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A strain gradient plasticity analysis of size effects in thin films
KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
2005 (English)Licentiate thesis, comprehensive summary (Other scientific)
Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2005. , 15 p.
Series
Trita-HFL. Report / Royal Institute of Technology, Solid Mechanics, ISSN 1654-1472 ; 0387
National Category
Other Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-380OAI: oai:DiVA.org:kth-380DiVA: diva2:9653
Presentation
2005-06-07, Sal Q2, Osquldas väg 10, Stockholm, 13:15
Supervisors
Note

QC 20101129

Available from: 2005-08-09 Created: 2005-08-09 Last updated: 2013-01-15Bibliographically approved
List of papers
1. Size-dependent yield strength of thin films
Open this publication in new window or tab >>Size-dependent yield strength of thin films
2005 (English)In: International journal of plasticity, ISSN 0749-6419, Vol. 21, no 9, 1834-1854 p.Article in journal (Refereed) Published
Abstract [en]

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

Keyword
constitutive behaviour; viscoplastic material; strain gradient plasticity
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-8034 (URN)10.1016/j.ijplas.2004.09.005 (DOI)000229867100008 ()2-s2.0-18444369672 (Scopus ID)
Note
QC 20100723Available from: 2008-02-26 Created: 2008-02-26 Last updated: 2010-11-29Bibliographically approved
2. Modelling of the interface between a thin film and a substrate within a strain gradient plasticity framework
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, Vol. 55, no 5, 939-955 p.Article 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.

Keyword
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: 2010-11-29Bibliographically approved

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