|
Environmentally Influenced Near-Threshold Fatigue Crack Growth in 7075-T651 Aluminum Alloy Pages: 12 Published: Jan 2000
Download this paper for $25
PDF (256K)
View License Agreement Source: STP1401-EB Abstract The near-threshold fatigue crack growth behavior of the 7075-T651 aluminum alloy was studied in laboratory air, vacuum, and an aqueous 3.5% NaCl solution. Results indicate that a rising stress ratio (R) enhanced the near-threshold fatigue crack growth by increasing the crack growth rate (da/dN) and decreasing the threshold stress intensity range (K) in both laboratory air and aqueous 3.5% NaCl solution. However, the reverse was observed in vacuum. It was also noticed that the near-threshold fatigue crack growth resistance was greatest in vacuum, intermediate in aqueous 3.5% NaCl solution, and lowest in laboratory air. Conversely, the crack growth rate at given values of AK were shown to be greatest in laboratory air, less in 3.5% NaCl solution, and lowest in vacuum. In both laboratory air and aqueous 3.5% NaCl solution, K, initially decreased with increasing R until a critical stress ratio of R = 0.5 was reached, which it then leveled off or decreased slightly. The K values for these two environments appear to converge at a higher R. On the other hand, in vacuum, the K, increased linearly with increasing R. In addition, at lower R, a greater resistance to near-threshold fatigue crack growth was detected in aqueous 3.5% NaCl solution than in laboratory air. This is presumably attributed to crack closure that has been induced by accumulation of corrosion product in the crack-tip.
| ||
