Testing of an impacted CFRP sample with various NDT methods

Abstract

This project includes the full NDT testing of an impact that was made with a portable, angle-adjustable impactor. Vacuum assisted resin transfer molding is used in the works to fabricate CFRP composites. Afterwards, impacts on CFRP sample are carried out with single angle (0°) but different energy (Max: 38.39 J and Min: 17 J) and defects created on near side (opposite to impact) name as D1, D2 and D3, respectively. On visual inspection, defect D1 and D2 comes in the category of BVID (Barely visible impact damage) and D3 in IVID (Invisible Impact damage). To detect the flaws in the composite, various nondestructive testing like phased array ultrasonic testing (PAUT) and local defect resonance (LDR) based Laser Doppler Vibrometer (LDV), Acoustic testing with piezoelectric transducer microphone, vibro-thermography (VT) tests are performed. PAUT picturized the shape and size of the delamination created between the layers. Further, LDR frequency based experiments were performed to detect the flaws. A wideband frequency sweep (1-500 kHz) excitation is provided to sample by contact type piezoelectric patch to detect and extract the LDR frequency of flaws with the help of LDV. Only BVID (D1 and D2) are detectable through LDV and corresponding to defects D1 and D2, LDR frequencies are found to be 219 kHz and 171.5 kHz, respectively. But, acoustic testing with piezoelectric microphone is able to detect BVID (D1, D2) as well as the IVID (D3) with LDR frequency 209.9 kHz, 178.2 kHz and 234.2 kHz, respectively. After extracting the LDR frequencies of defects, the VT experiment (with uncooled Micro-bolometer camera) is performed in narrow sweep excitation (130-250 kHz) range to verify the LDR frequency and corresponding to LDR frequency contour of scanned region of sample are presented. Various NDT methods are compared and found that VT is fastest can detect the flaws in real time within a minute.