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  • 1.
    Bergman, Greger
    et al.
    SSAB HardTech.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    A finite element model for thermomechanical analysis of sheet metal forming2004Ingår i: International Journal for Numerical Methods in Engineering, ISSN 0029-5981, E-ISSN 1097-0207, Vol. 59, nr 9, s. 1167-1186Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A thermal model based on explicit time integration is developed and implemented into the explicit finite element code DYNA3D to model simultaneous forming and quenching of thin-walled structures. A staggered approach is used for coupling the thermal and mechanical analysis, wherein each analysis is performed with different time step sizes. The implementation includes a thermal shell element with linear temperature approximation in the plane and quadratic in the thickness direction, and contact heat transfer. The material behaviour is described by a temperature-dependent elastic-plastic model with a non-linear isotropic hardening law. Transformation plasticity is included in the model. Examples are presented to validate and evaluate the proposed model. The model is evaluated by comparison with a one-sided forming and quenching experiment

  • 2.
    Esen, Sedat
    et al.
    Luleå tekniska universitet.
    Souers, P.C.
    Energetic Materials Center, Lawrence Livermore National Laboratory, Livermore, CA.
    Vitello, P.
    Energetic Materials Center, Lawrence Livermore National Laboratory, Livermore, CA.
    Prediction of the non-ideal detonation performance of commercial explosives using the DeNE and JWL++ codes2005Ingår i: International Journal for Numerical Methods in Engineering, ISSN 0029-5981, E-ISSN 1097-0207, Vol. 64, nr 14, s. 1889-1914Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The non-ideal detonation performance of two commercial explosives is determined using the DeNE and JWL++ codes. These two codes differ in that DeNE is based on a pseudo-one-dimensional theory which is valid on the central stream-tube and capable of predicting the non-ideal detonation characteristics of commercial explosives as a function of the explosive type, rock properties and blasthole diameter. On the other hand, JWL++ is a hydrocode running in a 2-D arbitrary Lagrangian-Eulerian code with CALE-like properties and can determine the flow properties in all stream lines within the reaction zone. The key flow properties (detonation velocity, pressure, specific volume, extent of reaction and reaction zone length) at the sonic locus on the charge axis have been compared. In general, it is shown that the flow parameters determined using both codes agree well. The pressure contours determined using the JWL++ are analysed in detail for two explosives at 165 mm blastholes confined in limestone and kimberlite with a view to further investigate the explosive/rock interface. The DeNE and JWL++ codes have been validated using the measured in-hole detonation velocity data.

  • 3.
    Karlsson, Lennart
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Numerical analysis of damped transient beam vibrations by use of Fourier transforms1985Ingår i: International Journal for Numerical Methods in Engineering, ISSN 0029-5981, E-ISSN 1097-0207, Vol. 24, nr 4, s. 683-689Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The objective of the present study is to investigate the applicability of the Fourier transform technique to the analysis of vibrating damped beam structures. The practical use of the method is demonstrated by calculating a measure of the noise emitted by a vibrating damped beam. Different distributed Winkler-type foundations are studied as a means of noise reduction in the vibrating damped beam structure. This type of damping can be applied to the drill rods employed in rock drilling

  • 4. Kjellmert, Bo
    A Chebyshev collocation multidomain method to solve the Reissner-Mindlin equations for the transient response of an anisotropic plate subjected to impact1997Ingår i: International Journal for Numerical Methods in Engineering, ISSN 0029-5981, E-ISSN 1097-0207, Vol. 40, nr 20, s. 3689-3702Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The transient response of an anisotropic rectangular plate subjected to impact is described through a Chebyshev collocation multidomain discretization of the Reissner-Mindlin plate equations. The trapezoidal rule is used for time-integration. The spatial collocation derivative operators are represented by matrices, and the subdomains are patched by natural and essential conditions. At each time level the resulting governing matrix equation is reduced by two consecutive block Gaussian eliminations, so that an equation for the variables at the subdomain corners has to be solved. Back-substitution gives the variables at all other collocation points. The time history as represented by computed contour plots has been compared with analytical results and with photos produced by holographic interferometry. The agreements are satisfactory

