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Détail de l'auteur
Auteur Richard LeSar
Documents disponibles écrits par cet auteur
Affiner la rechercheDiscrete dislocation dynamics simulations of plasticity at small scales / Caizhi Zhou in Acta materialia, Vol. 58 N° 5 (Mars 2010)
[article]
in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1565–1577
Titre : Discrete dislocation dynamics simulations of plasticity at small scales Type de document : texte imprimé Auteurs : Caizhi Zhou, Auteur ; S. Bulent Biner, Auteur ; Richard LeSar, Auteur Année de publication : 2011 Article en page(s) : pp. 1565–1577 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Dislocation dynamics Size effects Plasticity Résumé : Discrete dislocation dynamics simulations in three dimensions have been used to examine the role of dislocation multiplication and mobility on the plasticity in small samples under uniaxial compression. To account for the effects of the free surfaces a boundary-element method, with a superposition technique, was employed. Cross-slip motion of the dislocation was also included, and found to be critical to the modeling of the dislocation behavior. To compare directly with recent experiments on micropillars, simulation samples at small volumes were created by cutting them from bulk three-dimensional simulations, leading to a range of initial dislocation structures. Application was made to single-crystal nickel samples. Comparison of the simulation results and the experiments are excellent, finding essentially identical behavior. Examination of details of the dislocation mechanism illuminates many features unique to small samples and points directly to the importance of both the surface forces and cross-slip in understanding small-scale plasticity. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007678 [article] Discrete dislocation dynamics simulations of plasticity at small scales [texte imprimé] / Caizhi Zhou, Auteur ; S. Bulent Biner, Auteur ; Richard LeSar, Auteur . - 2011 . - pp. 1565–1577.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 58 N° 5 (Mars 2010) . - pp. 1565–1577
Mots-clés : Dislocation dynamics Size effects Plasticity Résumé : Discrete dislocation dynamics simulations in three dimensions have been used to examine the role of dislocation multiplication and mobility on the plasticity in small samples under uniaxial compression. To account for the effects of the free surfaces a boundary-element method, with a superposition technique, was employed. Cross-slip motion of the dislocation was also included, and found to be critical to the modeling of the dislocation behavior. To compare directly with recent experiments on micropillars, simulation samples at small volumes were created by cutting them from bulk three-dimensional simulations, leading to a range of initial dislocation structures. Application was made to single-crystal nickel samples. Comparison of the simulation results and the experiments are excellent, finding essentially identical behavior. Examination of details of the dislocation mechanism illuminates many features unique to small samples and points directly to the importance of both the surface forces and cross-slip in understanding small-scale plasticity. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409007678 Plastic deformation mechanisms of fcc single crystals at small scales / Caizhi Zhou in Acta materialia, Vol. 59 N° 20 (Décembre 2011)
[article]
in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7673–7682
Titre : Plastic deformation mechanisms of fcc single crystals at small scales Type de document : texte imprimé Auteurs : Caizhi Zhou, Auteur ; Irene J. Beyerlein, Auteur ; Richard LeSar, Auteur Année de publication : 2012 Article en page(s) : pp. 7673–7682 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Dislocation dynamics Size effects Small scales Dislocation starvation Cross-slip Résumé : Three-dimensional (3-D) dislocation dynamics simulations were employed to examine the fundamental mechanisms of plasticity in small-scale face-centered cubic single crystals. Guided by the simulation results, we examined two distinct modes of behavior that reflect the dominant physical mechanisms of plastic deformation at small scales. We found that the residence lifetimes of internal dislocation sources formed by cross-slip decrease as the system size decreases. Below a critical sample size (which depends on the initial density of dislocations) the dislocation loss rate exceeds the multiplication rate, leading to the loss of internal dislocation sources. In this case nucleation of surface dislocations is required to provide dislocations for deformation and the “starvation hardening” mechanism becomes the dominant deformation process. When the sample is larger than a critical size multiplication of internal dislocation sources provides the dominant mechanism for plastic flow. As the strain is increased the rising dislocation density leads to reactions that shut off these sources, creating “exhaustion hardening”. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006094 [article] Plastic deformation mechanisms of fcc single crystals at small scales [texte imprimé] / Caizhi Zhou, Auteur ; Irene J. Beyerlein, Auteur ; Richard LeSar, Auteur . - 2012 . - pp. 7673–7682.
Métallurgie
Langues : Anglais (eng)
in Acta materialia > Vol. 59 N° 20 (Décembre 2011) . - pp. 7673–7682
Mots-clés : Dislocation dynamics Size effects Small scales Dislocation starvation Cross-slip Résumé : Three-dimensional (3-D) dislocation dynamics simulations were employed to examine the fundamental mechanisms of plasticity in small-scale face-centered cubic single crystals. Guided by the simulation results, we examined two distinct modes of behavior that reflect the dominant physical mechanisms of plastic deformation at small scales. We found that the residence lifetimes of internal dislocation sources formed by cross-slip decrease as the system size decreases. Below a critical sample size (which depends on the initial density of dislocations) the dislocation loss rate exceeds the multiplication rate, leading to the loss of internal dislocation sources. In this case nucleation of surface dislocations is required to provide dislocations for deformation and the “starvation hardening” mechanism becomes the dominant deformation process. When the sample is larger than a critical size multiplication of internal dislocation sources provides the dominant mechanism for plastic flow. As the strain is increased the rising dislocation density leads to reactions that shut off these sources, creating “exhaustion hardening”. ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645411006094