Crack Paths 2012

investigated. A smoother evolution of b is predicted near the transition, compared to

equation 4b. In addition, b is equal to 1 at low strain range, so that fracture is controlled

merely by the normal stress and strain, which is not the case in the original criterion, for

which the m a x i m u bm is 0.862. To apply the criterion ahead of each node of the crack

front, Aseq was first averaged over a distance LI9Oum. The local value of b was then

computedusing eq. 5. Then the damagefunction, D Fwas computed along all potential

twisted planes, for a twist angle 0 ranging from 0 to 45°. The value of 0 corresponding

to the m a x i m uDm Fprovided the local direction of crack extension.

N U M E R I CA AN ALL Y S IOSFT H EE X P E R I M E NRTEASLU L T S

ComputedSIFs and analysis of crack growthrates

Figure 9 showsthe computedK1, K H and K111 profiles at peak load along the first and

eight crack front in specimen CCP5a. While mode I prevails, as expected, when the

crack plane is still normal to the loading axis, mode111 and —to a lesser extent- mode11

increase significantly whenslanted crack growth occurs.

a)

b)

14

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1

2

3

I1

5

6

width : y(mm)

8

2

width : ytmm)

Figure 9: SIFs at peak load along a) the 1st and b) 8th front, specimen CCP5a.

The crack growth rates measured at various depth in the same specimen are

A K 2 correlated to AK1 on Figure 10a and to AKeq = AK12+AKZ+(1—”’)onfig. 10b. i —v

While AKI fails to correlate all the data —with an upward curvature of the kinetic curve

for surface points-, AKsqprovides a muchbetter correlation, which provides additional

evidence that the opening and shear modescooperate for slanted crack growth.

84