TeraHertz non-destructive testing methods for plastics and composites

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Plastics are becoming an important construction material. Often to make a functioning part, plastic pieces need to be welded and bonded together. In the manufacturing process defects can occur, including contamination, air voids, delamination, etc.

Marker image in visible and THz light

At DOC we explore a new NDT technique using a TeraHertz (THz) imaging system. THz waves lies in the electromagnetic spectrum of the frequency range between 300 GHz and 10 THz, or equivalently of the wavelengths range from 30 µm to 1 mm. In THz regime, most non-metallic and non-polar media are ‘transparent’. The ‘opaque’ plastics under visible light can be easily seen through using a THz light source. Therefore the subsurface defects can be visualized. Another important advantage of the technique is that THz illumination is safe to the human body. As compared to x-ray radiography, it doesn’t require any special safety measures. As compared to ultrasonic inspection, THz waves can pass through a much thicker volume and they are not affected by ‘soft’ materials (in contrast to quickly damping acoustic waves in rubber).

Composite test plate

Using our system, we can detect small air holes in thermal plastics. Other contamination (imbedded impurity) or imperfection (e.g. delamination, cracks) can also be tested and detected with ease. Furthermore, THz NDT method can also be applied to complex composite materials to detect impurity and delamination.

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