Study Of Structural Health Monitoring For A Composite Horizontal Tail Of Aircraft

In recent years, guided waves-based damage identification techniques have attracted increasing attention in structural health monitoring (SHM) applications of aircraft structures because such techniques could intuitively indicate the structural health status. In this dissertation, a comprehensive study of guided waves-based structural health monitoring for a composite horizontal tail of aircraft is presented.First, based on a piezoelectric actuator/sensor system, guided wave propagation mechanism (the transducer piezoelectric properties, the transducer-panel interaction, the guided wave dispersion, and the damping properties) in resin matrix composite structures is numerically and experimentally investigated. The guided wave propagation problem is studied analytically by a model that accounts for the effects of the structural damage; the bond layer properties; the structural attachments; the stiffeners and the changing temperature upon the wave propagation are also discussed. Some wave propagation characteristics, such as wave group velocity and response amplitude, in the composite panels are numerically and experimentally characterized.The detection capability of a SHM system strongly depends on the placement of sensor network. An investigation was performed to develop a sensor placement method to maximize the performance of a SHM system with a minimal number of sensors for detection of damage in a full-scale composite horizontal tail structure. This optimization problem was formulated to maximize the probability of detection (POD) through selection of optimal sensor arrays placement between stiffeners. POD of sensor network is the ratio between the entire paths effective coverage and monitoring region area. Effective coverage of cross-stiffener paths (CRP) and uncross-stiffener paths (URP) are estimated by the guided wave propagation experiment in a multi-stiffeners composite specimen. For a targeted POD (98%), the proposed method is used to configure an SHM system with a minimal number of sensors to identify damage for a composite horizontal tail of aircraft. Base on the sensor network layout and the configuration of the tail structure, the signal transmission cables were designed and installed to minimize the influence of the added sensor network to the original structure.A monitoring system for aircraft structures has to be effective in a changing temperature environment. A spearman rank correlation coefficient-based damage index is brought forward to identify damage of the structure under changing temperature. Tests on an aluminum plate and a composite plate are conducted in respective to verify the effectiveness of the damage diagnosis method using the spearman rank correlation coefficient-based damage index. And then, the method is successively employed and on the composite horizontal tail of aircraft which exposed to temperature variations. The experimental results show that the method can: isolate damage-sensitive features from temperature variations, detect the existence of damage and identify its location.Monitoring of complex structures to provide real-time safety and reliability information regarding the structure poses significant technical challenges. In this approach, a hierarchical strategy is proposed in which adjacent smart sensors are grouped together to form sensor communities. The strategy is composed of damage rapid monitoring (DRM) stage and damage imaging diagnosis (DID) stage. In the DRM stage, damage index which bases on the canonical correlation coefficient is used to monitor the trend of damage extension. In the DID stage, the algorithm based on the spearman rank correlation analysis is adopted to estimate the structural damage influence area. The spearman rank correlation coefficients for sensing paths between the present state (with damage) and the reference state (without damage) were calculated, and the probability of the presence of damage in the monitoring area enclosed by the active sensor network was imaged to identify the damage. The effectiveness of the strategy is demonstrated by an in-service SHM experiment on a CFRP T-joint which was carried out prior to the full-scale composite horizontal tail test. An empirical relation between the damage identification threshold and damage influence area is obtained by simulation damage detection experiment on the full-scale composite horizontal tail.Finally, the effectiveness of the guided wave-based SHM technology is verified by an in-service SHM experiment of a full-scale composite horizontal tail structure. The experimental results shown that the monitored region is completely covered by the coverage of sensor network; the spearman rank correlation coefficient-based damage index accurately identifies damage under changing temperature; the in-service SHM strategy effectively diagnosis damage occurrence, extension tendency and influence area on the composite horizontal tail structure in different loading steps.