  • 5. Kjellmert, Bo
    A spectral method to solve the equations of linear elasticity for the transient response of a tube subjected to impact1999Ingår i: International Journal for Numerical Methods in Engineering, ISSN 0029-5981, E-ISSN 1097-0207, Vol. 45, nr 8, s. 1115-1133Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The transient response of a tube subjected to impact is described through Fourier-Galerkin and Chebyshev collocation multidomain discretizations of the equations of linear elasticity. The trapezoidal rule is used for time integration. For each Fourier mode the spatial collocation derivative operators are represented by matrices, and the subdomains are patched by natural and essential conditions. At each time level the resulting governing matrix equation is reduced by two consecutive block Gaussian eliminations, so that an equation for the complex Fourier coefficients at die subdomain corners has to be solved. Back-substitution gives the coefficients at all other collocation points. An inverse discrete Fourier transform generates, at optional time levels, the three components of the displacement field. Through this method the long-term evolution of the field may be calculated, provided the impact time is long enough. The time history as represented by computed contour plots has been compared with photos produced by holographic interferometry. The agreements are satisfactory.

  • 6.
    Kjellmert, Bo
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Comparative study of the behaviour of a direct solver and a preconditioned iterative solver for the equations arising from the discretization by Chebyshev collocation of a second-order partial differential equation on a square1991Ingår i: International Journal for Numerical Methods in Engineering, ISSN 0029-5981, E-ISSN 1097-0207, Vol. 32, nr 1, s. 527-539Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The behaviour is compared of two solvers for the discrete equations arising from the discretization using Chebyshev collocation of a second-order linear partial differential equation on a square. The alternative solvers considered are a direct solver and an iterative solver based on preconditioning with the matrix arising from finite-difference discretization of the governing equation. The total error of the collocation derivatives and the separate contributions from round-off and discretization error are examined. The efficiency of the two solvers is compared. The iterative solver is more efficient than the direct solver on fine grids for equations similar to the Poisson equation, provided that there are Dirichlet boundary conditions on at least three of the sides of the square.

  • 7.
    Lindgren, Lars-Erik
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Karlsson, Lennart
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Deformations and stresses in welding of shell structures1988Ingår i: International Journal for Numerical Methods in Engineering, ISSN 0029-5981, E-ISSN 1097-0207, Vol. 25, nr 2, s. 635-655Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The simulation of welding of shell structures is investigated in this paper. In order to verify the implementation of the shell element adopted, two different problems were studied. In the first problem the butt-welding of two plates was simulated. In the second problem the butt-welding of a thin-walled pipe was simulated. It is concluded from the analysis of the plate problem that the shell element is quite effective in the membrane state. The comparison between calculated values and experimental values for the residual stress field in the pipe shows that the shell element performs quite well in the analysis of a realistic problem

  • 8.
    Lindgren, Lars-Erik
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Runnemalm, Henrik
    Luleå tekniska universitet.
    Näsström, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Simulation of multipass welding of a thick plate1999Ingår i: International Journal for Numerical Methods in Engineering, ISSN 0029-5981, E-ISSN 1097-0207, Vol. 44, nr 9, s. 1301-1316Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Multipass butt welding of a very thick steel plate has been performed. Transient temperatures and residual stresses have been measured. The agreement between calculations and experiments is good. Two different approaches, quiet and inactive elements, for modelling multipass welding are compared. The first approach is straightforward to apply in most finite element codes. The inactive element method requires a code that can regenerate the finite element model automatically or otherwise very tedious manual work is necessary as the elements are added to the model when welds are laid. It is shown that both techniques give the same results but the computational effort is reduced by using inactive elements. It also circumvents the problem in the quiet element approach of choosing properties of elements in the model that represent the case when welds are not laid.

