Understanding the Effect of Aerospace Atmospheric Environments Containing Salts on Fatigue Crack Growth of AA7085

Fatigue crack growth is accelerated as a function of salt load density in atmospheric environments producing surface electrolyte droplets, suggesting that conventional testing environments may not accurately predict d a /d N particularly at high loading frequencies ( f ). Crack growth rates (d a /d N ) were determined for samples with NaCl deposited on the surface at densities between 10 and 1000 μg/cm 2 exposed to 80% RH air. Results showed the largest acceleration in d a /d N occurred for salt loads between 100 and 1000 μg/cm 2 . For frequencies above 1 Hz, 100 μg/cm 2 yielded higher d a /d N than both air and full immersion environments. A salt load of 10 g/cm 2 showed d a /d N similar to air without surface salts. For 50 μg/cm 2 , results were mixed with one sample showing accelerated d a /d N and the second showing a lower d a /d N . It is clear from this study that understanding the effects of surface salts on d a /d N is critical to preserve structural integrity.