Development of Acoustic Emission Methods for In-Flight Monitoring of Aircraft Structures

Abstract

This paper provides an overview of an ongoing program to utilize acoustic emission methods to detect fatigue crack growth in aircraft structure during operation. Experimental methods including instrumentation, test specimens, newly-developed sensors, and experimental procedures used in acquiring acoustic emission waveforms are described. Fretting noises are produced at the interfaces between 7075 aluminum plates and a steel bolt during fatigue cycling of three-part joint specimens. A two-channel waveform recorder and analyzer records the experimental data for subsequent pattern recognition analysis. The observed signals cluster into three distinct groups on the sinusoidal load curve. By varying experimental procedures, these groups of signals can be associated with crack growth, fretting, and crack opening.

Another apsect of the project is the development and evaluation of two new sensor designs having improved bandwidths. Calibration information and performance of these sensors in fatigue test monitoring are discussed. It is possible to obtain well-defined data sets from joint specimens that can be used in pattern recognition analysis. The results of such analysis is given in a companion paper. The future direction of this project in leading to in-flight AE monitoring of aircraft is also presented.