Fatigue Crack Paths 2003

-6

10

R = 0.5

100-8 -7

c y c le ]

/dN

d a

[ m /

3

110-01-09

10

5 %ferrite - 9 5 %perlite

5 0 %ferrite - 50 % perlite

1 0 0 %ferrite

50

Δ K [MPam 1/2 ]

Figure 2. Fatigue crack propagation results for the investigated ductile irons (R = 0.5).

10-6

R=0.75

-7

10

10-8

10-9

5 %ferrite - 9 5 %perlite

5 0 %ferrite - 5 0 %perlite

100%ferrite

10-10

10

50

Δ K [MPam1/2]

3

Figure 3. Fatigue crack propagation results for the investigated ductile irons (R = 0.75).

This debonding does not imply automatically a complete spheroid loosing from the

surface. Also spheroids that have less that half of their surface in contact with ferritic

matrix do not loose their grip to the surface.

As a consequence, the closure effect is enhanced by the graphite spheroids presence.

If the spheroid looses completely the grip with the ferritic matrix, the matrix ductile

deformation implies an increase of the hole dimension with a mechanism that is similar