RD&D-Programme 2004 - SKB

Figure 5-7. Part of cast insert and copper tube for compression testing.
A strength calculation showed that the relatively short length of this test canister does not
significantly affect the collapse load compared with a full-length canister.
Some presence of non-nodular graphite as well as casting defects such as small porosities, slag
particles and occasional larger casting flaws will not be able to be completely avoided in such
a large cast piece as a canister insert. Microscopic defects in occasional tensile test bars taken
from different locations in inserts will also result in relatively low values of ductility in particular.
This will cause some variation in obtained data. However, the results of strength calculations
and compression tests in an isostatic press indicate that the inserts nevertheless have a strength
that meets the design requirements with good margin. The continued work will be focused on
establishing material requirements that will ensure the strength of the inserts. Figure 5-8 shows
the graphite microstructure in different specimens from inserts.
A
B
Figure 5-8. Graphite microstructure in different specimens from inserts. Figure A shows a nodular
iron microstructure with well-developed graphite nodules. Figure B shows a partially defective
graphite microstructure with so-called “chunky graphite”.
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