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  • 1.
    Adolfsson, Erik
    et al.
    KTH, Superseded Departments, Solid Mechanics.
    Gudmundson, Peter
    KTH, Superseded Departments, Solid Mechanics.
    Matrix crack induced stiffness reductions in [(0(m)/90(n)/+theta(p)/-theta(q))(s)](m) composite laminates1995In: Composites Engineering, ISSN 0961-9526, Vol. 5, no 1, p. 107-123Article in journal (Refereed)
    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.

  • 2.
    Adolfsson, Erik
    et al.
    KTH, Superseded Departments, Solid Mechanics.
    Gudmundson, Peter
    KTH, Superseded Departments, Solid Mechanics.
    Matrix crack initiation and progression in composite laminates subjected to bending and extension1999In: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 36, no 21, p. 3131-3169Article in journal (Refereed)
    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.

  • 3.
    Adolfsson, Erik
    et al.
    KTH, Superseded Departments, Solid Mechanics.
    Gudmundson, Peter
    KTH, Superseded Departments, Solid Mechanics.
    Thermoelastic properties in combined bending and extension of thin composite laminates with transverse matrix cracks1997In: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 34, no 16, p. 2035-2060Article in journal (Refereed)
    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.

  • 4.
    Agde Tjernlund, Jessica
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Gamstedt, Kristofer
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Gudmundson, Peter
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Length-scale effects on damage development in tensile loading of glass-sphere filled epoxy2006In: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 43, no 24, p. 7337-7357Article in journal (Refereed)
    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.

  • 5.
    Alfthan, Johan
    et al.
    KTH, Superseded Departments, Solid Mechanics.
    Gudmundson, Peter
    KTH, Superseded Departments, Solid Mechanics.
    Linear constitutive model for mechano-sorptive creep in paper2004Report (Other academic)
  • 6.
    Alfthan, Johan
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Gudmundson, Peter
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Linear constitutive model for mechano-sorptive creep in paper2005In: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 42, no 24-25, p. 6261-6276Article in journal (Refereed)
    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.

  • 7.
    Alfthan, Johan
    et al.
    KTH, Superseded Departments, Solid Mechanics.
    Gudmundson, Peter
    KTH, Superseded Departments, Solid Mechanics.
    Östlund, Sören
    KTH, Superseded Departments, Solid Mechanics.
    A micromechanical model for mechanosorptive creep in paper2002In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 28, no 3, p. 98-104Article in journal (Refereed)
    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.

  • 8.
    Asp, Leif E.
    et al.
    Polymer Engineering, Luleå University of Technology.
    Berglund, Lars A.
    Polymer Engineering, Luleå University of Technology.
    Gudmundson, Peter
    KTH, Superseded Departments, Solid Mechanics.
    Effects of a composite-like stress state on the fracture of epoxies1995In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 53, no 1, p. 27-37Article in journal (Refereed)
    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.

  • 9. Bonnaud, Etienne
    et al.
    Gudmundson, Peter
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Lead-Free Solder Cyclic Plasticity Characterization for Drop Test Simulations2006In: Lead-Free Solder Cyclic Plasticity Characterization for Drop Test Simulations, 2006Conference paper (Refereed)
  • 10.
    Bonnaud, Etienne L.
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.). Infineon Technologies Sweden AB, Sweden .
    Gudmundson, Peter
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Influence of component position on lead-free solder interconnections during drop test2005Conference paper (Refereed)
    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.

  • 11.
    Dahlberg, Carl F. O.
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Gudmundsson, Peter
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Hardening and softening mechanisms at decreasing microstructural length scales2008In: Philosophical Magazine, ISSN 1478-6435, E-ISSN 1478-6443, Vol. 88, no 30-32, p. 3513-3525Article in journal (Refereed)
    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.

  • 12.
    Fredriksson, Per
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Gudmundson, Peter
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Competition between interface and bulk dominated plastic deformation in strain gradient plasticity2007In: Modelling and Simulation in Materials Science and Engineering, ISSN 0965-0393, E-ISSN 1361-651X, Vol. 15, no 1, p. S61-S69Article in journal (Refereed)
    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.

