List of Journal Publications
2010
2.
Shishvan, Siamak Soleymani, Nicola, L., Giessen, Erik Van Der
Bauschinger effect in unpassivated freestanding thin films Journal Article
In: JOURNAL OF APPLIED PHYSICS, vol. 107, no. 9, 2010.
Abstract | BibTeX | Tags: Bauschinger effect, discrete dislocation plasticity, polycrystals | Links:
@article{Shishvan2010,
title = {Bauschinger effect in unpassivated freestanding thin films},
author = {Siamak Soleymani Shishvan and L. Nicola and Erik Van Der Giessen},
doi = {10.1063/1.3407505},
year = {2010},
date = {2010-01-01},
journal = {JOURNAL OF APPLIED PHYSICS},
volume = {107},
number = {9},
publisher = {AMER INST PHYSICS},
abstract = {Two-dimensional (2D) discrete dislocation plasticity simulations are carried out to investigate the Bauschinger effect (BE) in freestanding thin films. The BE in plastic flow of polycrystalline materials is generally understood to be caused by inhomogeneous deformation during loading, leading to residual stress upon unloading. This inhomogeneity can be caused by dislocation pile-ups, variations in texture, grain orientations, and grain size. To study the BE, columnar-grained films as well as films with multiple grains across the thickness are considered. The film is modeled in a 2D framework by a unit cell consisting of an array of grains with different orientation. In order to capture the interaction among grains, we motivate and explore the use of an affine deformation assumption on the grain level to mimic the three-dimensional geometry in this framework. It is shown that the dispersion of grain size in a film together with the size-dependence of yield strength leads to significant BEs in bare films. Quantitative comparison of simulations with experimental data is provided.},
keywords = {Bauschinger effect, discrete dislocation plasticity, polycrystals},
pubstate = {published},
tppubtype = {article}
}
Two-dimensional (2D) discrete dislocation plasticity simulations are carried out to investigate the Bauschinger effect (BE) in freestanding thin films. The BE in plastic flow of polycrystalline materials is generally understood to be caused by inhomogeneous deformation during loading, leading to residual stress upon unloading. This inhomogeneity can be caused by dislocation pile-ups, variations in texture, grain orientations, and grain size. To study the BE, columnar-grained films as well as films with multiple grains across the thickness are considered. The film is modeled in a 2D framework by a unit cell consisting of an array of grains with different orientation. In order to capture the interaction among grains, we motivate and explore the use of an affine deformation assumption on the grain level to mimic the three-dimensional geometry in this framework. It is shown that the dispersion of grain size in a film together with the size-dependence of yield strength leads to significant BEs in bare films. Quantitative comparison of simulations with experimental data is provided.
2006
1.
Nicola, L., Xiang, Y., Vlassak, J. J., der Giessen, E. Van, Needleman, A.
Plastic deformation of freestanding thin films: Experiments and modeling Journal Article
In: JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS, vol. 54, no. 10, pp. 2089–2110, 2006.
Abstract | BibTeX | Tags: Bauschinger effect, Computer simulation, Dislocations, size effects, Thin films | Links:
@article{Nicola2006,
title = {Plastic deformation of freestanding thin films: Experiments and modeling},
author = {L. Nicola and Y. Xiang and J. J. Vlassak and E. Van der Giessen and A. Needleman},
doi = {10.1016/j.jmps.2006.04.005},
year = {2006},
date = {2006-01-01},
journal = {JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS},
volume = {54},
number = {10},
pages = {2089–2110},
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.},
keywords = {Bauschinger effect, Computer simulation, Dislocations, size effects, Thin films},
pubstate = {published},
tppubtype = {article}
}
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.
