The effects of stress ratio (R) and maximum applied stress-intensity factor
(K-max) on fatigue crack growth rate (da/dN) have been investigated. Fatig
ue crack growth behavior was analyzed by plotting applied cyclic stress-int
ensity factor (Delta K) versus applied K-max for an alpha+beta titanium all
oy (Ti 6-2-2-2-2) at several values of da/dN. This analysis revealed two di
stinct regions of fatigue crack growth behavior. At threshold da/dN (approx
imate to 10(-10) m/cycle) and for K-max < 4.6 MPa root m the threshold cycl
ic stress-intensity factor (Delta K-th) is greatly influenced by crack clos
ure. For closure free fatigue crack growth (K-max > 4.6 MPa root m), a subt
le but distinct decrease in Delta K-th is observed with increasing K-max. P
lots of Delta K versus K-max were also generated for AA 2024 test data prod
uced in two different studies; These data also revealed two distinct region
s of fatigue crack growth behavior consistent with the Ti 6-2-2-2-2 results
. This methodology can be used to. determine closure free fatigue crack gro
wth and to monitor subtle changes in Delta K-th.