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  • 1.
    Afzal, Mohammad
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Arteaga, Ines Lopez
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. Eindhoven University of Technology, Netherlands.
    Kari, Leif
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Numerical analysis of multiple friction contacts in bladed disks2018In: International Journal of Mechanical Sciences, ISSN 0020-7403, E-ISSN 1879-2162, Vol. 137, p. 224-237Article in journal (Refereed)
    Abstract [en]

    The damping potential of multiple friction contacts in a bladed disk is investigated. Friction contacts at tip shrouds and strip dampers are considered. It is shown that friction damping effectiveness can be potentially increased by using multiple friction contact interfaces. Friction damping depends on many parameters such as rotational speed, engine excitation order and mode family and therefore it is not possible to damp all the critical resonances using a single kind of friction contact interface. For example, a strip damper is more effective for the low nodal diameters, where blade/disk coupling is strong. The equations of motion of the bladed disk with multiple friction contacts are derived in the frequency domain for a cyclic structure with rotating excitations. A highly accurate method is used to generate the frequency response function (FRF) matrix. Furthermore, a finite element contact analysis is performed to compute the normal contact load and the contact area of the shroud interface at operating rotational speed. The multiharmonic balance method is employed in combination with the alternate frequency time domain method to find the steady state periodic solution. A low-pressure turbine bladed disk is considered and the effect of the engine excitation level, strip mass, thickness and the accuracy of FRF matrix on the nonlinear response curve are investigated in detail.

  • 2.
    Afzal, Mohammad
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Lopez-Arteaga, Ines
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. Eindhoven University of Technology.
    Kari, Leif
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Numerical analysis of multiple friction contacts in bladed disksIn: International Journal of Mechanical Sciences, ISSN 0020-7403, E-ISSN 1879-2162Article in journal (Other academic)
    Abstract [en]

    The damping potential of multiple friction contacts in a bladed disk, tip shroud and strip damper is investigated, showing that friction damping effectiveness can be potentially increased by using multiple friction contact interfaces. Friction damping depends on many parameters such as rotational speed, engine excitation order and mode family and therefore it is not possible to damp all the critical resonances using a single friction contact interface. For example, a strip damper is more effective for the low nodal diameters, where blade/disk coupling is strong. The equations of motion of the bladed disk with multiple friction contacts are derived in the frequency domain for a cyclic structure with rotating excitations and a highly accurate method is used to generate the frequency response function (FRF) matrix. Furthermore, a finite element contact analysis is performed to compute the normal contact load and the contact area of the shroud interface at operating rotational speed. The multiharmonic balance method is employed in combination with the alternate frequency time domain method to find the approximate steady state periodic solution. A low-pressure turbine bladed disk is considered and the effect of the engine excitation level, strip mass, thickness and the accuracy of FRF matrix on the nonlinear response curve are investigated in detail.

  • 3.
    Ashwear, Nasseradeen
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Influence of Temperature on the Vibration Properties of Tensegrity Structures2015In: International Journal of Mechanical Sciences, ISSN 0020-7403, E-ISSN 1879-2162, Vol. 99, p. 237-250Article in journal (Refereed)
    Abstract [en]

    Vibration health monitoring methods use the sensitivity of the natural frequencies to structural damage. Natural frequencies are sensitive to damage, but are also affected by environmental conditions like temperature changes. It is important to be able to distinguish between the effects of these different factors when using the vibration properties as a monitoring tool. This paper discusses the impact of damage and environment temperature changes on the natural frequencies of tensegrity ("tensile-integrity") structures, in particular noting that component bending is a prominent vibration mode, which motivates a use of non-linear beam elements with axial-bending coupling. The model considers not only thermal expansion effects, but also the change of the elastic modulus with temperature. Changes in natural frequencies produced by environment temperature changes are shown to be similar to the ones produced by damage. The geometry of tensegrity structures, the support conditions and the materials are found to be important factors. The sensitivity of the natural frequency to temperature changes is found to be dependent on pre-stress level.

  • 4.
    Asnafi, Nader
    Gränges Technology, Finspång, Sweden.
    On springback of double-curved autobody panels2001In: International Journal of Mechanical Sciences, ISSN 0020-7403, E-ISSN 1879-2162, Vol. 43, no 1, p. 5-37Article in journal (Refereed)
    Abstract [en]

    The springback of double curved autobody panels is studied theoretically and experimentally. Both steel and aluminum sheets are included in this investigation. The obtained results show that the springback is decreased with increasing binder force, increasing curvature, increasing sheet thickness and decreasing yield strength. This paper comprises also a discussion on the plastic strains and their influence on the springback.

  • 5.
    Bagheri, R.
    et al.
    University of Zanjan, Iran.
    Ayatollahi, M.
    University of Zanjan, Iran.
    Mousavi, S. Mahmoud
    Aalto University, Finland.
    Analysis of cracked piezoelectric layer with imperfect non-homogeneous orthotropic coating2015In: International Journal of Mechanical Sciences, ISSN 0020-7403, E-ISSN 1879-2162, Vol. 93, p. 93-101Article in journal (Refereed)
    Abstract [en]

    Abstract The fracture problem for a medium composed of a cracked piezoelectric strip with functionally graded orthotropic coating is studied. The layer is subjected to anti-plane mechanical and in-plane electrical loading. In this paper, we first address, the problem of a screw dislocation located in a substrate which is imperfectly bonded to the coating. Then, in order to model the cracked piezoelectric layer, by means of the dislocation solution, we construct integral equations for the layer, in which the unknown variables are dislocation densities. These unknowns are determined through satisfaction of the boundary conditions on the crack faces. By use of the dislocation densities, the field intensity factors are determined. Several examples are presented to demonstrate the applicability of the proposed solution. ", keywords = Piezoelectric strip; Functionally graded layer; Imperfect bonding; Multiple cracks; Stress intensity factors, isbn = 0020-7403, doi=https://doi.org/10.1016/j.ijmecsci.2014.11.025

