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  • 1. Adolfsson, E
    et al.
    Gudmundson, Peter
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Matrix crack closure effects on the thermoelastic properties of [(0/90/+q/-q)s]M composite laminates1994Konferensbidrag (Refereegranskat)
  • 2.
    Adolfsson, Erik
    et al.
    KTH, Tidigare Institutioner                               , Hållfasthetslära.
    Gudmundson, Peter
    KTH, Tidigare Institutioner                               , Hållfasthetslära.
    Matrix crack induced stiffness reductions in [(0(m)/90(n)/+theta(p)/-theta(q))(s)](m) composite laminates1995Ingår i: Composites Engineering, ISSN 0961-9526, Vol. 5, nr 1, s. 107-123Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Two- and three-dimensional linearly elastic glass/epoxy and carbon/epoxy laminates of the type [(0m/90n/ + theta(p)/ - theta(q))s]M containing periodically distributed matrix cracks have been analysed by aid of the finite element method. The presented finite element model enables modelling of several important thick and thin ply stacking sequences like cross-plies, angle plies and quasi-isotropic laminates. Due to periodicity it suffices to model a representative volume element of the laminate. The boundaries of this unit cell represent prospective crack surfaces. In this way varying crack configurations and crack densities could be simulated. By application of periodic boundary conditions the stiffness tensors for laminates containing different crack configurations were calculated. The results are presented in the form of reduced engineering stiffness parameters as functions of matrix crack densities for a thick quasi-isotropic [(0-degree/90-degrees/ + 45-degrees/ -45-degrees)s]M glass/epoxy laminate, a thick [(0-degree/90-degrees + 55-degrees/ - 55-degrees)s]M carbon/epoxy laminate and a thin (0-degree/ +45-degrees/ -45-degrees)s glass/epoxy laminate. Comparisons are made to an approximate analytic model developed previously. An excellent agreement between the analytic predictions and the finite element results was found for all cases under consideration.

  • 3.
    Adolfsson, Erik
    et al.
    KTH, Tidigare Institutioner                               , Hållfasthetslära.
    Gudmundson, Peter
    KTH, Tidigare Institutioner                               , Hållfasthetslära.
    Matrix crack initiation and progression in composite laminates subjected to bending and extension1999Ingår i: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 36, nr 21, s. 3131-3169Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An experimental investigation of matrix crack initiation and progression in glass/epoxy laminates of different stacking sequences is presented. The laminates have been loaded in extension and bending, and the degree of damage as function of the load has been recorded. The changes in certain elastic properties caused by the damage were also measured, and are compared to results from a previously developed approximate analytic model. An energy release rate resistance curve is adopted in an attempt to describe the initiation and progression of matrix cracks in the laminates. The amount of cracking is also viewed in relation to the strain transverse to the fibres in the ply under consideration, and the ply stresses at the onset of cracking are calculated. The different damage evolution criteria are compared to the experimental results, and their validity and reliability are discussed. By use of the ply strain transverse to the fibres as a critical parameter for damage evolution, the load-deformation curves of the tested laminates are simulated taking damage progression into account.

  • 4.
    Adolfsson, Erik
    et al.
    KTH, Tidigare Institutioner                               , Hållfasthetslära.
    Gudmundson, Peter
    KTH, Tidigare Institutioner                               , Hållfasthetslära.
    Thermoelastic properties in combined bending and extension of thin composite laminates with transverse matrix cracks1997Ingår i: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 34, nr 16, s. 2035-2060Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Approximate analytic expressions for the thermoelastic properties in combined bending and extension of composite laminates containing transverse matrix cracks are derived. The model covers two-dimensional laminates of arbitrary lay-up sequences. The derived expressions for the compliances and thermal expansion coefficients merely contain ply property data and crack distributions. In order to check the accuracy and reliability of the presented analytic method, some sample cracked geometries were examined by use of the finite element method. A good agreement was found between the numerically and analytically obtained results for all cases under consideration.

