MONITORING FATIGUE CRACK GROWTH IN 7075 T6 ALUMINUM USING CONTINUOUS SENSOR

摘要

Fatigue crack growth during the service of aging aircrafts has become an important issue and the monitoring of such cracks in hot spots is desirable. A structural health monitoring system using an acoustic emission technique under development for monitoring safety of such structures is described in this paper. A "continuous sensor" formed by connecting multiple sensor nodes in series arrangement to form a single channel sensor is proposed to monitor acoustic emission signals. This paper describes the work in progress on developing sensors, instrumentation, and measurement technique applicable to on-board monitoring of fatigue cracks in 7075-T6 aluminum lap joints. The traditional AE sensors as well as bonded nodes of continuous sensors described above were used to monitor acoustic emission signals emanating from crack growth in aluminum 7075 T6 specimens. It was possible to differentiate the signals due to crack growth from noise signals arising from fretting as well as RF pickup. The sensitivity of the bonded sensor under development was comparable to commercial high sensitivity resonant frequency AE sensors. The relationship between acoustic emission parameters and the crack growth rate in the aluminum specimens is examined.