Noncontact Epoxy Curing Monitoring and Subsurface Damage Detection

Abstract

Epoxies are an integral element of fiber-reinforced polymer composites, which are increasingly being used in various aerospace, automotive, civil, and naval structures. In addition, nanofillers, such as carbon nanotubes (CNT), are infused in epoxy resins to enhance their electromechanical (sensing) and thermal properties, among others. For both cases, and as innovative epoxy-based composites are being developed, monitoring and understanding their curing process is important for establishing manufacturing guidelines. Moreover, the ability to inspect for and to detect damage (e.g., defects created during manufacturing) is crucial for ensuring product quality and performance. The main objective of this study was to develop a noncontact technique for monitoring curing of epoxy and for detecting defects (or damage) in pristine and CNT-enhanced epoxy resins. First, electrical capacitance tomography (ECT) was employed for determining, in a noncontact fashion, the permittivity distribution of materials such as epoxy resins. Second, ECT was used for monitoring curing of pristine and CNTenhanced epoxy specimens. The results showed that reconstructed permittivity values of these specimens changed and correlated with curing times. Last, different sizes of damage were introduced to epoxy specimens. ECT was validated for its ability to detect the locations and sizes of these damage features