Abstract
Fatigue crack propagation studies in vacua of 1.33 mN m-2, on Ti-6 A1-4V, at growth rates of 10-7 to 10-4 mm/cycle have shown that a threshold for growth exists at ‡K values of 6.3 to 7.6 MN m-3/2. The value of the threshold level is microstructure dependent, but growth above this value was structure insensitive according to both growth rates and fracture surface observations. Some slow (≈ 10-8 mm/cycle) crack extension was observed below the threshold values but prolonged cycling reduced the growth rate to a vanishingly small level. Fracture surface observations indicated that growth in this region was microstructure sensitive. Comparison with previously performed air work on the same material showed that while structure insensitive growth rates in vacuum were slower than those in air by a factor of 3 to 4, the low ‡K value structure sensitive rates were slower than the air ones by at least three orders of magnitude. A hypothesis is proposed to explain this in terms of a propagation mechanism for the structure sensitive mode of fatigue crack growth.
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Research Fellow, Department of Physical Metallurgy, University of Birmingham, England
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Irving, P.E., Beevers, C.J. The effect of air and vacuum environments on fatigue crack growth rates in Ti-6Al-4V. Metall Trans 5, 391–398 (1974). https://doi.org/10.1007/BF02644106
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DOI: https://doi.org/10.1007/BF02644106