Effects of Surface Roughness in Adhesively Bonded CFRP Joints Using NDE

This work presents the details of experimental investigations to study the effects of surface roughness on adhesive joints’ strength and establish a correlation with corresponding Nondestructive Evaluation (NDE) parameters. NDE parameters are the quantifiable properties of specimens that NDE techniques can measure. The roughness at Single Lap Joint (SLJ) interfaces was varied using different emery grades of 36, 50, 60, and 80 CAMI scale. The change in roughness was evaluated through NDE tools viz., X-ray radiography testing (XRT), Acoustic Wave Propagation, and InfraRed Thermography (IRT). While X-ray images do not show any significant variation in intensities with roughness, roughness can be visualized after histogram equalization. The change in image intensities was observed with adherend thickness. The attenuation coefficient of acoustic waves for joints with different grades of roughness evaluated using the standard Hsu-Nielsen pencil source through pitch-and-catch method shows a correlation with the surface roughness. IRT shows the variation in the cooling constant with roughness and thickness of the adherends. This paper also demonstrates the thermal conductivity evaluation of the bonded specimen with IRT and the effect of surface roughness on it. The destructive tests evaluated the shear strength, and the NDE parameters were correlated with the shear strength of the SLJ.