Mahdi Javadinejad

Grade:  Ph.D.

Ph.D. Thesis:

Modeling of carbon nanotube reinforced epoxy nanocomposite by Multi-scale method

Year: Feb. 2014-Feb. 2019.

Abstract:

In this thesis, the Young's modulus and Poisson’s ratio of epoxy/carbon nanotubes (CNTs) anocomposite is predicated by the two-scale method approach. At the nanoscale, CNT, the interface between CNT and the matrix and a layer of the matrix around the CNT are modeled and the elastic behavior of the effective fiber (EF) has been identified. The interface between the nanotube and the matrix is considered as one of the main issues in modeling due to the importance of transferring the loads and increasing the mechanical properties of the nanocomposite. At this surface, due to the nature of the van der Waals bond between the carbon nanotube atoms and epoxy molecules, this nuclear behavior has been  developed on a continuous medium using the Cauchy-Buren rule. Adhesive behavior on the interface is based on the PPR model (Park-Paulino-Roesler), defined by the UEL subprogram. On an equivalent microfiber scale, as an ordinary amplifier, its elastic properties are extracted using virtual experiments, in representative volumes. In order to create a random pattern in terms of location and angle of positioning the equivalent fibers in representative representation, Script was used in Python language. By  performing a virtual stretching experiment, the elastic modulus and Poisson's nanocomposite coefficient have been extracted. The effect of different patterns of cluster accumulation of nanotubes on the properties of the site A nanocomposite has been studied through modeling. For the verification of the results, nanocomposite specimens were prepared according to the ASTM-D638 standard and tested for tensile stress tests. Comparison of the results of modeling and Halpan-Sai theory with experimental results showed The technique used in this study is more accurate than the Halpein-Sai theory in predicting mechanical properties. Considering the clustering of nanotubes in representative modeling, it influences the results and reduces the Young's modulus. Adding 1% of the crop of a multi-layered carbon nanotube to epoxy increases the 3-4% increase in the Young's modulus. Among models modeled for RVE, the model that models the clustering effect of nanotubes in 4 masses is most closely related to experimental results. Unlike Young's modulus, the Poisson coefficient obtained from nanocomposite modeling decreases with increasing nanotube volume fraction. This reduction in the 1% fraction of the amplifier for a model that examines the effect of half the nanotubes in 4 masses is less than 6.2%.

Keywords: Carbon nanotube; Effective fiber; Interface; Cohesive element