Corrosion Fatigue Crack Growth Behavior at Notched Hole in 7075-T6 Under Biaxial and Uniaxial Fatigue with Different Phases.

摘要

This research investigates fatigue crack propagation behavior in both air and saltwater (3.5% NaCl) environments from pre-cracked notched circular hole in a 7075-T6 cruciform specimen. With stress ratio of 0.5, biaxility stress ratio of unity, and frequency of applied load of 10 Hz, the crack growth behavior was investigated under in-plane biaxial tension-tension fatigue with 45 deg, 90 deg and 180 deg phase difference conditions and then compared to previous fatigue tests with no phase difference to study the effect of changing the phase differences between the applied loads on the crack growth rate. Finite Element Analysis (FEA) was used to calculate cyclic variation of stress intensity factors ( K) at the crack tips. The crack growth rate was observed using optical microscopy. This study shows that in the biaxial fatigue tests with phase difference of 45 deg, 90 deg and 180 deg, two fatigue cracks were shaped, symmetrical in case of 90 deg and 180 deg, while it s unsymmetrical for 45 deg phase difference case. For each phase difference and at a given average crack growth rate, the strain energy release rate of the non-split crack is equivalent to the sum of strain energy release rates of the two split cracks. In the saltwater environment, the corrosion accelerates the crack growth rate.