Environmental Engineering Reference
In-Depth Information
A
1
T
1
B
1
A
2
B
2
A
3
C
2
T
2
B
3
B
4
S
C
3
1
C
4
D
2
T
3
D
3
D
4
T
4
log (
t
r
)
Existing curves
Extrapolation
Loci of transition
3.20
Grant-Bucklin methodology for determining creep life.
that fall under this category. Here we provide a brief description of the Grant-
Bucklin method. Grant and Bucklin considered the fact that creep rupture
would be infl uenced by several time- and temperature-dependent effects
and hence mode of failure might not be uniform over the whole range of
time and temperature. They identifi ed distinct segments of the rupture curve
where one mode of failure might be dominant. These segments were later
described by linear relations (Fig. 3.20). By plotting the slopes of like seg-
ments against temperature, it is possible to extrapolate to temperatures out-
side the experimental range. Secondly the positions of the transition points
may be plotted on axes of temperature versus
t
r
for extrapolation. However
Penny and Marriott
87
indicate that such extensions are subjective and sensi-
tive to the ability or judgment of the analyst, albeit Grant and Bucklin imply
that reliable extrapolations of the rupture curves are not critically dependent
on the accurate determination of either slopes or transition points.
The algebraic methods are similar in a way to the parametric methods.
The difference lies in fi nding functions which can combine the effects of
stress, temperature and time into a single relation such as
=
constant.
(, ,)
c
[3.50 ]
f
t
r
T
Any function
f
(
σ
, t
r
, T
)
c
which can be separated into two functions such as
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