Environmental Engineering Reference
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white bands are dislocation channels in which irradiation damage (black
areas and black spots) is removed. In zirconium alloys the channels are in
the order of 0.01-0.30 µm wide depending on fl uence and irradiation tem-
perature, and each channel can accommodate large (50-300%) local strains.
The channels intersect the surface to cause large protrusions or slip steps
there (Adamson, 1968 ; Sharp, 1972 ).
In Zircaloy, the dislocation channels tend to form in a very a localized
area called a deformation band. For a simple uniaxial tensile test specimen
the sequence of formation is illustrated in Fig. 4.22. At point (A) the defor-
mation band begins to form and is fully formed at (B). At point (B) a second
deformation band forms perpendicular to the fi rst, and the specimen frac-
tures at point (D). Because virtually all the strain forms in the deformation
band, there is little or no deformation in the rest of the specimen gauge
length. A plot of measured strain along the length of a typical specimen is
given in Fig. 4.23. Since little plastic strain occurred outside deformation
bands, the true gauge length of the specimen is much shorter than the nomi-
nal specimen gauge length. Therefore, specimen geometry greatly infl uences
reported strain values. The effect of test specimen geometry on failure strain
is illustrated in Fig. 4.24 where the conventional value of uniform elongation
(UE) is plotted against gauge length for different specimen geometries of
70
482
A
60
414
B
50
345
C
40
276
A
B
30
207
D
20
138
E
10
69
0
0.01
0.02
0.03
0.04
Strain
4.22
Engineering stress-strain curve for Zircaloy-2 sheet that had
been irradiated at 280
°
C to a neutron fl uence of 5
×
1020 n/cm
2
and
subsequently tested at 300
°
C. (Source: Reprinted, with permission,
from Bement
et al
. (1965), copyright ASTM International, 100 Barr
Harbor Drive, West Conshohocken, PA 19428.)
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