Crack Paths 2009

decreases initially to a minimumvalue before it accelerates. The minimumvalue in the

crack growth rate or the “V” shaped curve of crack growth near a notch is often

characterized as the anomalous behavior of short F C Gattributed to a lack of crack

closure in the notch plastic zone [9].

Shin et al. [7] claimed a similar crack growth behavior in BS1470 S1C aluminium

single edge notched specimens with various notch root radii was observed as shown in

∆σ

Figure 2. The specimens were tested under C A loading with

and

. R = 05.0

app =15

M P a

Nevertheless, this is obviously not the case for the notch root radii

r 4.1= mm.It implies

some complicated mechanisms influencing the growth behavior of cracks from notches,

particularly near the small crack growth region, such as the behavior for the notch free

case.

1.00E-03

For D=2r=0.5

/cycle )

1.00E-04

For D=2r=1.0

1.00E-05

m

r a t e ( m

1.00E-06

1.00E-07

th

gwro

1.00E-08

a c k

1.00E-09

C r

1.00E-10

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

Cracklength, c ( m m )

Figure 1. F C Gin BS436050B steel specimens with different notch root radii

(D is notch depth in mm).

1.00E-04

/cycle )

Notchfree

r=1.4 m m

m m

r=0.4 m m

r a t e (

th

rwo

C r a c k g

1.00E-05

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0

Cracklength, c ( m m )

Figure 2. F C Gin BS1470S1Caluminium specimens with different notch root radii.

Using linear elastic fracture mechanics (LEFM) approach, El Haddad et al. [5]

analyzed the crack growth data in a G40.11 steel for different geometric discontinuities

subjected to a far field applied stress range

and R = 1− . They discovered

app ∆σ = 269

M P a

that crack growth rates for circular and elliptical hole specimens are initially higher than

that for the central cracked plate. However, the growth rate difference gradually reduces

and eventually disappears when fatigue cracks propagate out of notch inelastic stress

strain fields. Most importantly, they concluded that L E F Mfails to characterize F C G

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