Non destructive observation of defects in composite materials using time domain THz imaging

Terahertz waves can penetrate opaque materials and fingerprint spectra appear as those in infrared bands. The technique is expected to be used as a new non-invasive analysis method for various materials. The authors have applied terahertz time domain spectroscopy (THz-TDS) to observe cracks of two types of fibre-reinforced polymers (FRPs) which were Kevlar-and Carbon - FRPs in reflection mode. Internal defects, cracks or a void of Kevlar - FRP were clearly observed, which cannot be detected non-invasively by existing methods, such as ultrasound imaging. Although CFRP is highly reflective and the internal structure was hardly recognised observed, surface defects under the paint can be easily observed.