Section 7.5.3. Residual Strength Testing
Residual strength tests of fail safe structure are of special
importance. Interruption of a fatigue
test at the critical crack size for intact structure is crucial. If the crack grows longer, the stress for
rapid propagation is too low to give proper information on crack arrest
capabilities and on the strength of the remaining structure at that stress
(times the dynamic factor). Since these
properties are essential for the qualification as fail safe structure, a proper
evaluation is justified, even during design development tests.
After instability and arrest (or load path failure), if
successful, fatigue testing should be continued. At that point the JSSG-2006 Damage Tolerance Requirements assume
remaining structure damage. In testing,
this poses the same problems as the continuing damage. Therefore, it is recommended that the
remaining structure damage be developed in a natural way during damage
tolerance testing; artificially induced damage may also be incorporated where
necessary consistent with the initial flaw assumptions of the component. Again, fatigue cycling is discontinued when
the (calculated) critical size for the remaining structure damage is reached. Then a final residual strength test is
performed.