  • 5.
    Agde Tjernlund, Jessica
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Gamstedt, Kristofer
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Gudmundson, Peter
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Length-scale effects on damage development in tensile loading of glass-sphere filled epoxy2006Ingår i: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 43, nr 24, s. 7337-7357Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Particle-reinforced polymers are widely used in load-carrying applications. The effect of particle size on damage development in the polymer is still relatively unexplored. In this study, the effect of glass-sphere size on the damage development in tensile loaded epoxy has been investigated. The diameter of the glass spheres ranged from approximately 0.5-50 mu m. The first type of damage observed was debonding at the sphere poles, which subsequently grew along the interface between the glass spheres and epoxy matrix. These cracks were observed to kink out into the matrix in the radial direction perpendicular to the applied load. The debonding stresses increased with decreasing sphere diameter, whereas the length to diameter ratio of the resulting matrix cracks increased with increasing sphere diameter. These effects could not be explained by elastic stress analysis and linear-elastic fracture mechanics. Possible explanations are that a thin interphase shell may form in the epoxy close to the glass spheres, and that there is a length-scale effect in the yield process which depends on the strain gradients. Cohesive fracture processes can contribute to the influence of sphere size on matrix-crack length. Better knowledge on these underlying size-dependent mechanisms that control damage development in polymers and polymer composites is useful in development of stronger materials. From a methodology point of view, the glass-sphere composite test can be used as an alternative technique (although still in a qualitative way) to hardness vs. indentation depth to quantify length-scale effects in inelastic deformation of polymers.

  • 6. Alfthan, J.
    et al.
    Gudmundson, Peter
    Östlund, S.
    Micro-mechanical model for mechanosorptive creep2000Konferensbidrag (Övrigt vetenskapligt)
  • 7.
    Alfthan, Johan
    et al.
    KTH, Tidigare Institutioner                               , Hållfasthetslära.
    Gudmundson, Peter
    KTH, Tidigare Institutioner                               , Hållfasthetslära.
    Linear constitutive model for mechano-sorptive creep in paper2004Rapport (Övrigt vetenskapligt)
  • 8.
    Alfthan, Johan
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Gudmundson, Peter
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Linear constitutive model for mechano-sorptive creep in paper2005Ingår i: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 42, nr 24-25, s. 6261-6276Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The creep of paper is accelerated by moisture cycling. This effect is known as mechano-sorptive creep. It is assumed that this is an effect of transient stresses produced during moisture content changes in combination with non-linear creep behaviour of the fibres. The stresses produced by the moisture content changes are often much larger than the applied mechanical loads. If this is the case, the mechanical loads are only a perturbation to the internal stress state, and it will appear as if the mechano-sorptive creep is linear in stress. It is possible to take advantage of this feature. In the present report the pure moisture problem is first solved. The mechanical load is then treated as a perturbation of the solution to the moisture problem. Using this strategy, it is possible to linearize a non-linear network model for mechano-sorptive creep and to formulate a continuum model. As a result, the number of variables in the model is reduced. This is a significant improvement as it will be possible to use the linearized model to describe the material in a finite element program and solve problems with complicated geometries.

  • 9.
    Alfthan, Johan
    et al.
    KTH, Tidigare Institutioner                               , Hållfasthetslära.
    Gudmundson, Peter
    KTH, Tidigare Institutioner                               , Hållfasthetslära.
    Östlund, Sören
    KTH, Tidigare Institutioner                               , Hållfasthetslära.
    A micromechanical model for mechanosorptive creep in paper2002Ingår i: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 28, nr 3, s. 98-104Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The creep of paper is accelerated by moisture cycling, a phenomenon known as mechanosorptive creep or accelerated creep. In this paper stress created at bonds due to anisotropic swelling during absorption and desorption of moisture, in combination with nonlinear creep, are proposed to be the cause for mechanosorptive creep. Two simplifled models are first discussed in order to demonstrate the suggested mechanism. A three-dimensional fibre network model composed of elastic fibres and inelastic bonds is then studied by finite element calculations. The relative sliding in the bonds is described by a nonlinear creep model which, in combination with anisotropic hygroexpansion of the fibres results in accelerated creep of the network.

  • 10.
    Asp, Leif E.
    et al.
    Polymer Engineering, Luleå University of Technology.
    Berglund, Lars A.
    Polymer Engineering, Luleå University of Technology.
    Gudmundson, Peter
    KTH, Tidigare Institutioner                               , Hållfasthetslära.
    Effects of a composite-like stress state on the fracture of epoxies1995Ingår i: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 53, nr 1, s. 27-37Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The strain to failure of a transversely loaded composite is much lower than for the pure matrix in uniaxial tension. Several studies of composites suggest the triaxial matrix stress state as one of the explanations. In order to investigate this experimentally, a triaxial tensile test previously used for rubbers (the poker-chip test) was successfully applied to four epoxies in the glassy state. The chosen specimen geometry mimicked the most severe stress state in the matrix as determined by finite element analysis of a transversely loaded glass-fiber/epoxy composite. The poker-chip strains to failure in the primary loading direction were 0.5-0.8%, whereas uniaxial strains to failure were 1.8-7%. The triaxial stress state in composite matrices may therefore by itself be a sufficient explanation for low values of transverse composite strains to failure.

