MOLECULAR DYNAMIC SIMULATION OF THE STRESS IN METALLIC ALLOYS BY: - - PowerPoint PPT Presentation

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
• Characteristics of alloy
• Mechanical strength
• Resistance to deformation, corrosion
• Deformation resistance is dependent on dislocations
• Dislocation: a crack within the crystal structure.

SARAH BARTLEY, 2016

http://science.howstuffwo rks.com/transport/flight/ modern/turbine.htm

MOLECULAR DYNAMICS (MD)

• Computational classical mechanic modeling

method to study atomic and molecular interactions.

• The large scale simulation is able to give

precise calculations of the exact location of atoms in an experiment with the assistance

• f the potentials such as EAM, Morse,

Lennard jones, and etc.

LAMMPS(LARGE-SCALE ATOMIC/MOLECULAR MASSIVELY PARALLEL SIMULATOR)

• Classical MD simulator that is able to

simulate intermolecular interactions

• Is capable to be used on laptops and

desktops, but it is meant to be run on a 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] SARAH BARTLEY, 2016 Figure 1. The burger vector is equivalent to the sum

• f the change over time of the path of a dislocated

crystal.

http://www.ovito.org/man ual/particles.modifiers.disl

• cation_analysis.html

RESULTS ( RELAXATION  HEATING  COOLING)

SARAH BARTLEY, 2016 Figure 2. An image of the front view of the dislocation

• f a relaxed Nickel and

Aluminum bilayer structure. Figure 3. The representation of the dislocation respectively of the colors blue, green, and red are perfect, Shockley, and other.

RESULTS (NANO-INDENTION)

SARAH BARTLEY, 2016 In Figure 4. The green atoms in the structure represents an FCC structure which represents 75.3% of the structure. Figure 5. This is a front view of the

• simulation. The white matter represents the

defect mesh in the relaxed structure.

RESULTS (UNIAXIAL COMPRESSION OF AL AND NI)

SARAH BARTLEY, 2016 Figure 6. This is an image of the compression of Aluminum. As the Al structure is compressed, the Al solely FCC structure shifts to incorporate both a FCC and HCP structure. As the Al structure compresses, the amount of dislocations increase. Figure 7. This is an image of the compression of Nickel. As the Ni structure is compressed, it acts similarly to the Aluminum structure. There are no dislocations in the Ni structure.

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

• f 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