  • 13.
    Fredriksson, Per
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Gudmundson, Peter
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Modelling of the interface between a thin film and a substrate within a strain gradient plasticity framework2007In: Journal of the mechanics and physics of solids, ISSN 0022-5096, E-ISSN 1873-4782, Vol. 55, no 5, p. 939-955Article in journal (Refereed)
    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.

  • 14.
    Fredriksson, Per
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Gudmundson, Peter
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Size-dependent yield strength and surface energies of thin films2005In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 400-401, no 1-2 SUPPL., p. 448-450Article in journal (Refereed)
    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.

  • 15.
    Fredriksson, Per
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Gudmundson, Peter
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Size-dependent yield strength of thin films2005In: International journal of plasticity, ISSN 0749-6419, E-ISSN 1879-2154, Vol. 21, no 9, p. 1834-1854Article in journal (Refereed)
    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.

  • 16.
    Fredriksson, Per
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Gudmundson, Peter
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    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 composites2009In: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 46, no 22-23, p. 3977-3987Article in journal (Refereed)
    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.

  • 17.
    Gasser, T. Christian
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Gudmundson, Peter
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Dohr, Gottfried
    Med Univ Graz, Inst Cell Biol, Histol & Embryol & Ctr Mol Med.
    Failure mechanisms of ventricular tissue due to deep penetration2009In: Journal of Biomechanics, ISSN 0021-9290, E-ISSN 1873-2380, Vol. 42, no 5, p. 626-633Article in journal (Refereed)
    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.

  • 18.
    Giannakopoulos, A. E.
    et al.
    KTH, Superseded Departments, Solid Mechanics.
    Gudmundson, Peter
    KTH, Superseded Departments, Solid Mechanics.
    The Stresses Around A Partly Microcracked Hole In Certain Ceramic Materials Under Internal-Pressure.1991In: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 28, no 3, p. 329-339Article in journal (Refereed)
    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.

  • 19.
    Gouldstone, Andrew
    et al.
    Dept. of Mat. Sci. and Engineering, Massachusetts Inst. of Technology.
    Wikström, Adam
    KTH, Superseded Departments, Solid Mechanics.
    Gudmundson, Peter
    KTH, Superseded Departments, Solid Mechanics.
    Suresh, Subra
    Dept. of Mat. Sci. and Engineering, Massachusetts Inst. of Technology.
    Onset of plastic yielding in thin metal lines deposited on substrates1999In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 41, no 3, p. 297-304Article in journal (Refereed)
    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.

  • 20.
    Gudmundson, Peter
    KTH, Superseded Departments, Solid Mechanics.
    A unified treatment of strain gradient plasticity2004In: Journal of the mechanics and physics of solids, ISSN 0022-5096, E-ISSN 1873-4782, Vol. 52, no 6, p. 1379-1406Article in journal (Refereed)
    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.

  • 21.
    Gudmundson, Peter
    KTH, Superseded Departments, Solid Mechanics.
    Accelerated creep: Do we need more research?2006Conference paper (Other academic)
  • 22.
    Gudmundson, Peter
    KTH, Superseded Departments, Solid Mechanics.
    Acoustic emission and dynamic energy release rate for steady growth of a tunneling crack in a plate in tension1999In: Journal of the mechanics and physics of solids, ISSN 0022-5096, E-ISSN 1873-4782, Vol. 47, no 10, p. 2057-2074Article in journal (Refereed)
    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.

  • 23.
    Gudmundson, Peter
    KTH, Superseded Departments, Solid Mechanics.
    Anisotropic microcrack nucleation in brittle materials1990In: Journal of the mechanics and physics of solids, ISSN 0022-5096, E-ISSN 1873-4782, Vol. 38, no 4, p. 531-551Article in journal (Refereed)
    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.

  • 24.
    Gudmundson, Peter
    KTH, Superseded Departments, Solid Mechanics.
    Effects of cracks and other geometrical changes on the vibration of structures: with special application to turbine blades1982Doctoral thesis, comprehensive summary (Other academic)
  • 25.
    Gudmundson, Peter
    BBC Brown Boveri Research Centre.
    Eigenfrequency changes of structures due to cracks, notches or other geometrical changes1982In: Journal of the mechanics and physics of solids, ISSN 0022-5096, E-ISSN 1873-4782, Vol. 30, no 5, p. 339-353Article in journal (Refereed)
    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.