  • 11. Boer, C.R.
    et al.
    Gudmundson, Peter
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Rebelo, N
    Comparison of elasto-plastic FEM, rigid-plastic FEM and experiments for cylinder upsetting1982Konferensbidrag (Refereegranskat)
  • 12. Bonnaud, Etienne
    et al.
    Gudmundson, Peter
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Lead-Free Solder Cyclic Plasticity Characterization for Drop Test Simulations2006Ingår i: Lead-Free Solder Cyclic Plasticity Characterization for Drop Test Simulations, 2006Konferensbidrag (Refereegranskat)
  • 13.
    Bonnaud, Etienne L.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.). Infineon Technologies Sweden AB, Sweden .
    Gudmundson, Peter
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Influence of component position on lead-free solder interconnections during drop test2005Konferensbidrag (Refereegranskat)
    Abstract [en]

    When subjected to drop test, interconnections between components and test board experience high stresses mainly due to differential bending. Using analytical and numerical modal analysis, bending moments have here been calculated and shown to strongly depend on the location on the test board; the highest value not being found at the centre, as usually stated. In parallel, experiments to determine visco-plastic material properties at high strain rates (∼1s-1) for lead-free solder (SnAgCu) have been performed and used in drop test simulations. Inelastic strains calculated at different locations confirm results from the modal analyses and give a first insight into the development of a drop test failure criterion.

  • 14.
    Dahlberg, Carl F. O.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Gudmundsson, Peter
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Hardening and softening mechanisms at decreasing microstructural length scales2008Ingår i: Philosophical Magazine, ISSN 1478-6435, E-ISSN 1478-6443, Vol. 88, nr 30-32, s. 3513-3525Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A laminate structure with varying lamina thicknesses is used as a qualitative model of grain size dependence on yield behaviour in metallic materials. Both strain gradient plasticity and slip between layers are considered. It is shown that an inverse Hall-Petch effect can be generated in this way. For very small thicknesses, corresponding to very small grain sizes, sliding is the dominant mechanism and the strength then decreases with decreasing thickness. For larger thicknesses, strain gradient plasticity is controlling the deformation and the strength is, instead, increasing with decreasing thickness. Numerical examples are presented that demonstrate these mechanisms.

  • 15. Fredriksson, P.
    et al.
    Gudmundson, P.
    KTH, Tidigare Institutioner, Hållfasthetslära.
    FE-modelling of interface conditions within a strain gradient plasticity theory2006Konferensbidrag (Refereegranskat)
  • 16. Fredriksson, P.
    et al.
    Gudmundson, P.
    KTH, Tidigare Institutioner, Hållfasthetslära.
    Size dependent yield strength and surface energies of thin films2004Konferensbidrag (Övrigt vetenskapligt)
  • 17.
    Fredriksson, Per
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Gudmundson, Peter
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Competition between interface and bulk dominated plastic deformation in strain gradient plasticity2007Ingår i: Modelling and Simulation in Materials Science and Engineering, ISSN 0965-0393, E-ISSN 1361-651X, Vol. 15, nr 1, s. S61-S69Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the present report, the competition between dissipative plastic strain gradient effects in the bulk and in an interface is investigated within a strain gradient plasticity framework. The model of the interface is analysed in terms of hardening behaviour and strength for the case of a thin film with an elastic plastic interface. It is found that the yield strength of the film is increased by length scale effects both in the bulk material and the interface. The effect is governed by quite a simple rule, namely the weakest link of bulk and interface. In addition, if the interface is allowed to harden, three regions are observed for the bulk (interior) and interface of the film during an increasing load: (i) elastic bulk and rigid interface, (ii) both bulk and interface plastic and (iii) plastic bulk and rigid interface. The properties of the model are illustrated with numerical results from a parametric study.

