Nondestructive evaluation of carbon fiber reinforced polymer (CFRP)-timber interfacial debonding using active microwave thermography (AMT)

Abstract

Carbon fiber reinforced polymer (CFRP) is increasingly used to strengthen the flexural, shear, axial, and seismic performance of existing timber structures, but CFRP-timber interfacial debonding can substantially weaken the composite action and trigger catastrophic structural failure. Therefore, efficient nondestructive evaluation method is needed to inspect the interfacial debonding, flaws, and imperfections after the installation and periodically during the service of CFRP strengthened timber structures. This study is the first work to investigate nondestructive evaluation of CFRP-timber interfacial condition using active microwave thermography (AMT). AMT utilized microwave as an excitation to generate heat in CFRP and to indirectly detect the interfacial defect from the temperature anomaly on the surface of CFRP. Ten CFRP-timber specimens with different shapes and sizes of interfacial defects were tested under AMT. The experimental results showed that AMT can intuitively detect the CFRP-timber interfacial debonding at the earliest within 8 s to 11 s, which has advantages in speed and visualization. It should be noted that the blur effect can decrease the precision of detection of the shape, especially sharp corners, of the defect. The comparison between specimens with different parameters showed that larger areas of debonding can be detected easily while small ones cannot. In this study, defects with a diameter ≥ 7 mm can be detected.