Fatigue Crack Paths 2003

(a)

(b)

Loadstep-down

Figure 4. S E Mimages of fracture surfaces, ΔK1= 9, ΔK2 =12 M P am1/2 and R=0.05:

(a) typical dark band observed following load step-down, (b) high magnification image.

The crack growth rates inferred directly from the closure measurements, using

Elber´s approach and the characteristic da/dN versus ΔKeff relation of the material

obtained in previous work [3], are compared with the experimental da/dN in Fig. 5. The

crack growth rates inferred using Eq. 2 for crack lengths higher than half the monotonic

plastic zone established by the high block are also superimposed in such a Figure.

10-6435

1

Measured da/dN

Inferred from

Partial Closure (Eq.2)

c le ]

/d N [ m m /c y

Inferred directly from

d a

closure measurements

ΔK1=12MPam1/2

K Δ

K Δ

2

ΔK2=9MPam1/2

-2 -1 0 1 2 3 4 5 6

Crack lenght from load step event, a-aO [mm]

Figure 5. Comparison of predicted from closure measurements and observed crack

growth rates, ΔK2/ΔK1=0.75.