  • 6.
    Baravdish, George
    et al.
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Borachok, Ihor
    Ivan Franko Natl Univ Lviv, Ukraine.
    Chapko, Roman
    Ivan Franko Natl Univ Lviv, Ukraine.
    Johansson, B. Tomas
    Aston Univ, England.
    Slodicka, Marian
    Univ Ghent, Belgium.
    An iterative method for the Cauchy problem for second-order elliptic equations2018In: International Journal of Mechanical Sciences, ISSN 0020-7403, E-ISSN 1879-2162, Vol. 142, p. 216-223Article in journal (Refereed)
    Abstract [en]

    The problem of reconstructing the solution to a second-order elliptic equation in a doubly-connected domain from knowledge of the solution and its normal derivative on the outer part of the boundary of the solution domain, that is from Cauchy data, is considered. An iterative method is given to generate a stable numerical approximation to this inverse ill-posed problem. The procedure is physically feasible in that boundary data is updated with data of the same type in the iterations, meaning that Dirichlet values is updated with Dirichlet values from the previous step and Neumann values by Neumann data. Proof of convergence and stability are given by showing that the proposed method is an extension of the Landweber method for an operator equation reformulation of the Cauchy problem. Connection with the alternating method is discussed. Numerical examples are included confirming the feasibility of the suggested approach.

    The full text will be freely available from 2020-04-24 00:01
  • 7. Barsoum, I.
    et al.
    Faleskog, Jonas
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Pingle, S.
    The effect of stress state on ductility in the moderate stress triaxiality regime of medium and high strength steels2012In: International Journal of Mechanical Sciences, ISSN 0020-7403, E-ISSN 1879-2162, Vol. 65, no 1, p. 203-212Article in journal (Refereed)
    Abstract [en]

    Experiments on double notched tube specimens subjected to tension and torsion were conducted by Barsoum and Faleskog (2007) [8,9]. In this study a complementary experimental investigation was conducted on tensile round circumferentially notched bar specimens. The results from the current study were compared with the results from the double circumferentially notched tube specimens with stress triaxiality larger than 0.7 in order to asses the influence of the Lode parameter on ductility in the moderate stress triaxiality regime. The effective plastic strain, the stress triaxiality T and the Lode parameter L were determined at the center of the notch up to the point of onset of failure by means of finite element. The influence of the Lode parameter on the failure strain was significant for the high strength and low hardening material, whereas for the medium strength and high hardening material the influence of the Lode parameter was less distinguished. The experimental results were then analyzed with the micromechanical model proposed by Barsoum and Faleskog (2011) [15], which is based on the assumption that ductile failure is a consequence of that plastic deformation localizes into a band. The band consists of a square array of equally sized cells, with a spherical void located in the center of each cell, which allows for studying a single 3D unit cell with fully periodic boundary conditions. The unit cell is subjected to a proportional loading such that it resembles the stress state, in terms of T and L, from the experiments. The micromechanical model captures the experimental trend and the influence of L on ductility very well. It is found that the Lode parameter sensitivity increases by the combination of increase in the yield strength and decrease in strain hardening. The fractographical analysis reveals that this Lode parameter sensitivity is associated with the failure characteristics of the material.

  • 8.
    Blom, Peter
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Structural and vibroacoustics.
    Kari, Leif
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Structural and vibroacoustics.
    The frequency, amplitude and magnetic field dependent torsional stiffness of a magneto-sensitive rubber bushing2011In: International Journal of Mechanical Sciences, ISSN 0020-7403, E-ISSN 1879-2162, Vol. 60, no 1, p. 54-58Article in journal (Refereed)
    Abstract [en]

    A dynamic torsional stiffness model of a magneto-sensitive circular annular rubber bushing is presented where influences of frequency, amplitude and magnetic field dependence are included. This is achieved by employing a newly developed non-linear magneto-sensitive audio frequency constitutive equation in an engineering formula for the torsional stiffness of a rubber bushing. The engineering stiffness formula predicts the frequency and amplitude dependent stiffness in a simple way, based on geometric dimensions and the shear modulus. The shear modulus is provided by the rubber model. The results from these calculations predict and clearly display the possibility of controlling over a large frequency range, through the application of a magnetic field, the magneto-sensitive rubber bushing stiffness.

  • 9. Carlsson, S.
    et al.
    Biwa, S.
    Larsson, Per-Lennart
    KTH, Superseded Departments, Solid Mechanics.
    On frictional effects at inelastic contact between spherical bodies2000In: International Journal of Mechanical Sciences, ISSN 0020-7403, E-ISSN 1879-2162, Vol. 42, no 1, p. 107-128Article in journal (Refereed)
    Abstract [en]

    Normal inelastic contact between spherical bodies is examined theoretically and numerically. The analysis is focused on viscoplastic material behaviour. In particular the effect of Coulomb friction is analysed in some detail, both regarding global and field variables. It is shown that the solution to the problem of contact between two deformable spherical bodies is provided by the solution of the fundamental problem of indentation of a viscoplastic half-space by a rigid sphere. The indentation analysis is based on self-similarity and cumulative superposition of intermediate flat die solutions as outlined in detail in a previous study by Storakers et al. (International Journal of Solids and Structures 1997;34:3061-83). The results show that frictional effects, when global properties such as the contact area and the mean contact pressure are at issue, will only be of importance at close to perfectly plastic material behaviour. Even in such circumstances the difference between values given by the solutions for frictionless and for full adhesive contact is no more than approximately 10%. Accordingly, it can be concluded that frictional effects are essentially negligible, when, for example, material characterization of viscoplastic solids by Brinell indentation is of interest. The situation is, however, quite different when field variables are at issue. In this case, stress and strain fields can be substantially influenced by friction with possible implications for features such as crack initiation and crack growth,

  • 10.
    Ghassemali, Ehsan
    et al.
    School of Mechanical & Aerospace Engineering, Nanyang Technological University, Singapore.
    Tan, Ming-Jen
    School of Mechanical & Aerospace Engineering, Nanyang Technological University, Singapore.
    Jarfors, Anders E.W.
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting. Jönköping University, School of Engineering, JTH, Materials and Manufacturing.
    Lim, S.C.V.
    Materials Engineering, Monash University, Wellington Road, Clayton, Victoria, Australia.
    Optimization of axisymmetric open-die micro-forging/extrusion processes: An upper bound approach2013In: International Journal of Mechanical Sciences, ISSN 0020-7403, E-ISSN 1879-2162, Vol. 71, p. 58-67Article in journal (Refereed)
    Abstract [en]

    There is a trend towards component miniaturization and strong drive towards cost effective and sustainable metal forming techniques of miniaturized components. This paper presents an upper bound solution for the optimization of open-die forging/extrusion processes in the forming of micro-pins from a sheet metal. Using such an analytical modeling approach, the critical blank thickness, the resulting final part geometry, together with the required forming load were predicted based on the location of the neutral plane under the punch during the process. Based on the phenomenological findings of the process, the geometry size factor, x, was introduced explaining its relative importance to the model. Experimental results obtained from C11000 copper samples using a progressive microforming process was found to agree well with the results predicted by the model. The results were also validated with other results reported before from a similar process.

