FATIGUE TRESHOLD CRACK PROPAGATION IN AIR AND DRY ARGON FOR A TI-6A7-4V ALLOY

Fatigue crack propagation experiments on a Ti-6A1-4V alloy were carried out within the framework of linear elastic fracture mechanics. Crack propagation results encompassing a wide range of fatigue crack growth rates and stress intensity range were plotted in the conventional manner for studies conducted in room temperature air and dry argon environments. Corresponding fatigue striations formed in both environments were measured and compared with macroscopic crack extension rates. Examination of very low fatigue crack propagation rates at low stress intensity range levels disclosed a stress intensity threshold level below which Mode I fatigue crack propagation became insignificant. In a limited investigation at very low fatigue crack growth rates, the fatigue threshold levels were observed to decrease with increasing stress ratio. The influence of stress ratio also was observed at stress intensity range levels above the threshold; cyclic crack growth rates increased for the increased values of stress ratio. However, for the ranges of stress intensity, stress ratio, and growth rate considered in this work, the stress ratio influence appeared most pronounced at the lowest growth rates and lessened with increasing stress intensity range. Comparable fatigue crack growth tests (stress ratio equals 0.33) conducted on the Ti-6A1-4V alloy in air and inert dry argon at room temperature yielded almost identical results for cylic crack growth rates encompassing those associated with the fatigue threshold upward past 0.00001 in./cycle. Within this range, the fracture surface morphology changed from a cleavage-like appearance at threshold levels to a typical straited and dimpled appearance at higher growth rates. No significant difference in fatigue crack growth rate behavior was reported for Ti-6A1-4V specimens tested in either the STA (solution treated and aged) or STA plus annealed heat treated condition. /Author/

Media Info

  • Features: Figures; References; Tables;
  • Pagination: p. 125-140

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Filing Info

  • Accession Number: 00262239
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Oct 22 1974 12:00AM