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  • 201.
    Karlsson, Stefan
    et al.
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Jonson, Bo
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Johansson, Marie
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Enquist, Bertil
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Single-Side Ion Exchange Strengthening of Holed Float Glass2012In: Nordic Conference on Ceramic and Glass Technology, 2012Conference paper (Other academic)
    Abstract [en]

    The fracture strength of oxide glasses is to a large degree influenced by other factors than the inherent strength of the bonds in the vitreous network such as surface defects. Due to the brittle nature of glass, mechanical processing decreases the strength substantially. The aim of this study was to investigate ion exchange strengthening also known as chemical strengthening of commercially available mechanically processed soda-lime-silicate float glass and to compare it with as-received float glass by means of flexural fracture load. The dimensions of the samples were 66±2 x 66±2 mm and two series had 7 mm diamond drilled holes in the centre of each sample while one series was as-received. Ion exchange of sodium ions by larger potassium ions were performed by treating the air-side of a series of samples with a KNO3:KCl mixture at 450 °C. The flexural fracture load of both untreated and ion exchanged holed samples was measured by means of the coaxial double ring test. The ion exchanged samples showed an arithmetic mean fracture load increase of approximately 140% compared to untreated holed float glass. The drilled hole decreases the arithmetic mean fracture load to approximately 25% of as-received float glass whilst the strengthening effect of the ion exchange improves it to around 65% of as-received float glass.

  • 202.
    Karlsson, Stefan
    et al.
    Linnaeus University, Faculty of Technology, Department of Building and Energy Technology.
    Jonson, Bo
    Linnaeus University, Faculty of Technology, Department of Building and Energy Technology.
    Johansson, Marie
    Linnaeus University, Faculty of Technology, Department of Building and Energy Technology.
    Enquist, Bertil
    Linnaeus University, Faculty of Technology, Department of Building and Energy Technology.
    The effect of single-side ion exchange on the flexural strength of plain and holed float glass containing a drilled hole2013In: European Journal of Glass Science and Technology. Part A: Glass Technology, ISSN 1753-3546, Vol. 54, no 2, p. 66-71Article in journal (Refereed)
    Abstract [en]

    The effect of single-side ion exchange (using a KNO3:KCl mixture) on the ring-on-ring flexural strength of float glass has been studied. Two ion exchanged series, treated at 450 and 515°C, were investigated. The ion exchanged samples showed approximately 160 respectively 100% increases in their arithmetic mean strength compared to as-received float glass. Furthermore, a series of samples containing drilled holes were studied in order to investigate the effect of single-side ion exchange on such common construction elements. The samples that contained drilled holes were ion exchanged at 450°C and showed around 140% increase of the fracture load compared to the untreated samples containing drilled holes. As a general observation, the ion exchange treatment induced ~110 MPa compressive stresses (515°C) and ~180 MPa compressive stresses (450°C). The ion exchanged samples showed no significant increase in stiffness. 

  • 203.
    Karlsson, Stefan
    et al.
    Linnaeus University, Faculty of Technology, Department of Building and Energy Technology.
    Jonson, Bo
    Linnaeus University, Faculty of Technology, Department of Building and Energy Technology.
    Reibstein, Sindy
    Institute of Glass and Ceramics, Friedrich-Alexander University of Erlangen-Nuremberg.
    Wondraczek, Lothar
    Institute of Glass and Ceramics, Friedrich-Alexander University of Erlangen-Nuremberg.
    Surface ruby colouring of float glass by sodium-copper ion exchange2013In: European Journal of Glass Science and Technology. Part A: Glass Technology, ISSN 1753-3546, Vol. 54, no 3, p. 100-107Article in journal (Refereed)
    Abstract [en]

    In this paper, colouration of the tin side of commercial soda lime silicate float glass by copper ion exchange is described and characterised. Data on the resulting concentration vs. depth profiles, absorbance vs. depth profiles, UV-Vis spectra  and CIE-Lab colour coordinates are reported. Fundamental aspects of the process of colouration are described and discussed. Optimum saturation of colouration is achieved after ion exchange at 520 °C for 10 h, or at 500 °C for 20 h, respectively. The depth of the coloured layer increases with increasing treatment time. At the same time, a linear dependency is found between the value of a and b in the CIE-Lab colour space for variations of treatment time and temperature. The latter indicates broad tunability of colouration between different shades of ruby and varying colour saturation. It is shown that colour arises from a redox reaction between copper species and residual tin ions, and that the depth of the coloured layer is governed by the position of the tin hump. The critical concentration of tin and copper to achieve colour formation was found to be ~0.25 mol% and >1 mol%, respectively.