  • 11.
    Girhammar, Ulf Arne
    Department of TFE-Civil Engineering, Faculty of Science and Technology, Umeå University.
    A simplified analysis method for composite beams with interlayer slip2009In: International Journal of Mechanical Sciences, ISSN 0020-7403, E-ISSN 1879-2162, Vol. 51, no 7, p. 515-530Article in journal (Refereed)
    Abstract [en]

    A simplified static procedure is proposed for analysing and designing composite beams with interlayer slip. The method is parallel to the Eurocode 5 method, but it is general in nature and can be applied to arbitrary boundary and loading conditions. In contrast with Eurocode 5, a general and correct way of choosing the effective beam length of the problem is given by the present procedure, which is that the effective beam length equals the buckling length that is found in the corresponding column buckling problem. The procedure predicts the deflections and internal actions and stresses, in principle by replacing the fully composite bending stiffness (EI) with the effective (partially) composite bending stiffness (EIeff) in the expressions for these quantities in the corresponding fully composite beam. This effective bending stiffness depends on two non-dimensional parameters: the composite action parameter (shear connection stiffness) and the relative bending stiffness parameter. The method is applied to a number of simple practical cases and the results obtained have been compared with the exact values. The applicability of the simplified analysis procedure was found to be very good, except for interlayer shear stresses. The error in the Eurocode 5 procedure, as compared with the method proposed in this paper, can in some cases be up to almost 30% depending on the boundary conditions

  • 12.
    Girhammar, Ulf Arne
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    A simplified analysis method for composite beams with interlayer slip2009In: International Journal of Mechanical Sciences, ISSN 0020-7403, E-ISSN 1879-2162, Vol. 51, no 7, p. 515-530Article in journal (Refereed)
    Abstract [en]

    A simplified static procedure is proposed for analysing and designing composite beams with interlayer slip. The method is parallel to the Eurocode 5 method, but it is general in nature and can be applied to arbitrary boundary and loading conditions. In contrast with Eurocode 5, a general and correct way of choosing the effective beam length of the problem is given by the present procedure, which is that the effective beam length equals the buckling length that is found in the corresponding column buckling problem. The procedure predicts the deflections and internal actions and stresses, in principle by replacing the fully composite bending stiffness (EI(infinity)) with the effective (partially) composite bending stiffness (EI(eff)) in the expressions for these quantities in the corresponding fully composite beam. This effective bending stiffness depends on two non-dimensional parameters: the composite action parameter (shear connection stiffness) and the relative bending stiffness parameter. The method is applied to a number of simple practical cases and the results obtained have been compared with the exact values. The applicability of the simplified analysis procedure was found to be very good, except for interlayer shear stresses. The error in the Eurocode 5 procedure, as compared with the method proposed in this paper, can in some cases be up to almost 30% depending on the boundary conditions.

  • 13.
    Girhammar, Ulf Arne
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Composite beam-columns with interlayer slip: approximate analysis2008In: International Journal of Mechanical Sciences, ISSN 0020-7403, E-ISSN 1879-2162, Vol. 50, no 12, p. 1636-1649Article in journal (Refereed)
    Abstract [en]

    An approximate second order analysis procedure for composite beam-columns with interlayer slip subjected to transverse loading and axial compressive loads is developed. The magnification factors to be applied to the first order solutions in order to estimate the deflections and internal forces obtained by the second order analysis approach are presented. The method of applying magnification factors to internal axial forces is discussed. The approximate second order analysis procedure is developed for the four Euler cases with various transverse load conditions. The procedure is applied to and the accuracy is illustrated for simply supported partially beam-columns of steel and concrete, and timber and concrete with different bending stiffness and interlayer slip properties. The deflections and internal forces obtained by the approximate method compared extremely well, except for slip forces in case of very flexible shear connectors, with those obtained by the more rigorous second order analysis approach for different composite action (partial interaction) parameters (shear connector stiffness values). The study also shows that the magnification factor associated with the deflections can be utilized to estimate also the internal actions, except shear forces in case of very flexible shear connectors, in the second order case with minimal error for simply supported beam-columns. Thus. for members with shear connector stiffness of structural significance the proposed approximate method can be used in general for simply supported beam-columns. For other boundary and loading conditions, the approximate method needs to be re-evaluated. The approach of using one magnification factor greatly simplifies the analysis task for those components.

  • 14.
    Girhammar, Ulf Arne
    Department of TFE-Civil Engineering, Faculty of Science and Technology, Umeå University.
    Composite beam-columns with interlayer slip-Approximate analysis2008In: International Journal of Mechanical Sciences, ISSN 0020-7403, E-ISSN 1879-2162, Vol. 50, no 12, p. 1636-1649Article in journal (Refereed)
    Abstract [en]

    An approximate second order analysis procedure for composite beam-columns with interlayer slip subjected to transverse loading and axial compressive loads is developed. The magnification factors to be applied to the first order solutions in order to estimate the deflections and internal forces obtained by the second order analysis approach are presented. The method of applying magnification factors to internal axial forces is discussed. The approximate second order analysis procedure is developed for the four Euler cases with various transverse load conditions. The procedure is applied to and the accuracy is illustrated for simply supported partially beam-columns of steel and concrete, and timber and concrete with different bending stiffness and interlayer slip properties. The deflections and internal forces obtained by the approximate method compared extremely well, except for slip forces in case of very flexible shear connectors, with those obtained by the more rigorous second order analysis approach for different composite action (partial interaction) parameters (shear connector stiffness values). The study also shows that the magnification factor associated with the deflections can be utilized to estimate also the internal actions, except shear forces in case of very flexible shear connectors, in the second order case with minimal error for simply supported beam-columns. Thus, for members with shear connector stiffness of structural significance the proposed approximate method can be used in general for simply supported beam-columns. For other boundary and loading conditions, the approximate method needs to be re-evaluated. The approach of using one magnification factor greatly simplifies the analysis task for those components.

