Fatigue Crack Paths 2003

(1)

WCPε−=

The crack length ratio a/W is obtained from the polynomial relationship:

2 3 4 5 1 a a a u a u a u a u a u W = + + (2+)

0

where

1

(3)

1 u B E C = +

The coefficients a0 , ..., a5 were calibrated by Finite Element Analysis (FEA) and the

results are in good agreement with previous results obtained with the surface replication

technique, with influence function method and from the literature [13] (see Fig. 4).

0.9

0.8

B F S[13]

BFS, replica [14]

0.7

BFS,F E A

BFS, infl. funct.

0.6

0.5

a / W

0.4

0.3

0.2

0.1

0

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45

u

Figure 4. Calibration of a W as a function of u.

Test Method

The fatigue crack growth tests were conducted at a loading frequency of 10 Hz in lab

air. Constant load amplitude and continuous load-shedding procedures depending on the

F C Grate range of interest were used. In constant load amplitude tests the applied cyclic

load range (i.e. ΔP=Pmax-Pmin) was kept constant throughout the test, while in the

continuous load-shedding tests the load range was gradually decreased as the crack

propagated according to [15]. As R-ratio dependence is expected to occur also in this

class of materials, two load ratios R=Pmin/Pmax (0.1 and 0.5, respectively) were