  • 26.
    Gudmundson, Peter
    KTH, Superseded Departments (pre-2005), Solid Mechanics.
    Micromechanically based constitutive models for damage evolution in composite laminates2000In: International journal of damage mechanics, ISSN 1056-7895, E-ISSN 1530-7921, Vol. 9, no 1, p. 29-39Article in journal (Refereed)
    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.

  • 27.
    Gudmundson, Peter
    KTH, Superseded Departments (pre-2005), Solid Mechanics.
    Mikromekanik1999In: Mikromekanik, 1999Conference paper (Refereed)
  • 28.
    Gudmundson, Peter
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Modelling of length scale effects in viscoelastic materials2006In: European journal of mechanics. A, Solids, ISSN 0997-7538, E-ISSN 1873-7285, Vol. 25, no 3, p. 379-388Article in journal (Refereed)
    Abstract [en]

    A length scale dependent linear viscoelastic constitutive model is developed. First, a generalized Maxwell model that can describe standard linear viscoelasticity is considered. The model is then generalized to include effects of. viscous strain gradients. The formulation of additional boundary conditions resulting from the strain gradient terms is discussed. It is shown that the boundary conditions can be formulated in terms of a surface energy. As an example, the thermal expansion of a thin polymeric film on an elastic substrate is analyzed. It is shown that the relative thermal expansion in the thickness direction of the film decreases for sufficiently small film thicknesses, in accordance with experimental observations. This effect cannot be captured by a standard thermo-viscoelastic theory, which gives a constant thermal expansion independent of film thickness.

  • 29.
    Gudmundson, Peter
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Modelling of Matrix Cracking in Composite Laminates1997In: Modelling of Matrix Cracking in Composite Laminates, 1997Conference paper (Other academic)
  • 30.
    Gudmundson, Peter
    KTH, Superseded Departments, Solid Mechanics.
    On The Accuracy Of The Harmonic-Balance Method Concerning Vibrations Of Beams With Nonlinear Supports.1989In: Archive of applied mechanics (1991), ISSN 0939-1533, E-ISSN 1432-0681, Vol. 59, no 5, p. 333-344Article in journal (Refereed)
    Abstract [en]

    A homogeneous beam supported by a nonlinear cubic rotational spring and excited by a prescribed harmonic translational motion was analysed by the harmonic balance method. Harmonic and subharmonicsolutions were determined as functions of frequency, excitation amplitude and material damping.The results were verified against numerical time integrations of the governing nonlinear differential equations.The numerical method was based on a component mode synthesis technique, using free normal modes and inertia relief attachment modes. It was found that the predictions by the harmonic balance method werein excellent agreement with the numerical solution in a frequency interval covering the three first cantileveredeigen frequencies of the beam. The only exceptions were two narrow frequency intervals in which the numerical solution showed quasi periodic oscillations.

  • 31.
    Gudmundson, Peter
    KTH, Superseded Departments, Solid Mechanics.
    Strain gradient effects in viscoelasticity2005Conference paper (Refereed)
  • 32.
    Gudmundson, Peter
    KTH, Superseded Departments, Solid Mechanics.
    Strain gradient plasticity of multilayer thin films - hardening and weakening effects2006Conference paper (Other academic)
  • 33.
    Gudmundson, Peter
    Brown, Boveri and Co. Ltd., Research Cente.
    The dynamic behaviour of slender structures with cross-sectional cracks1983In: Journal of the mechanics and physics of solids, ISSN 0022-5096, E-ISSN 1873-4782, Vol. 31, no 4, p. 329-345Article in journal (Refereed)
    Abstract [en]

    A dynamic model for beams with cross-sectional cracks is discussed. It is shown that a crack can be represented by a consistent, static flexibility matrix. Two different methods for the determination of the flexibility matrix are discussed. If the static stress intensity factors are known, the flexibility matrix can be determined from an integration of these stress intensity factors. Alternatively, static finite element calculations can be used for the determination of the flexibility matrix. Both methods are demonstrated in the present paper. The mathematical model was applied to an edge-cracked cantilevered beam and the eigenfrequencies were determined for different crack lengths and crack positions. These results were compared to experimentally obtained eigenfrequencies. In the experiments, the cracks were modelled by sawing cuts. The theoretical results were, for all crack lengths, in excellent agreement with the experimental data. The dynamic stress intensity factor for a longitudinally vibrating, centrally cracked bar was determined as well. The results compared very well with dynamic finite element calculations. The crack closure effect was experimentally investigated for an edge-cracked beam with a fatigue crack. It was found that the eigenfrequencies decreased, as functions of crack length, at a much slower rate than in the case of an open crack.

