Abstract

In this work, multiwalled carbon nanotubes (MWCNTs) have been introduced in fiber reinforced polymer composites (FRPC) to enhance their capabilities in terms of sensing and improving electrical properties. Even though there have been extensive studies on incorporating MWCNTs into polymer matrix composites to monitor their integrity, no work has been found to provide a technique to detect, locate and quantify damage in large polymer composite structure (LPCS) and also to investigate electrical resistance behavior of glass fiber/epoxy/MWCNT composites subjected to multi-directional deformation.
The thesis is organized into two major sections: Developing two new structural health monitoring (SHM) techniques to detect, locate and quantify damages in LPCS, and investigating electrical resistance behavior of glass fiber/epoxy/MWCNT composites subjected to multi-directional deformation. In the first part of the thesis, two new, practical and real-time SHM techniques have been developed. One is for LPCS made of electrically non-conducive fibers and MWCNT networks. The other is for LPCS made of electrically conducive fibers and MWCNT networks. In these techniques, MWCNTs are added into epoxy matrix. This modified matrix is then incorporated with long fibers to make large composite plates. Two different strategies have been proposed for measuring electrical properties of LPCS depending on the type of fibers. The large plate is marked with grid points where electrically conductive silver paints are deposited. The electrical resistances and potentials between the grid points for electrically non-conductive fibers and conductive fibers reinforced polymer composite structures containing MWCNT are measured respectively. These values are used as reference sets. It has been shown that the occurrence of the damage makes the electrical properties between the contact points surrounding this damage change. The significant change in the electrical properties between contact points is used as an indication for detection, location and quantification of damage in the large plates. The SHM computer programs are written to provide the facility to detect, locate and quantify damage for the LPCSs in real-time. Two new concepts have been introduced for detecting, locating and quantifying damage in LPCSs using MWCNT networks. One is uniformity of MWCNT distribution. The other is sensitivity to change in electrical resistance. A new model of resistors network has been proposed for composite plates with different electrical conductivity as a result of different quantity of MWCNT. Theoretical analyses are performed based on Ohm’s and Kirchhoff’s laws using Matlab Simulink. Good agreement is found between experimental and simulation results.
In the second part of the thesis, the behavior of electrical resistance for glass fiber/epoxy composite laminates containing MWCNT subjected to uniaxial stresses along different directions is investigated. An explanation is provided for the electrical resistance behavior of the laminates containing MWCNT subjected to multi-directional deformation.