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Length-scale Dependent Dislocation Nucleation during Nanoindentation on Nanosized Gold Islands

Length-scale Dependent Dislocation Nucleation during Nanoindentation on Nanosized Gold Islands. Alex Gonzalez Department of Mechanical Engineering University of Arkansas Fayetteville, AR 72701 USA REU Advisor: Dr. Douglas Spearot REU 10 th Week Seminar – Monday July 20 th , 2009. Index.

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Length-scale Dependent Dislocation Nucleation during Nanoindentation on Nanosized Gold Islands

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  1. Length-scale Dependent Dislocation Nucleation during Nanoindentation on Nanosized Gold Islands Alex Gonzalez Department of Mechanical Engineering University of Arkansas Fayetteville, AR 72701 USA REU Advisor: Dr. Douglas Spearot REU 10th Week Seminar – Monday July 20th, 2009

  2. Index Objective: The objective of this project is to make indentations on nanosized islands of Au to generate dislocations and study the onset of plasticity through the four steps listed below… Step 1: Make and set boundary conditions. Step 2: Determine how to control thermo oscillations. Step 3: Indent sample and plot force v. depth curves to study plasticity. Step 4: Systematically indent closer to the free surface to study dislocation nucleation.

  3. Make and set boundary conditions • Simulation cell dimensions are N x 30 x N • (N=30,40,50,60) lattice units. • Indenter size is 5 angstrom radius. • Simulations • First: NVE – updates positions and velocities for groups of atoms. V is volume and E is energy. • Run simulation for certain amount of time periods • Second: NVT - uses Nose/Hoover thermostat with Tdamp and drag values. V is volume and T is temperature. • Run simulation for certain amount of time periods • Third: Energy Minimization – iteratively adjusting atom coordinates for lowest possible local potential energy • Lower indenter, minimize, lower indenter, minimize • Plot force as a function of depth. • Create free surface on YZ plane and indent closer to the free surface at steps of 5 lattice units.

  4. Role of thermo oscillation

  5. Role of thermo oscillation

  6. Force v. Depth Curves and Plasticity **Both cases have box dimensions of 40x30x40

  7. Atomistic displacement simulation Before, at, and after the peak close ups of Energy Minimization of a 40x30x40 Simulation cell Before Peak At Peak After Peak Indentation on surface Raise indenter

  8. Free surface dislocations 30 L.U. 25 L.U. 20 L.U. 10 L.U. 5 L.U. 15 L.U.

  9. Free surface analysis Dislocations forming from the free surface – Indenter 5 lattice units away from free surface. No free surface interaction – Indenter 10 lattice units away from free surface

  10. Conclusions Objective steps: Step 1: Make and set boundary conditions. Step 2: Determine how to control thermo oscillations. Step 3: Indent gold surface and plot force versus depth to understand the onset of plasticity. Step 4: Indent closer to the free surface to study dislocation nucleation in the presence of the free surface. Outcome • Better understanding of plastic behavior. • Produced results similar to that of published papers for pure Au. • Analyzed force v. depth curves and proved when plasticity occurs. • Gave evidence of activity before “peak” in force depth curve. • Showed evidence of dislocation nucleation from free surface.

  11. Alex Gonzalez REU 10th Week Seminar – Monday July 20th, 2009

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