Fracture Toughness of Sicp/2124Al Metal Matrix Composite

An experimental study was conducted to evaluate fracture toughness of metal matrix composite (MMC). The material was a 12,10,7.5 mm thick extrusion of 2124 aluminum alloy with 10 % Sic particulates. Specimen configuration and test procedure conformed to ASTM E399 Standard for compact specimens. It was found that special procedures were necessary to obtain fatigue cracks of controlled lengths in the preparation of precracked specimens for the MMC material. Fatigue loading with both minimum and maximum loads in compression was used to start the precrack. The initial precracking would stop by self-arrest. Afterwards, the precrack could be safely extended to the desired length by additional cyclic tensile loading .Test results meet practically all the E399 criteria for the calculation of plane strain fracture toughness of the material. A valid K1c, value of the Sicp/Al composite was established as K1c = 25.19MPa. The threshold stress intensity under which crack would cause to grow in the material was estimated as A K1c = 2 MPa R = 0.09 using the fatigue precracking data. Fractographic examinations show that failure occurred by the micromechanicsm involved with plastic deformation although the specimens broke by brittle fracture. The effect of precracking by cyclic loading in compression on fracture toughness is included in the discussion.