Fatigue Crack Paths 2003

γ

σ

β

σ

m

R

O

x=β∗Rm

t

t

2a=2γRm

2πRm

Figure 8. Through crack theory.

STRESSINTENSITFY A C T OERV A L U A T IFOON RT H EB O X

The first phase of the crack propagation was analysed by the model given in [6] for a

circumferentially cracked pipe with an internal, constant-length, finite-length surface

flaw subjected to pure bending loads:

π π ϑ

t a F t R M B 2 ⋅ ⋅

) / , / (

K

=

π

a

(6)

I

m

with, according to Article IWB-3650in Section XI of the A S M ECode (1992):

− + =

09967.0 1 . 1 ) / , / (

0057.5

ta

565.0

π ϑ

⎢⎣⎡

⎟⎠⎞⎜⎝⎛ πϑ ta

⎤

⎠⎞⎜⎝⎛ πϑ ta

(7)

t a F B

+

8329.2

− ⎟

⎥

⎥ ⎦

Figure 9. Schematic of surface-cracked pipe geometry and loading.

The second phase of the crack propagation (i.e. after reaching the through crack

condition) was analyzed by same model employed for the Pin.

M A T E R I AFLC GC U R V E

Based on experimental crack fronts and on analytical models for SIF evaluation, a series

of dNda - Δ Kdata points could be obtained. They were fitted with the Priddle equation: