Utilization of PVDF Sensors to Determine Impact Damage in Graphite/Epoxy Plates by Acousto-Ultrasonic Technique

The scope of this study into the use of metallized polyvinylidene fluoride (PVDF) foil sensors in the detection of impact damage of graphite/epoxy plates is twofold. First, it establishes that low energy impact damage, undetectable through visual examination and ultrasonic C-scan, can be detected through the acousto-ultrasonic (AU) technique. Secondly, it assesses the utility of PVDF sensors in obtaining AU signals. The AU approach to verification of material integrity is based on the premise that structural flaws will cause a greater attenuation of the ultrasonic pulse when compared to the attenuation of the signal through unflawed material. Through AU technique, material structural integrity can be determined by comparative means. Graphite/epoxy test plates were ultrasonically C-scanned, the PVDF sensors were adhesively bonded to the test plates and used to evaluate the structural integrity prior to impact testing. The plates were then subjected to impact and subsequently ultrasonically C-scanned to determine signal attenuation due to impact damage. Pattern classification was used to correlate impact damage with waveform changes and investigate waveform pattern repeatability. Acoustic signal characterization was accomplished using ICEPAK software.