Determination of Stress Intensity Factor for Cold-Worked Fastener Holes in 7075 Aluminum Using the Crack Growth Method.

摘要

Stress intensity factor calibrations were obtained for thru-the-thickness flaws emanating from cold-worked fastener holes in 7075-T6 aluminum alloy plate using the fatigue crack growth method. Cracks were periodically photographed to determine crack growth rate using a 35 mm camera actuated by a digital counter. Tests were conducted in laboratory air with constant amplitude loading, 30 Hz frequency, and R-factor = 0.05. The J.O. King sleeved cold-working process was used with a nominal diametral interference of 0.012 in. Open-hole specimens were tested at 16 KSI, 25 KSI, and 40 KSI remote stress. K calibrations for open cold-worked holes were in agreement with Grandt's linear superposition solution. Pin-loaded cold-worked holes, tested using a 2000 lb load transferred thru a 0.25 in. pin, showed a twenty-fold increase in fatigue life.