3.3. FCG behavior
The FCG rate of BM, AS-HAZ and WNZ are shown in Fig. 11. Generally, the
curve of FCG consists of three regions, namely, slow crack growth region
(I) in low stress intensity factor (ΔK) range,
stable propagation region or
Paris regime (II) in medium level
range of ΔK and rapid propagation
region (III) in high range of ΔK. In present work, the investigated
range of ΔK was about 7 to 30 MPa m1/2. From 7 to 20
MPa m1/2, all samples showed approximate linear
dependency of ΔK on the FCG rate, indicated characteristic of Paris
regime (II). In this region, BM
sample presented a consistently higher FCG rate as compared with
AS-HAZ and WNZ. The FCG rate of
AS-HAZ rose faster than WNZ with increasing of ΔK. When ΔK exceeded 20
MPa m1/2, a noticeable change in the slope of the
curve was observed, indicating that crack growth was entering into the
rapid propagation region (III). In this region, the FCG rate of BM and
AS-HAZ was close, much higher than that of WNZ.