  • 15.
    Girhammar, Ulf Arne
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Pan, Dan H
    Exact static analysis of partially composite beams and beam-columns2007In: International Journal of Mechanical Sciences, ISSN 0020-7403, E-ISSN 1879-2162, Vol. 49, no 2, p. 239-255Article in journal (Refereed)
    Abstract [en]

    The ordinary differential equations and general solutions for the deflection and internal actions and, especially, the pertaining consistent boundary conditions for partially composite Euler-Bernoulli beams and beam-columns are presented. Static loading conditions, including transverse and axial loading and first- and second-order analyses are considered. The theoretical procedure is applicable to general loading and boundary conditions for uniform composite beams and beam-columns with interlayer slip. Further, the exact closed form characteristic equations and their associated exact buckling length coefficients for composite Columns with interlayer slip are derived for the four Euler boundary conditions. It is shown that these coefficients are the same as those for ordinary fully composite (solid) columns, except for the Euler clamped-pinned case. For the clamped-pinned case, the difference between the exact buckling length coefficient and the corresponding value for solid Columns is less than 1.8%, depending oil the so-called composite action parameter and relative bending stiffness parameter. Correspondingly, the maximum deviation between the exact and approximate buckling load is at most 2.5%. These small differences can in most practical cases be neglected. Also, the maximum theoretical range for the relative bending stiffness for partially composite beams and beam-columns is derived. An effective bending stiffness, valuable in the determination of the critical buckling load for partially composite members, is derived. This effective bending stiffness is also Suitable for analysing approximate deflections and internal actions or stresses in composite beams with flexible shear connection. The beam-column analysis is applied to a specific case. The difference in the approaches to the first- and second-order analysis is illustrated and the results clearly show the magnification in the actions and displacements due to the second-order effect. The magnification of the internal axial forces is different from magnifications obtained for the other internal actions, since only that portion of an internal axial force that is induced by bending is magnified by the second-order effect.

  • 16.
    Girhammar, Ulf Arne
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Pan, Dan H
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Gustafsson, Anders
    Nanyan Technological University.
    Exact dynamic analysis of composite beams with partial interaction2009In: International Journal of Mechanical Sciences, ISSN 0020-7403, E-ISSN 1879-2162, Vol. 51, p. 565-582Article in journal (Refereed)
  • 17.
    Girhammar, Ulf Arne
    et al.
    Department of Applied Physics and Electronics, Civil Engineering, Umeå University.
    Pan, Danhua
    Department of Applied Physics and Electronics, Civil Engineering, Umeå University.
    Exact static analysis of partially composite beams and beam-columns2007In: International Journal of Mechanical Sciences, ISSN 0020-7403, E-ISSN 1879-2162, Vol. 49, no 2, p. 239-255Article in journal (Refereed)
    Abstract [en]

    The ordinary differential equations and general solutions for the deflection and internal actions and, especially, the pertaining consistent boundary conditions for partially composite Euler-Bernoulli beams and beam-columns are presented. Static loading conditions, including transverse and axial loading and first- and second-order analyses are considered. The theoretical procedure is applicable to general loading and boundary conditions for uniform composite beams and beam-columns with interlayer slip. Further, the exact closed form characteristic equations and their associated exact buckling length coefficients for composite columns with interlayer slip are derived for the four Euler boundary conditions. It is shown that these coefficients are the same as those for ordinary fully composite (solid) columns, except for the Euler clamped-pinned case. For the clamped-pinned case, the difference between the exact buckling length coefficient and the corresponding value for solid columns is less than 1.8% depending on the so-called composite action parameter and relative bending stiffness parameter. Correspondingly, the maximum deviation between the exact and approximate buckling load is at most 2.5%. These small differences can in most practical cases be neglected. Also, the maximum theoretical range for the relative bending stiffness for partially composite beams and beam-columns is derived. An effective bending stiffness, valuable in the determination of the critical buckling load for partially composite members, is derived. This effective bending stiffness is also suitable for analysing approximate deflections and internal actions or stresses in composite beams with flexible shear connection. The beam-column analysis is applied to a specific case. The difference in the approaches to the first- and second-order analysis is illustrated and the results clearly show the magnification in the actions and displacements due to the second-order effect. The magnification of the internal axial forces is different from magnifications obtained for the other internal actions, since only that portion of an internal axial force that is induced by bending is magnified by the second-order effect

  • 18.
    Girhammar, Ulf Arne
    et al.
    Department of TFE-Civil Engineering, Faculty of Science and Technology, Umeå University.
    Pan, Danhua
    Department of TFE-Civil Engineering, Faculty of Science and Technology, Umeå University.
    Gustafsson, Anders
    Division of Mathematical Sciences, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore.
    Exact dynamic analysis of composite beams with partial interaction2009In: International Journal of Mechanical Sciences, ISSN 0020-7403, E-ISSN 1879-2162, Vol. 51, no 8, p. 565-582Article in journal (Refereed)
    Abstract [en]

    The partial differential equations and general solutions for the deflection and internal actions and the pertaining consistent boundary conditions are presented for composite Euler-Bernoulli members with interlayer slip subjected to general dynamic loading. Both free and forced vibrations are treated. The solutions are shown to be unique and complete under certain conditions, and valid for all so-called restricted admissible boundary conditions. Specifically, the exact eigenmode length coefficients are derived for the four Euler BC. They differ from those valid for ordinary, fully composite (solid) beams, except for the pinned-pinned case. The maximum deviation for beams with the other three Euler BC is shown to be less than 2-6% with respect to the eigenmode length coefficient and 3-10% with respect to the eigenfrequency, respectively, depending on the two non-dimensional parameters, composite action or shear connector stiffness and relative bending stiffness parameters. However, these deviations occur in a rather narrow range of the determining parameters, so for most practical cases the eigenmode length coefficients given for solid (fully composite) beams can approximately be used also for partially composite beams. The procedures of analysing beam vibrations are applied to a specific case. These solutions illustrate the effect of interlayer connection on the peak velocity of the beam vibrations. The proposed analytical theory is verified by tests and finite element calculations

