Detection of Barely Visible Impact Damage in Composite Structures Using Backward Sweep Vibro-thermography Technique Utilizing Asymmetry in Local Defect Resonance

ABSTRACTIn this article, local defect resonance-based vibrothermography has been studied for different sweep direction and ranges. Two different carbon fiber-reinforced polymer (CFRP) composite plate has been fabricated from vacuum assisted resin transfer molding. In the first plate, a flat bottom hole has been made and two barely visible impact damages are created in other plate. The area of delamination has been determined from phased array ultrasound testing. Laser doppler vibrometry (LDV) has been performed first for different sweep ranges and directions. The CFRP plate is excited with a piezoelectric element at 150 Vpp and the vibration over defect area is captured using a single point laser doppler vibrometer, operating in scanning mode. It has been found that vibration amplitude at local defect resonance (LDR) frequency increases in narrow sweep range compared to a wideband excitation. Again, in both cases, it has been found that backward sweep produces more amplitude compared to forward one due to softening nonlinearity. An asymmetry in LDR frequency is also been observed when the sweep range is further narrowed. An uncooled microbolometer camera is used for reception in case of vibrothermography. Backward sweep is found to be more effective as compared to the forward one and the temperature increment increases in case of narrowband excitation range.KEYWORDS: Local defect resonance (LDR) asymmetryvibro-thermographylaser doppler vibrometryflat bottom hole (FBH)barely visible impact damage (BVID)carbon fiber reinforced polymer (CFRP) composite AcknowledgmentsThe corresponding author acknowledges Science and Engineering Research Board under Department of Science of Technology, India for funding this work vide grant no. CRG/2019/005045.Disclosure statementNo potential conflict of interest was reported by the author(s).Additional informationFundingThe work was supported by the Science and Engineering Research Board [CRG/2019/005045].