Crack Paths 2012

(18).

For completeness another one criterion has to be mentioned here. The MTU-criterion

by Dhondt [14] is very similar to the criterion by Schollmann et al., because it has the

same assumptions.

3D-criterion by RICHARD

The basis for this criterion is the following approach:

K 11

K V

K W

K I C K I I C

K I I I C

With u I 1 and v I w I 2 a cyclic comparative stress intensity factor can be defined

in order to reasonably describe fatigue crack growth:

_ AKI AKV 2 +%\/AKI2+5,336-AKH2+4-AKHI2

(20)

Fatigue crack growth starts, if A K V exceeds the threshold value of fatigue crack

growth AKth. Crack growth becomes unstable, if the fracture toughness KIC is reached.

This criterion by Richard is a good approximation to the criterion by Schollmann et al.

For the determination of the kinking angle (00 and the twisting angle y/O simple

approximation functions are given by [1]

l l 2 Q’ = $ 1 4 0 ° ' — H — 7 0 ° 21, 0 lKIl + lKIl + lKIIl lKIl+ lKIl+ lKIIl ( l l l

_ j I” = + 7 8 ° ~ ——— 3 3 ° ~ 22, 0 lKIl+lKIl+lKIIl lKIl+lKIl+lKIIl ‘ i l .1 [ l .1

For K120 and KII < 0 is $0 > 0 and for KII > 0 is $0 < 0. Furthermore, for K120 and

KIII < 0 is n10 > 0 and for KIII > 0 is l/lo < 0.

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