  • 18.
    Fredriksson, Per
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Gudmundson, Peter
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Modelling of the interface between a thin film and a substrate within a strain gradient plasticity framework2007Ingår i: Journal of the mechanics and physics of solids, ISSN 0022-5096, E-ISSN 1873-4782, Vol. 55, nr 5, s. 939-955Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Interfaces play an important role for the plastic deformation at the micron scale. In this paper, two types of interface models for isotropic materials are developed and applied in a thin film analysis. The first type, which can also be motivated from dislocation theory, assumes that the plastic work at the interface is stored as a surface energy that is linear in plastic strain. In the second model, the plastic work is completely dissipated and there is no build-up of a surface energy. Both formulations introduce one length scale parameter for the bulk material and one for the interface, which together control the film behaviour. It is demonstrated that the two interface models give equivalent results for a monotonous, increasing load. The combined influence of bulk and interface is numerically studied and it is shown that size effects are obtained, which are controlled by the length scale parameters of bulk and interface.

  • 19.
    Fredriksson, Per
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Gudmundson, Peter
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Size-dependent yield strength and surface energies of thin films2005Ingår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 400-401, nr 1-2 SUPPL., s. 448-450Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The strain gradient plasticity theory recently proposed by Gudmundson [P. Gudmundson, J. Mech. Phys. Solids 52 (2004) 1379-1406] is used to analyse the behaviour of a thin film on an elastic substrate. Boundary conditions for the film-substrate interface are introduced via a surface energy that depends on the plastic strain state at the interface. Finite element results show a strong dependence on the surface energy. If the surface energy is small, no size effects appear. On the other hand, if a stiff interface is simulated, corresponding to a large surface energy, a thickness dependence of the yield strength is found. The application of several alternative strain gradient models would predict a thickness dependent hardening, but strictly not a size dependence of the yield strength. The presently predicted thickness dependence on yield strength and hardening is supported by experimental results.

  • 20.
    Fredriksson, Per
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Gudmundson, Peter
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Size-dependent yield strength of thin films2005Ingår i: International journal of plasticity, ISSN 0749-6419, E-ISSN 1879-2154, Vol. 21, nr 9, s. 1834-1854Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Biaxial strain and pure shear of a thin film are analysed using a strain gradient plasticity theory presented by Gudmundson [Gudmundson, P., 2004. A unified treatment of strain gradient plasticity. Journal of the Mechanics and Physics of Solids 52, 1379-1406]. Constitutive equations are formulated based on the assumption that the free energy only depends on the elastic strain and that the dissipation is influenced by the plastic strain gradients. The three material length scale parameters controlling the gradient effects in a general case are here represented by a single one. Boundary conditions for plastic strains are formulated in terms of a surface energy that represents dislocation buildup at an elastic/plastic interface. This implies constrained plastic flow at the interface and it enables the simulation of interfaces with different constitutive properties. The surface energy is also controlled by a single length scale parameter, which together with the material length scale defines a particular material. Numerical results reveal that a boundary layer is developed in the film for both biaxial and shear loading, giving rise to size effects. The size effects are strongly connected to the buildup of surface energy at the interface. If the interface length scale is small, the size effect vanishes. For a stiffer interface, corresponding to a non-vanishing surface energy at the interface, the yield strength is found to scale with the inverse of film thickness.

  • 21.
    Fredriksson, Per
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Gudmundson, Peter
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Mikkelsen, Lars Pilgaard
    Tech Univ Denmark, Risø Natl Lab Sustainable Energy, Mat Res Dept.
    Finite element implementation and numerical issues of strain gradient plasticity with application to metal matrix composites2009Ingår i: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 46, nr 22-23, s. 3977-3987Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A framework of finite element equations for strain gradient plasticity is presented. The theoretical framework requires plastic strain degrees of freedom in addition to displacements and a plane strain version is implemented into a commercial finite element code. A couple of different elements of quadrilateral type are examined and a few numerical issues are addressed related to these elements as well as to strain gradient plasticity theories in general. Numerical results are presented for an idealized cell model of a metal matrix composite under shear loading. It is shown that strengthening due to fiber size is captured but strengthening due to fiber shape is not. A few modelling aspects of this problem are discussed as well. An analytic solution is also presented which illustrates similarities to other theories.

