Sweep vibrothermography and thermal response derivative spectroscopy for identification of local defect resonance frequencies of impacted CFRP

Abstract

Vibrothermography at local defect resonance (LDR) frequencies is a promising technique to localize the vibrational energy at defected area and enhance its detectability under a low excitation power. However, the technique is mainly limited by the fact that it makes use of the LDR frequencies already known from e.g. vibrational measurements. To overcome this limitation, thermal response derivative spectroscopy is suggested as a post-processing strategy for reference-free identification of LDRs in sweep vibrothermography. An impacted carbon fiber reinforced polymer (CFRP) coupon is tested under broadband frequency sweep excitation and its surface temperature is recorded by an infrared camera. The LDR frequencies associated with different regions of the defected area are then extracted by time derivative analysis of the resultant thermal response. Selected LDRs obtained through the proposed technique are individually validated by lock-in vibrothermography at corresponding frequencies.