  • 19.
    Grenestedt, Joachim L.
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Engineering, Physics and Mathematics.
    Bassinet, F.
    Influence of cell wall thickness variations on elastic stiffness of closed-cell cellular solids2000In: International Journal of Mechanical Sciences, ISSN 0020-7403, E-ISSN 1879-2162, Vol. 42, no 7, p. 1327-1338Article in journal (Refereed)
    Abstract [en]

    The stiffness of closed-cell low-density cellular solids, or solid foams, is affected by "imperfections" such as non-uniform cell shape and size, wavy distortions of cell walls, variations in cell wall thickness, etc. The present paper focuses on the influence of non-uniform cell wall thickness on stiffness. Calculations are performed on one model with different degrees of thickness variations. The model used is the flat-faced Kelvin structure, which consists of 14-sided polyhedra in a bcc arrangement. The results indicate that the stiffness of closed-cell cellular solids is not very sensitive to thickness variations. (C) 2000 Elsevier Science Ltd. All rights reserved.

  • 20.
    Gustavsson, Rolf K.
    et al.
    Vattenfall Research & Development.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Evaluation of impact dynamics and contact forces in a hydropower rotor due to variations in damping and lateral fluid forces2009In: International Journal of Mechanical Sciences, ISSN 0020-7403, E-ISSN 1879-2162, Vol. 51, no 9-10, p. 653-661Article in journal (Refereed)
    Abstract [en]

    Damages due to contact between the runner and the discharge ring have been observed in several hydroelectric power units. The damage can cause high repair costs of the runner and the discharge ring as well as considerable production losses.In this paper a rotor model of a 45 MW hydropower unit is used for the analysis of the rotor dynamical phenomena occurring due to contact between the runner and the discharge ring for different grade of lateral force on the turbine and bearing damping. The rotor model consists of a generator rotor and a turbine, which is connected to an elastic shaft supported by three isotropic bearings. The discrete representation of rotor model consist of 32 degrees of freedom, to increase the speed of the analysis the size of the model has been reduced with the IRS method to a system with 8 degrees of freedom.Results are presented in bifurcation diagrams, maximum contact force, Poincaré map and phase portrait. Simulations indicate that the contact forces between the turbine and the discharge ring are large, with considerable risks for serious damage as a consequence. The analysis shows that the risk for contact and damage are large for relatively small lateral turbine loads when the gap between the turbine and discharge ring is small and the contact stiffness is high.

  • 21. Hosseini-Hashemi, Sh.
    et al.
    Fadaee, M.
    Atashipour, Seyed Rasoul
    A new exact analytical approach for free vibration of Reissner-Mindlin functionally graded rectangular plates2011In: International Journal of Mechanical Sciences, ISSN 0020-7403, E-ISSN 1879-2162, Vol. 53, no 1, p. 11-22Article in journal (Refereed)
    Abstract [en]

    An exact closed-form procedure is presented for freevibration analysis of moderately thick rectangularplates having two opposite edges simply supported (i.e. Lévy-type rectangularplates) based on the Reissner–Mindlinplate theory. The material properties change continuously through the thickness of the plate, which can vary according to a power law distribution of the volume fraction of the constituents. By introducing some new potential and auxiliary functions, the displacement fields are analytically obtained for this plate configuration. Several comparison studies with analytical and numerical techniques reported in literature are carried out to establish the high accuracy and reliability of the solutions. Comprehensive benchmark results for natural frequencies of the functionallygraded (FG) rectangularplates with six different combinations of boundary conditions (i.e. SSSS–SSSC–SCSC–SCSF–SSSF–SFSF) are tabulated in dimensionless form for various values of aspect ratios, thickness to length ratios and the power law index. Due to the inherent features of the present exact closed-form solution, the present results will be a useful benchmark for evaluating the accuracy of other analytical and numerical methods, which will be developed by researchers in the future.

  • 22.
    Khurshid, M.
    et al.
    KTH Royal Institute of Technology, Sweden.
    Leitner, M.
    Montanuniversität Leoben, Austria.
    Barsoum, Z.
    KTH Royal Institute of Technology, Sweden.
    Schneider, C.
    RISE - Research Institutes of Sweden, Swerea, Swerea KIMAB.
    Residual stress state induced by high frequency mechanical impact treatment in different steel grades – Numerical and experimental study2017In: International Journal of Mechanical Sciences, ISSN 0020-7403, E-ISSN 1879-2162, Vol. 123, p. 34-42Article in journal (Refereed)
    Abstract [en]

    High frequency mechanical impact treatment is observed to increase the fatigue strength of welded joints. This technique induces compressive residual stresses, increases the local hardness, and reduces the stress concentration by modifying the weld toe radius. The goal of this study was to investigate residual stresses induced by ultrasonic impact treatment in S355, S700MC, and S960 grades steel experimentally and numerically. Plate specimens were manufactured and treated with different treatment intensities i.e. vibration amplitudes of the Sonotrode. The indentation depths were measured by the aid of a laser scanner and residual stresses using X-ray diffraction technique. The effect of steel grade and treatment intensity on the induced compressive residual stress state was firstly studied experimentally. In addition, displacement controlled simulations were carried out to estimate the local residual stress condition considering the effect of different material models. Both the numerically estimated and experimentally measured residual stresses were qualitatively in good agreement. Residual stress state in S355 and S700MC can be estimated well using combined strain rate dependent material model. No significant effect of the treatment intensity is observed on the indentation depth and residual stress state for S355 grade steel. The indentation depth decreases with the increase in the yield strength of the steel.

