Composite components get smart
Today's aircraft composite components feature innovative designs and multifaceted geometries that make it difficult to detect signs of fatigue or deeply hidden flaws. The aviation industry has, therefore, recognised the value of more sophisticated SHM systems as well as innovative ways to deploy them on such complex composite structures. Although SHM technology is still not mature, research and development has yielded promising results – in part because existing technology has been integrated into SHM systems. A case in point is work carried out in the project SCOPE (Self-sensing curved composite panel under operational load: Methodology platform for prediction of damage event). Researchers developed innovative methodologies based on available sensor technologies. Specifically, two different methodologies were adopted for active and passive sensing based on elastic wave propagation and electromechanical impedance (EMI). Guided ultrasonic wave propagation was suggested for wide-area inspection and EMI for identifying local damage. Before SCOPE, there were a number of available SHM technologies, but most research and experiments had been performed on simple structures. Researchers extended existing methodologies – initially developed for flat composite panels – for curved fuselage panels. The new damage detection methodologies are based on comparing the structure's current state to a reference structure without any damage. Accurate estimation of damage due to impact requires knowledge of the impact location and force magnitude as well theoretical prediction of the damage. To achieve the best possible estimation, more than 100 scenarios of various impact forces at different locations were required for generating meta-models. Once generated, meta-models were implemented to provide for damage detection. Furthermore, to detect reliably any damage prior to it becoming critical, sensors need to be positioned on the panel carefully. Researchers adopted an innovative approach based on maximum area coverage to find the optimal sensor layout and minimise blind spots. In this process, the number of sensors can remain low in pursuit of the highest probability of damage detection. SCOPE methodologies were validated against numerical data as well as experimental measurements collected on test coupons, mono-stringer and curved fuselage panels. The findings offered a starting point for recommendations for further testing. The first step towards applying the developed methodologies on actual size aircraft parts under real load conditions has been made.
Keywords
Aircraft, structural health monitoring, SCOPE, operational load, electromechanical impedance, composite panels
