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

ITER G 74 MA 8 01-05-28 W0.2
one of them would not appear necessary. Nevertheless, the used method used must be
justified.
B 3024.4 Elasto-visco-plastic analysis of a structure subjected to cyclic
loading
A large number of possible analysis methods are now available, but none of them are today
qualified to describe all aspects of the cyclic behavior of materials. The imposition of any
one of them would not appear necessary. Nevertheless, the method used must be justified.
Note: A combined elasto-visco-plastic analysis is necessary only when the effects of creep
and plasticity cannot be separated from one another. In many cases it is possible to separate
the effects as follows. Most models of plasticity are independent of time. If the time frame
for plastic stains is rapid compared with the time frame for creep, then one can assume that
creep strains are constant during a plastic loading period and that plastic strains are constant
during the creep periods between plastic loadings. If plasticity and creep effects are not
separable, then the formulation of the constitutive law becomes more difficult.
BÊ3024.5 Limit analysis (collapse load)
The deformation of a structure made of a rigid-perfectly plastic material increases without
bound at a loading level called the collapse load. Limit analysis methods can be used to
calculate the collapse load or a lower bound to the collapse load.
A given loading is less than or equal to the collapse load if there is a stress distribution which
satisfies the laws of equilibrium at all points that does not violate the material yield criterion
at any point. This theorem allows a lower bound to be defined for the collapse load.
In the case of elasto-plastic analysis and experimental analysis, the collapse load, by
convention, is defined as the loading for which the overall permanent deformation of the
structure equals the deformation which would occur by purely elastic behavior.
BÊ3025 Zones of calculation
In some cases it may be necessary for computational purposes to divide a component into
several zones for analyzing a single type of damage. In such cases, an overall analysis of the
component shall be carried out to determine the loads or displacements to be applied at the
boundaries of each zone for each load case considered. Care should be taken to ensure that
boundary conditions applied are sufficiently accurate or conservative. The accuracy may be
checked by a combination of the following:
a. showing that both stresses and displacements are consistent at the boundaries of
the zone;
b. refinement of the mesh.
Note: the application of displacement boundary conditions to a sub-model requires care.
Two examples are given below.
Say that an elastic analysis of a larger model is used to determine the displacement boundary
conditions for a smaller sub-model, yet the sub-model is expected to operate in the plastic
SDC-IC, Appendix B. Guidelines for Analysis page 34