Change search
Refine search result
1 - 19 of 19
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 1.
    Bremberg, Daniel
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Dhondt, Guido
    Automatic 3-D crack propagation calculations: a pure hexahedral element approach versus a combined element approach2009In: International Journal of Fracture, ISSN 0376-9429, E-ISSN 1573-2673, Vol. 157, no 1-2, p. 109-118Article in journal (Refereed)
    Abstract [en]

    This article presents an evaluation of two different crack prediction approaches based on a comparison of the stress intensity factor distribution for three example problems. A single edge notch specimen and a quarter circular corner crack specimen subjected to shear displacements and a three point bend specimen with a crack inclined to the mid-plane are examined. The stress intensity factors are determined from the singular stress field close to the crack front. Two different fracture criteria are adopted for the calculation of an equivalent stress intensity factor and crack deflection angle. The stress intensity factor distributions for both numerical methods agree well to available reference solutions. Deviations are recorded at crack front locations near the free surface probably due to global contraction effects and the twisting behaviour of the crack front. Crack propagation calculations for the three point bending specimen give results that satisfy intuitive expectations. The outcome of the study encourages further pursuit of a crack propagation tool based on a combination of elements.

  • 2.
    Elmukashfi, Elsiddig
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Kroon, Martin
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Numerical analysis of dynamic crack propagation in rubber2012In: International Journal of Fracture, ISSN 0376-9429, E-ISSN 1573-2673, Vol. 177, no 2, p. 163-178Article in journal (Refereed)
    Abstract [en]

    In the present paper, dynamic crack propagation in rubber is analyzed numerically using the finite element method. The problem of a suddenly initiated crack at the center of stretched sheet is studied under plane stress conditions. A nonlinear finite element analysis using implicit time integration scheme is used. The bulk material behavior is described by finite-viscoelasticity theory and the fracture separation process is characterized using a cohesive zone model with a bilinear traction-separation law. Hence, the numerical model is able to model and predict the different contributions to the fracture toughness, i.e. the surface energy, viscoelastic dissipation, and inertia effects. The separation work per unit area and the strength of the cohesive zone have been parameterized, and their influence on the separation process has been investigated. A steadily propagating crack is obtained and the corresponding crack tip position and velocity history as well as the steady crack propagation velocity are evaluated and compared with experimental data. A minimum threshold stretch of 3.0 is required for crack propagation. The numerical model is able to predict the dynamic crack growth. It appears that the strength and the surface energy vary with the crack speed. Finally, the maximum principal stretch and stress distribution around steadily propagation crack tip suggest that crystallization and cavity formation may take place.

  • 3.
    Faleskog, Jonas
    et al.
    KTH, Superseded Departments, Solid Mechanics.
    Nilsson, Fred L.
    KTH, Superseded Departments, Solid Mechanics.
    Conditional failure probabilities in weakest link modelling2004In: International Journal of Fracture, ISSN 0376-9429, E-ISSN 1573-2673, Vol. 125, no 04-mar, p. 349-351Article in journal (Refereed)
  • 4.
    Hallström, Stefan
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Grenestedt, Joakim L
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Mixed mode fracture of cracks and wedge shaped notches in expanded PVC foam1998In: International Journal of Fracture, ISSN 0376-9429, E-ISSN 1573-2673, Vol. 88, no 4, p. 343-358Article in journal (Refereed)
    Abstract [en]

    Fracture initiated from a sharp crack or wedge shaped notch in a homogeneous material, subjected to different loading is considered. Singularities in the stress fields at edges and vertices are discussed. A point-stress criterion is used to predict fracture for sharp cracks as well as 90° wedge notches in expanded PVC foam. The point-stress criterion is formulated in a manner allowing failure predictions in general 3D stress situations. The influence of non-singular T-stress at cracks is discussed and substantiated by experimental results.