  • 204.
    Karlsson, Stefan
    et al.
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Jonson, Bo
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Wondraczek, Lothar
    Institute of Glass and Ceramics, Friedrich-Alexander University of Erlangen-Nuremberg .
    Colouration of float glass by copper ion exchange2011Conference paper (Other academic)
  • 205.
    Karlsson, Stefan
    et al.
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Jonson, Bo
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Wondraczek, Lothar
    Institute of Glass and Ceramics, Friedrich-Alexander University of Erlangen-Nuremberg .
    Copper colouration of the surface of float glass by ion exchange2012Conference paper (Other academic)
  • 206.
    Karlsson, Stefan
    et al.
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Jonson, Bo
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Wondraczek, Lothar
    Institute of Glass and Ceramics, Friedrich-Alexander University Erlangen-Nürnberg.
    Copper, silver, rubidium and caesium ion exchange in soda-lime-silicate float glass by direct deposition and in line melting of salt pastes2012In: European Journal of Glass Science and Technology. Part A: Glass Technology, ISSN 1753-3546, Vol. 53, no 1, p. 1-7Article in journal (Refereed)
    Abstract [en]

    We report the change of surface composition on commercial soda-lime-silica (SLS) float glass which results from single-side exchange of Na+ by Cu+, Ag+, Rb+ and Cs+, respectively. Ion exchange is achieved by in line melting of a directly deposited salt paste in a prolonged annealing procedure. Concentration profiles obtained and computed effective diffusion coefficients, as well as apparent activation energies for diffusion, are reported. Depending on exchange species, treatment time and treatment temperature, the penetration depths are in the range of 10-20 μm for K+, Cu+, Rb+ and Cs+. A penetration depth of >100 μm can readily be obtained for Ag+.

  • 207.
    Karlsson, Stefan
    et al.
    RISE Research Institutes of Sweden, Sweden.
    Wondraczek, Lothar
    University of Jena, Germany.
    Ali, Sharafat
    Linnaeus University, Faculty of Technology, Department of Built Environment and Energy Technology.
    Jonson, Bo
    Linnaeus University, Faculty of Technology, Department of Built Environment and Energy Technology.
    Kinetics of chemical strengthening and trends in effective diffusion coefficients2019In: 25th International Congresson Glass (ICG 2019); ABSTRACT BOOK: June 9–14, 2019Boston, Massachusetts USA, American Ceramic Society, 2019, p. 167-167Conference paper (Refereed)
    Abstract [en]

    Alkali cation exchange has received significant attention with respect to introducing compressive stress in the glass surface, a process frequently called chemical strengthening. Besides mechanical properties may also other properties such as optical, electrical and chemical properties be modified using ion exchange of various monovalent ions. The mobility of monovalent ions varies and the relations of structural and effective diffusion coefficients may help to understand how to improve the ion exchange kinetics of soda lime silicates. We discuss the trends in the effective diffusion coefficients when exchanging Na+ for various monovalent cations (K+, Cu+, Ag+, Rb+ and Cs+) by their correlations to physico-chemical properties. The most significant correlations were found to be the bond dissociation energy and the electronic cation polarizability, indicating that electron localization and the rupture of bonds are of importance for the ion exchange rate.

  • 208.
    Karlsson, Stefan
    et al.
    RISE Res Inst Sweden;Friedrich Schiller Univ Jena, Germany.
    Wondraczek, Lothar
    Friedrich Schiller Univ Jena, Germany.
    Ali, Sharafat
    Linnaeus University, Faculty of Technology, Department of Built Environment and Energy Technology. Corning Inc, USA.
    Jonson, Bo
    Linnaeus University, Faculty of Technology, Department of Built Environment and Energy Technology.
    Trends in Effective Diffusion Coefficients for Ion-Exchange Strengthening of Soda-Lime-Silicate Glasses2017In: Frontiers in materials, ISSN 2296-8016, Vol. 4, article id UNSP 13Article in journal (Refereed)
    Abstract [en]

    Monovalent cations enable efficient ion-exchange processes due to their high mobility in silicate glasses. Numerous properties can be modified in this way, e.g., mechanical, optical, electrical, or chemical performance. In particular, alkali cation exchange has received significant attention, primarily with respect to introducing compressive stress into the surface region of a glass, which increases mechanical durability. However, most of the present applications rely on specifically tailored matrix compositions in which the cation mobility is enhanced. This largely excludes the major area of soda-lime-silicates (SLS) such as are commodity in almost all large-scale applications of glasses. Basic understanding of the relations between structural parameters and the effective diffusion coefficients may help to improve ion-exchanged SLS glass products, on the one hand in terms of obtainable strength and on the other in terms of cost. In the present paper, we discuss the trends in the effective diffusion coefficients when exchanging Na+ for various monovalent cations (K+, Cu+, Ag+, Rb+, and Cs+) by drawing relations to physicochemical properties. Correlations of effective diffusion coefficients were found for the bond dissociation energy and the electronic cation polarizability, indicating that localization and rupture of bonds are of importance for the ion-exchange rate.

  • 209.
    Konnerth, Johannes
    et al.
    BOKU-University of Natural Resources and Applied Life Sciences, Austria.
    Eiser, Martina
    Competence Center for Wood Composites and Wood Chemistry, Austria.
    Jäger, Andreas
    Vienna University of Technology, Austria.
    Bader, Thomas K.
    Vienna University of Technology, Austria.
    Hofstetter, Karin
    Follrich, Jürgen
    Competence Center for Wood Composites and Wood Chemistry, Austria.
    Ters, Thomas
    BOKU-University of Natural Resources and Applied Life Sciences, Austria.
    Hansmann, Christian
    Competence Center for Wood Composites and Wood Chemistry, Austria.
    Wimmer, Rupert
    ood Technology and Wood-based Composites Unit, Germany.
    Macro- and micro-mechanical properties of red oak wood (Quercus rubra L.) treated with hemicellulases2010In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 64, no 4, p. 447-453Article in journal (Refereed)
    Abstract [en]

