Hybrid composite materials reinforced with unidirectional fibers and small-scale micro-or nanoparticles provide benefits compared to traditional composites. The present paper shows the experimental investigation of carbonfiber-reinforced polymers modified by the addition of 0.5-5 wt% of milled carbon fibers and 0.1-0.5 wt% of single-wall carbon nanotubes. Both fillers were analyzed from technological point of view. The impact on mechanical and physical properties was revealed and discussed. Main attention was paid to quasi-static tensile and flexural properties as well as fatigue behavior under tension-tension mode. The maximal improvement in static tensile strength by 8.6% (from 682 to 741 MPa) and flexural strength by 14% (from 649 to 740 MPa) was achieved by the addition of 0.3 wt% single-wall carbon nanotubes. Short beam shear strength increased by 18%. Fatigue durability was highly improved as well. The strengthening mechanisms are attributed to the improvement of shear interfacial properties. In contrast to single-wall carbon nanotubes, milled carbon fibers enhanced the properties by 3%-9% only at static loading, while fatigue properties are negatively affected.

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