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Showing papers by "Jeffrey W. Kysar published in 2006"


Journal ArticleDOI
TL;DR: In this paper, the authors explored the natural thermal vibration behaviors of single-walled carbon nanotubes and their quantitative contributions to the apparent thermal contraction behaviors, and they found that the thermo-mechanical behavior of singlewalled single-wall carbon nanoteubes is exhibited through the competition between quasi-static thermal expansion and dynamic thermal vibration, while the vibration effect is more prominent and induces apparent contraction in both radial and axial directions.
Abstract: It is of fundamental value to understand the thermo-mechanical properties of carbon nanotubes. In this paper, by using molecular dynamics simulation, a systematic numerical investigation is carried out to explore the natural thermal vibration behaviors of single-walled carbon nanotubes and their quantitative contributions to the apparent thermal contraction behaviors. It is found that the thermo-mechanical behavior of single-walled carbon nanotubes is exhibited through the competition between quasi-static thermal expansion and dynamic thermal vibration, while the vibration effect is more prominent and induces apparent contraction in both radial and axial directions. With increasing temperature, the anharmonic interatomic potential helps to increase the bond length, which leads to thermally induced expansion. On the other hand, the higher structural entropy and vibrational entropy of the system cause the carbon nanotube to vibrate, and the apparent length of nanotube decreases due to various vibration modes. Parallel analytical and finite element analyses are used to validate the vibration frequencies and provide helpful insights. The unified multi-scale study has successfully decoupled and systematically analyzed both thermal expansion and contraction behaviors of single-walled carbon nanotube from 100 to 800 K, and obtained detailed information on various vibration modes as well as their quantitative contributions to the coefficient of thermal expansion in axial and radial directions. The results of this paper may provide useful information on the thermo-mechanical integrity of single-walled carbon nanotubes, and become important in practical applications involving finite temperature.

82 citations


Journal ArticleDOI
TL;DR: In this paper, Kysar et al. presented experimental results and finite element simulations of plastic deformation around a cylindrical void in single crystals to compare with the analytical solutions in a companion paper, where the results of the simulation are in good agreement with the prediction by the anisotropic slip line theory.

67 citations


Journal ArticleDOI
TL;DR: Raman microprobe analysis used here to probe the nanocrystal cores of thick, fractured electrophoretically deposited films of 3.2 nm diameter CdSe nanocrystals finds that the crack dimensions determine the overall in-plane film strain and the film biaxial modulus.
Abstract: The mechanical stability of nanocrystal films is critical for applications, yet largely unexplored. Raman microprobe analysis used here to probe the nanocrystal cores of thick, fractured electrophoretically deposited films of 3.2 nm diameter CdSe nanocrystals measures ∼2.5% in-plane tensile strain in cores of unfractured films. The crack dimensions determine the overall in-plane film strain, ∼11.7%, and the film biaxial modulus, ∼13.8 GPa, from which the biaxial modulus of the trioctylphosphine oxide ligand matrix is inferred, ∼5.1 GPa.

33 citations


Journal ArticleDOI
TL;DR: An ab initio analysis based on the density functional theory is carried out to investigate the effects of axial strain and radial pressure on the radial breathing mode (RBM) frequency of individual single-walled carbon nanotubes with armchair and zigzag chiralities.
Abstract: An ab initio analysis based on the density functional theory is carried out to investigate the effects of axial strain and radial pressure on the radial breathing mode (RBM) frequency of individual single-walled carbon nanotubes with armchair and zigzag chiralities. It is found that the RBM frequency is not sensitive to axial tensile strain or small axial compressive strain. When the axial compressive strain exceeds a critical value, the RBM frequency is significantly reduced. On the other hand, the RBM frequency is highly sensitive to the radial pressure; a pressure of 1GPa can increase the RBM frequency by about 8cm−1. Under a high radial pressure, the difference between the frequencies of the positive and negative half periods of the RBM vibration sharply increases, which may lead to the separation of the RBM peaks. Very good agreement is found between the present numerical analysis and previous experimental results.

10 citations


Journal ArticleDOI
TL;DR: In this article, single crystal nanowires of gold were fabricated from a single grain of pure gold leaf by standard lithographic techniques, with center section of 7μm in length, 250nm in width, and 100nm in thickness.
Abstract: Freestanding single crystal nanowires of gold were fabricated from a single grain of pure gold leaf by standard lithographic techniques, with center section of 7μm in length, 250nm in width, and 100nm in thickness. The ends remained anchored to a silicon substrate. The specimens were deflected via nanoindenter until plastic deformation was achieved. Nonlocalized and localized plastic deformations were observed. The resulting force-displacement curves were simulated using continuum single crystal plasticity. A set of material parameters which closely reproduce the experimental results suggests that the initial critical resolved shear stress was as high as 135MPa.

8 citations


Proceedings ArticleDOI
01 Jan 2006
TL;DR: In this article, anisotropic slip line theory is employed for the construction of slip line fields for both orientations and compared with numerical results for laser shock peening by a micron sized laser beam.
Abstract: Laser shock peening by a micron sized laser beam is a process in which compressive residual stresses are induced in order to improve material fatigue life of micro scale components. The size of the laser target interaction zone is of the same order of magnitude as the target material grains and thus the effects of anisotropic material response must be taken into account. Single crystals are therefore chosen to study such anisotropy. It is also of interest to investigate the response of symmetric and asymmetric slip systems with respect to the yield surface. In presented work, analytic, numerical and experimental investigations of two different orientations, (110) and (11¯4) of aluminum single crystals are studied. Anisotropic slip line theory is employed for the construction of slip line fields for both orientations and compared with numerical results. Theory is further used to explain the difference in plastic deformation for two different orientations. Lattice rotations on the top surface and cross section are also measured using Electron Backscatter Diffraction (EBSD), while residual stress is measured using X-ray microdiffraction. Both the analytical and numerical models are then validated via experimental results.Laser shock peening by a micron sized laser beam is a process in which compressive residual stresses are induced in order to improve material fatigue life of micro scale components. The size of the laser target interaction zone is of the same order of magnitude as the target material grains and thus the effects of anisotropic material response must be taken into account. Single crystals are therefore chosen to study such anisotropy. It is also of interest to investigate the response of symmetric and asymmetric slip systems with respect to the yield surface. In presented work, analytic, numerical and experimental investigations of two different orientations, (110) and (11¯4) of aluminum single crystals are studied. Anisotropic slip line theory is employed for the construction of slip line fields for both orientations and compared with numerical results. Theory is further used to explain the difference in plastic deformation for two different orientations. Lattice rotations on the top surface and cross sect...

4 citations