  • 5.
    Kroon, Martin
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Steady-state crack growth in rubber-like solids2011In: International Journal of Fracture, ISSN 0376-9429, E-ISSN 1573-2673, Vol. 169, no 1, p. 49-60Article in journal (Refereed)
    Abstract [en]

    The fracture toughness of rubber-like materials depends on several factors. First there is the surface energy required to create new crack surface at the crack tip. Second, a significant amount of energy is dissipated through viscoelastic processes in the bulk material around the crack tip. Third, if the crack propagates very rapidly, inertia effects will come into play and contribute to the fracture toughness. In the present study, a computational framework for studying high-speed crack growth in rubber-like solids under conditions of steady-state is proposed. Effects of inertia, viscoelasticity and finite strains are included. The main purpose of the study is to study the contribution of viscoelastic dissipation to the total work of fracture required to propagate a crack in a rubber-like solid. The model was fully able to predict experimental results in terms of the local surface energy at the crack tip and the total energy release rate at different crack speeds. In addition, the predicted distributions of stress and dissipation around the propagating crack tip are presented.

  • 6.
    Kroon, Martin
    et al.
    KTH, Superseded Departments, Solid Mechanics.
    Faleskog, Jonas
    KTH, Superseded Departments, Solid Mechanics.
    A probabilistic model for cleavage fracture with a length scale-influence of material parameters and constraint2002In: International Journal of Fracture, ISSN 0376-9429, E-ISSN 1573-2673, Vol. 118, no 2, p. 99-118Article in journal (Refereed)
    Abstract [en]

    A probabilistic model for the cumulative probability of failure by cleavage fracture with a material related length scale is developed in this study. The model aims at describing the random nature of fracture in ferritic steels in the brittle-to-ductile transition temperature region. The model derives from use of an exponential function to describe the distribution of microstructural entities eligible to take part in the fracture initiation process, where also a dependence on effective plastic strain is incorporated. A nonlocal stress measure, calculated as the average stress in a spherical volume, drives the contribution to failure probability of an infinitesimal material volume. The radius of the spherical volume enters as the material length in this model. This length has a significant influence on failure probability predictions in geometries exposed to strong stress gradients as found ahead of cracks. The material length is associated with a fracture toughness threshold value. In a fracture application three model parameters need to be estimated based on testing; a parameter directly related to the mean fracture toughness, a parameter that primarily is related to crack-tip constraint effects and the material length parameter. The model is explored in a parametric study showing model features in concord with typical features found in toughness distributions from fracture mechanics testing in the transition region.

  • 7.
    Nilsson, Fred L.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    A tentative method for determination of cohesive zone properties in soft materials2005In: International Journal of Fracture, ISSN 0376-9429, E-ISSN 1573-2673, Vol. 136, no 04-jan, p. 133-142Article in journal (Refereed)
    Abstract [en]

    A method is outlined for the determination of cohesive zone properties in soft materials. The goal of the study was to extend earlier work assuming linear kinematics and linear elasticity to include non-linear kinematics and finite elasticity Explicit results for cohesive traction determination are given and discussed. A comparison is made between expressing the cohesive law in a Lagrangian or an Eulerian description, respectively Some implications of either choice are discussed. Two suitable geometries for experimental use are analysed as examples of the method.

  • 8.
    Nilsson, Fred L.
    KTH, Superseded Departments, Solid Mechanics.
    Dynamic stress-intensity factors for an orthotropic infinite strip with a semi-infinite crack2000In: International Journal of Fracture, ISSN 0376-9429, E-ISSN 1573-2673, Vol. 104, no 3, p. L17-L21Article in journal (Refereed)
    Abstract [en]

    A clamped infinite strip of an orthotropic material and containing a semi-infinite crack is considered,. The strip is loaded by time-dependent translations of the boundaries and the dynamic stress-intensity factor is obtained using a path independent integral. The solution is found to be of the same form as for the corresponding isotropic case.

