Abstract:

Discrepancy in reported elastic properties for nanocomposites is argued to be most likely a result of either variations in the size of reinforcement or lack of control of the composite microstructure. In general, there will be a size variation in nanotubes in a given composite, contribution from each nanotube diameter and the volume percentage that tubes of a definite diameter occupy within the composite toward the overall elastic modulus is modeled. In this work, Digimat-FE is used to generate a realistic three dimensional microstructure for the current carbon nanotube/ epoxy composite. A system of aligned carbon nanotubes embedded in epoxy matrix is modeled. In the system of aligned multi walled carbon nanotubes, the entire volume of the model has been divided into finite individual sub-composites, each one containing a specific nanotube diameter with a local volume fraction. A second model showed a single representative volume element for the current nano-composite, in which the carbon nanotubes were simulated as a randomly (fully) dispersed, where all particles have been separated from each other. Moreover, a micromechanical approach for modeling short fiber composites was developed to account for the structure of the multi-walled carbon nanotube reinforcement and predict the elastic modulus of the nanocomposite as a function of the constituent properties, reinforcement geometry and nanotube structure. Finite element results show increase in elastic modulus with increasing aspect ratio for composites with high filler loading (3 vol%). Micromechanical predictions highlight the structure or size influence of the nanotube reinforcement on the properties of the nanocomposite. The nanocomposite elastic properties were found to particularly be sensitive to the nanotube diameter, since larger diameter nanotubes showed a lower effective modulus and occupied a greater volume fraction in the composite relative to smaller-diameter nanotubes.