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Atomistic modeling of failure in iron
Norwegian University of Science and Technology, Faculty of Engineering Science and Technology, Department of Engineering Design and Materials.
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis is based on three research papers, all concerning molecular dynamics (MD) simulations of failure properties in pure iron. The first two papers examine iron crystals with cracks deformed in Mode I tensile testing, with different geometrical constraints. In Paper I we have reviewed fracture mechanics in light of atomistic simulations, and shown a possible way to link atomistic and multiscale simulations of cracks to the crack initiation toughness of the material. Stress-intensity factors and effective surface energies were calculated from atomistic penny-shaped cracks and multiscale edge crack simulations. The influence of T-stress/constraint level was examined.

Paper II is devoted to the study of penny-shaped cracks, comparing this geometry with the more commonly studied through-thickness cracks. It was found that the fracture mechanisms in specific crystallographic orientations were similar, but that the penny-shaped crack was able to change shape during loading in order to favor dislocation emission over unstable fracture.

The last paper, Paper III, is a study of size and strain rate effects in compression of nanopillars, where three crystallographic orientations were simulated. A size-strengthening effect was found for pillars compressed along (100) and (110) directions, and a lower strain rate was shown to result in lower maximal stress before deformation began.

Place, publisher, year, edition, pages
NTNU, 2012.
Series
Doctoral theses at NTNU, ISSN 1503-8181 ; 2012:129
National Category
Other material science
Identifiers
URN: urn:nbn:no:ntnu:diva-16866ISBN: 978-82-471-3541-9 (printed ver.)ISBN: 978-82-471-3542-6 (electronic ver.)OAI: oai:DiVA.org:ntnu-16866DiVA: diva2:538784
Public defence
2012-05-08, 10:08
Available from: 2012-07-02 Created: 2012-06-29 Last updated: 2012-07-06Bibliographically approved
List of papers
1. Atomistic modeling of micromechanisms and T-stress effects in fracture of iron
Open this publication in new window or tab >>Atomistic modeling of micromechanisms and T-stress effects in fracture of iron
2012 (English)In: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 79, 180-190 p.Article in journal (Refereed) Published
Abstract [en]

In this paper we explore a possible method to couple atomistic modeling of initiation of fracture in iron with displacement constraints taken from continuum considerations. Molecular dynamics is used to examine the effect of a penny-shaped crack, and the quasi-continuum method is used as a platform for performing multiscale analysis. The modified boundary layer approach enables us to examine the influence of constraint (geometry, crack size and mode of loading) on the fracture mechanisms by changing the T-stress (the constant term in the stress series expansion). The results are discussed in relation to how constraint influences upon the crack initiation toughness. (C) 2011 Elsevier Ltd. All rights reserved.

Keyword
Fracture, Atomistic modeling, Iron, T-stress, Dislocations
Identifiers
urn:nbn:no:ntnu:diva-16870 (URN)10.1016/j.engfracmech.2011.10.012 (DOI)000301276000012 ()
Note

The article is reprinted with kind permission from Elsevier, sciencedirect.com

Available from: 2012-07-02 Created: 2012-07-02 Last updated: 2012-07-06Bibliographically approved
2. Atomistic modeling of penny-shaped and through-thickness cracks in bcc iron
Open this publication in new window or tab >>Atomistic modeling of penny-shaped and through-thickness cracks in bcc iron
(English)Manuscript (preprint) (Other academic)
Identifiers
urn:nbn:no:ntnu:diva-16871 (URN)
Available from: 2012-07-02 Created: 2012-07-02 Last updated: 2013-07-12Bibliographically approved
3. Modeling of size and strain rate effects in compression tests of iron nanopillars
Open this publication in new window or tab >>Modeling of size and strain rate effects in compression tests of iron nanopillars
(English)Manuscript (preprint) (Other academic)
Identifiers
urn:nbn:no:ntnu:diva-16872 (URN)
Available from: 2012-07-02 Created: 2012-07-02 Last updated: 2012-07-02Bibliographically approved

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