  • 34.
    Gudmundson, Peter
    Brown Boveri Research Cent.
    Tuning of turbine blades: a theoretical approach.1983In: Journal of engineering for power, ISSN 0022-0825, Vol. 105, no 2, p. 249-255Article in journal (Refereed)
    Abstract [en]

    A perturbation method is described which predicts the changes in eigenfrequencies resulting from geometrical changes of a structure. This dependence is represented by dimensionless functions, one for each eigenfrequency, which vary over the surface of the structure. The functions are presented for each eigenfrequency as isoline plots. The method was applied to a turbine blade and a rectangular beam.

  • 35.
    Gudmundson, Peter
    et al.
    KTH, Superseded Departments, Solid Mechanics.
    Alpman, Johan
    Structures Department, The Aero. Res. Institute.
    Initiation and growth criteria for transverse matrix cracks in composite laminates2000In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 60, no 2, p. 185-195Article in journal (Refereed)
    Abstract [en]

    Cecchin and Monti [Cecchin E, Monti A. Experimental techniques for analysis of matrix crack evolution in composite laminates. Masters thesis, Department of Solid Mechanics, Royal Institute of Technology (KTH), Stockholm, Sweden, 1998.] have presented experimental results using off-axis loaded tensile specimens that made it possible to introduce transverse matrix cracks which started from one edge of a specimen and arrested before reaching the other edge. Matrix crack positions and lengths were registered as functions of the applied load through optical images which were captured at regular external load intervals. In the present paper, the experimental data from Cecchin and Monti are analysed. Since several transverse matrix cracks appeared in each specimen and crack growth can be observed at different load levels, a single macroscopic specimen generates lots of data for crack initiation and propagation. Glass/epoxy cross-ply laminates with two different transverse ply thicknesses are investigated. The results strongly indicate that the energy release rate is a relevant measure for prediction of crack growth whereas the local strain controls matrix crack initiation.

  • 36.
    Gudmundson, Peter
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Dahlberg, Carl F. O.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Isotropic strain gradient plasticity model based on self-energies of dislocations and the Taylor model for plastic dissipation2019In: International journal of plasticity, ISSN 0749-6419, E-ISSN 1879-2154, Vol. 121, p. 1-20Article in journal (Refereed)
    Abstract [en]

    A dislocation mechanics based isotropic strain gradient plasticity model is developed. The model is derived from self-energies of dislocations and the Taylor model for plastic dissipation. It is shown that the same microstructural length scale emerges for both the energetic and the dissipative parts of the model. Apart from a non-dimensional factor of the order of unity, the length scale is defined as the Burgers vector divided by the strain for initiation of plastic deformation. When the structural length scale approaches this microstructural length scale, strengthening effects result. The present model predicts an increased initial yield stress that is controlled by the energetic contribution. For larger plastic strains, the hardening is governed by the dissipative part of the model. The theory is specialized to the simple load cases of tension with a passivation layer that prohibits plastic deformation on the surfaces as well as pure bending with free and fixed boundary conditions for plastic strain. Simulations of initial yield stress for varying thicknesses are compared to experimental observations reported in the literature. It is shown that the model in a good way can capture the length scale dependencies. Also upper bound solutions are presented for a spherical void in an infinite volume as well as torsion of a cylindrical rod. The model is as well applied to derive a prediction for the Hall-Petch effect.

