Polymers reinforced with carbon fibres (CFRP) or glass fibres (GFRP) have a spectrum of failure that is much broader than for metals. The established techniques developed for metals are not powerful enough for this new situation. Therefore, new techniques are explored that provide information which is specific for the kind of failure or flaw. This response depends on the interaction mechanism involved.

There are various kinds of excitation to which the sample under inspection may react. Microwaves to which metals are opaque may propagate in polymers and, due to the anisotropy of the complex dielectric tensor, provide information on local fibre orientation. This is the base for microwave raster scan imaging of orientiation fields, e. g. of injection moulded parts. Lower frequencies of electromagentic waves are suited to monitor processes, e. g. curing (dielectric spectroscopy).

The propagation of acoustic waves suffers from high attenuation and scattering by fibers. On the other hand one can monitor fibre orientation this way also in depth. The angular accuracy may be higher than with microwaves. However, the method requires liquid coupling with the inspected sample.

Dynamic thermography at low frequencies is quite efficient in remote detection of subsurface flaws in laminates and other layered polymer materials. Depth information is obtained e. g. from the frequency dependence of phase angle images.

The paper will present examples obtained with various techniques. Comparison is made for the kind of information that is provided.