IGCAR : Annual Report - Indira Gandhi Centre for Atomic Research

IGC
Annual Report 2007
K Jd
, MPa.m 0.5
350
300
250
200
150
100
50
9Cr-1Mo Base Metal
K Jd
from Inst. PCVN testing at 1.12 m/s
Master Curve plotted with T 0 dy = -45 O C
[ASTM E-1921(05)]
Validity Limit Line
0
215.5 218 220.5 223 225.5 228 230.5
plasticity, increase constraint
and thus reduce fracture
toughness. This combined
effect has raised speculation
regarding the adoption of the
quasi static Master Curve shape
even in dynamic situation and it
needs to be experimentally
resolved. Experimental
verification of this aspect has
been carried out with plain
9Cr-1Mo steel. It may be noted
that the 9Cr-1Mo steel is one of
the candidate materials for
wrapper in future Fast Breeder
Reactors aiming a burn up
>200,000 MWD/t. To this end,
predicting dynamic fracture
toughness based reference
dy
temperature (T 0 ) is important
for ensuring the integrity of
critical component under
accidental/dynamic loading
scenario.
Dynamic fracture toughness
(K Jd ) of plain 9Cr-1Mo steel has
Temperature, K
p f
=0.98
p f
=0.5
p f
=0.02
Fig.2 Dynamic fracture toughness results of 9Cr-1Mo steel with respect to the
ASTM E 1921 master curve
been determined from
instrumented impact testing
with pre-crackled Charpy
specimens. The dynamic
loading gives rise to inertial
oscillations in the specimen
originating from interactions of
forward and reflected stress
waves. Towards getting a load
signal with minimum oscillation
effects, testing has been
conducted at a reduced
loading rate (~1.12 m/s). The
calculated stress intensity factor
has been ~10 6 Mpa.m 0.5 /s,
which is well regarded as a
dynamic situation. It has been
noticed that increase in loading
rate up to 5.12 m/s, the
maximum capacity of the
available Charpy machine,
affects the stress intensity factor
rate only marginally.
At temperatures of 213, 218,
220.5, 223, 225.5, 228 and -
dy
233 K, T 0 have been
determined to be 225.85,
227.25, 210.91, 208.87 and
209.53 K respectively. If the
same invariance of the Master
Curve holds good even in this
high loading rate then
dy
theoretically, the T 0 results
obtained from all the test
temperatures within the DBTT
regime would show the same
dy
values. Apparently, the T 0
values show differences in the
present campaign. However,
taking into account the
experimental uncertainties
involved in a dynamic fracture
toughness evaluation
procedure, it is reasonable to
dy
say that the T 0 remains
practically unchanged (±10 K)
within the DBTT regime. The
dy
lower T 0 values at the higher
test temperatures can be
attributed to the loss of
constraints at the crack tip.
Thus, it is proposed that the
same invariant shape of the
Master Curve describing the
fracture toughness variation
under quasi-static condition
also can be applied in the high
dy
strain rate loading. The T 0 of
the 9Cr-1Mo steel is
conservatively predicted as of -
228 K and the same has been
chosen to index the Master
Curve, as shown in Fig. 2.
Except a few, the individual
dynamic fracture toughness
data has been seen to lie well
within the 98% and 2%
confidence limit.
R&D FOR FBRs 49