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Gudmundson, P. & Dahlberg, C. F. O. (2019). Isotropic strain gradient plasticity model based on self-energies of dislocations and the Taylor model for plastic dissipation. International journal of plasticity, 121, 1-20
Open this publication in new window or tab >>Isotropic strain gradient plasticity model based on self-energies of dislocations and the Taylor model for plastic dissipation
2019 (English)In: International journal of plasticity, ISSN 0749-6419, E-ISSN 1879-2154, Vol. 121, p. 1-20Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
PERGAMON-ELSEVIER SCIENCE LTD, 2019
Keywords
Strain gradient plasticity, Size effects, Initial yield stress, Dislocation mechanics
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-261940 (URN)10.1016/j.ijplas.2019.05.004 (DOI)000487566600001 ()
Note

QC 20191015

Available from: 2019-10-15 Created: 2019-10-15 Last updated: 2019-10-15Bibliographically approved
Mussa, A., Lindbergh, G., Klett, M., Gudmundson, P., Svens, P. & Lindström, R. (2018). Inhomogeneous active layer contact loss in a cycled prismatic lithium-ion cell caused by the jelly-roll curvature. Journal of Energy Storage, 20, 213-217
Open this publication in new window or tab >>Inhomogeneous active layer contact loss in a cycled prismatic lithium-ion cell caused by the jelly-roll curvature
Show others...
2018 (English)In: Journal of Energy Storage, E-ISSN 2352-152X, Vol. 20, p. 213-217Article in journal (Refereed) Published
Abstract [en]

Internal resistance is a key parameter that affects the power, energy, efficiency, lifetime, and safety of a lithium-ion battery. It grows due to chemical and mechanical battery wear during ageing. In this work, the effect of the jelly-roll winding curvature on impedance rise is investigated. NMC electrode samples, harvested from the curved as well as the flat regions of the jelly-roll from cycle-aged and calendar-aged prismatic cells (25 Ah, hard casing) are investigated by electrochemical impedance spectroscopy. After cycling, larger impedance rise is observed at the outer radius (concave) of the curved region compared to the inner radius (convex) or the flat region of the jelly-roll, and the difference increases with a decrease in the jelly-roll radius of curvature, from the cell skin towards the core. To identify the causes behind the observed difference in the impedance rise, investigations at different external compression (0 and 2.5 MPa) and temperature (5 and 25 °C) are performed. The results show that contact loss between the current collector and the active layer is the main source of the difference in impedance rise. Mechanical mechanisms that may cause the contact loss are discussed and design recommendations to mitigate the rise in impedance are given. 

Place, publisher, year, edition, pages
Elsevier Ltd, 2018
Keywords
Bending stress, Contact loss, Curvature, Diffusion induced stress (DIS), Lithium-ion battery, Mechanical ageing, Electrochemical impedance spectroscopy, Ions, Stresses, Diffusion induced stresses (DIS), Lithium-ion batteries
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-236555 (URN)10.1016/j.est.2018.09.012 (DOI)000451147100021 ()2-s2.0-85054131101 (Scopus ID)
Funder
Swedish Energy Agency, 30770-3
Note

Funding text: This work was supported by the Swedish Energy Agency ( 30770-3 ) under the program Energy Efficient Vehicles, the StandUp for Energy, the Battery Fund Program, and Swedish Electromobility Centre. Dr. Fernanda Marzano (Scania CV AB) is acknowledged for helping with the cell opening. Appendix A. QC 20181127

Available from: 2018-11-27 Created: 2018-11-27 Last updated: 2018-12-11Bibliographically approved
Gudmundsson, P. (2016). Foreword (president, KTH). Paper presented at 19 June 2016 through 23 June 2016. 6th International Congress on Arsenic in the Environment, AS 2016, xxxv-xxxvi
Open this publication in new window or tab >>Foreword (president, KTH)
2016 (English)In: 6th International Congress on Arsenic in the Environment, AS 2016, p. xxxv-xxxviArticle in journal (Refereed) Published
Place, publisher, year, edition, pages
CRC Press/Balkema, 2016
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:kth:diva-207511 (URN)2-s2.0-85016960526 (Scopus ID)
Conference
19 June 2016 through 23 June 2016
Note

