An innovative nondestructive perspective for the prediction of the effect of environmental aging on impacted composite materials

In this work, three different types of laminates, each one realized with thirteen layers of fabric in epoxy matrix, have been inspected. In the first one, only aramid fiber is used, whilst the other two are hybrid laminates reinforced with basalt and aramid fibers disposed either in an intercalated or in a sandwich-like structure. All laminates were impacted with an energy of 12.5 J. Inspection of the impacted laminates has been performed by using different nondestructive testing (NDT) methods, such as infrared thermography (IRT), near-infrared reflectography (NIRR) and transmittography (NIRT) and ultraviolet (UV) imaging. Subsequently, impacted laminates were subjected to accelerated aging in an environmental chamber and then inspected again by IRT and digital speckle photography (DSP) using, in the latter technique, an innovative methodology of image speckle processing. Finally, a comparison between the Fast Fourier transform (FFT) and the wavelet transform (WT) techniques applied to the IRT data is reported along with a discussion about the optimal choice of the scales related to the complex Morlet wavelet. Combining these techniques, useful information was obtained to elucidate the structural changes on these laminates after accelerated environmental aging process.