MOLECULAR DYNAMIC SIMULATION OF THE STRESS IN

METALLIC ALLOYSBY: 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

of 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, 2016http://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

of the change over time of the path of a dislocated

crystal.

http://www.ovito.org/man

ual/particles.modifiers.disl

ocation_analysis.html

RESULTS ( RELAXATION HEATING COOLING)

SARAH BARTLEY, 2016

Figure 2. An image of the

front view of the dislocation

of 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

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