  • 23.
    Khurshid, Mansoor
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Leitnerb, M.
    Barsoum, Zuheir
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Schneider, C.
    Residual stress state induced by High Frequency Mechanical Impact Treatment in different steel grades -numerical and experimental study2017In: International Journal of Mechanical Sciences, ISSN 0020-7403, E-ISSN 1879-2162, Vol. 123, p. 34-42Article in journal (Refereed)
    Abstract [en]

    High frequency mechanical impact treatment is observed to increase the fatigue strength of welded joints. This technique induces compressive residual stresses, increases the local hardness, and reduces the stress concentration by modifying the weld toe radius. The goal of this study was to investigate residual stresses induced by ultrasonic impact treatment in S355, S700MC, and S960 grades steel experimentally and numerically. Plate specimens were manufactured and treated with different treatment intensities i.e. vibration amplitudes of the Sonotrode. The indentation depths were measured by the aid of a laser scanner and residual stresses using X-ray diffraction technique. The effect of steel grade and treatment intensity on the induced compressive residual stress state was firstly studied experimentally. In addition, displacement controlled simulations were carried out to estimate the local residual stress condition considering the effect of different material models. Both the numerically estimated and experimentally measured residual stresses were qualitatively in good agreement. Residual stress state in S355 and S700MC can be estimated well using combined strain rate dependent material model. No significant effect of the treatment intensity is observed on the indentation depth and residual stress state for S355 grade steel. The indentation depth decreases with the increase in the yield strength of the steel.

  • 24.
    Larsson, Per-Lennart
    KTH, Superseded Departments, Solid Mechanics.
    Investigation of sharp contact at rigid-plastic conditions2001In: International Journal of Mechanical Sciences, ISSN 0020-7403, E-ISSN 1879-2162, Vol. 43, no 4, p. 895-920Article in journal (Refereed)
    Abstract [en]

    Sharp contact problems are examined theoretically and numerically. The analysis is focused on elastic-plastic material behaviour and in particular the case when the local plastic zone arising at contact is so large that elastic effects on the mean contact pressure will be small or negligible. It is shown that, save for the particular case of a rigid-plastic power-law material, at such conditions, there is no single representative value on the uniaxial stress-strain curve that can be used in order to evaluate the global parameters at contact. However, the present numerical results indicate that good accuracy predictions for the mean contact pressure can be achieved when this variable is described by two parameters corresponding to the stress levels at, approximately, 2 and 35% plastic strain. Regarding the size of the contact area, it is shown that this quantity is very sensitive to elastic effects and any general correlation with material properties is complicated at best. The numerical analysis is performed by using the finite element method and the theoretical as well as the numerical results are compared with relevant experimental ones taken from the literature. From a practical point of view, the presented results are directly applicable to material characterization or measurements of residual mechanical fields by sharp indentation tests, but also for situations such as contact in gears or in electronic devices.

  • 25.
    Linares Arregui, Irene
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Alfredsson, B.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Elastic-plastic characterization of a high strength bainitic roller bearing steel-experiments and modelling2010In: International Journal of Mechanical Sciences, ISSN 0020-7403, E-ISSN 1879-2162, Vol. 52, no 10, p. 1254-1268Article in journal (Refereed)
    Abstract [en]

    Monotonic and cyclic deformations were studied for a high strength bainitic roller bearing steel. The temperature of 75 °C corresponded to normal roller bearing conditions. The materials showed hydrostatic influence on yielding, but no or marginal influence of plastic deformation on density change. Therefore, a linear elastic constitutive model with pressure dependent yielding, non-associated flow rule, combined non-linear kinematic and isotropic hardening was necessary to characterize the cyclic behaviour. A stepwise process is detailed for determining the material parameters of the pressure dependent model, where particular attention was placed on the hardening parameters. One set of parameters was sufficient to describe all tested load ranges including compressive ratchetting. Some comparative tests were performed at room temperature, 150 °C and on martensitic specimens at 75 °C. The temperature influence was limited to the isotropic hardening parameters.

  • 26.
    Linares Arregui, Irene
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Alfredsson, Bo
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Non-linear elastic characterisation of a high strength bainitic roller bearing steel2013In: International Journal of Mechanical Sciences, ISSN 0020-7403, E-ISSN 1879-2162, Vol. 68, p. 1-15Article in journal (Refereed)
    Abstract [en]

    A small but not negligible non-linear elastic behaviour was detected when investigating cyclic uniaxial push-pull experiments on a high strength bainitic steel. Cyclic torsion experiments led to the conclusion that the shear modulus was relatively constant. A non-linear elastic model was implemented where the bulk modulus was extended with a second order term related to the elastic dilatation and where the shear modulus was constant. The material presented a strength differential effect (SDE), with larger yield stress in compression than in tension. Consequently, the non-linear elastic model was combined with a plasticity model that incorporated a Drucker-Prager yield surface, non-associated flow rule and combined non-linear hardening. Expressions that include non-linear elasticity were derived for the elastic-plastic hardening and the compliance tensors. The extended material model predicted the elastic-plastic results from cyclic push-pull experiments. Also, a phenomenological analysis of the cyclic elastic response showed isotropic damage in the elastic moduli. The steady-state damage increased linearly with the cyclic plastic strain range.

  • 27.
    Rentmeester, Rikard
    et al.
    SAAB AB Aeronaut, Broderna Ugglas Gata, SE-58254 Linkoping, Sweden.
    Nilsson, Larsgunnar
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    On mixed isotropic-distortional hardening2015In: International Journal of Mechanical Sciences, ISSN 0020-7403, E-ISSN 1879-2162, Vol. 92, p. 259-268Article in journal (Refereed)
    Abstract [en]

    Mixed isotropic-distortional hardening allows for individual stress-plastic strain relations in different straining directions. Such hardening can be obtained by allowing the parameters in the effective stress function depend on anisotropy functions of the equivalent plastic strain. A methodology to calibrate these anisotropy functions is proposed in this work, and is demonstrated on an austenitic strainless steel. A high exponent eight parameter effective stress function for plane stress states is utilised. The anisotropy functions are calibrated by the use of experimental data from uniaxial tensile test data in three material directions and a balanced biaxial test. The plastic anisotropy is evaluated at a finite number of plastic strains, and it is assumed to vary piecewise linearly with respect to the equivalent plastic strain. At each level of plastic strain, the anisotropy is correctly represented, even if rather large increments in plastic strain are used in the calibration. It was found that there are at least two sets of anisotropy functions which satisfy the conditions in the calibration procedure. The resulting uniaxial stress-strain relations from the two sets of anisotropy functions in four additional straining directions, not included in the calibration set, were compared to the corresponding experimental data. From this validation, one of the anisotropy function sets could be discarded, whereas the other one gave a good prediction of the stress-strain relations in all the four additional directions. (C) 2015 Elsevier Ltd. All rights reserved.