  • 37.
    Gudmundson, Peter
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Fredriksson, Per
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Interface conditions in strain gradient plasticity theories2005In: Interface conditions in strain gradient plasticity theories, 2005Conference paper (Refereed)
  • 38.
    Gudmundson, Peter
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Wikström, Adam
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Stresses in Thin Films and Interconnect Lines2001In: Stresses in Thin Films and Interconnect Lines, 2001Conference paper (Refereed)
  • 39.
    Gudmundson, Peter
    et al.
    KTH, Superseded Departments, Solid Mechanics.
    Wikström, Adam
    KTH, Superseded Departments, Solid Mechanics.
    Stresses in thin films and interconnect lines2002In: Microelectronic Engineering, ISSN 0167-9317, E-ISSN 1873-5568, Vol. 60, no 1-2, p. 17-29Article in journal (Refereed)
    Abstract [en]

    The mechanical behavior of thin films and interconnect lines is investigated. Firstly, theoretical models of thermal stress evolution in thin films and passivated or unpassivated lines are considered. Secondly, the effect of texture in a copper thin film with a columnar grain structure is studied from a theoretical point of view. The film consists of three different constituents with (111), (100) and randomly oriented texture. Global properties as well as local stress distributions are considered in detail within a thermoelastic framework. The results are in qualitative agreement with available experimental results. Implications with regards to plastic behavior are briefly discussed. Finally, the potential of the curvature measurement technique for experimental stress evaluation in thin films is considered for initially flat and curved substrate/film systems.

  • 40.
    Gudmundson, Peter
    et al.
    Tre konsulter AB.
    Wüthrich, C.
    Brown Boveri Forschungszentrum.
    Die Werkstoffdämpfung von Stählen bei hohen Dehnungsamplituden1986In: Materialwissenschaft und Werkstofftechnik, ISSN 0933-5137, E-ISSN 1521-4052, Vol. 17, no 8, p. 286-292Article in journal (Refereed)
    Abstract [de]

    Am Beispiel von zwei martensitischen Chromstählen (X 22 CrMoV 12 1, X 20 Cr 13) und eines kaltverformten Austeniten (X 12 CrNiWTi 16 13) wird die amplitudenabhängige Werkstoffdämpfung bei Raumtemperatur untersucht. Die martensitischen Werkstoffe weisen infolge der magneto-elastischen Effekte eine hohe amplitudenabhängige Dämpfung auf. Es kann gezeigt werden, daß eine Erhöhung der Festigkeit durch Absenken der Anlaßtemperatur zu einer Abnahme der Werkstoffdämpfung führt. Der untersuchte austenitische Werkstoff besitzt nach Kaltverformung eine beträchtliche Dämpfung, die jedoch beim Tempern bereits bei Temperaturen oberhalb von 100 °C auf die bei Austeniten üblichen tiefen Werte absinkt. Dieser Effekt wird der Verankerung der Versetzungen beim Tempern zugeschrieben.

    Damping of Steels at High Strain Amplitudes

    The amplitude dependent damping has been investigated in two martensitic chromium steels (X 22 CrMoV 12 1, X 20 Cr 13) and a cold worked austenitic steel (X 12 CrNiWTi 16 13) at room temperature. Due to the magneto-elastic effects, the martensitic steels show a strong amplitude dependent damping. It cound be shown that the damping is reduced remarkably by a reduction of the annealing temperature. The austenitic material shows a very high damping in the cold worked condition. Tempering at relatively low temperatures (above 100 °C) reduces damping to the low values usually expected for austenitic materials. This effect was attributed to the pinning of dislocations during tempering.

  • 41.
    Gudmundson, Peter
    et al.
    Swedish Institute of Composites.
    Zang, Weilin
    Swedish Institute of Composites.
    An analytic model for thermoelastic properties of composite laminates containing transverse matrix cracks1993In: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 30, no 23, p. 3211-3231Article in journal (Refereed)
    Abstract [en]

    An analytical model for the prediction of the thermoelastic properties of composite laminates containing matrix cracks is presented. In particular, transverse matrix cracks with their crack surfaces parallel to the fibre direction and perpendicular to the laminate plane are treated. Two- and three-dimensional laminates of arbitrary layup configurations are covered by the model. The presented expressions for stiffnesses, thermal expansion coefficients, strain contributions from release of residual stresses and local average ply stresses and strains do solely contain known ply property data and matrix crack densities. The key to the model is the judicious use of a known analytical solution for a row of cracks in an infinite isotropic medium. The model has been verified against numerically determined stiffnesses, thermal expansion coefficients and local average ply stresses for matrix cracked angle-ply and cross-ply laminates. Comparisons to experimental data for cross-ply laminates are also presented. It is shown that the present model to a very good accuracy can predict thermoelastic properties of matrix cracked composite laminates at varying matrix crack densities and layup configurations.

