Damage detection in self-sensing composite tubes via electrical impedance tomography

Fiber reinforced polymer composites are widely used in the automotive, aerospace, and energy sectors owing to their high specific stiffness and strength. With their increasing use, there arises the need to continuously monitor the health of these composites. Current methods of health monitoring in filament wound composites include embedding optical fibers and piezoelectric sensors during the manufacturing process. These methods, in addition to making the manufacturing process difficult, introduce weak spots in the structure. Alternatively, nanofiller modification of the matrix imparts conductive properties to the composite which can be coupled with imaging modalities such as electrical impedance tomography (EIT) for damage localization. To date, however, EIT has been limited exclusively to planar structures such as rectangular coupons. Because such simple shapes are hardly representative of many real composite parts, this work explores the potential of extending EIT to complex shapes for damage detection. Specifically, non-planar multiply connected domains are considered (i.e. carbon black-modified glass fiber/epoxy composite tubes). Our results show that multiple through-holes as small as 7.94 mm can accurately be detected on a tube with length-to-diameter ratio of 132.4 mm-to-66.2 mm (aspect ratio of 2:1). Further, it was observed that the sensitivity of EIT improved with decreasing tube aspect ratio. EIT was also successful in detecting sub-surface damage caused by low-velocity impacts. These preliminary results indicate that the combination of self-sensing via piezoresistivity and EIT has much greater potential and broader applicability for composite structural health monitoring (SHM) than the prevailing, planar geometry-centric state of the art suggests.