Crack Paths 2012

A P P L I C A T I O N L O WC Y C LFER E T T I NFGA T I G ULEIFEA N A L Y S I S

Then we will apply this extended critical distance theory on the fretting fatigue life

prediction. In Fig. 8 (left upper) the S-N curve of Ni-Mo-V steel smooth specimen in

complete reversed loading conditions (R=-1), and in Fig. 8 (left under) the crack

propagation characteristic of cracked specimen is shown. From these material

characteristics we can obtain the critical distance rP is 0.011mmand rP’ is 2.13mmas

shown in Fig. 8 (right). The stress distributions in fretting conditions were calculated

using F E Mmodel as shown in Fig. 9. The calculated example of stress distribution near

the contact edge is shown in Fig. 10. The mean contact pressure σp and mean axial

S-N Curveof s m o o t shpecimen Crackp opagati nra e

Specificdistancea n dstress

Ni-Mo-VSteel

1 0 0 5 0 0 1 0 0 0

103

104

105

106

107

108

σ

B = 7 0 5 M P a

N u m b eofrcyclesto failure Nf

σ

= 3 6 0 M P a

W 0

σW0 andԥ.th

1000

σ

B

Estimatedcycleto failure

㻷

㻵㻯

500

σ

w 0

σ B a n d . Ϩ C

σ

a = 2 0 0 M P a

䌚 㻷

Stressdistribution in

㼠㼔

fretting m o d e l

100

㻜㻚㻜㻝

㻜㻚㻝

㻝

㻝㻜

Distance r ( m m )

Fig.8 Derivation of specific distance in low cycle fatigue region and estimation of low

cycle fretting fatigue life

Contactedge Contactpressurep Axial load σa P a d Con actsurface Specime

Fig. 10 Calculated result of stress distributions

Fig.9 F E MFretting model

stress σa in this case are 200MPaand 100MParespectively.

The critical distance on each loading conditions can be estimated by reflecting these

stress distributions on Fig. 8 (right) as shown by dotted line. The low cycle fretting

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