Damage Detection in Complexly Shaped Carbon Fiber Pre-Preg via Segmented Electrical Impedance Tomography

Abstract

The rise of fiber-reinforced composites in structural and load-bearing applications necessitates effective nondestructive evaluation (NDE) methods for inspection. However, many existent NDE methods struggle with factors such as complex shapes, internal geometries, in-service monitoring, etc. Electrical impedance tomography (EIT)---owing to strengths such as sensitivity to a wide variety of deleterious effects, applicability to complex shapes, and potential for continuous in-service monitoring---has recently attracted attention as an inspection modality for conductive composites, especially carbon fiber composites. Despite growing interest in EIT, it is a comparatively new NDE modality and therefore requires additional rigor before it can be accepted as a trusted inspection tool. In particular, we herein make three important contributions that address bottlenecks to using EIT as a composite inspection tool: First, EIT is applied to a carbon fiber/epoxy pre-impregnated (pre-preg) composite. This is important because pre-preg is the standard for high-strength composites, and little-to-no work has been done to validate EIT on this material. Second, a novel segmented approach is used. This approach uses only a subset of the total EIT electrodes to image just one section of the component at a time, which reduces the computational cost of EIT and consequently makes it more amenable to in-service inspections. And third, this work validates the effectiveness of EIT on a complex shape with internal geometry. Our results show that EIT, combined with the mixed prior regularization method, is able to adeptly detect and localize multiple damages in a stiffened tube structure produced out of carbon fiber/epoxy pre-preg with no non-relevant or false-positive indications. Further, by using the segmented approach, EIT is able to independently image the inner and outer parts of the geometry.