Nonwoven reinforced composites arise as an innovative material class, especially in the context of recycling of carbon fibres. These are initially in staple fibre form and thus also have a finite length in the later semi-finished product. At the same time, a certain fibre length distribution also exists due to the recycling origin. In the simplest case, all single filaments are randomly distributed, i.e. in isotropic fibre orientation. However, a superordinate preferred fibre direction is more effective in terms of the best possible utilization of the underlying anisotropic single fibre properties. Also significantly higher fibre volume contents as well as impregnation quality can be achieved using this approach. Corresponding technical implementations are the subject of current research and development projects along various processing routes.

Reliable measurement of such fibre orientations is thus essential for further development in this field. In the present approach, the intrinsic anisotropic conductivity of the carbon fibre base is utilized to define a measurand for the fibre alignment by means of non-destructive eddy-current sensor technology. For this purpose, a magnetic field is induced in the material, which is interfered by conductive elements like carbon fibres. The presented study shows that hereby a sufficiently high resolution can be obtained to allow direct definition of a quantitative measurement standard. Also it is demonstrated that this method works as an In-Line-Modification, and thus offers additional advantages for parallel process development.

The determined fibre alignment vectors are compared with mechanical test results, such as tensile and bending tests, for various angles. Complete polar diagrams can be recorded if required. Results reveal that the measurement method works robustly as a quick and efficient tool as a basis for further evaluation.