Crack Paths 2012

Fig. 8: Stress-life curves for flange material with

and without overloads by load ratio RS = 0.

Table 2: summaryof fatigue results.

Slope Kponinete Nominal fatigue strength at the knee Scatter

band

Sa,k [MPa]

k

Nk

1/TS

5·105

166

R S =-1 recAeisv-ed without O L 5.5

1.14

5·105

157

with O L 5.8

1.18

Flange without O L 10.7

5·105

219

1.30

with O L 7.3

5·105

193

1.24

5·105

156

R S = 0 recAeisv-ed without O L 6.2

1.18

1·106

143

with O L 7.7

1.11

Flange without O L 9.9

5·105

197

1.29

with O L 9.3

1·106

162

1.31

In the case of flange material, the scatter of experimental results is muchhigher than

the scatter in the as-received state. In general overloads have a negative influence on the

fatigue life and the flange material is more negatively influenced by the application of

overloads. In the case of RS = 0 the overloads result also in a change of the position of

the knee point.

Metallographic analysis

The detailed and systematic examination of the fracture surfaces reveal that the fracture

modes of the as-received and the flange material differ significantly, independent from

the load ratio or the occurrence of overloads. According to the linear elastic fracture

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