Abstract
Structural health monitoring results obtained with the electro-mechanical (E/M) impedance technique and Lamb wave transmission methods during fatigue crack propagation of an Arcan specimen instrumented with piezoelectric wafer active sensors (PWAS) are presented. The specimen was subjected in mixed-mode fatigue loading and a crack was propagated in stages. At each stage, an image of the crack and the location of the crack tip were recorded and the PWAS readings were taken. Hence, the crack-growth in the specimen could be correlated with the PWAS readings. The E/M impedance signature was recorded in the 100 - 500 kHz frequency range. The Lamb-wave transmission method used the pitch-catch approach with a 3-count sine tone burst of 474 kHz transmitted and received between various PWAS pairs. Fatigue loading was applied to initiate and propagate the crack damage of controlled magnitude. As damage progressed, the E/M impedance signatures and the waveforms received by receivers were recorded at predetermined intervals and compared.