Environmental Engineering Reference
In-Depth Information
In this case, the mathematical expectation of the number of projected defects
in the
i-
i-th element of the structure is determined from:
i
i
v
(
t
+
Dt
) =
Cv
×
(
t
),
[4.43]
d
d
ins
i
d
d
where
i
v
(τ
1
) is the mathematical expectation of the number of projected
defects in the
i
i-th element after metal inspection of metal in the consecutive
operating periods of the facilities.
Analysis of the fracture mechanisms
66-69
shows that the critical crack
growth can occur as a result of brittle, ductile or elastic-plastic fracture.
The conditions defining the scope of these fracture mechanisms, in
accordance with Ref. 69, may be described as follow:
- zone of brittle fracture
2
i
lC
i
F
K
−
1
0
≤
l
<
1.2,
[4.44]
R
i
i
i
where
RRR
is the the flow stress;
- zone of ductile fracture
2
= (
+
)/2
F
mp
0,2
i
lC
i
F
K
−
1
1.2
≤
l
<
7.0;
[4.45]
R
- zone of elastic-plastic fracture
2
i
lC
i
F
K
−
1
l
≥
7.0.
[4.46]
R
There is no critical crack growth leading to the formation of a continuous
crack in the zone of brittle fracture if
i
i
[4.47]
Critical crack growth, leading to large-scale destruction, does not occur
K
()
t≤ t
K
( .
l
l
lC
l
if
i
i
[4.48]
In the zone of elastic-plastic fracture there is no critical crack growth,
leading to the formation of continuous cracks, according to Ref. 69, if the
point with coordinates
K
()
t≤ t
K
( .
l
l
Cl
i
K
(τ
l
),
S
(τ
l
) is within the area bounded by the
i
curve (Fig. 4.4)
−
l
/2
8
π
K
i
()
t= t× ×
S
i
()
lnsec
S
× t
i
()
,
[4.49]
r
1
r
1
2
r
1
π
2
where
i
i
i
i
i
i
i
t= t t t=st t st
is the equivalent stress, defined by the von Mises criterion
70
.
Critical crack growth, leading to large-scale failure, does not
KKKS
()
()/
( ; ()
()/
R
( ;
()
r
1
I
1
IC
1
r
1
eq
1
1
eq
1
p
0.2
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