Plastic deformation of freestanding thin films : Experiments and modeling

L. NICOLA, Y. XIANG, J. J. VLASSAK, E. VAN DER GIESSEN, A. NEEDLEMAN*

*Corresponding author for this work

Research output: Journal PublicationsJournal Article (refereed)peer-review

198 Citations (Scopus)

Abstract

Experimental measurements and computational results for the evolution of plastic deformation in freestanding thin films are compared. In the experiments, the stress-strain response of two sets of Cu films is determined in the plane-strain bulge test. One set of samples consists of electroplated Cu films, while the other set is sputter-deposited. Unpassivated films, films passivated on one side and films passivated on both sides are considered. The calculations are carried out within a two-dimensional plane strain framework with the dislocations modeled as line singularities in an isotropic elastic solid. The film is modeled by a unit cell consisting of eight grains, each of which has three slip systems. The film is initially free of dislocations which then nucleate from a specified distribution of Frank-Read sources. The grain boundaries and any film-passivation layer interfaces are taken to be impenetrable to dislocations. Both the experiments and the computations show: (i) a flow strength for the passivated films that is greater than for the unpassivated films and (ii) hysteresis and a Bauschinger effect that increases with increasing pre-strain for passivated films, while for unpassivated films hysteresis and a Bauschinger effect are small or absent. Furthermore, the experimental measurements and computational results for the 0.2% offset yield strength stress, and the evolution of hysteresis and of the Bauschinger effect are in good quantitative agreement.

Original languageEnglish
Pages (from-to)2089-2110
Number of pages22
JournalJournal of the Mechanics and Physics of Solids
Volume54
Issue number10
Early online date19 Jun 0019
DOIs
Publication statusPublished - Oct 2006
Externally publishedYes

Bibliographical note

Acknowledgments:
LN and AN are grateful for support from the Materials Research Science and Engineering Center at Brown University (NSF Grant DMR-00520651). YX and JV would like to acknowledge financial support from the National Science Foundation (NSF Grant DMR-0133559) and from the Materials Research Science and Engineering Center of the National Science Foundation under NSF Grant DMR-0213805. The work by LN and EVdG is partly funded by the Netherlands Institute for Metals Research.

Keywords

  • Bauschinger effect
  • Computer simulation
  • Dislocations
  • Size effects
  • Thin films

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