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Precursor Damage Inception Quantification in Composites Using Coda Wave Interferometry based on Taylor Series Expansion Technique



Precursor damages in composite material develops in the form of matrix cracking, fiber breakage, deboning, wrinkling, micro buckling etc. However, it is extremely challenging to detect those damages in their early stage using conventional Structural Health Monitoring (SHM) methods. Most of the times, these damages remain undetected for the long time. Ultrasonic coda wave interferometry (CWI) technique based on Taylor series expansion theory is extremely sensitive to small changes in the medium. Here, we implement this technique for the first time to detect damage precursor in woven carbon fiber composite laminates (CFRP). One American Society of Testing and Materials (ASTM) standard specimen were tested under high cycle (10Hz) tensile-tensile fatigue loading. Two high frequency piezoelectric (PZT) sensors were mounted on the specimen as sensor and actuator. Pitch-catch experiments were performed at a regular interval of 5,000 cycles until 300,000 cycles. A standard 5 count tone burst signal was used for the actuation. Stretch parameter, which is measure of relative velocity change in the medium is calculated at 5,000 cycle’s interval. Scanning Acoustic Microscopy with 25MHz transducer was used to Quasi-longitudinal (QL) wave velocities over the gage length of the specimen. QL velocities were calculated at the interval of 10,000 cycle. Cumulative damage growth in the composite specimen from both the methods are correlated. To verify both the techniques, optical microcopy imaging was also performed at the interval of 20,000 cycles to investigate the development of the precursor damages in the specimen.

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