  • 22.
    Gasser, T. Christian
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Gudmundson, Peter
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Dohr, Gottfried
    Med Univ Graz, Inst Cell Biol, Histol & Embryol & Ctr Mol Med.
    Failure mechanisms of ventricular tissue due to deep penetration2009Ingår i: Journal of Biomechanics, ISSN 0021-9290, E-ISSN 1873-2380, Vol. 42, nr 5, s. 626-633Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Lead perforation is a rare but serious complication of pacemaker implantations, and in the present study the associated tissue failure was investigated by means of in-vitro penetration of porcine and bovine ventricular tissue. Rectangular patches from the right ventricular free wall and the interventricular were separated, bi-axially stretched and immersed in physiological salt solution at 37 C before load displacement curves of m total 891 penetrations were recorded. To this end flat-bottomed cylindrical punches of different diameters were used, and following mechanical testing the penetration were histological analyzed using light and electron microscopes. Penetration pressure, i.e. penetration force divided by punch cross-sectional area decreased slightly from 2.27(SD 0.66) to 1.76 (SD 0.46) N mm(2) for punches of 1.32 to 2.30 mm in diameter, respectively. Deep penetration formed cleavages aligned with the local fiber orientation of the tissue, and hence, a mode-I crack developed, where the crack faces were wedged open by the advancing punch. The performed study derived novel failure data from ventricular tissue due to deep penetration and uncovered associated failure mechanisms. This provides information to derive mechanical failure models, which are essential to enrich our current understanding of failure of soft biological tissues and to guide medical device development.

  • 23. Gebart, B.R.
    et al.
    Gudmundson, Peter
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Lundemo, C.Y.
    An evaluation of alternative injection strategies in RTM1992Konferensbidrag (Refereegranskat)
  • 24. Gebart, B.R.
    et al.
    Gudmundson, Peter
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Strömbeck, L.A.
    Lundemo, C.Y.
    Analysis of the permeability in RTM reinforcements1991Konferensbidrag (Refereegranskat)
  • 25.
    Giannakopoulos, A. E.
    et al.
    KTH, Tidigare Institutioner                               , Hållfasthetslära.
    Gudmundson, Peter
    KTH, Tidigare Institutioner                               , Hållfasthetslära.
    The Stresses Around A Partly Microcracked Hole In Certain Ceramic Materials Under Internal-Pressure.1991Ingår i: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 28, nr 3, s. 329-339Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the present work we examine the stress field around a hole in certain ceramic materials. The hole is under internal pressure in plane strain conditions. The material behavior is initially isotropic linearly elastic and upon loading develops microcracks. The damage is assumed to be anisotropic and microcracking is believed to take place along preferred orientations. A damaged constitutive law, appropriate for the microcracking assumptions, is used to derive exact results for the stress fields in this particular problem. The present analysis may find applications in the experimental investigation of ceramic materials behaving as anisotropically microcracking solids.

  • 26.
    Gouldstone, Andrew
    et al.
    Dept. of Mat. Sci. and Engineering, Massachusetts Inst. of Technology.
    Wikström, Adam
    KTH, Tidigare Institutioner                               , Hållfasthetslära.
    Gudmundson, Peter
    KTH, Tidigare Institutioner                               , Hållfasthetslära.
    Suresh, Subra
    Dept. of Mat. Sci. and Engineering, Massachusetts Inst. of Technology.
    Onset of plastic yielding in thin metal lines deposited on substrates1999Ingår i: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 41, nr 3, s. 297-304Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A thermoelastic analysis of patterned lines on substrates to determine the critical conditions for the onset of yielding is investigated, which provides a new analytical tool for determining the yield properties of lines relative to those of films of the same thickness. Verification of the theory is provided with the aid of finite element simulations, and a method for experimentally extracting the plastic properties of lines is also outlined.

  • 27. Grenestedt, J.L.
    et al.
    Gudmundson, Peter
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Layup optimization of composite material systems1993Ingår i: / [ed] Pedersen, P., Amsterdam: Elsevier, 1993, s. 311-336Konferensbidrag (Refereegranskat)
    Abstract [en]

    Layup optimization of laminated composite structures is considered. Lamination parameters rather than layup angles and ply thicknesses are used as design parameters, thus any physically possible layup is included and the number of design variables is kept small; twelve for the most general layup. These twelve parameters are functions of the in-plane coordinates if the layup changes from point to point in the structure. It is shown that the feasible region of the parameters is convex, and the object functions to be maximized (stiffnesses, vibration frequencies, or buckling loads) are concave functions; local optima are therefore avoided and the optimization is accordingly significantly simplified. In order to use these parameters for optimization, their feasible region has to be known. The current knowledge is summarized, and some new results concerning the feasible region of the parameters of an orthotropic laminate are presented. When the feasible region of the lamination parameters is known, optimization of general composite material structures can efficiently be performed. A number of simple examples are included, such as flat in-plane homogeneous (same layup and thickness in every point) plates concerning deflections under uniform loads, vibration frequencies, and buckling under uni-axial or shearing loads.

