Guided Wave-based Structural Health Monitoring for a Composite Aircraft Fuselage under Mechanical Load

Abstract

The introduction of composite materials in aeronautics has brought numerous advantages, along with unique damage and failure modes. The structure health is currently ensured with an increase in non-destructive inspection activities and a damage-tolerant design. Among other techniques, Guided Wave-based Structural Health Monitoring (GW-SHM) has gained interest as a cost and time effective alternative to traditional non-destructive techniques. One of the main challenges for GW-SHM is the influence of environmental and operational conditions. Aircraft structures undergo a broad range of mechanical load conditions, affecting the GW-SHM system. A full-scale CFRP door surrounding structure was instrumented with a GW-SHM system and tested under mechanical load. The test object has a dimension of 4100 x 5700 mm and covers 9 frames, 17 stringers, 4 windows and the door surround structure. A hydraulic test rig was used to apply three load cases in quasi-static conditions on the structure: tension, lateral bending and vertical bending. A network of robust piezocomposite transducers to monitor the structure has been designed and manufactured during the project. The network is organized in arrays, which include the transducers, cabling and a connecting base plate for optimized sensor installation. A multiplexing module is directly connected to the base plate enabling a fast and reliable sensor connection, a drastic cable weight reduction, and a modular design. The load influence on the GW-SHM system has been analysed: on the transducer network as well as on the damage identification performance. The transducers were monitored using electromechanical impedance throughout the test campaign in order to check for debonding from the structure and piezoceramic breakage. Finally, a data-driven approach to damage identification has allowed the detection and localization of barely visible impact damage introduced during the test campaign.