Page 188 - Handbook of Materials Failure Analysis

184 CHAPTER 7 Investigation of failure behavior of tubular components

(a) 10 m (b) 10 m
FIGURE 7.24
SEM images of fracture surfaces of axially cracked Zircaloy-4 fuel-clad specimens with a 0 /W
value of (a) 0.474 and (b) 0.632.

7 CONCLUSION
It is important to ensure the integrity of the thin-walled Zircaloy fuel-clad tubes in a
nuclear reactor in order to prevent the release of radioactive fission products to the
reactor environment.
For longer residence time in the reactor, these tubes should have superior mechan-
ical properties and adequate resistance to axial crack propagation. In this work, the
ring-tension tests were carried out on ring-specimens machined from the fuel-clad
tubes. Both the specimen and the loading mandrel were modeled through FE anal-
ysis in order to evaluate the load-displacement behavior of the test setup. By com-
paring the load-displacement response as obtained from FE analysis with that of
experiment, the material stress-strain curve was evaluated following an inverse
analysis procedure.
The fracture resistance behavior of axially cracked tubular specimens machined
from the same fuel-clad tubes has also been evaluated. Specimens with different
a 0 /W ratios ranging from 0.1 to 0.5 were tested in two different test setups. Two dif-
ferent geometries of loading mandrels were used in order to vary the state of crack-tip
stress in the axially cracked tubular components. The total plastic deformation
energy versus ductile crack extension data was observed to be more or less same
for different values of initial crack lengths of the specimens in the test setup with
conical mandrel. This indicates that the ductile fracture resistance behaviors (in
terms of J-R curve) of long thin-walled axially cracked tubes are nearly independent
of initial crack lengths provided the crack-tip is far away from the boundaries. This
method can be applied to the tubular components of different industries in order to
evaluate their fracture resistance properties. This will help in integrity analysis and
residual life assessment of the critical thin-walled tubular components.