  • 28. Gudmundson, P.
    A unified treatment of strain gradient plasticity2002Konferensbidrag (Övrigt vetenskapligt)
  • 29. Gudmundson, P.
    Analytical-numerical methods for the study of large deformations of solids, Part I: survey1980Rapport (Övrigt vetenskapligt)
  • 30. Gudmundson, P.
    Fracture and damage of composite laminates1994Ingår i: Engineering Mechanics of Fibre Reinforced Polymers and Composite Structures / [ed] J. Hult and F. Rammerstorfer, Udine: CISM | International Centre for Mechanical Sciences , 1994, s. 111-139Kapitel i bok, del av antologi (Övrigt vetenskapligt)
  • 31. Gudmundson, P.
    Integral equations for anti-plane shear1989Rapport (Övrigt vetenskapligt)
  • 32. Gudmundson, P.
    Isokrona spännings- töjningsdiagram och viskoelasticitetsteori för termoplaster1985Rapport (Övrigt vetenskapligt)
  • 33. Gudmundson, P.
    Strain gradient plasticity, surface energies and consistent boundary conditions2002Konferensbidrag (Övrigt vetenskapligt)
  • 34. Gudmundson, P.
    The boundary integral equation (BIE) method - A new effective tool for stress calculations1980Rapport (Övrigt vetenskapligt)
  • 35. Gudmundson, P.
    et al.
    Wikström, A.
    Thermoelastic analysis of thin lines on substrates1999Konferensbidrag (Refereegranskat)
  • 36.
    Gudmundson, Peter
    KTH, Tidigare Institutioner, Hållfasthetslära.
    A unified treatment of strain gradient plasticity2004Ingår i: Journal of the mechanics and physics of solids, ISSN 0022-5096, E-ISSN 1873-4782, Vol. 52, nr 6, s. 1379-1406Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A theoretical framework is presented that has potential to cover a large range of strain gradient plasticity effects in isotropic materials. Both incremental plasticity and viscoplasticity models are presented. Many of the alternative models that have been presented in the literature are included as special cases. Based on the expression for plastic dissipation, it is in accordance with Gurtin (J. Mech. Phys. Solids 48 (2000) 989; Int. J. Plast. 19 (2003) 47) argued that the plastic flow direction is governed by a microstress q(ij) and not the deviatoric Cauchy stress sigma'(ij) that has been assumed by many others. The structure of the governing equations is of second order in the displacements and the plastic strains which makes it comparatively easy to implement in a finite element programme. In addition, a framework for the formulation of consistent boundary conditions is presented. It is shown that there is a close connection between surface energy of an interface and boundary conditions in terms of plastic strains and moment stresses. This should make it possible to study boundary layer effects at the interface between grains or phases. Consistent boundary conditions for an expanding elastic-plastic boundary are as well formulated. As examples, biaxial tension of a thin film on a thick substrate, torsion of a thin wire and a spherical void under remote hydrostatic tension are investigated.

  • 37.
    Gudmundson, Peter
    KTH, Tidigare Institutioner, Hållfasthetslära.
    Accelerated creep: Do we need more research?2006Konferensbidrag (Övrigt vetenskapligt)
  • 38.
    Gudmundson, Peter
    KTH, Tidigare Institutioner                               , Hållfasthetslära.
    Acoustic emission and dynamic energy release rate for steady growth of a tunneling crack in a plate in tension1999Ingår i: Journal of the mechanics and physics of solids, ISSN 0022-5096, E-ISSN 1873-4782, Vol. 47, nr 10, s. 2057-2074Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The dynamic steady state growth of tunneling cracks in membrane loaded isotropic Kirchhoff plates is considered. Explicit solutions for the asymptotic displacement and velocity fields are presented. It is shown that the asymptotic fields are inversely proportional to the square root of distance from the crack tip, and that a wake may or may not develop behind the crack tip depending on the static membrane state. If the crack tip velocity is smaller than a certain critical velocity, the asymptotic solution will completely vanish. An explicit solution for the dynamic energy release rate is also presented. Due to elastic waves radiated from the crack tip, the dynamic energy release rate will generally be smaller than the corresponding static energy release rate.