  • 28.
    Song, Yubao
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Feng, Leping
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Liu, Zibo
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Wen, Jihong
    Yu, Dianlong
    Suppression of the vibration and sound radiation of a sandwich plate via periodic design2019In: International Journal of Mechanical Sciences, ISSN 0020-7403, E-ISSN 1879-2162, Vol. 150, p. 744-754Article in journal (Refereed)
    Abstract [en]

    This paper investigates the suppression of vibration and sound radiation of a sandwich plate through the use of periodic design. A periodic sandwich plate is constructed and its dispersion relation is calculated. The vibration and sound radiation properties of the periodic sandwich plate are studied. Via the comparison of the periodic and bare sandwich plate, the effects of the periodic design on the vibration and sound radiation are analysed. Further, to know the sound radiation properties better, sound radiation efficiency of the periodic and bare sandwich plates is compared. In addition, the effects of the boundary conditions on the properties of the periodic sandwich plate are analysed. The numerical results demonstrate that the vibration and sound radiation are greatly suppressed over the stop band of the periodic sandwich plate. The suppression can also be obtained in part of pass bands. It is also shown that the periodic design can be an effective method for the reduction of the sound radiation efficiency. The suppression for the vibration and sound is greater than that caused by only increasing the mass of the plate in the designing frequency range.

  • 29.
    Sun, Fengzhen
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Gamstedt, E. Kristofer
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Mechanics.
    Experimental and numerical investigation on shear banding during nanomachining of an amorphous glassy polymer2019In: International Journal of Mechanical Sciences, ISSN 0020-7403, E-ISSN 1879-2162, Vol. 151, p. 13-21Article in journal (Refereed)
    Abstract [en]

    This paper discusses the shear banding phenomenon which took place during nanomachining of an amorphous glassy polymer. The nanomachining were carried out with varying machining conditions (depth of cut, machining speed), and the morphologies of the machined surfaces were characterized using atomic force microscopy. The experiments reveal the occurrence of shear band as the critical machining condition is reached. The shear banding was rationalized by the effect of adiabatic heating during machining. Finite element modelling of nanomachining was conducted using an existing elastic-viscoplastic model for this polymer, which accounts for the adiabatic heating due to plastic dissipation. The simulation was then compared with the experiment. It shows that the simulation can capture the main features of shear banding in nanomachining, indicating that the machining is controlled by a localized deformation mechanism. This work can be helpful in optimizing the processing parameters to improve the surface quality of optical products.

  • 30.
    Synnegård, Erik
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Gustavsson, Rolf K.
    Vattenfall Research & Development , Vattenfall Power Consultant AB Mechanical and Process Engineering, Kyrkogatan 4, Gävle.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Influence of cross-coupling stiffness in tilting pad journal bearings for vertical machines2016In: International Journal of Mechanical Sciences, ISSN 0020-7403, E-ISSN 1879-2162, Vol. 111-112, p. 43-54Article in journal (Refereed)
    Abstract [en]

    This paper evaluates how cross-coupling coefficients affects the dynamics of a vertical rotor with tilting pad journal bearings. For vertical machines, the bearing properties are dependent on the bearing load and direction. As a result, it generally requires that bearing properties are calculated at each time step using the governing fluid dynamic equations. This method gives a good representation of the bearing but computational time increases and can cause stability problems. In this study the bearing properties are instead modelled as a function of eccentricity and its direction. Hence, the bearing properties can be evaluated at each time step without solving Navier-Stokes or Reynold's equation. The main advantage of using this method is to decrease the computational time. The cross-coupling stiffness and damping coefficients are usually neglected since they are small compared to the radial stiffness and damping coefficients. In this paper, the simulated unbalanced response is compared to experimental results and it is seen that the cross-coupling stiffness for vertical machines can influence the dynamics. It is shown that the cross-coupling can be of the same order of magnitude as the radial stiffness component depending on the shaft angular position in the bearing. Including cross-coupling increases higher frequency components and the experiments show similar behaviour. Hence the cross-coupling stiffness and damping coefficients should be included when simulating vertical machines subjected to high loads or when the detailed dynamical behaviour is important to investigate.

  • 31.
    Tan, Z.
    et al.
    Luleå tekniska universitet.
    Li, Wen Bin
    Luleå tekniska universitet.
    Persson, B.
    Volvo.
    On analysis and measurement of residual stresses in the bending of sheet metals1994In: International Journal of Mechanical Sciences, ISSN 0020-7403, E-ISSN 1879-2162, Vol. 36, no 5, p. 483-491Article in journal (Refereed)
    Abstract [en]

    A new method for evaluating distribution of residual stresses in bent sheet metals is presented. Due to the non-uniform distribution of strain and stress across thickness, springback on unloading induces residual stress in a bent specimen. The authors have formulated the problem and shown that the springback and residual stresses can be expressed as a function of geometric parameters and material properties of sheet metals, e.g. bending curvature, thickness, Young's modulus, work-hardening index, etc. The layer-removing method was used to determine the residual stresses in the study. By simulating the layer-removing process, analytical measurement of the residual stress was made. The analytical results were compared with the experimental data measured, and a good agreement was found.

