    Abstract [en]

    One major problem arising in finite element analysis of welding is the long computer times required for a complete three-dimensional analysis. An adaptive strategy for coupled thermo-mechanical analysis of welding is applied in order to reduce the computer time. The paper describes a generic posteriori error formulation that evaluates both the thermal and the mechanical error distribution. It is combined with a hierarchic remeshing strategy using a so-called graded element. The error indicator together with the known movement of the local heat source is used to predict areas of refinement. An increased accuracy is obtained with a reduced computational effort

  • 9.
    Salehi, Saeed
    et al.
    Hydraulic Machinery Research Institute, School of Mechanical Engineering, College of Engineering, University of Tehran, Tehran, Iran.
    Raisee, Mehrdad
    Hydraulic Machinery Research Institute, School of Mechanical Engineering, College of Engineering, University of Tehran, Tehran, Iran.
    Cervantes, Michel J.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics. Water Power Laboratory, Norwegian University of Science and Technology, Trondheim, Norway.
    Nourbakhsh, Ahmad
    Hydraulic Machinery Research Institute, School of Mechanical Engineering, College of Engineering, University of Tehran, Tehran, Iran.
    An efficient multifidelity ℓ1-minimization method for sparse polynomial chaos2018In: Computer Methods in Applied Mechanics and Engineering, ISSN 0045-7825, E-ISSN 1879-2138, Vol. 334, p. 183-207Article in journal (Refereed)
    Abstract [en]

    The Polynomial Chaos Expansion (PCE) methodology is widely used for uncertainty quantification of stochastic problems. The computational cost of PCE increases exponentially with the number of input uncertain variables (known as curse of dimensionality). Therefore, use of PCE for uncertainty quantification of industrial applications with large number of uncertain variables is challenging. In this paper, a novel methodology is presented for efficient uncertainty quantification of stochastic problems with large number of input random variables. The proposed method is based on PCE with combination of ℓ1-minimization and multifidelity methods. The developed method employs the ℓ1-minimization method to recover important coefficients of PCE using low-fidelity computations. The low-fidelity evaluations should be accurate enough to capture the physical trends well. After that the multifidelity PCE method is utilized to correct a subset of recovered coefficients using high-fidelity computations. A threshold parameter is defined in order to select the subset of recovered coefficients to be corrected. Two challenging analytical and CFD test cases namely, the Ackley function and the transonic RAE2822 airfoil with combined operational and geometrical uncertainties are considered to examine the performance of the methodology. It is shown that the proposed method can reproduce accurate results with much lower computational cost than the classical full Polynomial Chaos (PC), and ℓ1-minimization methods. It is observed that for the considered examples, the present method can achieve comparable accuracy with respect to the full PC and the ℓ1-minimization methods with significantly lower number of samples.

  • 10.
    Sheng, Daichao
    et al.
    Luleå University of Technology.
    Axelsson, Kennet B.
    Luleå University of Technology.
    Knutsson, Sven
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Finite element analysis for convective heat diffusion with phase change1993In: Computer Methods in Applied Mechanics and Engineering, ISSN 0045-7825, E-ISSN 1879-2138, Vol. 104, no 1, p. 19-30Article in journal (Refereed)
    Abstract [en]

    Whereas phase-change problems associated with heat conduction have been well studied during the last three decades, very little attention has been paid to phase changes taking place in convective heat diffusion. Numerical methods dealing with conventional phase change problems do not directly work in cases where a fluid is concerned. In this paper, an enthalpy method is extended to solve phase-change problems associated with fluids. By using the concept enthalpy, the governing equations are first reformulated into a single quasi-linear partial differential equation that implicitly takes into account the condition of phase change. This equation together with appropriate initial and boundary conditions are then decomposed into two sets of equations respectively representing a convection and a diffusion problem. The decomposition is accomplished in such a way that no phase contradiction occurs between the two separate problems. The convection problem is solved by the method of step by step characteristics and the diffusion problem by a Galerkin finite element method. Numerical examples demonstrate that the numerical method produces reasonable results.