  • 9.
    Liu, Wing Kam
    et al.
    Northwestern University, Department of Mechanical Engineering, Evanston, IL.
    Siad, Larbi
    University of Reims.
    Tian, Rong
    Northwestern University, Department of Mechanical Engineering, Evanston, IL.
    Lee, Sanghoon
    Northwestern University, Department of Mechanical Engineering, Evanston, IL.
    Lee, Dockjin
    Sungkyunkwan University, School of Mechanical Engineering, Suwon.
    Yin, Xiaolei
    Northwestern University, Department of Mechanical Engineering, Evanston, IL.
    Chen, Wei
    Northwestern University, Department of Mechanical Engineering, Evanston, IL.
    Chan, Stephanie
    Northwestern University, Department of Material Science, Evanston, IL.
    Olson, Gregory B.
    Northwestern University, Department of Material Science, Evanston, IL.
    Lindgren, Lars-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Horstemeyer, Mark F.
    Mississippi State University, Department of Mechanical Engineering.
    Chang, Yoon-Suk
    Sungkyunkwan University, School of Mechanical Engineering, Suwon.
    Choi, Jae-Boong
    Sungkyunkwan University, School of Mechanical Engineering, Suwon.
    Kim, Young Jin
    Sungkyunkwan University, School of Mechanical Engineering, Suwon.
    Complexity science of multiscale materials via stochastic computations2009Ingår i: International Journal for Numerical Methods in Engineering, ISSN 0029-5981, E-ISSN 1097-0207, Vol. 80, nr 6-7, s. 932-978Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    New technological advances today allow for a range of advanced composite materials, including multilayer materials and nanofiber-matrix composites. In this context, the key to developing advanced materials IS file understanding of the interplay between the various physical scales present. from the atomic level Interactions to the microstructaral composition and the marcoscale behavior Using the developing 'multiresolution data sets mechanics' the 'predictive science-based governing laws of the materials microstructure evolutions' are derived and Melted into a 'stochastic multiresolution design framework' Under such a framework. the governing laws Of the materials microstructure evolution will be essential to assess, across multiple scales. The impact of multiscale material design. geometry design of a structure and the manufacturing process conditions, by following the cause-effect relationship from structure property and then to performance The future Integrated multiscale analysis system will be Constructed based on a probabilistic complexity science-based mathematical framework. its verification, validation and uncertainty quantification tire done through carefully designed experiments, and file life-cycled materials design for products design and manufacturing is performed through the use of petascale computing. The various techniques of microstructure reconstruction result in the genetation of model microstructures that, at some level, has the same statistical properties as the real heterogenous media. Having reconstructed the heterogeneous medium. one can then evaluate Its effective properties via direct numerical simulation and compare these values with experimentally measured properties of the actual medium. The proposed analysis will be dynamic in nature to capture the multi-stage historical evolvement of material/structure performance over the life span of a product. In addition to providing more accurate assessment of structure performance with stochastic multiscale analysis. our development will provide the capability of predicting failures and system reliability to enable more reliable design and decisions in product development.

  • 10.
    Luo, Chouping
    et al.
    Luleå tekniska universitet.
    Klisinski, Marek
    Luleå tekniska universitet.
    Application of piece-wise linear weight functions for 2D 8-node quadrilateral element in contact problems2004Ingår i: International Journal for Numerical Methods in Engineering, ISSN 0029-5981, E-ISSN 1097-0207, Vol. 61, nr 2, s. 159-188Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The present study is a continuation of our previous work with the aim to reduce problems caused by standard higher order elements in contact problems. The difficulties can be attributed to the inherent property of the Galerkin method which gives uneven distributions of nodal forces resulting in oscillating contact pressures. The proposed remedy is use of piece-wise linear weight functions. The methods to establish stiffness and/or mass matrix for 8-node quadrilateral element in 2D are presented, i.e. the condensing and direct procedures. The energy and nodal displacement error norms are also checked to establish the convergence ratio. Interpretation of calculated contact pressures is discussed. Two new 2D 8-node quadrilateral elements, QUAD8C and QUAD8D, are derived and tested in many examples, which show their good performance in contact problems.