  • 9.
    Nilsson, Fred L.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Large displacement aspects on fracture testing with double cantilever beam specimens2006In: International Journal of Fracture, ISSN 0376-9429, E-ISSN 1573-2673, Vol. 139, no 2, p. 305-311Article in journal (Refereed)
    Abstract [en]

    The double cantilever beam specimen for fracture testing was investigated for large displacement conditions. J-expressions were derived for arbitrary loading of the beam-ends. As special cases two different loadings, transverse force and bending moment were studied. Explicit relations for use in experimental situations were derived.

  • 10. Sorensen, B. F.
    et al.
    Gamstedt, E. Kristofer
    Jacobsen, T. K.
    Equivalence of J integral and stress intensity factor approaches for large scale bridging problems2000In: International Journal of Fracture, ISSN 0376-9429, E-ISSN 1573-2673, Vol. 104, no 4, p. L31-L36Article in journal (Refereed)
    Abstract [en]

    The application of the J integral to problems involving large scale crack bridging is discussed. Using some simple examples for which close form analytical solutions exist, it is shown that there is a complete agreement between analysis based on stress intensity factors and the J integral. A simple method for deriving the bridging law from J integral measurements is outlined.

  • 11.
    Stec, Mateusz
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Faleskog, Jonas
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Influence of grain size on arrest of a dynamically propagating cleavage crack in ferritic steels-micromechanics2009In: International Journal of Fracture, ISSN 0376-9429, E-ISSN 1573-2673, Vol. 158, no 1, p. 51-71Article in journal (Refereed)
    Abstract [en]

    Cleavage fracture in ferritic steels is controlled by several critical steps. First a microcrack must nucleate, grow and overcome barriers, such as grain boundaries. The latter is examined here by use of a periodic, axisymmetric model representing two grains. A microcrack nucleated at the center in one grain is driven by a constant remotely applied stress towards the second grain. The cleavage planes of the grain in which the microcrack is nucleated coincide with the principal loading direction. In the adjacent grain, due to misalignment in possible cleavage planes, the propagation direction changes and separation occurs in mixed mode, involving both normal and shear separations. The temperature dependence of the mechanical properties of the material is accounted for by use of a temperature dependent elasto viscoplastic material model. The largest grain size that can arrest a rapidly propagating microcrack is defined as the critical grain size. The effects of stress state and temperature on the critical grain size are examined. The influence of mismatch in lattice orientation between two adjacent grains in terms of a tilt angle is both qualitatively and quantitatively described. It is shown that the critical grain size is influenced by plastic geometry change and prestraining, which depend on the applied stress state. The results also show that a microcrack can be arrested in an adjacent grain under specific conditions.

  • 12.
    Stec, Mateusz
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Faleskog, Jonas
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Micromechanical modeling of grain boundary resistance to cleavage crack propagation in ferritic steels2009In: International Journal of Fracture, ISSN 0376-9429, E-ISSN 1573-2673, Vol. 160, no 2, p. 151-167Article in journal (Refereed)
    Abstract [en]

    In ferritic steels a propagating cleavage microcrack changes its propagation direction as it advances from grain to grain. This is due to differences in the orientation of the cleavage planes of two neighboring grains. In order to reach a cleavage plane in a new grain, a microcrack must first penetrate the grain boundary. Grain boundaries therefore act as natural barriers in cleavage fracture. The influence of a grain boundary and the associated misorientation in cleavage planes on crack arrest is here examined using a 3D finite element model with axisymmetric periodicity, representing two grains whose cleavage planes are tilted and twisted relative to each other. The temperature dependent mechanical properties of ferrite are modeled using a temperature dependent viscoplastic response. The development of the crack front as the microcrack penetrates through a grain boundary is here presented. The influence of the twist misorientation on the critical grain size, defined as the largest grain size that can arrest a rapidly propagating microcrack, is examined in a temperature range corresponding to the ductile to brittle transition (DBT) region. It is shown that when both tilt and twist misorientation are present, the influence of tilt and twist, respectively, on crack growth resistance can be decoupled.

