Fatigue Crack Paths 2003

level. A critical plane model built according to these hypotheses was found to predict

pretty well the fatigue to initiation under constant amplitude multiaxial loading [2-4] but

some problems have still to be solved and particularly how to accumulate damage

produced by two different loading modes, e.g. tension and torsion (Fig. 1).

1,00

0,90

0,80

0,70

0,60

D f

0,50

/ D

0,40

0,30

0,20

0,10

0,00

0,00

0,20

0,40

0,60

0,80

1,00

N / Nf

(a)

220

200

Torsion

180

160

140

Tension

120

100

80

60

40

20

0

Accumulatedplastic meso-strain (damage)

(b)

Figure 1. Evolution of (a) damage in tension and (b) mesoscopic yield limit in function

of the accumulated plastic mesoscopic strain for two loading modes: tension and

torsion. The hydrostatic stress that occurs in tension (not in torsion) leads to a

modification of the cyclic plastic response of the crystal.