Automatic Testing of Carbon Fibers

Testing of carbon fibers with FAVIMAT+ and ROBOT 2

FAVIMAT+ and ROBOT 2

The importance of carbon fibers as a reinforcement material in energy-saving lightweight composites is well accepted. Fast and reliable, i.e. automated, linear-density- and tensile testing of carbon fibers thus becomes increasingly important. Due to the special properties of carbon fibers an automatic handling of individual filaments has been considered to be problematic. TEXTECHNO in Mönchengladbach realizes an automated test of linear-density- and tensile properties on such carbon filaments in their automatic fiber test system FAVIMAT+ with ROBOT 2.

For such automatic testing of carbon fibers the filaments are first inserted into a magazine. The magazine storage of the ROBOT 2 system can take up to 20 magazines with 25 fibers each. The linear-density-, tensile-, as well as elastic properties are then tested fully automatically. The vibroscopic linear-density test as well as the tensile- and elasticity test are performed in the FAVIMAT+ single-fiber tester. These tests are done on exactly the same fiber section and clamping the fiber only once. In comparison to the testing of laminated rovings, this method has a big advantage: First results are already available after a few minutes and not only after several hours.

Test section for single fiber testing

FAVIMAT+ test section

Also without the automation described above, the FAVIMAT+ is employed successfully by producers and users of carbon fibres as well as in research institutes. It is a universal tester, suitable for all types of fibres. Its excellent length- and force resolution (down to 0.1 µN) makes it an interesting testing instrument also for other applications as for instance tensile tests on nano nonwovens. During the vibroscopic linear-density test, the instrument automatically determines the resonance frequency of the basic transversal oscillation under a well-defined tension and oscillating length. Taking the density of the tested material into account, the effective cross-section can easily be determined. Here, the precision is in general better than a determination by optical means. The measuring principle can be extended to a complete vibrational analysis for the determination of further parameters such as the bending stiffness.

The combined measurement of cross section and tensile strength on the same single carbon fiber filament allows to translate the force-elongation curve directly into a stress-elongation curve. This is done by normalizing the forces measured in cN by the individual cross sectional areas of each carbon fiber to receive the stresses in GPa during the tensile test. Likewise, also the derivatives of these stress-elongation curves are directly available in the units of GPa yielding an immediate measurement of the modulus of the fiber.  

combined cross section and tensile test on carbon fibers

Force-elongation, stress-elongation and modulus measured on a sample of 20 carbon fibers with FAVIMAT+

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