    Red oak wood (Quercus rubra L.) samples were submitted to an enzymatic treatment with a commercial mixture of hemicellulases aiming at the selective depolymerization and removal of the hemicelluloses. Mechanical properties of treated samples were characterized and compared with untreated samples at two hierarchical levels. At the macrolevel, tensile properties revealed to be less sensitive to degradation of the cell wall matrix compared to compression and hardness properties. Results obtained through indentation at the microlevel indicated that hardness and the so-called reduced modulus of treated wood were significantly lowered. Accordingly, hardness and reduced elastic modulus have proven to be most sensitive to modification of the cell wall matrix by reducing the content of hemicelluloses. It is proposed that transversal and shear stresses, which are mainly carried by the cell wall matrix, are additional parameters having strong effects on elastic modulus obtained by nanoindentation. Micromechanical modeling was employed to confirm the observed changes. There is consistency between the measured and the modeled properties, obtained at both the microlevel and the macrolevel of wood.

  • 210.
    Kroon, Martin
    Royal Institute of Technology (KTH).
    A constitutive framework for modelling thin incompressible viscoelastic materials under plane stress in the finite strain regime2011In: Mechanics of time-dependant materials, ISSN 1385-2000, E-ISSN 1573-2738, Vol. 15, no 4, p. 389-406Article in journal (Refereed)
    Abstract [en]

    Rubbers and soft biological tissues may undergo large deformations and are also viscoelastic. The formulation of constitutive models for these materials poses special challenges. In several applications, especially in biomechanics, these materials are also relatively thin, implying that in-plane stresses dominate and that plane stress may therefore be assumed. In the present paper, a constitutive model for viscoelastic materials in the finite strain regime and under the assumption of plane stress is proposed. It is assumed that the relaxation behaviour in the direction of plane stress can be treated separately, which makes it possible to formulate evolution laws for the plastic strains on explicit form at the same time as incompressibility is fulfilled. Experimental results from biomechanics (dynamic inflation of dog aorta) and rubber mechanics (biaxial stretching of rubber sheets) were used to assess the proposed model. The assessment clearly indicates that the model is fully able to predict the experimental outcome for these types of material.

  • 211.
    Kroon, Martin
    Royal Institute of Technology, (KTH).
    A constitutive model for strain-crystallising rubber-like materials2010In: Mechanics of materials (Print), ISSN 0167-6636, E-ISSN 1872-7743, Vol. 42, no 9, p. 873-885Article in journal (Refereed)
    Abstract [en]

    In the present paper, a constitutive model for strain-crystallising rubber is proposed. The constitutive behaviour is formulated in terms of a strain energy function, where the full network approach is adopted. The Arrhenius equation provides the basis for the crystallite nucleation law. The full network approach allows for the development of an anisotropic crystal structure. The model was applied to experimental results from uniaxial tensile tests. Strain-crystallisation causes a hysteresis in the stress–stretch relation, but according to the model predictions, the effect of crystallisation is not sufficient to explain the mechanical hysteresis observed in the tensile tests. Hence, additional viscoelasticity associated with amorphous polymer chains must be included. The model was fully able to predict both the stress vs. stretch relations and the crystallinity vs. stretch relations from the experiments.

  • 212. Kroon, Martin
    A Probabilistic Model for Cleavage Fracture with a Length Scale2003In: Presented at 5th Euromech Solid Mechanics Conference, 17-22 August, 2003, Thessaloniki, Greece, 2003Conference paper (Refereed)
  • 213.
    Kroon, Martin
    Royal Institute of Technology KTH.
    A theoretical assessment of the influence of myosin filament dispersion on smooth muscle contraction2011In: Presented at ASME Summer Bioengineering Conference, 22-25 June, 2011, ASME Press, 2011, p. 145-146Conference paper (Refereed)
    Abstract [en]

    A new constitutive model for the biomechanical behavior of smooth muscle tissue is employed to investigate the influence of statistical dispersion in the orientation of myosin filaments. The number of activated cross-bridges between the actin and myosin filaments governs the contractile force generated by the muscle and also the contraction speed. A strain-energy function is used to describe the mechanical behavior of the smooth muscle tissue. The predictions from the constitutive model are compared to histological and isometric tensile test results for smooth muscle tissue from swine carotid artery. In order to be able to predict the active stress at different muscle lengths, a filament dispersion significantly larger than the one observed experimentally was required. Furthermore, a comparison of the predicted active stress for a case of uniaxially oriented myosin filaments and a case of filaments with a dispersion based on the experimental histological data shows that the difference in generated stress is noticeable but limited. Thus, the results suggest that myosin filament dispersion alone cannot explain the increase in active muscle stress with increasing muscle stretch.

