낙하충격시험을 통한 평직 CFRP 적층판의 충격손상 감지와 유의 충격손상 신호의 정량적 평가

초록

A PVDF (polyvinylidene fluoride) piezoelectric sensor has been applied to diverse structures and equipment because it can be processed in various size and shapes. Moreover, the PVDF sensor has outstanding piezoelectric performance capable of detecting the impact vibration and the stress wave due to impact damages. In this study, the PVDF sensor was used to measure the vibrations from the impact on a plain woven CFRP (carbon fiber-reinforced plastics) laminate, and a methodology for identifying the impact damage was presented based on the measured signals. Drop impact tests were conducted on the CFRP specimen to analyze impact responses and vibration signals in terms of impact energies and as a result, it was confirmed that absorbed energy by the CFRP specimen increased dramatically when the impact energy higher than 5 J was loaded to the specimen. Vibration signals were classified as significant impact damage signals and normal impact signals in terms of the absorbed energy. Subsequently, the frequency components of two types of signals were compared via continuous wavelet transformation, and it was confirmed that signals higher than 32 khz was generated when the significant impact damage occurred. Signal energy was examined via discrete wavelet transformation to evaluate the signal quantitatively, and it was known that the signal energy was clearly high when the significant impact damage occurred. In conclusion, the methodology of detecting the significant impact damages using the PVDF sensor was proposed, and this would be utilized in the fields of structural health monitoring and non-destructive testing.

키워드