Carbon fiber reinforced aluminum matrix composites are used as advanced materials in aerospace and electronic industries. In order to investigate role of aspect ratio of carbon fiber on fracture toughness of aluminum matrix composite, the composite was produced using stir casting. Al–8.5%Si–5%Mg selected as a matrix. The samples were prepared with three volume fractions (1, 2 and 3) and three aspect ratios (300, 500 and 800). Three-point bending test was performed on the specimens to evaluate the fracture toughness of the materials. The results showed that the fracture toughness of composites depends on both fiber volume fraction and aspect ratio. Scanning electron microscopy (SEM) was employed to elucidate the fracture behavior and crack deflection of composites. The study also, showed that the toughening mechanism depends strongly on fiber volume fraction, aspect ratio and the degree of wetting between fiber and matrix.

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