  • 214. Kroon, Martin
    A Theoretical Model for Saccular Cerebral Aneurysm Growth: Deformation and Stress Analysis2007In: Presented at Summer Bioengineering Conference, 20-24 June, 2007, Keystone, Colorado, 2007Conference paper (Refereed)
  • 215.
    Kroon, Martin
    Royal Institute of Technology (KTH).
    An 8-chain model for rubber-like materials accounting for non-affine chain deformations and topological constraints2011In: Journal of elasticity, ISSN 0374-3535, E-ISSN 1573-2681, Vol. 102, no 2, p. 99-116Article in journal (Refereed)
    Abstract [en]

    Several industrial applications involve rubber and rubber-like materials, and it is important to be able to predict the constitutive response of these materials. In the present paper, a new constitutive model for rubber-like solids is proposed. The model is based on the 8-chain concept introduced by Arruda and Boyce (J. Mech. Phys. Solids 41, 389–412, 1993) to which two new components are added. Real polymer networks do not deform affinely, and in the proposed model this is accounted for by the inclusion of an elastic spring, acting in series with the representative polymer chain. Furthermore, real polymer chains are not completely free to move, which is modelled by imposing a topological constraint on the transverse motions of the representative polymer chain. The model contains five model parameters and these need to be determined on the basis of experimental data. Three experimental studies from the literature were used to assess the proposed model. The model was able to reproduce experimental data performed under conditions of uniaxial tension, generalised plane deformation, and biaxial tension with an excellent accuracy. The strong predictive abilities together with the numerically efficient structure of the model make it suitable for implementation in a finite element context.

  • 216.
    Kroon, Martin
    Royal Institute of Technology, (KTH).
    An asymptotic analysis of dynamic crack growth in rubber2011In: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 78, no 17, p. 3111-3122Article in journal (Refereed)
    Abstract [en]

    Asymptotic analyses of the mechanical fields in front of stationary and propagating cracks are important for several reasons. For example, they facilitate the understanding of the mechanical and physical state in front of crack tips, and they enable prediction of crack growth. Furthermore, efficient modelling of arbitrary crack growth by use of XFEM (extended finite element method) requires accurate knowledge of the asymptotic crack tip fields. The present study focuses on the asymptotic fields in front of a crack that propagates dynamically in rubber. Static analyses of this type of problem have been made in previous studies. In order to be able to compare the present results with these earlier studies, the constitutive model from Knowles and Sternberg (J. Elast. 3:67–107, 1973) was adopted. It is assumed that viscoelastic stresses become negligible compared with the singular elastic stresses close to the crack tip. The present analysis shows that in materials with a significant hardening, the inertia term in the equations of motion becomes negligible in the asymptotic analysis. However, for a neoHookean type of model, inertia comes into play and causes a maximum theoretical crack speed that equals the shear wave speed.

  • 217. Kroon, Martin
    Analysis of dynamic crack propagation in rubber2012In: Presented at 10th World Congress on Computational Mechanics, 8-13 July, 2012, 2012Conference paper (Refereed)
  • 218.
    Kroon, Martin
    Royal Institute of Technology, (KTH).
    Asymptotic mechanical fields at the tip of a mode I crack in rubber-like solids2014In: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 51, no 10, p. 1923-1930Article in journal (Refereed)
    Abstract [en]

    Asymptotic analyses of the mechanical fields in front of stationary and propagating cracks facilitate the understanding of the mechanical and physical state in front of crack tips, and they enable prediction of crack growth and failure. Furthermore, efficient modelling of arbitrary crack growth by use of XFEM (extended finite element method) requires accurate knowledge of the asymptotic crack tip fields. In the present work, we perform an asymptotic analysis of the mechanical fields in the vicinity of a propagating mode I crack in rubber. Plane deformation is assumed, and the material model is based on the Langevin function, which accounts for the finite extensibility of polymer chains. The Langevin function is approximated by a polynomial, and only the term of the highest order contributes to the asymptotic solution. The crack is predicted to adopt a wedge-like shape, i.e. the crack faces will be straight lines. The angle of the wedge and the order of the stress singularity depend on the hardening of the strain energy function. The present analysis shows that in materials with a significant hardening, the inertia term in the equations of motion becomes negligible in the asymptotic analysis. Hence, there is no upper theoretical limit to the crack speed.

  • 219.
    Kroon, Martin
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Dynamic Crack propagation in Rubber2016In: Presented at 24th International Congress of Theoretical and Applied Mechanics (ICTAM), Montreal, Canada, August 21-26, 2016, 2016Conference paper (Refereed)
  • 220.
    Kroon, Martin
    Malmö University.
    Dynamic Energy Release Rates in Rubber2016In: Presented at European Congress on Computational Methods in Applied Sciences and Engineering (ECCOMAS), Crete, Greece, June 5-10, 2016, 2016Conference paper (Refereed)
  • 221.
    Kroon, Martin
    Royal Institute of Technology, (KTH).
    Dynamic steady-state analysis of crack propagation in rubber-like solids using an extended finite element method2012In: Computational Mechanics, ISSN 0178-7675, E-ISSN 1432-0924, Vol. 49, no 1, p. 73-86Article in journal (Refereed)
    Abstract [en]

    In the present study, a computational framework for studying high-speed crack growth in rubber-like solids under conditions of plane stress and steady-state is proposed. Effects of inertia, viscoelasticity and finite strains are included. The main purpose of the study is to examine the contribution of viscoelastic dissipation to the total work of fracture required to propagate a crack in a rubber-like solid. The computational framework builds upon a previous work by the present author (Kroon in Int J Fract 169:49-60, ). 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. The predicted distributions of stress and dissipation around the propagating crack tip are presented. The predicted crack tip profiles also agree qualitatively with experimental findings.