  • 11.
    Meng, Jingjing
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi. School of Resources and Safety Engineering, Central South University, Changsha, China.
    Huang, Jinsong
    Discipline of Civil, Surveying and Environmental Engineering, Faculty of Engineering and Built Environment, The University of Newcastle, Callaghan, New South Wales, Australia.
    Lin, Hang
    School of Resources and Safety Engineering, Central South University, Changsha, China.
    Laue, Jan
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Li, Kaihui
    Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Kowloon, Hong Kong.
    A static discrete element method with discontinuous deformation analysis2019Ingår i: International Journal for Numerical Methods in Engineering, ISSN 0029-5981, E-ISSN 1097-0207, Vol. 120, nr 7, s. 918-935Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    For discrete element methods (DEMs), integrating the equation of motion based on Newton's second law is an integral part of the computation. Accelerations and velocities are involved even for modeling static mechanics problems. As a consequence, the accuracy can be ruined and numerous calculation steps are required to converge. In this study, we propose a static DEM based on discontinuous deformation analysis (DDA). The force of inertia is removed to develop a set of static equilibrium equations for distinct blocks. It inherits the advantages of DDA in dealing with distinct block system such as jointed rock structures. Furthermore, the critical numerical artifact in DDA, ie, artificial springs between contact blocks, is avoided. Accurate numerical solution can be achieved in mere one calculation step. Last but not the least, since the method is formulated in the framework of mathematical programming, the implementation can be easily conducted with standard and readily available solvers. Its accuracy and efficiency are verified against a series of benchmarks found in the literature.

  • 12.
    Oldenburg, Mats
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Nilsson, Larsgunnar
    Linköping Institute of Technology.
    Position code algorithm for contact searching1994Ingår i: International Journal for Numerical Methods in Engineering, ISSN 0029-5981, E-ISSN 1097-0207, Vol. 37, nr 3, s. 359-386Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A new global search method for general contact systems is developed and implemented in the DYNA3D program, along with a recent contact interface algorithm. The concept of `position codes' for efficient global contact searching is presented. With the position code algorithm, the problem of sorting and searching in three dimensions is transformed to a process of sorting and searching within a one-dimensional array. The cost of contact searching is of the order of N log2 N, where N is the number of nodes in the system. The proposed algorithms are uncomplicated and the implementation into any finite element code is straightforward. Numerical experiments are presented in order to examine the behaviour of the algorithms in different aspects.

  • 13.
    Runesson, Kenneth
    et al.
    Chalmers University of Technology.
    Samuelsson, Alf
    Chalmers University of Technology.
    Bernspång, Lars
    Numerical technique in plasticity including solution advancement control1986Ingår i: International Journal for Numerical Methods in Engineering, ISSN 0029-5981, E-ISSN 1097-0207, Vol. 22, nr 3, s. 769-788Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Numerical techniques applied to the consistent formulation of plasticity, which is based on convex analysis, are investigated. For each time step the stress is found as the projection in complementary energy of the elastic stress onto the set of plastically admissible stresses, while the velocity field is the extremal of a non-quadratic functional. Explicit formulas for von Mises' yield criterion with mixed hardening are developed and the nonlinear equations arising from finite element discretization are solved, for comparison, by a number of Newton-type iteration procedures with line search and arc-length control. A few numerical examples with proportional and non-proportional loading are analyzed.

  • 14.
    Samuelsson, A.
    et al.
    Chalmers University of Technology.
    Wiberg, N-E
    Chalmers University of Technology.
    Bernspång, Lars
    Study of the efficiency of iterative methods for linear problems in structural mechanics1986Ingår i: International Journal for Numerical Methods in Engineering, ISSN 0029-5981, E-ISSN 1097-0207, Vol. 22, nr 1, s. 209-218Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The efficiency of iterative methods in linear structural mechanics is studied. The efficiency concerns the calculation time, the numerical accuracy and the core storage needed. We state that iterative methods are effective in connection with hierarchical improvement of a primary approximation. Three iterative methods are studied: the conjugate gradient method preconditioned by a modified incomplete factorization matrix, the same method preconditioned by a matrix obtained from natural factors on elemental level, and a Jacobi integration preconditioned by viscous relaxation split in an element-by-element way. We make comparisons with direct methods, Gaussian elimination and factorization by use of natural factors.

