On fatigue behaviour of small cracks induced by foreign-object-damage in Ti-6Al-4V

MIRCO DANIEL CHAPETTI

Turin

Conferencia; 11th International Conference on Fracture (ICF11); 2005

ICF Committee, Carpinteri, Mai, Ritchie

A threshold curve method previously developed was applied to analyze the high-cycle fatigue threshold of small cracks induced by foreign-object damage (FOD) in Ti-6Al-4V alloy for which experimental results can be obtained from recent publications. Experimental results found in the literature showed that the small cracks induced by FOD in Ti-6Al-4V alloys could propagate at DK as small as 1 MPa m1/2, i.e., well below the ¡°worst-case¡± DKthR threshold of 1.9 MPa m1/2 for long cracks in this alloy (load ratio R=0.95). According to the results obtained in the present work the threshold for propagation of small cracks (¡Ý20mm) can be as small as 0.8 MPa m1/2 considering a stress ratio R = 0.8, for which the threshold for long cracks is about 2.3 MPa m1/2. Further, the minimum stress ratio R at which the analyzed cracks can propagate seems to be about 0.6, for which the threshold for large cracks is about 2.7 MPa m1/2. It is also shown that for microstructurally small cracks the absence of crack closure effect is not the only reason for the observed faster propagation rates and lower propagation thresholds when compared with long cracks.