  • 39.
    Gudmundson, Peter
    KTH, Tidigare Institutioner                               , Hållfasthetslära.
    Anisotropic microcrack nucleation in brittle materials1990Ingår i: Journal of the mechanics and physics of solids, ISSN 0022-5096, E-ISSN 1873-4782, Vol. 38, nr 4, s. 531-551Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A constitutive model for anisotropic microcracking in brittle materials is developed. The model is based on a stress controlled microcrack nucleation criterion, which can vary in a random way between different microcracks. The effects of microcrack closure and a random distribution of residual stresses are included in the analysis. The resultant inelastic strains are determined using a standard homogenization technique Numerical results are presented for three simple loading cases : pure tension, biaxial tension and triaxial tension. Crack tip shielding resulting from microcrack nucleation is also analysed, and numerical results of are presented for two different microcrack nucleation criteria.

  • 40.
    Gudmundson, Peter
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Changes in modal parameters resulting from small cracks1984Konferensbidrag (Refereegranskat)
  • 41. Gudmundson, Peter
    Corner problems1989Rapport (Övrigt vetenskapligt)
  • 42. Gudmundson, Peter
    Determination of optimal design modifications using experimental modal parameters1986Konferensbidrag (Refereegranskat)
  • 43.
    Gudmundson, Peter
    KTH, Tidigare Institutioner, Hållfasthetslära.
    Effects of cracks and other geometrical changes on the vibration of structures: with special application to turbine blades1982Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
  • 44.
    Gudmundson, Peter
    BBC Brown Boveri Research Centre.
    Eigenfrequency changes of structures due to cracks, notches or other geometrical changes1982Ingår i: Journal of the mechanics and physics of solids, ISSN 0022-5096, E-ISSN 1873-4782, Vol. 30, nr 5, s. 339-353Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A first order perturbation method is presented which predicts the changes in resonance frequencies of a structure resulting from cracks, notches or other geometrical changes. The eigenfrequency changes due to a crack are shown to be dependent on the strain energy of a static solution which is easily obtainable for small cracks and other small cut-outs. The method has been tested for three different cases, and the predicted results correlate very closely to experimental and numerical results.

  • 45. Gudmundson, Peter
    Initiation versus growth criteria for transverse matrix cracks1999Konferensbidrag (Refereegranskat)
  • 46.
    Gudmundson, Peter
    KTH, Tidigare Institutioner, Hållfasthetslära.
    Length scale effects for plasticity on the micron scale2006Konferensbidrag (Övrigt vetenskapligt)
  • 47.
    Gudmundson, Peter
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Material Mechanics2006Bok (Övrigt vetenskapligt)
  • 48.
    Gudmundson, Peter
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Micromechanically based constitutive models for damage evolution in composite laminates1997Konferensbidrag (Refereegranskat)
  • 49.
    Gudmundson, Peter
    KTH, Tidigare Institutioner                               , Hållfasthetslära.
    Micromechanically based constitutive models for damage evolution in composite laminates2000Ingår i: International journal of damage mechanics, ISSN 1056-7895, E-ISSN 1530-7921, Vol. 9, nr 1, s. 29-39Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The structure of micromechanically based constitutive models for composite laminates developing transverse matrix cracks, local delaminations, fibre/matrix debonding and fibre fractures is discussed. Nondimensional damage variables describing these four damage modes are introduced and the principal form of a damage dependent constitutive law is formulated. As a special case transverse matrix cracking is investigated in further detail. A previously developed model for stiffness changes resulting from transverse matrix cracking is presented, and criteria for initiation and growth of transverse cracks are discussed. In particular, limitations of the linear elastic fracture mechanics approach are investigated and a cohesive zone model capturing crack bridging effects is suggested.

  • 50.
    Gudmundson, Peter
    KTH, Tidigare Institutioner (före 2005), Hållfasthetslära.
    Mikromekanik1999Ingår i: Mikromekanik, 1999Konferensbidrag (Refereegranskat)
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