Detecting of interfacial defects in CFRP−concrete bonded joints using dynamic speckle patterns of excited surface

Abstract

An optical-acoustic method (OAM) for identification of interfacial defects in carbon fibre reinforced polymer (CFRP)−concrete bonded joints is proposed. To detect and identify defects by this method, the unidirectional CFRP plate is excited by a harmonic elastic waves, and a series of dynamic speckle patterns (DNSPs) of the plate surface is produced by an imaging system. The local area of the plate directly above the interfacial defect, i.e. a region of interest (ROI), is considered as a circular membrane that oscillates at its fundamental resonance frequency under the action of an elastic wave. An optical-acoustic system (OAS) mock-up implementing this method, after generating and registering the DNSPs sequences allows forming an optical spatial response from the ROI and determining its dimensions, close to dimensions of a detected interfacial defect. To verify the proposed OAM, series of artificial circular disbonds in CFRP-concrete bonded joints were produced and optical spatial responses at the fundamental resonance frequency of each defect were obtained using the developed OAS mock-up. It is shown that obtained experimental dependency of the fundamental resonance frequency on the artificial defect radius is close to the same theoretical dependence plotted on the basis of the Rayleigh quotient frequency.