Crack Paths 2009

K

K

R = 0

0.67891 moapx

moapx

0.240 0.68

Rdecreasing

0 0.2 0.4 0.6 0.8 1

Kov/Kmax=1.9, 1.5,1.t1

O L ara 

1.7

Steady state

1.5

K ov

ΔKov/ΔK= 1.25

K max

Kmin

R=0.75,0.5,0.25,0

0

1 1.2 1.4 1.6 1.8 0

K

ov

a)

b)

K

max

ov,p

Figure 2. Plane stress crack opening load ratio following the application of an overload

cycle: a) as a function of crack extension [6], and b) peak value [6].

Figure 3 displays the results for the crack opening load ratio as determined using the

finite thickness model. In Fig. 3a, the crack extension is thus normalised by the finite

thickness overload plastic zone size. Curves for several values of the non-dimensional

parameter η = Kmax/(σf√h) are provided. The peak opening load ratio is shown in Fig. 3b

as a function of Kov/Kmax and η. It can be seen in both figures that a decrease in the

parameter η leads to a reduction in the change in opening load ratio. Therefore, for a

fixed Kmax, R and σf an increased plate thickness will result in less crack growth

retardation. Figures 2b and 3b also demonstrate the potential for complete crack arrest

by choosing an appropriate overload ratio for the given material and load conditions.

a)

0.48621 1

00..86420 0

0.5 Kov/Kmax = 1.5, R = 0, ν = 0.3 1 η = 2, 1, 0.5

1.5 Plane stress la ain

1.5

2 Plane stress

moapx K

K

ov,pOLr aa

moapx

R = 0, ν = 0.3

η = 2, 1, 0.5

Plane strain

K

ov

b)

K

max

Figure 3. Thickness effect on the crack opening load ratio following the application of

an overload cycle: a) as a function of crack extension [7], and b) peak value [7].

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