  • 13.
    Thesken, J.C.
    et al.
    KTH, Superseded Departments, Solid Mechanics.
    Gudmundson, Peter
    Swedish Institute of Composites.
    Application Of A Moving Variable Order Singular Element To Dynamic Fracture-Mechanics.1991In: International Journal of Fracture, ISSN 0376-9429, E-ISSN 1573-2673, Vol. 52, no 1, p. 47-65Article in journal (Refereed)
    Abstract [en]

    An elasto-dynamic moving element formulation incorporating a variable order singular element to enhance the local crack tip description is presented. The moving mesh zone is embedded in a finite global mesh providing a functional tool for the analysis of dynamic crack growth experiments. In the following, the necessary numerical techniques are developed and tested using problems possessing analytical solutions. The promising results reported here motivate further work to include viscoplastic material behavior in the formulation.

  • 14.
    Trädegård, Annika
    et al.
    KTH, Superseded Departments, Solid Mechanics.
    Nilsson, Fred
    KTH, Superseded Departments, Solid Mechanics.
    Östlund, Sören
    KTH, Superseded Departments, Solid Mechanics.
    J-Q characterization of propagating cracks1998In: International Journal of Fracture, ISSN 0376-9429, E-ISSN 1573-2673, Vol. 94, no 4, p. 357-370Article in journal (Refereed)
    Abstract [en]

    An investigation is performed to determine to what extent the state at a growing crack tip vicinity can be characterised by J and Q calculated from FE analyses of successively stationary crack tip positions. FE models in two-dimensionals of single edge notch bend and double edge cracked panel specimens with several different crack lengths are used to cover a range of load and constraint levels. The stress and strain fields are compared between different specimens keeping J- and Q-values equal. A remeshing technique in the commercial FE-code ABAQUS is used to enhance the efficiency of the analysis. The results show that the J-Q-theory provides reasonably accurate crack tip characterization also for growing cracks. This leads to the conclusion that FE analyses of successive stationary cracks rather than full FE propagation analyses are sufficient. The limit of validity for propagation is similar to the validation limit for the stationary case, although somewhat more restrictive.

  • 15.
    Zang, Weilin
    et al.
    KTH, Superseded Departments (pre-2005), Solid Mechanics.
    Gudmundson, Peter
    KTH, Superseded Departments (pre-2005), Solid Mechanics.
    A Boundary Integral Method For Internal Piece-Wise Smooth Crack Problems1988In: International Journal of Fracture, ISSN 0376-9429, E-ISSN 1573-2673, Vol. 38, no 4, p. 275-294Article in journal (Refereed)
    Abstract [en]

    A new boundary integral method for plane elasticity problems with internal piece-wise smooth cracksis presented. The method can be applied to both infinite and finite geometries. A numerical technique which combines a collocation method for the cracks and the standard BEM technique for the outer boundary is used to solve the integral equations. Numerical examples are presented and compared either to existing solutions or to FEM calculations. All of the results provided by the present method are shown to be very accurate for both smooth and kinked cracks in both finite and infinite geometries.

  • 16.
    Zang, W.L.
    et al.
    KTH, Superseded Departments, Solid Mechanics.
    Gudmundson, Peter
    KTH, Superseded Departments, Solid Mechanics.
    Kinked cracks in bonded half-planes modeled by an integral equation method1992In: International Journal of Fracture, ISSN 0376-9429, E-ISSN 1573-2673, Vol. 54, no 1, p. 65-78Article in journal (Refereed)
    Abstract [en]

    Based on the integral equation for resultant forces along a crack, a boundary integral equation method for the solution of kinked cracks in bonded half-planes is presented. The equation only contains a weak logarithmic singularity and is valid for every point along the crack lines. Numerical results are presented to illustrate the efficiency and reliability of the method.

