MOLECULAR DYNAMIC SIMULATION OF THE STRESS IN METALLIC ALLOYS BY: SARAH BARTLEY RESEARCH MENTOR: DR. JUANA MORENO REU TEAM MEMBERS: DR. KA MING TAM CIMM REU 2016 LOUISIANA STATE UNIVERSITY , DEPARTMENT OF PHYSICS & ASTRONOMY NICHOLSON HALL, TOWER DR. , BATON ROUGE, LA 70803-4001 SARAH BARTLEY, 2016
APPLICATIONS AND CHARACTERISTICS OF ALLOYS • Applications of alloys • Superalloys • Able to maintain its form at temperatures close to its melting point. • Ni based alloys is the most popular choice because it has a higher temperature resistance. • Ex: Gas Turbine http://science.howstuffwo • Characteristics of alloy rks.com/transport/flight/ • Mechanical strength modern/turbine.htm • Resistance to deformation, corrosion • Deformation resistance is dependent on dislocations • Dislocation: a crack within the crystal structure. SARAH BARTLEY, 2016
MOLECULAR DYNAMICS (MD) • Computational classical mechanic modeling LAMMPS(LARGE-SCALE ATOMIC/MOLECULAR MASSIVELY method to study atomic and molecular PARALLEL SIMULATOR) interactions. • Classical MD simulator that is able to • The large scale simulation is able to give simulate intermolecular interactions precise calculations of the exact location of • Is capable to be used on laptops and atoms in an experiment with the assistance of the potentials such as EAM, Morse, desktops, but it is meant to be run on a Lennard jones, and etc. parallel machine. • Free and open source code SARAH BARTLEY, 2016 http://lammps.sandia.gov/
OVITO (OPEN VISUALIZATION TOOL) • The DXA (Dislocation Extraction Algorithm) in the visualizer package, Ovito, calculates the dislocation in the simulation by the equation below. [5] http://www.ovito.org/man ual/particles.modifiers.disl ocation_analysis.html Figure 1. The burger vector is equivalent to the sum of the change over time of the path of a dislocated crystal. SARAH BARTLEY, 2016
RESULTS ( RELAXATION HEATING COOLING) Figure 2. An image of the Figure 3. The representation of the dislocation front view of the dislocation respectively of the colors blue, green, and red of a relaxed Nickel and are perfect, Shockley, and other. Aluminum bilayer structure. SARAH BARTLEY, 2016
RESULTS (NANO-INDENTION) In Figure 4. The green atoms Figure 5. This is a front view of the in the structure represents an simulation. The white matter represents the FCC structure which represents defect mesh in the relaxed structure. 75.3% of the structure. SARAH BARTLEY, 2016
RESULTS (UNIAXIAL COMPRESSION OF AL AND NI) Figure 7. This is an image of the Figure 6. This is an image of the compression of Nickel. As the Ni compression of Aluminum. As the Al structure is compressed, it acts similarly structure is compressed, the Al solely FCC to the Aluminum structure. There are no structure shifts to incorporate both a FCC dislocations in the Ni structure. and HCP structure. As the Al structure SARAH BARTLEY, 2016 compresses, the amount of dislocations increase.
DISCUSSION For simulations with fewer time steps and atoms, the DXA does not detect dislocation in the structure after cooling. For the 146,542 atom simulation with 2000 time steps heated to 1000K, 610 dislocation are detected. A simulation of uniaxial compression was performed on Al[4] and Ni with the dimensions of [(0,0,0) to (10,10,10)]. For the 4,000 atom Ni simulation, the phenomenon, dislocation starvation, occurs. SARAH BARTLEY, 2016
REFERENCES • Prakash, A., Guénolé, J., Wang, J., Müller, J., Spiecker, E., Mills, M., . . . Bitzek, E. (2015). Atom probe informed simulations of dislocation – precipitate interactions reveal the importance of local interface curvature. Acta Materialia, 92, 33-45. doi:10.1016/j.actamat.2015.03.050 • LAMMPS Molecular Dynamics Simulator. (n.d.). Retrieved June 07, 2016, from http://lammps.sandia.gov/ • (n.d.). Retrieved June 07, 2016, from http://science.howstuffworks.com/transport/flight/modern/turbine.htm • Uniaxial Compression. (March 14, 2016). Retrieved June 22, 2016, from https://icme.hpc.msstate.edu/mediawiki/index.php/Uniaxial_Compression • Ovito. (n.d.). Retrieved July 22, 2016, from http://www.ovito.org/ SARAH BARTLEY, 2016
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