Conference code: 175559; Export Date: 22 May 2017; Editorial; Correspondence Address: Gudmundson, P.; KTH Royal Institute of Technology, Sweden. QC 20170607

Available from: 2017-06-07 Created: 2017-06-07 Last updated: 2017-06-07Bibliographically approved
Gasser, T. C., Gudmundson, P. & Dohr, G. (2009). Failure mechanisms of ventricular tissue due to deep penetration. Journal of Biomechanics, 42(5), 626-633
Open this publication in new window or tab >>Failure mechanisms of ventricular tissue due to deep penetration
2009 (English)In: Journal of Biomechanics, ISSN 0021-9290, E-ISSN 1873-2380, Vol. 42, no 5, p. 626-633Article in journal (Refereed) Published
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.

Keywords
Deep penetration, Ventricular tissue, In-vitro experiment, Lead, perforation, Tissue splitting, human aortic tissue, needle insertion, thoracic aorta, tension tests, soft solids, propagation, strength, dissections, simulation, stiffness
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-18336 (URN)10.1016/j.jbiomech.2008.12.016 (DOI)000264957900010 ()2-s2.0-61849096687 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
Fredriksson, P., Gudmundson, P. & Mikkelsen, L. P. (2009). Finite element implementation and numerical issues of strain gradient plasticity with application to metal matrix composites. International Journal of Solids and Structures, 46(22-23), 3977-3987
Open this publication in new window or tab >>Finite element implementation and numerical issues of strain gradient plasticity with application to metal matrix composites
2009 (English)In: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 46, no 22-23, p. 3977-3987Article in journal (Refereed) Published
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.

Keywords
Finite element method; Strain gradient plasticity; Metal matrix composites; Strengthening; Dislocations
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-8036 (URN)10.1016/j.ijsolstr.2009.07.028 (DOI)000271483900005 ()2-s2.0-70349156782 (Scopus ID)
Note
QC 20100723. Uppdaterad från submitted till published (20100723).Available from: 2008-02-26 Created: 2008-02-26 Last updated: 2017-12-14Bibliographically approved
Strömbro, J. & Gudmundson, P. (2008). An anisotropic fibre-network model for mechano-sorptive creep in paper. International Journal of Solids and Structures, 45(22-23), 5765-5787
Open this publication in new window or tab >>An anisotropic fibre-network model for mechano-sorptive creep in paper
2008 (English)In: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 45, no 22-23, p. 5765-5787Article in journal (Refereed) Published
Abstract [en]

In this paper a simplified network model for mechano-sorptive creep is presented, which is a further development of an earlier paper [Strombro, J., Gudmundson, P., 2008. Mechanosorptive creep under compressive loading - a micromechanical model. International journal of Solids and Structures 45 (9), 2420-2450.]. It is assumed that the anisotropic hygro-expansion of the fibres leads to large stresses at the fibre bonds when the moisture content changes. The resulting stress state will accelerate creep if the fibre material obeys a constitutive law that is non-linear. Fibre kinks are included in order to capture experimental observations of larger mechano-sorptive effects in compression than in tension. Moisture dependent material parameters and anisotropy in the fibre distribution have been introduced. Theoretical predictions based on the model are compared to experimental results for an anisotropic paper both under tensile and compressive loading at varying moisture content and it is found that the important features in the experiments are captured by the model. Different kinds of drying conditions have also been examined.

Keywords
Mechano-sorptive creep, Accelerated creep, Paper, Modelling, Moisture changes, Humidity change, Sorption, Fibres, Creep, Network model, Fibre network, Mathematical model, Fibre bonding, Tension, Compression, Anisotropy
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-7946 (URN)10.1016/j.ijsolstr.2008.06.010 (DOI)000260273300008 ()2-s2.0-51649092462 (Scopus ID)
Note
QC 20100910. Uppdaterad från submitted till published (20100910).Available from: 2008-01-31 Created: 2008-01-31 Last updated: 2017-12-14Bibliographically approved
Dahlberg, C. F. O. & Gudmundsson, P. (2008). Hardening and softening mechanisms at decreasing microstructural length scales. Philosophical Magazine, 88(30-32), 3513-3525
Open this publication in new window or tab >>Hardening and softening mechanisms at decreasing microstructural length scales
2008 (English)In: Philosophical Magazine, ISSN 1478-6435, E-ISSN 1478-6443, Vol. 88, no 30-32, p. 3513-3525Article in journal (Refereed) Published
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.

