Crack Paths 2012

50 μ m crack length there is 62%deviation between KI for normal and mixed mode

crack. Moreover, it can be seen that after the crack length 0.5 m mthe crack is governed

by axial bulk stress and the extracted SIFs are yielding to results, which was calculated

analytically for Double Edge Notch Tension (DENT)specimen form [20].

1.8

20

Mixed Mode

1.46

D E N T

10

x/a

Normal Crack

0

ો܉ ܠ ܑ܉ ܔ ξૈ܉

01.6821

-1.5

-1

-0.5

0 0.5

1 1.5

۹ ۷

-10

l(μm)

Deviation

P a )

-20

**************************************

50

62%

-30

( M

100 12.2%

-40

150 3.5%

0.4

200 0.6%

-50

-760

FEA, Q=40N

Analytical solution

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

0.20

FEA,Q=30N A, Q=20N

Cracklength (mm)

Figure 4. Validation of F E Amodel of fretting fatigue w th analytical solution

Figure 5. Distribution of normalized

calculated SIFs V Scrack length

Fig. 6 illustrates the effect of different tangential load at the contact interface on the

calculated SIFs for cracks normal to the fatigue specimen surface and mixed mode

crack propagation. The trend can be extended to all cases. From the crack length 200

μm, the crack will be governed by axial stress, which is relatively far from contact

region. Moreover, this graph shows the relation between tangential stress distributions

inside the fatigue specimen at trailing edge of contact. It is interesting to note that with

increasing the tangential load from 20 N to 40 N, the tangential stress also increases

near contact interface and reaches a plateau far from contact area.

1224680246800

68120246800

(

Mixed Mode, Q=40N

Mixed Mode, Q=30N

Mixed Mode, Q=20N

)

Normal Crack, Q=40N

M P a )

K I( M P a (m m)

Normal Crack, Q=30N

Normal Crack, Q=20N

Tangential stress, Q=40N

Tangential stress, Q=30N

Tangential stress, Q=20N

40

20

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Crack length (mm)

Figure 6. Comparison of SIFs and tangential stress ( ߪ ௫௫) for different tangential loads

7

357