Crack Paths 2006

cracks. FCI and early stage I mode II F C Gare both cyclic plastic shear processes [5]. Thus,

it is expected to have them along the plane of maximumcyclic shear stress range, 'Wmax. The

plane of 'Wmax was identified within the seven probable FCI sites. Table 1 lists 'Wmax for the

sites together with the corresponding angles and minimumand maximumvalues of W. The

different entrance angles to the surface for different contact sites are commonexperimental

observations in FF tests throughout different contact geometries, e.g. [4, 5].

23,,45,6

-131500 0.00

0.01

0.02

-24200 0

0.01

0.02

0.03

8,10,12

7 13

9,11

12300 0

0.003

0.006

-24200 0

0.004 0.008 0.012 3,5 29,41,16,81120

5305

1

713

3,5

1

2

1-050

4014

9,11

1LOADINGSTATUS7 13

3,5 2 84,6

190,12124

-100

7,13

4,6,8

-400

1

EL2E0M18ENT

10,12

3,5

-24200 0

0.005

0.01 2

0.015

125050 0

0.003

0.006

12300

4015

9 11

1

3,5,9

1

2

4,6,

2

8

12

6

23

3,5

0

4011

0

0.006 2

0.012

183

11

3

9 11

5

7,13

8

10,12

8

9,11

4,6

7

10,12

4,6

12 13

13

1

1

10,12

8 10

2 4

6

7

7

LOADING STATUS

J

SHEARSTRAIN,

Fig. 4 variation of W acting on the plane of 'Wmax plotted against the corresponding shear

strain, J, for the sites which experience cyclic plastic strain

The stress field generated within the whole analysed sector is generally tri-axial and non

proportional, particularly during the disk acceleration and deceleration. During both phases,

the ratio of the principal stresses and the bi-axial ratio continuously change, the

corresponding Mohr’s circles of stresses and strains continuously alter their centres and sizes

and the principal axes are continuously rotating. The present results may give an answer of

the question relevant to the direction of the early fatigue growth of the initiated cracks. FCI

and early stage I modeII F C Gare both cyclic plastic shear processes [5]. Thus, it is expected

to have them both along the plane of maximumcyclic shear stress range, 'Wmax. The plane of

'Wmax was identified within the seven probable FCI sites. Table 1 lists 'Wmax for the sites

together with the corresponding angles and minimum and maximumvalues of W. The

different entrance angles to the surface for different contact sites are commonexperimental

observations in FF tests throughout different contact geometries, e.g. [4, 5]. Figure 4 shows,

for the initiation sites, the variation of W acting on the plane of 'Wmax plotted against the corresponding shear strain, J. It is suggested to link the cyclic plastic shear strain range, 'Jp,

resulting from the second cycle with the duration of the initiation of stage I fatigue crack, Ni.

The possibility of developing an early stage I crack to a stage II crack can be addressed.

Fatigue cracks are likely to develop in regions of tension. Thus, there are two possibilities

for the growth development of initiated fatigue cracks. At some instance (i) an early stage I

F C Gmay become non-propagating or (ii) a change from early stage I modeII F C Gto a stage

II mode I F C Gmay take place. The three disc elements 4011, 4015 and 5305 do not

experience tensile principal stresses as a result of the applied loading and, thus, an initiated

crack within those elements is expected to stop propagation. The initiated crack in the other

four elements may develop and propagate through their material with a deviation in their

crack paths. ModeI F C Gis controlled by the maximumrange of cyclic tensile stress, 'VT. In