Non-destructive evaluation of puncture region in polyethylene composite by terahertz and X-ray radiation

An ultra-high molecular weight polyethylene composite sample has been non-destructively imaged via X-ray and Terahertz waves. The sample stopped a projectile, which resulted in delaminations, a bulge, and a chamber. Although the X-ray computed tomography reliably showed all interesting internal features of the sample, the axial resolution was moderate and artefacts and deformations limited its performance. A terahertz time domain spectroscopy system was used both for transmission and reflection raster scanning of the sample. The propagation of the THz pulse through the sample was compared with a theoretical model. Transmission investigations roughly determined the distribution of delaminations and size of the chamber. The reflection scanning through the time-of-flight analysis and signal processing enabled a detailed 3D imaging of the sample. A very good agreement of X-ray and THz images was achieved. Both measurement methods were compared and discussed.