Abstract
Strong size effects have been experimentally observed when microstructural features approach the geometric dimensions of the sample. In this work experimental investigations and discrete dislocation analyses of plastic deformation in metallic thin films have been performed. Columnar grains representative of the film microstructure are here considered. Simulations are based on the assumptions that sources are scarcely available in geometrically confined systems and nucleation sites are mainly located at grain boundaries. Especially, we investigated the influence on the mesoscopic constitutive response of the two characteristic length scales, i.e., film thickness and grain size. The simulated plastic response qualitatively reproduces the experimentally observed size effects while the main deformation mechanisms appear to be in agreement with TEM analyses of tested samples. A new interpretation of size scale plasticity is here proposed based on the probability of activating grain boundary dislocation sources. Moreover, the key role of a parameter such as the grain aspect ratio is highlighted. Finally, the unloading behavior has been investigated and a strong size dependent Bauschinger effect has been found. An interpretation of these phenomena is proposed based on the analysis of the back stress distribution within the samples.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 2091-2117 |
| Number of pages | 27 |
| Journal | International journal of plasticity |
| Volume | 22 |
| Issue number | 11 |
| DOIs | |
| State | Published - Nov 2006 |
Funding
The support of the NSF under grants number CMS-00304472, CMS-0120866 and DMR-0315561 is gratefully acknowledged. We express our appreciation to Bei Peng, Yong Zhu and Francois Barthelat for obtaining the experimental results reported in this work. The authors are also grateful to the Supercomputer Centers at University of Illinois at Urbana Champaign (NCSA resources) and at University of California at San Diego (NPACI resources) for providing allocations to run the calculations. The SEM and TEM work was carried out in the Center for Microanalysis of Materials, University of Illinois, which is partially supported by the U.S. Department of Energy under Grant DEFG02-96-ER45439. We are particularly thankful to James Mabon, Michael Marshal and Ivan Petrov for their input and assistance in the SEM and TEM work.
Keywords
- Bauschinger effect
- Discrete dislocation dynamics
- Frank-Read sources
- Grain boundaries
- Plasticity
- Size effects
- Thin films
ASJC Scopus subject areas
- General Materials Science
- Mechanics of Materials
- Mechanical Engineering