  • 222. Kroon, Martin
    Dynamic steady-state crack propagation in rubber-like solids2011Conference paper (Refereed)
  • 223.
    Kroon, Martin
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Energy release rates in rubber during dynamic crack propagation2015In: Presented at ASME Applied Mechanics and Material Conference, July 25-29, 2015, 2015Conference paper (Refereed)
  • 224.
    Kroon, Martin
    Royal Institute of Technology, (KTH).
    Energy release rates in rubber during dynamic crack propagation2014In: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 51, no 25-26, p. 4419-4426Article in journal (Refereed)
    Abstract [en]

    The theoretical understanding of the fracture mechanics of rubber is not as well developed as for other engineering materials, such as metals. The present study is intended to further the understanding of the dissipative processes that take place in rubber in the vicinity of a propagating crack tip. This dissipation contributes significantly to the total fracture toughness of the rubber and is therefore of great interest from a fracture mechanics point of view. To study this, a computational framework for analysing high-speed crack growth in a biaxially stretched rubber under plane stress is therefore formulated. The main purpose is to investigate the energy release rates required for crack propagation under different modes of biaxial stretching. The results show, that inertia comes into play when the crack speed exceeds about 50 m/s. The total work of fracture by far exceeds the surface energy consumed at the very crack tip, and the difference must be attributed to dissipative damage processes in the vicinity of the crack tip. The size of this damage/dissipation zone is expected to be a few millimetres.

  • 225.
    Kroon, Martin
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Experimental measurement of energy release rate in polyethylene2017In: The 14th International Conference on Fracture, Rhodes, Greece, June 18-23, 2017, Rhodes, 2017Conference paper (Refereed)
  • 226. Kroon, Martin
    Material Characterization of Biological Membranes by Inverse Analysis2008In: Presented at 22nd International Congress of Theoretical and Applied Mechanics, 24-30 August, 2008, 2008Conference paper (Refereed)
  • 227.
    Kroon, Martin
    Royal Institute of Technology (KTH).
    Material Properties of Inhomogeneous Hyperelastic Membranes Assessed by Inverse Analysis2009Conference paper (Refereed)
  • 228. Kroon, Martin
    Modelling of fibroblast-controlled restructuring of collagen gels2010In: Presented at 6th World Congress in Biomechanics, 1-6 August, 2010, 2010Conference paper (Refereed)
  • 229. Kroon, Martin
    Numerical analysis of steady-state crack growth in rubber2012In: Presented at 10th World Congress on Computational Mechanics, 8-13 July, 2012, 2012Conference paper (Refereed)
  • 230. Kroon, Martin
    Numerical analysis of steady-state crack growth in rubber-like solids2011In: Presented at US National Congress on Computational Mechanics, 24-28 July, 2011, 2011Conference paper (Refereed)
  • 231.
    Kroon, Martin
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Rate-Dependent Crack Propagation in Polyethylene2019In: Proceedings of the First International Conference on Theoretical, Applied and Experimental Mechanics / [ed] Gdoutos, E E, Springer, 2019, p. 194-198Conference paper (Refereed)
    Abstract [en]

    Crack growth in semi-crystalline polymers, represented by polyethylene, is considered. The material considered comes in plates that had been created through an injection-molding process. Hence, the material was taken to be orthotropic. Material directions were identified as MD: molding direction, CD: transverse direction, TD: thickness direction. Uniaxial tensile testing was performed in order to establish the direction-specific elastic-plastic behaviour of the polymer. In addition, the fracture mechanics properties of the material was determined by performing fracture mechanics testing on plates with side cracks of different lengths. The fracture mechanics tests were filmed using a video camera. Based on this information, the force vs. load-line displacement could be established for the fracture mechanics tests, in which also the current length of the crack was indicated, since crack growth took place. Crack growth was modelled using a rate-dependent cohesive zone. The problem was analyzed using Abaqus, and the crack growth experiments were simulated. The experiments could be well reproduced. Furthermore, the direction-specific work of fracture had been established from the experiments and these energies could be compared to the values of the J-integral from the simulations for the different crack lengths.

  • 232. Kroon, Martin
    Saccular Aneurysm Growth in a Human Middle Cerebral Aneurysm: Deformation and Stress Analysis2007In: Presented at 44th Annual Meeting of the Society of Engineering Science, 21-24 October, 2007, 2007Conference paper (Refereed)
  • 233. Kroon, Martin
    Some aspects of crack propagation in rubber2015In: Presented at 5th B. Broberg Symposium, August 24-25, 2015, 2015Conference paper (Refereed)
  • 234.
    Kroon, Martin
    Royal Institute of Technology, (KTH).
    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.

  • 235. Kroon, Martin
    Strengthening and Remodelling of Collagenous Networks2009In: Presented at 7th Euromech Solid Mechanics Conference, 7-11 September, 2009, 2009Conference paper (Refereed)
  • 236. Kroon, Martin
    Transiently cross-linked actin networks2012In: Presented at 10th World Congress on Computational Mechanics, 8-13 July, 2012, 2012Conference paper (Refereed)
  • 237.
    Kroon, Martin
    et al.
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Andreasson, E.
    Tetra Pak, Sweden;Blekinge Institute of Technology, Sweden.
    Persson Jutemar, E.
    Tetra Pak, Sweden.
    Petersson, V.
    Tetra Pak, Sweden.
    Persson, L.
    Tetra Pak, Sweden.
    Dorn, Michael
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Olsson, P.A.T.
    Malmö University, Sweden.
    Anisotropic elastic-viscoplastic properties of at finite strains of of injection-moulded low-density polyethylene2018In: Experimental mechanics, ISSN 0014-4851, E-ISSN 1741-2765, Vol. 58, no 1, p. 75-86Article in journal (Refereed)
    Abstract [en]

