Servizio Comunitario di Informazione in materia di Ricerca e Sviluppo - CORDIS

Non-destructive methods for fibre orientation evaluation in polymer composites

A series of four non-destructive methods were retained to provide efficient remote techniques for the fibre orientation evaluation in polymer composites: thermal diffusion through its two variants thermal ellipsometry and lock-in thermography, microwaves transmission, light scattering, and ultrasonic backscattering. They complement each other with respect to materials and applicability.

If the material is transparent enough in the visible spectrum the light scattering approach provides valuable informations both on fibre orientation and fibre concentration. A prototype for light scattering analysis was built. If the sample is flat, not sensitive to water and small enough to be immersed in a tank, then ultrasonic backscattering may be applicable with an acceptable effort, especially since conventional C-scan units can be modified (prototype developed). If water coupling is not acceptable then the choice between microwaves transmission method and heat transfer method depends whether on the inspected component is filled with heat conductive fibres or not (prototypes developed) for depth information, orientation measurements require either an array of focused beams (possibly time-modulated) or a scanning unit which moves one laser focus across the sample in a raster fashion.

It seams that microwaves and ultrasonics require about half an hour for an raster image of orientation and for the thermal approach, a couple of minutes is necessary for the measurement. Scanning force microscopy (SFM) has been successfully used to provide high contrast images of polished sections of glass fibre and carbon fibre polymer composites. Mechanical properties of a series of Round Robin samples were measured to provide local flexural modulus, ultimate flexural strength, and ultimate yield strain. The date obtained by the methods were compared to each other in order to assess the merits of the retained non-destructive evaluation (NDE) methods. Correlations were found between actual fibre orientation distribution, mechanical properties of the materials, and NDE results.