  • 11.
    Svoboda, Ales
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Häggblad, Hans-åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Karlsson, Lennart
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Simulation of hot isostatic pressing of a powder metal component with an internal core1997In: Computer Methods in Applied Mechanics and Engineering, ISSN 0045-7825, E-ISSN 1879-2138, Vol. 148, no 3-4, p. 299-314Article in journal (Refereed)
    Abstract [en]

    This paper presents a finite element simulation of the thermomechanical phenomena occurring during Hot Isostatic Pressing (HIP) of a powder metal component which includes a graphite core. The thermomechanical coupling is achieved in a staggered step manner. The staggered step approach considers the coupled thermomechanical response of solids, including nonlinear effects in both the thermal and mechanical analyses. The creep behaviour of the powder material during densification is modelled using the constitutive equations of thermal elasto-viscoplastic type with compressibility. The various mechanical material properties are assumed to be functions of temperature and relative density. The mechanical solution also includes large deformation and strains. The thermal problem includes temperature and relative density dependent specific heat and thermal conductivity. The constitutive equations and relations for thermal characteristics are implemented into the implicit nonlinear finite element code, PALM2D. The simulation of the HIP process of a component with internal core is chosen as an application example. The component, injection molding tool, is produced of a hot isostatically pressed stainless tool steel with an internal cavity which is achieved by inserting a graphite core into the HIP container. To verify the result of the simulation, the geometry of the capsule and the coated core are measured both before and after pressing using a computer controlled measurement machine (CMM). The measured geometry is compared with the simulated final shapes of the container and internal core. A computer-aided concurrent engineering system (CACE) is used for the complete manufacturing process from the design of the component and finite element simulation to the inspection of the final geometry.

  • 12. Wikman, Bengt
    et al.
    Svoboda, Ales
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Häggblad, Hans-åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    A combined material model for numerical simulation of hot isostatic pressing2000In: Computer Methods in Applied Mechanics and Engineering, ISSN 0045-7825, E-ISSN 1879-2138, Vol. 189, no 3, p. 901-913Article in journal (Refereed)
    Abstract [en]

    In modelling of hot isostatic pressing (HIP) of powder materials the constitutive model should be able to describe different deformation mechanisms during the consolidation process. In the early stage, the consolidation is dominated by granular behaviour. As temperature and pressure increase in the powder the deformation can be described by a viscoplastic model. Experimental observations show substantial time-independent deformation in the early stage. At this stage of the densification process, pores in the powder are still interconnected. This cannot be described properly by a viscoplastic model. The inconsistency between the deformation mechanisms can be treated by a combined elasto-plastic and elasto-viscoplastic model. Here a granular plasticity model is combined with a viscoplastic model. In previous works the viscoplastic model, power-law breakdown, has been used to describe the entire deformation process. The combined model is implemented into an in-house finite deformation code for the solution of coupled thermomechanical problems. The simulation of a hot isostatic pressing test with dilatometer is performed in order to compare calculated results with the experimental measurement. The results from previously performed analysis carried out with a viscoplastic model only are also compared. Analysis with the combined material model shows good agreement with the experiment for the whole densification process.

  • 13.
    Östlund, Rickard
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Golling, Stefan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Oldenburg, Mats
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Microstructure based modeling of ductile fracture initiation in press-hardened sheet metal structures2016In: Computer Methods in Applied Mechanics and Engineering, ISSN 0045-7825, E-ISSN 1879-2138, Vol. 302, p. 90-108Article in journal (Refereed)
    Abstract [en]

    The manufacturing of sheet metal components with spatially varying microstucture composition and mechanical properties using press-hardening technology is now an established practice in the automotive industry. To estimate the performance envelopes of such components, a multi-scale approach to ductile fracture prediction based on mean-field homogenization is proposed. Two non-interacting fracture criteria are formulated in terms of the local average stress field, referring to inter-phase and intra-phase fracture mechanisms. The overall ductility is governed by the weakest constituent or interface present in the multiphase material. Moreover, instabilities related to the strain localization problem at the macroscale are treated by embedding discontinuities in the element formulation. These are triggered by a localization criterion derived via bifurcation analysis of the homogenized material. Issues concerning numerical implementation include a forward Euler scheme for integrating the mean-field equations, suitable for explicit finite element analysis of heterogeneous materials. Tensile specimens with ten distinctly different microstructure compositions are evaluated, for which useful predictions of the overall force-displacement response and fracture elongations are demonstrated.

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