    Injection-moulding is one of the most common manufacturing processes used for polymers. In many applications, the mechanical properties of the product is of great importance. Injection-moulding of thin-walled polymer products tends to leave the polymer structure in a state where the mechanical properties are anisotropic, due to alignment of polymer chains along the melt flow direction. The anisotropic elastic-viscoplastic properties of low-density polyethylene, that has undergone an injection-moulding process, are therefore examined in the present work. Test specimens were punched out from injection-moulded plates and tested in uniaxial tension. Three in-plane material directions were investigated. Because of the small thickness of the plates, only the in-plane properties could be determined. Tensile tests with both monotonic and cyclic loading were performed, and the local strains on the surface of the test specimens were measured using image analysis. True stress vs. true strain diagrams were constructed, and the material response was evaluated using an elastic-viscoplasticity law. The components of the anisotropic compliance matrix were determined together with the direction-specific plastic hardening parameters.

  • 238.
    Kroon, Martin
    et al.
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Andreasson, Eskil
    Tetra Pak.
    Modeling of damage and crack growth in semi-crystalline polymers2017In: Proceedings of NSCM 30: The 30th Nordic Seminar on Computational Mechanics, 25-27 October, 2017 / [ed] J. Høgsberg. N.L. Pedersen, DTU Mechanical Engineering , 2017, p. 108-108Conference paper (Refereed)
    Abstract [en]

    t. Crack growth in semi-crystalline polymers, represented by polyethylene, is considered. The material considered comes in plates that had been created through an injection-molding process. Hence, the material was taken to be orthotropic. Material directions were identified as MD: molding direction, CD: transverse direction, TD: thickness direction. Uniaxial tensile testing was performed in order to establish the direction-specific elastic-plastic behaviour of the polymer. In addition, the fracture mechanics properties of the material was determined by performing fracture mechanics testing on plates with side cracks of different lengths. The fracture mechanics tests were filmed using a video camera. Based on this information, the force vs. load-line displacement could be established for the fracture mechanics tests, in which also the current length of the crack was indicated, since crack growth took place. In parallel to the experimental testing, an anisotropic plasticity model for finite strains was developed, which accounts for orthotropic elasticity and orthotropic plastic yielding and hardening. That plasticity model was implemented as a user subroutine in Abaqus. The crack growth experiments were then simulated using Abaqus, using the implemented plasticity model in combination with a damage model. Different types of crack initiation and growth criteria were explored, and the force-displacement-crack length data from the experiments could be well reproduced. Furthermore, the direction-specific work of fracture had been established from the experiments and these energies could be compared to the values of the J-integral from the simulations for the different crack lengths.

  • 239.
    Kroon, Martin
    et al.
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Andreasson, Eskil
    Tetra Pak.
    Olsson, Pär
    Malmö University.
    Assessment of fracture energy of polyethylene2017In: Svenska mekanikdagar 2017 Uppsala 12-13 juni, Uppsala universitet, 2017, p. 49-49Conference paper (Refereed)
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  • 240.
    Kroon, Martin
    et al.
    Malmö University.
    Faleskog, Jonas
    A J2-J3-dependent constitutive model for porous plasticity2016In: Presented at International Symposium on Plasticity, Big Island, Hawaii, January 3-9, 2016, 2016Conference paper (Refereed)
  • 241.
    Kroon, Martin
    et al.
    Royal Institute of Technology.
    Faleskog, Jonas
    Royal Institute of Technology.
    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.

  • 242.
    Kroon, Martin
    et al.
    Royal Institute of Technology.
    Faleskog, Jonas
    Royal Institute of Technology.
    Influence of crack deflection into the carbide/ferrite interface on cleavage fracture initiation in ferritic steels2008In: Mechanics of materials (Print), ISSN 0167-6636, E-ISSN 1872-7743, Vol. 40, no 8, p. 695-707Article in journal (Refereed)
    Abstract [en]

    In this and a companion study (Kroon, M., Faleskog, J., 2005. Micromechanics of cleavage fracture initiation in ferritic steels by carbide cracking. J. Mech. Phys. Solids 53, 171–196), the initiation of cleavage fracture in ferritic steels is studied. The initiation is modelled explicitly in the form of a microcrack, which nucleates in a brittle carbide and propagates into the surrounding ferrite. The carbide is modelled as an elastic cylinder and the ferrite as an elastic viscoplastic material. The crack growth is modelled using a cohesive surface, in which the tractions are governed by a modified exponential cohesive law. The advancing microcrack, which has nucleated in the carbide, may either continue into the ferrite or deflect into the interface between the carbide and the ferrite. Special attention is given to the influence of the mode mixity factor ββ, which is defined as the ratio between the shear and tensile strength of the interface between the carbide and the ferrite. Crack growth in the interface occurs in shear mode and is driven by a fibre loading mechanism. For mode mixity values β⩽0.2β⩽0.2, the crack deflects into the interface. The results indicate that crack growth in the interface can have a profound influence on the macroscopic fracture toughness of ferritic steels.

