Additively manufactured (AM) alloy usually inevitably contains defects
during manufacturing processor in service. Defects, as a harmful factor,
could significantly reduce the fatigue performance of materials. This
paper shows that the location and introduced form of defects play an
important role in high cycle and very high cycle fatigue (VHCF) behavior
of selective laser melting Ti-6Al-4V alloy. The fatigue life descends
linearly with stress amplitude for interior defect induced failure.
While for artificial surface defect induced failure, the fatigue life
descends at first, and then exhibits a plateau region feature. We also
observed competition of interior crack initiation with fine granular
area feature in VHCF regime. The paper indicates that only the size or
the stress intensity factor range of the defect is not an appropriate
parameter describing the effect of defect on the fatigue crack
initiation. Finally, the effect of artificial surface defect on high
cycle and VHCF strength is modeled, i.e. the fatigue strength σ,
fatigue life N and defect size ( area)
(square root of projection area of defect
perpendicular to principal stress direction) is expressed as σ=
CN( area)
for N0 and
σ= CN (
area) for
N≥N , where C, a and
n are constants, N is the number of cycles at
the knee point.