Abstract: A method and an apparatus for detecting and measuring cracks in plate-like structures using acoustic emission technique are disclosed. A false aperture transducer is designed to provide a criterion for filtering out extraneous noise in the acoustic emission signal based on modal analysis by computing the ratio of the high-frequency peak amplitude to low-frequency peak amplitude of the signal. A calibration curve correlating crack depth to the amplitude ratio can be obtained by simulating crack growth in a fracture specimen coupled to a test structure or field structure, and measuring acoustic emission signal in the structure by the false aperture transducer. The calibration curve correlates simulated crack depth percentage with computed peak amplitude ratio of the measured signal.

Abstract: The invention simulates acoustic emission signals produced by crack growth within a structure so that listening equipment may properly be calibrated to listen for acoustic emission signals from actual structural crack growth. The invention has several embodiments which generate acoustic emission signals from a crack growing in a specimen such that the acoustic emission signals have a broad bandwidth as the crack grows. The acoustic emission signals produced by the growing crack can be introduced into a structure being monitored through a cone-shaped portion which is bonded to the structure being monitored.