Experimental and Numerical Study of defects like FBH and BVID on CFRP using Vibro-thermography technique

Abstract

This work mainly focuses on the study of the vibro-thermography effect using the concept of LDR on the circular-shaped FBH and low velocity impact (i.e., < 10 m/s) created on CFRP plates of dimensions (a) 130*65*3 mm and (b) 100*100*3.5 mm using an end milling tool and a low velocity portable impactor, respectively. The composite sample is fabricated using the VARTM method. To find out the LDR frequency of FBH and surface crack, the sample is vibrated by providing wide band sweep excitation to the PZT element, which is glued to the composite sample. The LDR frequencies of circular-shaped FBH and low velocity impact are found to be 20.6 kHz and 171.5 kHz, respectively. The maximum outof-plane displacement at LDR frequency of defect (BVID) will result in a greater temperature increment because of both friction and viscoelastic effects, which are captured through an uncooled thermal camera. The temperature increment around BVID is found to be (nearly 1 °C) greater than that of FBH (nearly 0.48 ° C). Multiple sweep excitations are provided over the defect (FBH) to increase the temperature increment, which in turn increases the visibility of the FBH in the thermal image. To show the vibro-thermographic effect of BVID numerically, the data of an arbitrary BVID is exported from PAUT to COMSOL. Next, numerical simulation is done in COMSOL, and the temperature increment over defects (FBH and BVID) is found to be in good agreement with the experimental results.