Electromagnetic Inductive Coupling Analysis (EMICA): A new tool for imaging internal defects in carbon fiber composites

Carbon fiber laminates enjoy a wide range of applications from innovative architectural design to aerospace and the safety overwrap for pressure vessels. In the case of carbon fiber overwrapped pressure vessels (COPVs), the overwrap thickness can vary from 6 mm (0.25 inch) for thin-walled COPV up to 25 mm (~ 1”) or more for thick walled COPV, depending on the vessel type. The failure mechanisms for carbon fiber are more complex than for metals and monitoring COPVs for defects or fatigue over their lifetime is further complicated by the thickness of the carbon fiber used. In this paper, we introduce a new technique, Electro-Magnetic-Inductive-Coupling-Analysis, or EMICA, which can detect damage inside thick carbon fiber laminate pieces. EMICA is based on the interaction of the repeating three-dimensional conducting structure of carbon fiber and low-frequency electromagnetic waves to highlight defects such as delamination and fiber disruptions, well below the laminate surface. In this paper, we demonstrate EMICA in flat carbon fiber laminates up to 12 mm (~ 0.5”) thick, made in-house, with known defects hidden through the thickness of the piece that cannot be detected via visual inspection.