Environmental Engineering Reference
In-Depth Information
D
inner
D
inner
4.1
Schematization of a discontinuity.
n
a
= 1;
n
φ
is the safety factor along the crack length,
n
φ
= 1.
4.1.2 Growth of the discontinuity under cyclic loading
The development (growth) of a discontinuity with the original sizes
a
0
and
c
0
under the influence of
N
cycles can be determined using the equation:
m
da
dK
=
C
1
,
[4.2]
dN
1
−
R
where
C, m
are the constants depending on material and operating
conditions;
R
is the stress ratio, for a pressure cylinder it is equal to 0;
Δ
K
1
is the range of the stress intensity factor.
The stress intensity factor for a nonuniform stress distribution in the
vicinity of the crack is determined by the equation
5
:
K
1
= Yσ
1
(
a
/1000)
0.5
,
where
Y
= [2 - 0.82(
а
/
с
)]/{1 - [0.89 - 0.57(
а
/
с
)
0.5
]
3
(
а
/
с
)
1.5
}
3.25
,
σ
1
= 0.61 σ
А
+ 0.39 σ
В
+
+[0.11 (
а
/
с
) - 0.28(
а
/
s
)(1 - (
a
/
c
)
0.5
)](σ
А
- σ
В
);
σ
A
is the stress at the crack tip; σ
B
is the stress on the surface of the
component at the crack root.
For a particular case
Y
=
1.12
.
Integrating the expression [4.2] we get:
π
Search WWH ::
Custom Search