iter structural design criteria for in-vessel components (sdc-ic)

ITER G 74 MA 8 01-05-28 W0.2
A conservative approximation of the fatigue usage fraction can be obtained by
considering Fe = 0 . In that case, the fatigue usage fraction for the type of strain
cycle j is equal to the sum of the fatigue usage fraction for each interval k, which
is the ratio of the number of strain cycles nk to the maximum allowable number
( N j ) for this type of cycle, determined from the unirradiated fatigue curves,
k
multiplied by the correction factor f k:
N é M j
V = å êå
f
j=
1 ê
ëk
= 1
k
n
N
k
( )
j k
B 3323. Calculation of equivalent strain range De
ù
ú
ú
û
B 3323.1 Elastic analysis (Time-independent fatigue)
When elastic analysis is used to calculate the response of a structure, the range of strains
obtained does not account for plastic strains which would occur if the real behavior of the
material were taken into consideration . The method outlined below is aimed at providing an
estimate of the "real" strain range De on the basis of the results of the elastic analysis. This is
achieved by evaluating the amplification of the strain, and the resulting strain range, due to
plasticity as well as cyclic hardening or softening of the material as represented by the cyclic
stress-strain curves given in A.5.9.
( ( ) ) at
To apply the rules of this section, the total stress intensity range Dstot = D P + Q + F
the point under consideration and for each of the cycles must be calculated elastically, using
the procedure given in B 2550. This range can be obtained either by a sufficiently detailed
calculation of the region concerned or by using an appropriate stress concentration factor.
The value of the total effective strain range De is the sum of four scalar strains
De , De , De , De
:
1 2 3 4
De = De + De + De + De
1 2 3 4
These four terms are determined using a uniaxial cyclic stress-strain curve (see A.MAT.5.7 in
Appendix A) corresponding to the highest temperature (Tmax) and the lowest neutron fluence
(Ft)min at the point examined during the cycle concerned.
For cyclically hardening materials, the monotonic stress-strain curve is taken as a lower
bound of the cyclic curve.
For irradiation hardening materials, the virgin material cyclic curve is taken as a lower bound
of the irradiated material cyclic curve.
Calculation of De 1:
B 3323.1.1 Elastic strain range
SDC-IC, Appendix B. Guidelines for Analysis page 46