  • 42.
    Gudmundson, Peter
    et al.
    KTH, Superseded Departments, Solid Mechanics.
    Zang, Weilin
    Thermoelastic properties of microcracked composite laminates1993In: Mechanics of composite materials, ISSN 0191-5665, E-ISSN 1573-8922, Vol. 29, no 2, p. 107-114Article in journal (Refereed)
  • 43.
    Gudmundson, Peter
    et al.
    Swedish Institute of Composites.
    Östlund, Sören
    Swedish Institute of Composites.
    First Order Analysis of Stiffness Reduction Due to Matrix Cracking.1992In: Journal of composite materials, ISSN 0021-9983, E-ISSN 1530-793X, Vol. 26, no 7, p. 1009-1030Article in journal (Refereed)
    Abstract [en]

    In this paper the reduction in effective elastic constants of composite lami nates due to matrix cracking is considered. A general easily applicable theory valid for two- and three-dimensional analysis of thin as well as thick laminates is presented. The theory is based on the change of elastic energy in a laminate at the appearance of a matrix crack in one layer. This information combined with a dilute approximation , i.e., different matrix cracks are considered not to interact with each other, is utilized to estimate the re duction of elastic constants for a certain crack density. The theory is asymptotically exact for nk « 1, where nk is the number of cracks per unit thickness of the cracked ply and a correct value of the slope of the stiffness reduction crack density curve is obtained at nk = 0.

  • 44.
    Gudmundson, Peter
    et al.
    SWEDISH INST. COMPOSITES.
    Östlund, Sören
    SWEDISH INST. COMPOSITES.
    Numerical verification of a procedure for calculation of elastic-constants in microcracking composite laminates.1992In: Journal of composite materials, ISSN 0021-9983, E-ISSN 1530-793X, Vol. 26, no 17, p. 2480-2492Article in journal (Refereed)
    Abstract [en]

    In two recent papers Gudmundson and Ostlund have presented a simple to use theory for calculation of reduced thermoelastic constants in composite laminates with matrix cracks. The theory is valid for two- and three-dimensional laminates of arbitrary layups and is asymptotically exact for dilute and infinite microcrack densities. Furthermore, the theory is based solely on ply property data and matrix crack densities. No experimentally determined or unknown theoretical parameters are required. The theory predicts changes in all coefficients of the elastic stiffness and thermal expansion coefficient tensors. In previous papers the accuracy of the present theory has been investigated for cross ply laminates by comparisons to experimental results from the literature and two-dimensional finite element calculations. However, in order to become a powerful tool in the analysis of cracked composite laminates the theory must be verified at intermediate crack densities also for angle ply laminates. Unfortunately no useful experimental results for such laminates have been found in the literature and numerical methods must be considered for the verification. In the present paper the approximate theory is compared with three-dimensional finite element calculations of cracked thick [THETA, - THETA]M glass fiber reinforced epoxy laminates for a wide range of different matrix crack densities. The finite element calculations can be considered as exact for all crack densities within the present formulation, and errors are due only to the numerical algorithm. It is found that the dilute theory in combination with the theory for infinite crack densities to a surprisingly good accuracy cover all ranges of crack densities.

  • 45.
    Gudmundson, Peter
    et al.
    SWEDISH INST. COMPOSITE.
    Östlund, Sören
    SWEDISH INST. COMPOSITE.
    Prediction Of Thermoelastic Properties Of Composite Laminates With Matrix Cracks.1992In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 44, no 2, p. 95-105Article in journal (Refereed)
    Abstract [en]

    A theory is presented for the determination of changes in the elastic compliance tensor and the thermal expansion coefficients due to matrix cracking. Effects of residual stresses are taken into account. The theory is valid for two- or three-dimensional laminates of arbitrary lay-ups and is asymptotically exact for dilute micro-crack densities. For large micro-crack densities an alternative model is described which is asymptotically exact for large crack densities. Combined, the two models cover to a good approximation the whole range of micro-crack densities. The theory is applied to a micro-cracking cross-ply GFRP laminate for which the stress/strain curve is calculated. Data are also presented for changes in thermomechanical properties of angle ply laminates as functions of the lay-up angle.

