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Open Access Publications from the University of California

Curing and Subsurface Damage Monitoring of Epoxy and Epoxy-based Composites

  • Author(s): Fan, Gaochen
  • Advisor(s): Loh, Kenneth J
  • et al.

Due to their extraordinary material properties, epoxy has been widely used in various industries. Moreover, nanomaterials are infused into epoxy to enhance their mechanical performance and for encoding different functionalities, such as for fiber reinforced polymer (FRP) composites. However, additives in the epoxy matrix can affect curing and the mechanical properties of FRP structures. Therefore, the main objective of this thesis was to investigate the use of electrical capacitance tomography (ECT) for monitoring curing and subsurface damage in pristine epoxy and nanocomposite epoxy. In short, ECT uses a set of noncontact electrodes and interrogates a sensing area using different patterns of electric field excitations. Boundary capacitance measurements obtained simultaneously are used as inputs for solving the ECT inverse problem to reconstruct the electrical permittivity distribution of the sensing area. The hypothesis was that curing and damage of epoxy would result in permittivity changes that could be detected and localized by ECT. The thesis first starts with a detailed description of the ECT theory and system. Second, to test the hypothesis, pristine epoxy was subjected to ECT for monitoring curing, which was then validated using ultrasonic wave tests. Then, ECT was used to monitor the curing of carbon nanotube-based epoxies whose electrical properties are sensitive to strain. Both pristine and nanocomposite epoxy results confirmed the hypothesis that permittivity decreased with increasing curing time, and ECT can be used as a noncontact and noninvasive curing monitoring tool. Last, epoxy specimens with different geometries were drilled with holes to simulate damage. The results indicated that ECT was not only able to reconstruct the shape of the specimens but was also able to identify the location and severity of damage.

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