Fatigue Crack Paths 2003

500 μ m

(a)

(b)

1 m m

200 μ m

(c)

(d)

Figure 3. S E Manalyses of fracture at the welded joint: a) examined region; b) and c)

modeII damage on the fracture surface; d) a secondary crack showing a

stepwise pattern.

F E MA N A L Y S Y S

General Description

In order to confirm the hypothesis of a first mode II propagation followed by branching

or kinking transition to mode I, 3D F E Manalysis were carried out using the commercial

finite element package A B A Q UVSersion 6.2 [13]. 20-node solid elements have been

used and crack surfaces contact was introduced by master-slave surface method. Figure

4 shows the finite element mesh for the first step. KI and KII values at the crack tip were

obtained from relative crack opening displacement ΔUz and sliding displacement ΔUx of

crack nodes, by means of well knownformulations [14]:

U G

K

= 2−π Δ

as L 0 (1)

z

π ν 2 ) 4 3 (

I

L

U G

(2)

K II = 2 )π 1πΔ( 2 − ν as L 0 x

L