  • 243.
    Kroon, Martin
    et al.
    Royal Institute of Technology.
    Faleskog, Jonas
    Royal Institute of Technology.
    Micromechanics of cleavage fracture initiation in ferritic steels by carbide cracking2005In: Journal of the mechanics and physics of solids, ISSN 0022-5096, E-ISSN 1873-4782, Vol. 53, no 1, p. 171-196Article in journal (Refereed)
    Abstract [en]

    Cleavage fracture in ferritic steels is often initiated in brittle carbides randomly distributed in the material. The carbides break as a result of a fibre loading mechanism in which the stress levels in the carbides are raised, as the surrounding ferrite undergoes plastic deformation. The conditions in the vicinity of the nucleated micro-crack will then determine whether the crack will penetrate or be arrested by the ferrite. The ferrite is able to arrest nucleated cracks through the presence of mobile dislocations, which blunt and shield the microcrack and thus lowers the stresses at the crack tip. Hence, the macroscopic toughness of the material directly depends on the ability of the ferrite to arrest nucleated micro-cracks and in turn on the plastic rate sensitivity of the ferrite. The initiation of cleavage fracture is here modelled explicitly in the form of a micro-crack, which nucleates in a brittle carbide and propagates into the surrounding ferrite. The carbide is modelled as an elastic cylinder or in a few cases an elastic sphere and the ferrite as an elastic viscoplastic material. The crack growth is modelled using a cohesive surface, where the tractions are governed by a modified exponential cohesive law. It is shown that the critical stress, required to propagate a microcrack from a broken carbide, increases with decreasing plastic rate sensitivity of the ferrite. The results also show that a low stress triaxiality and a high aspect ratio of the carbide promote the initiation of cleavage fracture from a broken carbide.

  • 244.
    Kroon, Martin
    et al.
    Royal Institute of Technology, (KTH).
    Faleskog, Jonas
    Royal Institute of Technology, (KTH).
    Numerical implementation of a J2- and J3-dependent plasticity model based on a spectral decomposition of the stress deviator2013In: Computational Mechanics, ISSN 0178-7675, E-ISSN 1432-0924, Vol. 52, no 5, p. 1059-1070Article in journal (Refereed)
    Abstract [en]

    A new plasticity model with a yield criterion that depends on the second and third invariants of the stress deviator is proposed. The model is intended to bridge the gap between von Mises’ and Tresca’s yield criteria. An associative flow rule is employed. The proposed model contains one new non-dimensional key material parameter, that quantifies the relative difference in yield strength between uniaxial tension and pure shear. The yield surface is smooth and convex. Material strain hardening can be ascertained by a standard uniaxial tensile test, whereas the new material parameter can be determined by a test in pure shear. A fully implicit backward Euler method is developed and presented for the integration of stresses with a tangent operator consistent with the stress updating scheme. The stress updating method utilizes a spectral decomposition of the deviatoric stress tensor, which leads to a stable and robust updating scheme for a yield surface that exhibits strong and rapidly changing curvature in the synoptic plane. The proposed constitutive theory is implemented in a finite element program, and the influence of the new material parameter is demonstrated in two numerical examples.

  • 245.
    Kroon, Martin
    et al.
    Royal Institute of Technology.
    Faleskog, Jonas
    Royal Institute of Technology.
    Öberg, Hans
    Royal Institute of Technology.
    A probabilistic model for cleavage fracture with a length scale: parameter estimation and predictions of growing crack experiments2008In: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 75, no 8, p. 2398-2417Article in journal (Refereed)
    Abstract [en]

    A probabilistic model for the cumulative probability of failure by cleavage fracture was applied to experimental results where cleavage fracture was preceded by ductile crack growth. The model, introduced by Kroon and Faleskog [Kroon M, Faleskog J. A probabilistic model for cleavage fracture with a length scale – influence of material parameters and constraint. Int J Fract 2002;118:99–118], includes a non-local stress with an associated material related length scale, and it also includes a strain measure to account for the number of nucleated cleavage initiation sites. The experiments were performed on single edge cracked bend test specimens with three different crack lengths at the temperature 85 °C, which is in the upper transition region for the steel in question. The ductile rupture process is modelled using the cell model for nonlinear fracture mechanics. The original cleavage fracture model had to be modified in order to account for the substantial number of cleavage initiators being consumed by the ductile process. With this modification, the model was able to accurately capture the experimental failure probability distribution.

  • 246.
    Kroon, Martin
    et al.
    Royal Institute of Technology.
    Faleskog, Jonas
    Royal Institute of Technology.
    Öberg, Hans
    Royal Institute of Technology.
    A probabilistic model for cleavage fracture with a length scale: parameter estimation and predictions of stationary crack experiments2004In: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 71, no 1, p. 57-79Article in journal (Refereed)
    Abstract [en]

    This study presents a large experimental investigation in the transition temperature region on a modified A508 steel. Tests were carried out on single-edge-notch-bend specimens with three different crack depth over specimen width ratios to capture the strong constraint effect on fracture toughness. Three test temperatures were considered, covering a range of 85 °C. All specimens failed by cleavage fracture prior to ductile tearing. A recently proposed probabilistic model for the cumulative failure by cleavage was applied to the comprehensive sets of experimental data. This modified weakest link model incorporates a length scale, which together with a threshold stress reduce the scatter in predicted toughness distributions as well as introduces a fracture toughness threshold value. Model parameters were estimated by a robust procedure, which is crucial in applications of probabilistic models to real structures. The conformity between predicted and experimental toughness distributions, respectively, were notable at all the test temperatures.

