Abstract: The flight loading fatigue test on airframe forms is the most crucial part of the full scale aircraft fatigue test, and its main aim is to expose the weakest area of key structures of the aircraft and to understand characteristics of the fatigue crack initiation and growth. The real-time monitoring of key stress-concentrated and poorly accessible locations are detailed by using acoustic emission (AE) technique. Through analysis of AE characteristic, the information about the starting time of crack initiation and structure fracture in the monitoring area can be timely obtained. The methods of obtaining useful AE signals under high background noise are detailed, including the use of resonants sensor and spatial filtering technique, mutual verification between characteristic parameter trend analysis based on statistical average and related parameter trend analysis based on amplitude, and the use of combination of loading filtering, amplitude filtering and spatial filtering. Case studies show that the proposed fast processing method for AE signals successfully fulfils real-time monitoring of the crack initiation and growth process around the bolt hole.

Key words: Acoustic emission (AE), Aircraft, Fatigue test, Trend analysis