The reinforcement of C/SiC composites by short fibers is more cost efficient than applying fabric reinforcements. However, undesirable mechanical properties such as low strength and high scattering limit the use of short fiber reinforced C/SiC for new applications. Therefore, the aim of this work was to increase the reliability and the mechanical strength by systematically verifying the most important parameters. More specifically, the objective was to determine the influence of fiber length, fiber orientation and bimodal fiber composition on the mechanical properties; the fiber content was held constant at 35 vol.-%.
The short fiber reinforced plates (150 x 150 x 3 mm³) were processed using liquid silicon infiltration (LSI). 3K HTA carbon fiber tows were chopped in the desired length of 6, 12 and 24 mm. The flexural strength was determined by three- and four-point bending tests and were conducted according to industrial standard operating procedure DIN 658-3. A fiber pre-impregnation were tested with thermoplastic resin showing a low viscosity.
With this new manufacturing process, excellent bending strengths could be achieved by different preparations of the composite materials. Isotropic, short fiber composite materials resulted in bending strength values above 100 MPa and orientated short fiber composite materials had an average strength greater than 160 MPa. To determine the mechanism behind the increase in strength, further investigations included scanning electron microscopy (SEM) to analyze fractured surfaces, as well as optical microscopy to investigate the cross sections and different methods for measuring the fiber orientation, e.g. the computed tomography were applied.
In conclusion, it was shown that by optimization of fiber length and orientation C/SiC-short fiber reinforced material could be used as high-performance material.