Crack Paths 2009

Fig. 1: Modelling of relevant crack sizes

Fig. 2: Modelling of crack growth in fish-eye

log da/dN

1

3

a

a int

0

1

3

ai

ai

a

b/x3

a

0

b

a i

x3

aint x

a

∆ K

log

T H E R M O M E C H A NAIPCPAR LO A C H

Previous studies [7,8] have investigated the temperature evolution on surface specimens

during tests in the gigacycle fatigue domain. Two recordings are given Figs 3 and 4 for

a low alloyed chromium steel. Figure 3 is the entire recording from the beginning of the

test. At first time, the temperature increases rapidly, followed by a stabilization. The

temperature variation depends on the material and its microstructure and on the stress

amplitude level (∆σ);the higher the stress, the higher the temperature reached. At the

end of the test, the temperature increases rapidly. Figure 4 is an enlargement (coming

from an other specimen of low alloyed chromium steel) of the test end . In fig. 3 the

sample was refreshed during the test, whereas it is not the case for the test of fig. 4.

Fig. 3: Temperature evolution on the

Fig. 4: Temperature evolution at the test

surface sample

end.

250

200

°C )

150

p(érature

100

Tme

50

0

0,0

4,0x106 8,0x106 1,2x107 1,6x107 2,0x107 2,4x107

Nombresdes cycles

In order to better understand these thermal effects and to make a connection with the

crack initiation and propagation, a thermo-mechanical model was developped [8]. The

numerical resolution of the thermal problem allows the determination of the temperature

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