  • 17.
    Östlund, Sören
    KTH, Superseded Departments, Solid Mechanics.
    Large scale yielding for dynamic crack growth in a strip geometry1991In: International Journal of Fracture, ISSN 0376-9429, E-ISSN 1573-2673, Vol. 49, no 3, p. 219-237Article in journal (Refereed)
    Abstract [en]

    Dynamic crack growth in a strip geometry has been studied by a convective formulation of the finite element method. The strip is assumed to be made of a material described by an elastic-viscoplastic constitutive equation and the loading conditions are plane strain mode I. The plastic strain-rates are characterized by a power-law overstress model giving an asymptotic elastic singularity at the crack tip. Two different types of loading on the strip geometry have been investigated. In the first geometry the horizontal boundaries parallel to the crack plane were subjected to prescribed displacements perpendicular to the crack plane and the crack tip was loaded in essentially the same way as for a crack in a plate subjected to tensile loading perpendicular to the crack. The second type of loading consisted of a prescribed rotation of the trailing edge in the moving finite element mesh. This created primarily bending loading of the structure.The crack tip energy flow has been calculated for different levels of yielding around the crack tip. The results are compared to the true small scale yielding solution obtained from a boundary layer analysis.The results reported indicate that for the tensile loading there exists a rather wide range of load levels for which the boundary layer solution gives a good description of the fields around the crack tip. For the bending loading the results indicate that the boundary layer solution is a correct description only in cases of extremely small scale yielding. Comparisons between large scale yielding and the boundary layer solution are also made for the effective stress and the effective plastic strain.

  • 18.
    Östlund, Sören
    KTH, Superseded Departments, Solid Mechanics.
    On numerical modeling and fracture criteria of dynamic elastic-viscoplastic crack growth1990In: International Journal of Fracture, ISSN 0376-9429, E-ISSN 1573-2673, Vol. 44, no 4, p. 283-299Article in journal (Refereed)
    Abstract [en]

    Dynamic steady-state small-scale yielding crack propagation in an elastic-viscoplastic structure is studied by a convective formulation of the finite element method. The loading condition is mode I plane strain.The plastic strain-rates are characterized by a power-law overstress model based on a general theory by Perzyna. For values of the stress exponent less than 3, the elastic strain-rates are more singular than the plastic strain-rates and consequently the near tip fields will exhibit an asymptotic elastic behaviour. The size of the zone where this elastic singularity dominates is typically of the order 10–3–10–5 of the size of the active plastic zone. These relatively small dimensions severely complicate the finite element modeling. Although the energy flow is calculated with a path-independent integral of J-integral type, its value will be dependent on the size of the near-tip elements unless extremely small finite elements are used. This is an important difference compared with many other situations, for example the elastic case and a stationary crack in a power-law hardening material, where the use of a path-independent integral improves the numerical accuracy even if the crack tip region is modeled with a rather coarse mesh. This size effect is discussed in detail. An application of the results with numerical data for a realistic situation shows that the crack tip energy flow might be vanishingly small compared to the energy dissipation in the plastic region. This indicates that the energy flow to the crack tip is perhaps not an appropriate parameter for the description of small-scale yielding crack growth in the present type of material model.The paper also contains an investigation of the introduction of a variable order singular element at the element positions adjacent to the crack tip. It is shown that this type of element does not improve the numerical behaviour in the present formulation.

  • 19.
    Östlund, Sören
    et al.
    KTH, Superseded Departments, Solid Mechanics.
    Karenlampi, P.
    Structural geometry effect on the size-scaling of strength2001In: International Journal of Fracture, ISSN 0376-9429, E-ISSN 1573-2673, Vol. 109, no 2, p. 141-151Article in journal (Refereed)
    Abstract [en]

    The sensitivity of the empirical exponent of Bazant's size-effect scaling law on structural geometry is clarified through numerical experiments. For large centre- cracked tension panels, made of a linearly softening material, the best-fitting exponent is 0.90, whereas for large edge-cracked panels it is 0.75. For edge-cracked panels, the value of the exponent increases as a function of increasing crack-length-to-width-ratio. The results indicate that with structures of brittleness numbers below unity, reliable predictions of strength require the size-effect scaling law to be fitted for any particular structural geometry.

1 - 19 of 19
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf