Exploitable results
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.
Results from method and prototype already qualified in composite polymer; BRITE/EURAM 2 BRE2-CT92-0139 (proposal 5081-91);
Optical light scattering diagnosis to measure fibre orientation and concentration for a depth-resolved quantification in composite polymers.
New methods for evaluating concentration and orientation of fibres in special cases samples issued from light scattering codes are proposed.
Original light scattering prototype with a 2 crossed polarization camera system (prototype devoted to laboratory developments).
Various versions of potential industrial prototypes 2 crossed polarization camera system and camera systems are proposed.
This method and prototype can be extended to various media, such as:
diphasic media: aerosols, dust, powder, emulsion, colloids, paint, ink;
sprays and injectors;
environment, pollution by dust and particles: asbestos, water process, filtration, grinding, pulverizing;
textile;
medical: pneumology.
The innovative aspects are clear (remote non-destructive diagnosis, independent and direct measurement of depth-resolved fibre orientation and concentration, simple prototype, very small but significative resolution volume, no limitation of working distance, small measuring time adapted for on-line diagnosis, etc.) and prototype specifications well known and tested by standard media.
Reduction of wastes and trial and error procedures will permit small and medium enterprises to compete in a better way with larger companies.
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