Advancing damage characterization in hybrid natural woven composites through the development of a novel thermography sequencing procedure

Employing proper algorithms to process the acquired thermal sequences in either the spatial or frequency domain plays a crucial role in enhancing the defect/damage detectability in composite materials by means of Infrared Thermography. However, the performance of these algorithms may be questioned when inspecting woven composites, as their weave pattern can hinder the defect identification, thereby making their characterization very challenging. In this regard, the aim of this paper is to develop an effective thermographic procedure that first removes the periodic weave disturbance and reduces the temporal noise from the sequence and then post-processes it to obtain quantitative information on the depth and size of the damaged area. The procedure has been applied to natural hybrid woven composites made of flax and basalt fiber reinforced polypropylene matrix. In particular, two different matrices have been compared: neat and with the addition of a coupling agent, which have been subjected to drop weight impacts using masses of 3, 6, and 9 kg while maintaining a constant energy level of 3 J. The damage was characterized by using profilometric results and processing thermographic data derived from pulse thermography tests. The obtained outcomes were critically discussed to assess how the impact velocity values affect the damaged area.