  • 15.
    Svoboda, Ales
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Lindgren, Lars-Erik
    Oddy, Alan S.
    Oddy/McDIll Numerical Investigations Sciences, Inc..
    Effective stress function algorithm for pressure-dependent plasticity applied to hot isostatic pressing1998Ingår i: International Journal for Numerical Methods in Engineering, ISSN 0029-5981, E-ISSN 1097-0207, Vol. 43, nr 4, s. 587-606Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An algorithm for unconditionally stable and accurate integration of elasto-viscoplastic pressure-dependent constitutive model is presented. Rate form constitutive equations of thermal-elastoviscoplastic type with compressibility take into account the changes in relative density. The algorithm computes the deviatoric and volumetric creep strains by finding the value of the effective stress which satisfies the functional relationship, the effective stress function. Thus, one non-linear scalar equation is solved to find the unknown volumetric and deviatoric components of creep strain tensor. The tangent modulus is evaluated consistent with the integration algorithm. The application of the method to the simulation of hot isostatic pressing of metal powder is shown. The paper presents the solution of the verification problem and comparison with the experimental result.

  • 16.
    Varna, Janis
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Oldenbo, Magnus
    Volvo, Göteborg.
    An incremental 2D constitutive model accounting for linear viscoelasticity and damage development in short fibre composites2005Ingår i: International Journal for Numerical Methods in Engineering, ISSN 0029-5981, E-ISSN 1097-0207, Vol. 64, nr 11, s. 1509-1528Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A model accounting for linear viscoelasticity and microdamage evolution in short fibre composites is described. An incremental 2D formulation suitable for FE-simulation is derived and implemented in FE-solver ABAQUS. The implemented subroutine allows for simulation close to the final failure of the material. The formulation and subroutine is validated with analytical results and experimental data in a tensile test with constant strain rate using sheet moulding compound composites. FE-simulation of a four-point bending test is performed using shell elements. The result is compared with linear elastic solution and test data using a plot of maximum surface strain in compression and tension versus applied force. The model accounts for damage evolution due to tensile loading and neglects any damage evolution in compression, where the material has higher strength. Simulation and test results are in very good agreement regarding the slope of the load-strain curve and the slope change.

  • 17.
    Zeng, L.F.
    et al.
    Chalmers University of Technology.
    Wiberg, N-E
    Chalmers University of Technology.
    Bernspång, Lars
    Adaptive finite element procedure for 2D dynamic transient analysis using direct integration1992Ingår i: International Journal for Numerical Methods in Engineering, ISSN 0029-5981, E-ISSN 1097-0207, Vol. 34, nr 3, s. 997-1014Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An adaptive h-version finite element procedure is presented for a 2D elastodynamic transient analysis using direct integration. The procedure modifies the spatial discretization, i.e. the mesh, in time so that the spatial discretization error can be controlled in each time instant. We analyse an a priori error estimate for the total energy which shows that an a posteriori error estimate developed by Zienkiewicz and Zhu for linear elastostatics can reasonably be extended to dynamic transient analysis. For the time integration, both explicit and implicit time integration schemes can be coupled with the procedure. However, the study in this paper is confined to the use of the Newmark scheme. Numerical examples are used to study the performance of the error estimate and to illustrate the adaptive procedure. Obtained numerical results indicate that: (i) the extension of the Zienkiewicz-Zhu estimate to dynamic transient analysis is useful; (ii) the presented adaptive procedure can, in an efficient way, provide a finite element solution with a user-controlled accuracy.

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