Non-contact embedded sensing by Magnetostrictive Carbon Fiber Reinforced Polymer (MagCFRP): A smart material for early inter-lamina localized damage detection

Abstract

Although failure mechanics and plasticity of composite materials is a relatively new and volatile field, it has been long realized in the composite materials community that a composite’s true integrity lies in the constituents’ interfacial health. Composite materials allow scientists and engineers to design structural architectures with directional stress, strain, and thermal fields in mind while simultaneously reducing the system’s overall weight. While there are advantages to using composite materials like carbon fiber reinforced polymers (CFRPs), designing and implementing long-term sustainable aerospace structures out of CFRPs is bottlenecked by the brittle catastrophic failure mechanism high strength carbon composites exhibit. As the demand for these materials in critical loading regimes increases, it is paramount that scientists and engineers understand how CFRPs will behave in real-time and in predictive models for load profiles. This research’s motivation comes from the US Army’s future vertical lift vehicle initiative to transition from interval-based maintenance to condition-based maintenance (CDB). This paper explores a real-time, non-contact, and non-destructive evaluation (NDE) method for composite materials by performing localized magnetic flux scans (32 mm² field of view) of CFRP embedded with Terfenol-D ( $\approx 100$ microns in diameter), a magnetostrictive material. For Magnetostrictive Carbon Fiber Reinforced Polymer (MagCFRP) elastic regime testing, there was an observed localized magnetic flux gradient of more than 5 mT (4%) with a reversible flux of 100%. For MagCFRP elastic-plastic regime testing, a localized magnetic flux gradient of more than 3 mT (2%) with a reversible flux of only 25% was observed. Terfenol-D embedded CRFPs have shown promising results for detecting instantaneous stress and strain levels and detecting deviations in inter-lamina residual stress after critical loading. Acoustic emission (AE), Digital Image Correlation (DIC), and X-ray computed tomography (CT) scanning were used to validate the observed results.