Research Experiences for Undergraduates
Summer 2001
Project Summary
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Research Experiences for Undergraduates Summer 2001 Project Summary |
Project Title: Mechanical Properties of Carbon Nanotubes
Student Name: Radika Rupasinghe
Student’s home institution: Hope College
Research Advisor(s): Dr. Janice Pawloski
Source of Support: NASA
During the past decade Nano-structured materials have excited considerable interest in the material research community partly due to their potentially remarkable mechanical properties. Carbon nanotubes could potentially have a Young’s modulus as high as 1TPA and a Tensile strength approaching 100 GPa. The design and fabrication of these materials are performed on the nanometer scale with the ultimate goal of obtaining highly desirable macroscopic properties.
NASA Langley Research Center in Hampton, Virginia has developed a method for modeling structure-property relationships of nano-structured materials. This method serves as a link between computational chemistry and solid mechanics by substituting discrete molecular structures with an equivalent-continuum model. This substitution may be accomplished by equating the vibrational potential energy of a nano-structured material with the strain energy of representative truss and continuum models.
After reading the following research papers, "Theoretical investigation of thermo-mechanical behavior of carbon nanotube-based composites using the integral transform method", "Carbon Nanotubes", and Equivalent-continuum modeling of Nano-structured materials-Langley Research Center", we started out by duplicating the truss model which the researches at Langley Research Center had modeled. In the truss model, each truss element corresponds to a chemical bond or a significant non-bonded interaction. The stretching potential of each bond corresponds with the stretching of the corresponding truss element and it is assumed that each truss joint is pinned. Our first attempt was a truss model of a hexagonal sheet.
Model 1- Hexagonal sheet
We used two types of elements to create the hexagonal structure. The
type a element represented the bond interaction between two C’s and the
type b element represented the non-bonded interaction between two C’s.
Their properties are given below in Table no: 1
Table no: 1
| Type of element | Cross-sectional area | Length of element | Modulus of elasticity |
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After experimenting with 2-D models we decided to test these deformations
on a 3-D model of a truss.
To accomplish this we used LINK8 3-D spar. It was actually the hexagonal
sheet rapped around to form a cylinder (model 2). The material properties
of the elements were same as in model 1
Model 2
| Element type | Real constant # | Material # | |
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The deformed radius and the original radius of the nodes 181 through
200 were taken into account. The Poisson’s ratio and the modulus of elasticity
of the truss were calculated using Excel. As we changed the stiffness of
type b elements the Poisson’s ratio and the overall stiffness was calculated.
Although we were able to match the overall stiffness of the truss with
the model that was designed at Langley we were unable to match the Poisson’s
ratio.
Slide show of Radika Rupasinghe's work