Accurate multiple-site damage localization of aircraft composite structures under environmental and operational conditions

Abstract

During the long-term use of the aircraft, due to fatigue load and other reasons, composite materials usually suffer Multiple-Site Damages (MSD), which will lead to a rapid decrease in the residual strength of the structure. Therefore, the research of MSD appear very important. In order to monitor MSD, imaging method based on Guided wave (GW) is an effective method. However, aircraft are usually faced with complex environmental and operational conditions (EOCs) when they are in service, which will bring non-negligible uncertainties to the acquired GW signals and cause unreliable damage diagnosis results. Therefore, a MSD imaging method based on GW and Gaussian Mixture Model (GMM) is proposed to suppress the influence of EOCs on the GW signals and to realize reliable imaging and localization of MSD. First, by adopting GMM to characterize the EOCs and measuring its variation in the monitoring process, an only sensitive to damage (OSD) feature parameter is proposed to identify the damage subareas. Then, for each recognized damage subarea, the OSD feature signals of every GW path are constructed by GMM to combine with the delay-and-sum (DAS) algorithm and to realize reliable damage imaging under EOCs. Finally, the damage imaging of each subarea are merged to obtain a MSD imaging result, thereby realizing MSD localization. GW signals under varying temperatures of the carbon fiber composite plate was measured by experiment and then processed by the proposed method, and the MSD was located accurately.