  • 247.
    Kroon, Martin
    et al.
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Olsson, P.
    Malmö University.
    Andreasson, E.
    Tetra Pak.
    Petersson, V.
    Estimation of the essential work of fracture of for an LDPE material2017In: The 8th International Conference on Fracture of Polymers, Composites and Adhesives, Les Diablerets, Schwitzerland, 10-14 September, 2017, 2017Conference paper (Refereed)
  • 248.
    Kroon, Martin
    et al.
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Rubin, M. B.
    Technion Israel Inst Technol, Israel.
    Influence of thermal recovery on predictions of the residual mechanical state during melting and solidification2020In: Mechanics of materials (Print), ISSN 0167-6636, E-ISSN 1872-7743, Vol. 141, p. 1-12, article id 103258Article in journal (Refereed)
    Abstract [en]

    A thermomechanically consistent Eulerian plasticity model with work hardening is adopted for studying the residual mechanical state resulting from loading at elevated temperatures. The isotropic plasticity model includes the standard effect of thermal softening as well as specific modeling of thermal recovery. The model parameters and functions were calibrated to data for an austenitic stainless steel 316L. The model is applied in two numerical examples: a case of uniaxial tension and a circular disk that is exposed to a temperature load. The influence of thermal recovery is examined for each example by comparing the response of the complete model with thermal recovery to that when thermal recovery is omitted. The results of the second example indicate the importance of modeling thermal recovery for accurate prediction of residual stresses for problems dealing with melting and solidification.

  • 249.
    Kumar, Anuj
    et al.
    Natural Resources Institute Finland (Luke), Finland.
    Ryparová, Pavla
    Czech Technical University in Prague, Czech Republic.
    Hosseinpourpia, Reza
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Adamopoulos, Stergios
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Prošek, Zdeněk
    Czech Technical University in Prague, Czech Republic.
    Žigone, Jure
    Czech Technical University in Prague, Czech Republic.
    Petrič, Marko
    University of Ljubljana, Slovenia.
    Hydrophobicity and resistance against microorganisms of heat and chemically crosslinked poly(vinyl alcohol) nanofibrous membranes2019In: Chemical Engineering Journal, ISSN 1385-8947, E-ISSN 1873-3212, Vol. 360, p. 788-796Article in journal (Refereed)
    Abstract [en]

    Poly(vinyl alcohol) (PVA) is a water-soluble, semi-ionic and biocompatible polymer with excellent chemical and thermal stability. The chemical crosslinking of PVA membrane improve its stability towards humidity and water. In the present work, PVA nanofibrous membranes were fabricated using roller electrospinning techniques. The prepared membranes were crosslinked by heat treatment, glutaraldehyde dipping, and glutaraldehyde vapour. Furthermore, octadecyltrichlorosilane (OTS) treatment was used for hydrophobization of the crosslinked membranes. The prepared crosslinked membranes were analysed by scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR). The hydrophobization of PVA nanofibrous membranes were analysed by employing optical goniometer and auto-dynamic vapour sorption (AVS) techniques. Further, the PVA membranes were tested against algae and mould growth at in-vitro laboratory conditions. The SEM and FTIR results revealed significant differences in the morphology of the PVA nanofibrous membranes and in chemical bond formation due to crosslinking treatments. Water contact angle and AVS data confirmed a hydrophobization of PVA membranes by the treatments.

  • 250.
    Kumar, Anuj
    et al.
    Czech Technical University in Prague, Czech Republic ; University Centre for Energy Efficient Buildings of Technical University in Prague, Czech Republic.
    Ryparová, Pavla
    Czech Technical University in Prague, Czech Republic.
    Škapin, Andrijana Sever
    Slovenian National Building and Civil Engineering Institute, Slovenia.
    Humar, Miha
    University of Ljubljana, Slovenia.
    Pavlič, Matjaž
    University of Ljubljana, Slovenia.
    Tywoniak, Jan
    Czech Technical University in Prague, Czech Republic ; University Centre for Energy Efficient Buildings of Technical University in Prague, Czech Republic.
    Petr, Hajek
    Czech Technical University in Prague, Czech Republic ; University Centre for Energy Efficient Buildings of Technical University in Prague, Czech Republic.
    Žigon, Jure
    University of Ljubljana, Slovenia.
    Petrič, Marko
    University of Ljubljana, Slovenia.
    Influence of surface modification of wood with octadecyltrichlorosilane on its dimensional stability and resistance against Coniophora puteana and molds2016In: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 23, p. 3249-3263Article in journal (Refereed)
    Abstract [en]

    A relatively new approach for wood protection against fungal decay is based on hydrophobization of wood and on lowering its moisture content. Water repellence of wood can be increased by polymerization of hydrophobic monomers in wood cell walls. It was found that Norway spruce wood after treatment with octadecyltrichlorosilane exhibited reduced water uptake by the wood cell walls, lowered water vapour sorption, and significantly increased dimensional stability of wood in terms of anti-swelling efficiency. Hydrophobicity and lower equilibrium moisture content were shown to cause increased resistance of the treated samples against brown-rot decay and molds.

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