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Six cylinders (16 cm diameter with 6 mm wall thickness) were manufactured from two unreinforced aluminum alloy and four silicon carbide (SiC) whisker reinforced aluminum composites. Curved, subthickness, Charpy sized specimens were used to measure the fracture toughness, KIc in accordance with ASTM E 399. For the more ductile, unreinforced alloys, the British crack opening displacement (COD) method was used as an elastic-plastic approximation of the fracture toughness. The results rank the relative toughness of the aluminum alloy metal matrix composite (MMC) materials.
The test program was successful in demonstrating the changes in fracture toughness due to the addition of SiC whiskers, notch acuity, and prior hydrostatic straining. A new procedure was developed by which materials can be successfully fatigue precracked (FPC) by utilizing the notched strength ratio in bending. This procedure eliminates the cost of the excessive waste commonly generated in attempting to fatigue precrack fracture toughness specimens by conventional techniques.
fracture toughness testing, silicon carbide whiskers/aluminum cylinders, hydrostatic strain, notch acuity effects, matrix effects
President, L. Raymond & Associated, Irvine, CA
Materials engineer, Naval Oceans Systems Center, San Diego, CA