1. Rappture GUI for Carbon Nano Tube Arrays’ mechanical and thermal property simulation By Yide Wang Professor Tim Fisher Sridhar Sadasivam

2. Introduction  Motivation 1. Carbon nanotube is a high thermal conducting and mechanical reliable material to build thermal interface. 2. Modeling of carbon nanotube arrays is in atomistic level which makes the computational simulation extremely expensive. Coarse grain simulation technique reduces the degree of freedom leading to the tractable simulation process. 3. A Rappture graphical user interface is to be built to perform coarse grain simulation. It combines the model initialization, calculation and result processing together by only acquiring geometrical and thermal input parameters.  Objectives 1. The graphical user interface is built to simulate a experiment process with a substrate pressing against carbon nanotube arrays. 2. The GUI is capable of generating the initial positions of beads, LAMMPS input script, running LAMMPS, plotting stress and strain curve, calculating young’s modulus, contact area between substrate and CNTs, equivalent resistance and visualization of the compression motion.

3. Method o Build an interface obtaining parameters from user 1. Parameters that specify the initial position of CNTs 2. Parameters that specify that how the virtue experiment is set up o Use MATLAB to write a program that generates the initial position of CNTs and input script for LAMMPS. o Call LAMMPS by the GUI. o Extract useful information from results returned from LAMMPS. 1. Write a program to read through all the files that stores results 2. Plot the stress and strain curve. 3. Display the Young’s modulus. 4. Display the contact area between CNTs and their substrate for each position of the substrate and their corresponding equivalent thermal resistance. 5. display visualized compression motion by plotting coordinates of each bead for each position of the substrate

4. Results Figure 1 – user interface

5. Figure 2 – file containing initial positionFigure 3 – input script for LAMMPS The data file containing initial position and the input script are generated automatically by the GUI. The data file is called in the input script.

6. Figure 4 – The GUI is running LAMMPS After the input script is generated, the GUI will start LAMMPS automatically

7. Figure 5 – displaying result The figure four shows a stress and strain curve with it’s curve fit displaying on the GUI.

8. Figure 6 – Young’s modulus The Young’s modulus is calculated using the slope of curve fit of the stress- strain curve

9. Figure 7– Effective resistance The effective resistance is calculated using the contact area between substrate and CNTs and their equivalent resistance of each individual CNT

10. This video shows the experimental process that CNTs are pressed against a substrate

11. Conclusions  The tool can be used to run various simulations with different parameters without manually processing different files and software.  The results from LAMMPS can be visualized by the tool easily.