Page 385 - Biaxial Multiaxial Fatigue and Fracture
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The Environment Effect on Fatigue Crack Growth Rates in 7049 Aluminium Alloy ut ... 369
Figure 5 shows the dependence of thresholds hKth on R and the hKth and K,, relationship
at different R-ratios for UA and OA 7049 A1 alloy in ambient air and in vacuum, respectively.
An L-shape curve is obtained for the OA alloy over the entire R range for air as well as for
vacuum. An increasing hKth with decreasing R is necessary in order to accomplish crack
growth, even at a negative R-ratio = -1, whereas no further increase of hKth is observed for
the UA alloy below R=O.O5.
tc, [MPamlR]
Fig. 5. Threshold hKth versus R-ratio (a) and K,,,,,. (b) for the UA
and OA A1 7049 alloy in air and vacuum.
