Laser-based Structural Training Algorithm for AE Localization and Damage Accumulation Visualization in a Composite Wing Skin with Various Sub-structures

Abstract

Acoustic emission (AE) is a transient phenomenon in which an elastic wave propagates to a structure as a result of structure damage such as micro-cracks, internal-cracks, friction, fiber breakage and fiber matrix debonding in a structure. AE encompasses a lot of information related to the integrity of the structure. Particularly, AE is used to overcome the difficulties in detecting damages that are hard to detect, such as micro-cracks and internal cracks. Composite structures are widely used in high technology structures due to their high stiffness to weight ratio. However, the source localization in the composite structure has been difficult for years due to variables such as wave propagation direction and speed along the fiber direction. In this paper, we propose laser scan based structural training technique with a single AE sensor (lead zirconate titanate sensor) in a real composite wing skin with a spar and stringers. This technique compensates the difference in characteristics between actual AE and laser-induced elastic wave in the frequency domain using a structural training algorithm. Source localization was performed using cross-correlation based waveform similarity between actual AE and laser-simulated AE A pencil-lead break method, which is a standard method to mimic the AE induced by actual composite damage. The proposed laser scan based structural training technique derive 4.36 mm error distance in average in the actual composite wing skin structure with a spar and stringers. The flexibility of this technique for various amplitude of damaged signals, which induced cracks was verified by using various diameter of pencil-lead. To visualize the accumulated damage, the concept of damage index, which quantify AE is appended at localized point. Finally, we implemented the damage project system to intuitively identify the damage location in large wing skin structures.