Crack Paths 2006

Table 1, the plane of maximum'VT is identified for each initiation site together with the

corresponding angles and minimumvalue of normal stresses. The results corresponding to

the maximumcyclic normal stress are different.

Figure 5 presents the sites of the seven elements. The planes of 'Wmax, label 1, represent

the direction of early stage I cracks, see Table 1. The planes of 'VTmax, label 2, represent the

direction of the stage II cracks. The planes of 'Wmax within the elements 24, 2018 and 4014

have their shear stresses alternating in sign. This may result in F C Gboth deeply into the

material and towards the surfaces. The latter development suggests a possible mechanism

responsible for the formation of free relatively large material particles inside the mouth of

fretting cracks, i.e. the shaded areas. Those particles have borders matching the borders of

the corresponding crack mouth [1, 8 and 9].

reference plane drawnat the initiation site normal

to the line of symmetryof the analysed sector

1

2324

4014 4015

E L E M E N5T305

2018

4011 1

B Blade side

D Disk side

L C SLower C o m m o n

1

U C SUpper Surface

N P CStage I m o d eII

Non-PropagatingCrack

Fig. 5 possible cracking development of cracks initiated by FF

1 stage I crack 2 pl n // f etted surface 'W

3 stage II crack

I angle between1 and2

3

m a x

2

2

I

+ve 'Wmax

(a)

(b)

3

1

1

F R E T T T ESDU R F A C E

3

2

-ve 'Wmax

2

I

1

1

(c)

(d)

3

Fig. 6 Possible mechanism to form particles inside the mouth of FF cracks

The shear stress acting on the FCI plane is represented in Fig. 6 by two arrows. That plane

divides the considered material into two parts. The inclination of the critical plane of 'VTmax