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  • 1.
    Börjesson, Lars
    et al.
    Luleå tekniska universitet.
    Lindgren, Lars-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Simulation of multipass welding with simultaneous computation of material properties2001Inngår i: Journal of engineering materials and technology, ISSN 0094-4289, E-ISSN 1528-8889, Vol. 123, nr 1, s. 106-111Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Multipass butt welding of two 0.2 m thick steel plates has been investigated. The objective is to calculate residual stresses and compare them with measured residual stresses. The material properties depend on temperature and temperature history. This dependency is accounted for by computing the microstructure evolution and using this information for computing material properties. This is done by assigning temperature dependent material properties to each phase and applying mixture rules to predict macro material properties. Two different materials have been used for the microstructure calculation, one for the base material and one for the filler material

  • 2.
    Chowdhury, K.A.
    et al.
    Department of Aerospace Engineering, Texas A&M University.
    Talreja, Ramesh
    Benzerga, Ahmed Amine
    Department of Aerospace Engineering, Texas A&M University.
    Effects of manufacturing-induced voids on local failure in polymer-based composites2008Inngår i: Journal of engineering materials and technology, ISSN 0094-4289, E-ISSN 1528-8889, Vol. 130, nr 2, s. 0210101-0210109Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents results of a computational study focused on examining the role of manufacturing-induced voids in the initiation and growth of damage at the microstructural level in polymer matrix composites loaded in tension normal to fibers. The polymer deformation is described by an improved macromolecular constitutive model accounting for strain-rate-, pressure-, and temperature-sensitive yielding, isotropic hardening before peak yield, intrinsic postyield softening, and rapid anisotropic hardening at large strains. A new craze model that accounts for craze initiation, growth, and breakdown mechanisms is employed. An energy-based criterion is used for cavitation induced cracking that can lead to fiber/matrix debohding. The role of voids is clarified by conducting a comparative study of unit cells with and without voids. The effects of strain rate and temperature are investigated by a parametric study. The overall composite stress-strain response is also depicted to indicate manifestation of microlevel failure on macroscopic behavior

  • 3. Jonsson, Mikael
    et al.
    Karlsson, Lennart
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Lindgren, Lars-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Deformations and stresses in butt-welding of large plates with special reference to the mechanical material properties1985Inngår i: Journal of engineering materials and technology, ISSN 0094-4289, E-ISSN 1528-8889, Vol. 107, nr 4, s. 265-270Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Simulation of automatic butt-welding of large plates was investigated. Two different steels were considered. The plates were tack-welded before the butt-welding. The simulation includes the tack-welding, the butt-welding and the cooling to room temperature. The simulations should lead to an understanding of the mechanics behind the change in gap width in front of the moving arc, which is of importance in automatic welding production. The residual stresses due to the butt-welding were also studied. The magnitude and the distribution of the residual stress are important in design of welded structures.

  • 4.
    Lindgren, Lars-Erik
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Carlestam, A.
    SSAB Oxelösund AB.
    Jonsson, Mikael
    Computational model of flame-cutting1993Inngår i: Journal of engineering materials and technology, ISSN 0094-4289, E-ISSN 1528-8889, Vol. 115, nr 4, s. 440-445Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A computational model for simulation of flame-cutting has been developed. Two different cutting conditions are compared with respect to the residual stresses. The first case is a plate cut at room temperature and the other is the cutting of a preheated plate. The model depends on measured micro-structure to estimate the required heat input. The model is verified by comparing the calculations for the preheated plate with experimentally obtained residual stresses. Lower residual stresses in the preheated plate prevents subsequent cracking

  • 5. Marklund, Erik
    et al.
    Varna, Janis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Wallström, Lennart
    Nonlinear viscoelasticity and viscoplasticity of flax/polypropylene composites2006Inngår i: Journal of engineering materials and technology, ISSN 0094-4289, E-ISSN 1528-8889, Vol. 128, nr 4, s. 527-536Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In tensile tests the flax/polypropylene composites clearly show nonlinear behavior in loading and hysteresis loops in unloading. In creep tests performed at different load levels the response was nonlinear viscoelastic, and after recovery, viscoplastic strains were detected. No degradation in stiffness could be seen and thus nonlinear viscoelasticity and viscoplasticity were assumed to be the main cause for the observed behavior. The fracture surface of a specimen that experienced creep rupture at 24 MPa was investigated using a scanning electron microscope. The viscoplastic response was studied experimentally and described by a power law with respect to time and stress level in the creep test. The nonlinear viscoelasticity was described using Schapery's model. The application of Prony series and a power law to approximate the viscoelastic compliance was investigated. Both descriptions have accuracy sufficient for practical applications. However, at high stresses the attempts to describe the viscoelastic compliance by a power law with a stress-independent exponent failed and therefore stress dependence of this exponent was included in the data analysis. The accuracy within the considered stress range is good, but the thermodynamic consistency of this procedure has to be proven.

  • 6. Mattsson, David
    et al.
    Varna, Janis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Average strain in fiber bundles and its effect on NCF composite stiffness2007Inngår i: Journal of engineering materials and technology, ISSN 0094-4289, E-ISSN 1528-8889, Vol. 129, nr 2, s. 211-219Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Transverse strain in bundles governs transverse cracking in noncrimp fabric (NCF) composites. Finite element (FE) analysis shows that this strain may be significantly lower than the applied macroscopic strain component in the same direction. This feature is important for damage evolution modeling. The isostrain assumption which in different combinations is widely used in stiffness models is inadequate because the strain in different mesoelements (bundles of different orientation and matrix regions) is assumed the same. Analyzing by FEM the importance of media surrounding the bundle on average transverse strain it was found that an increasing ratio of the bundle transverse stiffness to the matrix stiffness leads to a decrease of the strain in the bundle. An increase of the stiffness in the same direction in adjacent layers leads to an increase of the transverse strain in the bundle. Higher bundle volume fraction in the layer leads to larger transverse strain in the bundle. These trends are described by a power law and used to predict the average strain in bundles. The calculated H matrix which establishes the relationship between strains in the mesoelement and representative volume element strains is used to calculate the "effective stiffness" of the bundle. This effective stiffness is the main element in simple but exact expressions derived to calculate the stiffness matrix of NCF composites. Considering the three-dimensional (3D) FE model as the reference, it was found that all homogenization methods used in this study have sufficient accuracy for stiffness calculations, but only the presented method gives reliable predictions of strains in bundles.

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