THE EFFECT OF PARTICULATE SIC ON FATIGUE CRACK-GROWTH IN A CAST-EXTRUDED ALUMINUM-ALLOY COMPOSITE

Detailed micromechanical analyses of fatigue crack growth have been performed on a composite with 15 vol pct particulate SiC in a peak-aged 2014 aluminum alloy matrix. This composite was manufactured by the Dural Aluminum Composities Company, San Diego, CA, by casting and extrusion. About 3 pct intermetallic particles were found in the matrix alloy in addition to those expected for this material. Fatigue cracks were grown from approximately threshold to rapid fracture. Analyses of the crack tips were performed by stereoimaging at low and intermediate stress intensities and just prior to the onset of rapid fracture. Detailed maps of strain were derived, and a considerable influence of SiC particles on strain was found. Analyses of microcracks near the main crack were made and found to have only a small influence on fracture. Fatigue threshold was explained on the basis of measured and calculated crack closure.