In this work, a composite pipe is subjected to multiple cycles of mechanical loading/unloading in a three point bending configuration. The specimen is instrumented with eight piezoelectric wafer active sensors (PWAS), used as passive receivers of acoustic emission signals during loading. Amplitude-frequency and amplitude-duration analysis of the signals allows detection of different damage mechanisms. Active monitoring is done using PWAS successively as transmitters and receivers of guided waves, in a pitch-catch configuration. Signals are collected for each chosen excitation frequency in the range 200-300 kHz. Scans are recorded between successive loadings of the specimen to assess the state of damage at each stage, and compare against the ‘pristine’ condition. The axisymmetric L(0,2) mode at 230-250 kHz is shown to be attractive for long distance propagation between axially aligned sensors. Cross-comparison of tuning curves obtained from the pristine condition and test data show attenuation in amplitude of the L(0,2) mode, respectively. Based on this, a damage index is proposed.
Neha Chandarana, Constantinos Soutis, and Matthieu Gresil, "Passive and active monitoring for defect detection and quantification in composites," Proc. SPIE 10600, Health Monitoring of Structural and Biological Systems XII, 1060020 (Presented at SPIE Smart Structures and Materials + Nondestructive Evaluation and Health Monitoring: March 08, 2018; Published: 27 March 2018); https://doi.org/10.1117/12.2296513.
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