Keywords
Bulk/interface competition, Intergrain boundary sliding, Inverse Hall-Petch effect, Strain gradient plasticity
National Category
Engineering and Technology Applied Mechanics
Identifiers
urn:nbn:se:kth:diva-11503 (URN)10.1080/14786430802014688 (DOI)000261804000004 ()2-s2.0-57849154930 (Scopus ID)
Funder
Swedish Research Council, 621-2005-5759
Note

QC 20101007

Available from: 2009-11-17 Created: 2009-11-17 Last updated: 2017-12-12Bibliographically approved
Strömbro, J. & Gudmundson, P. (2008). Mechano-sorptive creep under compressive loading: a micromechanical model. International Journal of Solids and Structures, 45(9), 2420-2450
Open this publication in new window or tab >>Mechano-sorptive creep under compressive loading: a micromechanical model
2008 (English)In: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 45, no 9, p. 2420-2450Article in journal (Refereed) Published
Abstract [en]

The creep of paper is accelerated by moisture cycling, an effect known as mechano-sorptive creep. It has also been observed that the mechano-sorptive effects are larger in compression than in tension. In this paper a simplified network model for mechano-sorptive creep is presented. It is assumed that the anisotropic hygroexpansion of the fibres leads to large stresses at the fibre-fibre bonds when the moisture content changes. The resulting stress state will accelerate creep if the fibre material obeys constitutive laws that are non-linear in stress. Geometrical fibre effects are included in the model in order to capture experimental observations of the differences between paper loaded in tension and compression. Theoretical predictions based on the developed model are compared to experimental results for paper both under tensile and compressive loading at varying moisture content. The important features in the experiments are captured by the model, i.e. the creep is accelerated by the moisture cycling and the mechano-sorptive effects are larger in compression than in tension.

Keywords
mechano-sorptive creep, accelerated creep, paper, modelling, moisture changes, humidity change, sorption, fibres, creep, network model, fibre network, mathematical model, fibre bonding, tension, compression
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-7945 (URN)10.1016/j.ijsolstr.2007.12.002 (DOI)000254982400003 ()2-s2.0-40649090096 (Scopus ID)
Note
QC 20100910. Uppdaterad från in press till published (20100910).Available from: 2008-01-31 Created: 2008-01-31 Last updated: 2017-12-14Bibliographically approved
Fredriksson, P. & Gudmundson, P. (2007). Competition between interface and bulk dominated plastic deformation in strain gradient plasticity. Modelling and Simulation in Materials Science and Engineering, 15(1), S61-S69
Open this publication in new window or tab >>Competition between interface and bulk dominated plastic deformation in strain gradient plasticity
2007 (English)In: 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) Published
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.

Keywords
yield strength, single-crystals, length scale, thin-films
National Category
Mechanical Engineering Materials Engineering
Identifiers
urn:nbn:se:kth:diva-16339 (URN)10.1088/0965-0393/15/1/S06 (DOI)000243728800007 ()2-s2.0-34247257389 (Scopus ID)
Note
Conference: IUTAM Symposium on Plasticity at the Micron Scale. Tech Univ Denmark, Lyngby, DENMARK. MAY 21-25, 2006 Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
Fredriksson, P. & Gudmundson, P. (2007). Modelling of the interface between a thin film and a substrate within a strain gradient plasticity framework. Journal of the mechanics and physics of solids, 55(5), 939-955
Open this publication in new window or tab >>Modelling of the interface between a thin film and a substrate within a strain gradient plasticity framework
2007 (English)In: 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) Published
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.

Keywords
dislocations; constitutive behaviour; strain gradient plasticity
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-8035 (URN)10.1016/j.jmps.2006.11.001 (DOI)000246942500003 ()2-s2.0-34047123676 (Scopus ID)
Note
QC 20100723Available from: 2008-02-26 Created: 2008-02-26 Last updated: 2017-12-14Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0002-0307-8917

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