Using the X-ray method of stress measurement for Ti-6Al-4V alloys, the residual stress near the crack was measured for annealed (AN) and solution treated and aged (STA) titanium alloys, under the condition that the measured X-ray stress was in satisfactory agreement with the applied stress under tension. The residual stress measured in the wake of the propagating fatigue crack, σ
r, was compressive, resulting in a smaller crack opening displacement,
COD, than theorized. The measured σ
r and
COD-values let us understand the fatigue crack propagation rate
da/dN in terms of the effective stress intensity factor
Keff. As a result, the
da/dN under the same
Keff-value was smaller in the AN specimen with zigzag crack growth than in the STA specimen with straight crack growth, although the
da/dN-Keff relationship under various stress amplitudes was represented by a straight line in a log-log scale separately for the AN and STA specimens.
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