Effect of fiber length on the mechanical properties of high dosage carbon reinforced

Short fibers are effective reinforcements in strengthening and toughening polymer materials. It is reported that even small amounts of fibers drastically increased composite strength. However, for high fiber dosage the dispersion and interface adhesion is quite poor reaching to lower stiffness and strength efficiency. The effects of fiber length on mechanical properties of low content of short fiber reinforced composites is usually associated with a gain with the increasing of fiber length, but for high dosage this statement is not entirely consensual. This paper intends to contribute for the better understanding of the effect of the fiber length on the mechanical performance of high dosage fiber reinforced composites. Composite plates were manufactured by compression moulding, using short carbon fibers reinforcements (2, 4 and 6 mm in length) with 60% wt fiber fraction and the Biresin®CR120 resin as matrix. The specimens were machined from the plates for desired dimensions to the tensile and DMA tests. High dosage composites exhibits very low efficiency parameters both in stiffness and particularly in tensile strength. Stiffness increases in order of 25% when fiber length increases from 2mm to 4mm, but afterwards decreases for 6mm fiber length composites. The same tendency was observed for the tensile strength meaning that poor fiber dispersion and disorder was achieved for 6mm fiber length. The results of DMA indicate, however, that modulus storage increases when fiber length increases from 2mm to 6mm.