  • 46.
    Gudmundson, Peter
    et al.
    KTH, Superseded Departments, Solid Mechanics.
    Östlund, Sören
    KTH, Superseded Departments, Solid Mechanics.
    Stress Singularity At The Free-Surface Of A Dynamically Growing Crack.1990In: Journal of applied mechanics, ISSN 0021-8936, E-ISSN 1528-9036, Vol. 57, no 1, p. 112-116Article in journal (Refereed)
    Abstract [en]

    The stress singularity at the intersection between the crack front and the free surface of a dynamically growing crack in a linear elastic isotropic material has been numerically evaluated by an especially developed finite element program. The singularity parameter (), defined by ~ R−1, is presented as a function of the crack-tip velocity and the angle (ß)between the crack front and the free surface. The angle (ß) at which the singularity () equals 0.5 was found to be 101 deg almost independently of the crack-tip velocity.

  • 47.
    Gudmundsson, Peter
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Foreword (president, KTH)2016In: 6th International Congress on Arsenic in the Environment, AS 2016, p. xxxv-xxxviArticle in journal (Refereed)
  • 48.
    Hoffelner, W.
    et al.
    Brown Boveri Research Centre.
    Gudmundson, Peter
    Brown Boveri Research Centre.
    A fracture mechanics analysis of ultrasonic fatigue1982In: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 16, no 3, p. 365-371Article in journal (Refereed)
    Abstract [en]

    The method of ultrasonic fatigue finds increasing interest in materials science. Especially, fatigue crack growth rates near the threshold stress intensity range, Δ”K0, can be determined with this method in reasonable times providing no frequency and corrosion effects exist. But for an accurate application of this technique it is necessary to improve the testing systems and also the determination of the dynamic cyclic stress intensity range, Δ”K. In this paper, fatigue crack growth experiments at ultrasonic frequencies with different mean stresses and also the calculation of the dynamic stress intensity range with finite elements are treated. On this basis fatigue crack growth curves at room temperature of the alloys Hastelloy X and IN 800 were measured and compared with results obtained at low frequencies. No significant influence of frequency could be found in these materials.

  • 49.
    Johnson, Mikael
    et al.
    KTH, Superseded Departments, Solid Mechanics.
    Gudmundson, Peter
    KTH, Superseded Departments, Solid Mechanics.
    Broad-band transient recording and characterization of acoustic emission events in composite laminates2000In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 60, no 15, p. 2803-2818Article in journal (Refereed)
    Abstract [en]

    Acoustic emission (AE) transients due to different kinds of microdamage, such as matrix cracking, fiber breakage and local delaminations, have been recorded in glass/epoxy composite laminates. Different stacking sequences, [0 degrees, 90(2)degrees](S), [90(2)degrees, 0 degrees](S), [+45 degrees, -45 degrees](S) and [0(4)degrees], were used in order to trigger different crack mechanisms during tensile testing. The AE transients were recorded as functions of time by the use of broad-band AE transducers. In the experiments, it was observed that different types of cracks generated acoustic emission signals varying in amplitude, duration time and frequency content. It was also seen that the same type of crack produced signals with different characteristics depending on the layer in which the crack appeared and its orientation compared to the location of the transducer. The majority of signals from the tests could be divided into a few main groups. Typical signals and characteristics representing these groups are presented in the paper. The observations show that there is a potential in future development of quantitative methods for identification of damage development in composite laminates.

  • 50.
    Johnson, Mikael
    et al.
    KTH, Superseded Departments, Solid Mechanics.
    Gudmundson, Peter
    KTH, Superseded Departments, Solid Mechanics.
    Experimental and theoretical characterization of acoustic emission transients in composite laminates2001In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 61, no 10, p. 1367-1378Article in journal (Refereed)
    Abstract [en]

    Transient wave propagation resulting from transverse matrix cracking in cross-ply composite tensile test specimens are investigated both theoretically and experimentally. In the experiments, broad-band transducers and a fast data-acquisition system enable measurements of transients in a frequency interval up to 1 MHz. The theoretical predictions are based on a model which utilizes a finite-element discretization of the cross-section of the specimen and a Fourier representation of the axial and time dependence. The comparisons between experimental and theoretical results are encouraging. Weak points in the experimental technique and in the theoretical model are identified.

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