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  • 1.
    Atashipour, Seyed Rasoul
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Girhammar, Ulf Arne
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Al-Emrani, Mohammad
    Chalmers tekniska högskola .
    Exact Lévy-type solutions for bending of thick laminated orthotropic plates based on 3-D elasticity and shear deformation theories2017Inngår i: Computers & structures, ISSN 0045-7949, E-ISSN 1879-2243, Vol. 163, s. 129-151Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Exact solutions for static bending of symmetric laminated orthotropic plates with different Lévy-type boundary conditions are developed. The shear deformation plate theories of Mindlin-Reissner and Reddy as well as the three-dimensional elasticity theory are employed. Using the minimum total potential energy principle, governing equilibrium equations of laminated orthotropic plates and pertaining boundary conditions are derived. Closed-form Lévy-type solutions are obtained for the governing equations of both theories using separation of variables method and different types of classical boundary conditions, namely simply-supported, clamped and free edge, are exactly satisfied. Thereafter, 3-D elasto-static equations for orthotropic materials are solved for bending analysis of laminated plates using two different approaches. First, the method of separation of variables is utilized and an exact closed-from solution is achieved for simply-supported laminated orthotropic plates. Next, a combined Fourier-Differential Quadrature (DQ) approach is employed to present a semi-numerical solution for bending of laminated orthotropic plates with Lévy-type boundary conditions based on the three-dimensional elasticity theory. High accuracy of the presented solutions are proven and comprehensive comparative numerical results are provided and discussed. Presented comparative numerical results can serve as benchmark for investigating the correctness of new solution methods which may be established in the future.

  • 2. Bernspång, Lars
    et al.
    Samuelsson, A.
    Chalmers University of Technology.
    Kussner, M.
    Technische Hochschule Darmstadt.
    Wriggers, P.
    Technische Hochschule Darmstadt.
    The consistent strain method in finite element plasticity1995Inngår i: Computers & structures, ISSN 0045-7949, E-ISSN 1879-2243, Vol. 54, nr 1, s. 27-33Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An algorithm for finite element analysis of problems in elastoplasticity with continuous stress and strain approximation is presented. By a global iteration procedure, equilibrium is preserved at the nodes in a weak sense, and the local constitutive relation between stresses and strains is satisfied. A high order numerical integration is used to achieve a good quality stiffness matrix and to evaluate the boundary between elastic and plastic regions in the case of partly plastic elements.

  • 3.
    Girhammar, Ulf Arne
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Atashipour, Seyed Rasoul
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Analysis of shear deflections of deep composite box-type of beams using different shear deformation models2015Inngår i: Computers & structures, ISSN 0045-7949, E-ISSN 1879-2243, Vol. 155, s. 42-53Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The deflection of deep box-type elements due to shear deformations is treated. A closed-form expression for the shear correction factor is derived by using an energy approach. The high accuracy and reliability of the developed procedure is demonstrated by comparing its results with accurate 3-D finite element results and also with the results of the conventional theories of Timoshenko with constant shear coefficient and of Reddy–Bickford applied to this kind of cross-section. A comprehensive and comparative parametric study is presented to investigate the effects of various mechanical properties and geometric dimensions for the different models. Unlike the higher-order shear deformation theories, which are accurate only for beams with rectangular cross-sections, there is a very good agreement between the results of the proposed method and the 3-D FE model. Clearly, the proposed energy method is applicable to more complicated cross-sections, including those with abrupt changes in the geometry, e.g. due to holes.

  • 4.
    Lindgren, Lars-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Improvements of the program "A versatile two-dimensional mesh generator with automatic bandwidth reduction"1987Inngår i: Computers & structures, ISSN 0045-7949, E-ISSN 1879-2243, Vol. 25, nr 4, s. 637-638Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Some simple modifications of the Fortran-code for the mesh generator of L. L. Durocher and A. Gasper are described. The changes make it possible to exclude five large data arrays and at the same time speed up the calculations somewhat

  • 5.
    Massih, A.R.
    et al.
    ABB Atom AB.
    Isaksson, P.
    Luleå tekniska universitet.
    Ståhle, Per
    Luleå tekniska universitet.
    Modelling the behaviour of a control-element blade during irradiation1997Inngår i: Computers & structures, ISSN 0045-7949, E-ISSN 1879-2243, Vol. 64, nr 5-6, s. 1113-1127Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The control-rod elements in a boiling-water reactor contain natural boron carbide (B4C) powder, used as neutron-absorber material and clad in stainless-steel blades. During in-reactor service, the internal production of helium gas and point defects in neutron-irradiated boron carbide cause swelling which can induce significant contact stresses in the blade causing, eventually, stress-corrosion cracking of the blades. In this work, a finite-element analysis of a control-rod blade consisting of B4C powder and stainless-steel cladding has been performed using ADINA. An algorithm for the finite-element calculation of a porous material such as B4C powder has been developed and which models both swelling and consolidation behaviour of B4C powder. The Drucker-Prager constitutive law has been used to model the consolidation effect. The model has been verified with an analytical solution for a simple geometry. A number of cases with B4C powder in contact with stainless steel and using the actual blade design have been studied for which contact stresses, the displacements and the effective stresses are calculated. Finally, the model has been used to predict the deformation of the blade during irradiation under B4C swelling and irradiation-induced creep of stainless steel

  • 6.
    Santiago, Aldina
    et al.
    University of Coimbra.
    Silva, Luís Simões da
    University of Coimbra.
    Real, Paulo Vila
    University of Aveiro.
    Veljkovic, Milan
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Numerical study of a steel sub-frame in fire2008Inngår i: Computers & structures, ISSN 0045-7949, E-ISSN 1879-2243, Vol. 86, nr 15-16, s. 1619-1632Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Steel framed buildings are generally designed with "simple" shear-resisting connections, and lateral forces are resisted by vertical bracing and shear walls. When a beam is considered then the effects of the longitudinal restraints by the adjacent structure and the rotational restraint by the connections has to be taken into account. Because of structural interaction, the beam behaviour at elevated temperature is rather complex. This paper presents a numerical parametric study of a structural system consisting of an exposed steel beam restrained between a pair of fire protected steel columns. The structural sub-frame is modelled using 3D shell elements, thereby taking into account the effect of the local failure modes, and the realistic behaviour of the sub-frame exposed to natural fire. The numerical model accounts for the initial geometrical imperfections, non-linear temperature gradient over the cross-section, geometrical and material nonlinearity and temperature dependent material properties. Results obtained using a general Finite Element software - LUSAS and a fire dedicated software - SAFIR, are compared. The influence of following variables: beam span/depth ratio, lateral restraint, gradient temperature within the cross-section and mechanical load level is presented in the paper. The failure modes, the development of the internal forces and displacements throughout the analysis are considered to exemplify the effects of the variables considered.

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