Wen Bo Li (EngSci 1T6)

Oceans after oceans, seas after seas, after more than a half day of flight, my research partner and I finally arrived in the small but famous city state of Singapore. Illuminated with lights in the middle of the night, we took a taxi in the clean streets of the city with neat rows of tropical trees planted on both sides, and were awed by the sights of the famous buildings that symbolized this great city of the East. In this serene and astonishing view, the taxi driver gave an overview of Singapore in heavy-accented English, and to my mind, we were visiting an image of Toronto on the other side of the world: proud in its academic institutions, the National University of Singapore to which we were bound, is a fair match against the University of Toronto; unique in its skyline, just like Toronto with its soaring CN Tower, its grand buildings are easily recognizable by many; lastly, home to many different people in Asia and around the world, it is a multicultural city of the East, just as Toronto is one of the West.

For half of our time, my partner and I were occupied in the offices and labs of the university, conducting the research assigned to us by our supervisors, who were Professor C.M. Wang and Ph. D. student A.N. Roy Chowdhury. Our work was to conduct research on the properties of carbon nanotubes (CNTs). Our task specifically was to use computer simulation software to investigate and characterize the properties of CNTs under different types of strains and stresses, and then make a simplified model called the continuum shell model, which would accurately predict the behaviour of CNTs without the need for long simulation, and thus would save time and resources needed in running these simulations.

In the first part of our research, we used a software called LAMMPs, which is capable of modelling 3D CNTs and intramolecular interactions within the nanotube to investigate the reactions of CNTs under compressive, tensile, and torsional strain. We used it to test and observe the stress-strain behaviour of all types of CNTs – zigzag, armchair, and chiral – and a variety of different variables within these types. The CNT variables we tested for included the orientation of the CNT, diameter of the CNT, the length of the CNT, and for torsional strain, the direction of the torque. By compiling the results from the LAMMPS program, we characterized the behaviour of many CNTs under these three types of strains.

In the second part of our research, we attempted to use the results we gathered from the simulations in order to devise a continuum shell model that was accurate enough so that the critical buckling force of different kinds of CNTs can be quickly predicted. The continuum shell model transforms any CNT into a thin-walled hollow cylinder, which roughly matches the density distribution of the matter which makes up the CNT, but uses solid mechanics to approximate the atomistic effects which truly determine the behaviour of CNTs, which we did so by using a software called ABAQUS. To find an accurate model, the properties of the cylinder must be determined by a formula from the properties of the CNT, and we used the modelling technique used by our supervisors in our attempt to find the most accurate model. However, we did not succeed in our attempt. One of the properties which determined the amount of force required to buckle the CNT was the young’s modulus of the cylinder, and it is determined by the stress-strain slope of the CNT during its buckling process. From the formula determining the properties of the CNT, there is a linear relationship between the young’s modulus and the critical buckling force of the CNT, which means that CNTs with higher young’s moduli are stronger; however, this contradicts our LAMMPS simulation results, as armchair CNTs, which have a higher young’s modulus than zigzag CNTs, interestingly had a lower critical buckling force. In this way, we proved the infeasibility of this particular way of modelling the behaviour of CNTs.

My Singapore experience has been one of the best I have ever had. Our supervisors were very helpful in our efforts, and it is with their assistance that we produced a successful report. My experience was made even richer by my classmates who also conducted research at the university. In the other half of our time, we would spend time together to talk about what has been going on in our work and sometimes explore the city together. On a few weekends, we would leave the island altogether, and go to Malaysia to see its twin towers, ride bikes on a remote island, and visit the beaches on an Indonesian island. In this way, we each learned about the different personalities on this trip, and in time, to nowhere did we go without everyone in the group together. It was truly a memorable summer.