Comparative statistical analysis of fatigue crack growth data

摘要

The differences in fatigue crack propagation behavior in 7075-T6 aluminum alloy between specimens damaged by corrosion and those in a baseline (noncorroded) condition are examined using a statistical hypothesis test. Middle tension plate specimens were corroded on one side in the laboratory and subjected to constant load amplitude (K-increasing) tests in dry and moist air environments. The results show that there is a statistically-significant increase in fatigue crack growth rates in the corroded material for stress intensity values based on nominal thickness. When the specimen thicknesses were reduced to account for corrosion material loss, the difference disappeared in most of the instances examined here. In one case, the thickness correction was found to predict fatigue crack growth rates that were slower in the corroded material. This anomalous result suggests that full tickness corrections may not be appropriate at higher stress intensity ranges.