  • 32.
    Thiery, Florian
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Gustavsson, Rolf K.
    Vattenfall Research & Development.
    Aidanpää, Jan-Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Dynamics of a misaligned Kaplan turbine with blade-to-stator contacts2015In: International Journal of Mechanical Sciences, ISSN 0020-7403, E-ISSN 1879-2162, Vol. 99, p. 251-261Article in journal (Refereed)
    Abstract [en]

    Rotor-to-stator contacts can occur in hydropower systems due to mechanical and electrical misalignment as well as high unbalance forces. It can result in high impact forces and damages in case of malfunction of the machine. As a result, a real hydropower rotor is studied to evaluate the different types of dynamic motion due to multiple impacts when it is initially misaligned. In this paper, the simplicity of its blade rubbing modelling allows us to evaluate in a fast and efficient way the dynamics of this system as a function of several design parameters. It is observed that the global dynamics of the system are similar to simple bladed Jeffcott rotors when scaled with the number of blades. Since the rotor runs at its operating point, the contact forces are also evaluated at nominal speed. A parametric study - as a function of contact stiffness and damping - is performed and results are given in terms of Poincaré sections, bifurcation diagrams and maximum displacements at steady state. These simulations are used to determine if the system is safe to operate. It can be used to design hydropower rotors by choosing the operating speed in a suitable range, or to analyse if the machine can be stopped before a catastrophe occurs

  • 33.
    Wredenberg, Fredrik
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Larsson, Per-Lennart
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    On the effect of substrate deformation at scratching of soft thin film composites2010In: International Journal of Mechanical Sciences, ISSN 0020-7403, E-ISSN 1879-2162, Vol. 52, no 7, p. 1008-1014Article in journal (Refereed)
    Abstract [en]

    In the present paper scratching of soft thin film/substrate structures, using sharp conical indenters, is studied theoretically and numerically. For simplicity, but not out of necessity, the material behavior of the film as well as the substrate is described by classical elastoplasticity accounting for large deformations. Explicit material parameters are chosen in order to arrive at representative results as regards material behavior and indenter geometry. The main efforts are devoted towards an understanding of the influence from the film/substrate boundary on global scratching properties at different material combinations. Global quantities to be investigated include scratch hardness, contact area and apparent coefficient of friction at scratching. The numerical investigation is performed using the finite element method (FEM) and the numerical strategy is discussed in some detail. (C) 2010 Elsevier Ltd. All rights reserved.

  • 34.
    Zamani, Mohammadreza
    et al.
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting.
    Dini, Hoda
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting.
    Svoboda, Ales
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting.
    Lindgren, Lars-Erik
    Division of Mechanics of Solid Materials, Luleå University of Technology, Luleå, Sweden.
    Seifeddine, Salem
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting.
    Andersson, Nils-Eric
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting.
    Jarfors, Anders
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting.
    A dislocation density based constitutive model for as-cast Al-Si alloys: Effect of temperature and microstructure2017In: International Journal of Mechanical Sciences, ISSN 0020-7403, E-ISSN 1879-2162, Vol. 121, p. 164-170Article in journal (Refereed)
    Abstract [en]

    The flow stress of an as-cast Al-Si based alloy was modeled using a dislocation density based model. The developed dislocation density-based constitutive model describes the flow curve of the alloy with various microstructures at quite wide temperature range. Experimental data in the form of stress-strain curves for different strain rates ranging from 10−4 to 10−1 s−1 and temperatures ranging from ambient temperature up to 400 °C were used for model calibration. In order to model precisely the hardening and recovery process at elevated temperature, the interaction between vacancies and dissolved Si was included. The calibrated temperature dependent parameters for different microstructure were correlated to the metallurgical event of the material and validated. For the first time, a dislocation density based model was successfully developed for Al-Si cast alloys. The findings of this work expanded the knowledge on short strain tensile deformation behaviour of these type of alloys at different temperature, which is a critical element for conducting a reliable microstructural FE-simulation.

  • 35.
    Zamani, Mohammadreza
    et al.
    Department of Materials and Manufacturing, School of Engineering, Jönköping University.
    Dini, Hoda
    Department of Materials and Manufacturing, School of Engineering, Jönköping University.
    Svoboda, Ales
    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.
    Seifeddine, Salem
    Department of Materials and Manufacturing, School of Engineering, Jönköping University.
    Andersson, Nils-Eric
    Department of Materials and Manufacturing, School of Engineering, Jönköping University.
    Jarfors, Anders E.W.
    Department of Materials and Manufacturing, School of Engineering, Jönköping University.
    A dislocation density based constitutive model for as-cast Al-Si alloys: Effect of temperature and microstructure2017In: International Journal of Mechanical Sciences, ISSN 0020-7403, E-ISSN 1879-2162, Vol. 121, p. 164-170Article in journal (Refereed)
    Abstract [en]

    The flow stress of an as-cast Al-Si based alloy was modeled using a dislocation density based model. The developed dislocation density-based constitutive model describes the flow curve of the alloy with various microstructures at quite wide temperature range. Experimental data in the form of stress-strain curves for different strain rates ranging from 10−4 to 10−1 s−1 and temperatures ranging from ambient temperature up to 400 °C were used for model calibration. In order to model precisely the hardening and recovery process at elevated temperature, the interaction between vacancies and dissolved Si was included. The calibrated temperature dependent parameters for different microstructure were correlated to the metallurgical event of the material and validated. For the first time, a dislocation density based model was successfully developed for Al-Si cast alloys. The findings of this work expanded the knowledge on short strain tensile deformation behaviour of these type of alloys at different temperature, which is a critical element for conducting a reliable microstructural FE-simulation.

  • 36.
    Zhou, Yang
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Nordmark, Arne
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Multi-parametric stability investigation for thin spherical membranes with contacts2017In: International Journal of Mechanical Sciences, ISSN 0020-7403, E-ISSN 1879-2162, Vol. 131-132, p. 334-344Article in journal (Refereed)
    Abstract [en]

    The instability behavior for a thin truncated spherical membrane completely filled with fluid or containing both gas and fluid, fixed on a circular platform and in contact with two vertical planes was investigated. Different penalty functions for contacts, and symmetry aspects of the discretized model were studied, and gave effects on instability behavior. Stability conclusions for the multi-parametric problems were made using generalized eigenvalue analyses, showing limit points, bifurcation points and turning point. Contact conditions were shown to introduce bifurcations and secondary paths, dependent on the contact implementations and discretizations. Their effects on stability behaviors in connection with various controlling equations are discussed.

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