Environmental Engineering Reference
In-Depth Information
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t
r
(s)
3.21
Monkman-Grant plot for cp-Ti tubing.
91
constant
c
[3.51 ]
f
(,
t
T
)
f
()
f
(
t
T
)
t
,
T
f
(
f
(
)
f
t
T
)
=
f
(
)
f
r
f
f
(
)
f
tt
,
r
f
r
is similar to the time-temperature method of parametric types. In addition to
these methods, there are several other methods which have been proposed
and found to provide reasonable predictions. Monkman and Grant
90
pro-
posed a relationship between the steady-state strain rate and rupture time:
[3.52 ]
ε
t
κ
,
sr
where
is a material constant known as the Monkman-Grant constant.
Figure 3.21 depicts such a plot for internally pressurized cp-Ti tubing.
91
Other methods of extrapolation include the
κ
-projection
method advo-
cated by Wilshire and co-workers
92
,
93
where the total creep curve is described
by a series of
θ
parameters. Wilshire
92
suggests that for most materials the
secondary creep region is only an
infl ection
that appears to be a constant
over a limited strain range. Hence it was emphasized that creep life mod-
eling should take into account the total creep curve including the tertiary
creep regime rather than just focusing on the secondary creep rates. On this
premise, Wilshire and co-workers advocated the
θ
θ
-projection
concept where
the total creep curve would be described as
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