ssc-367 - Ship Structure Committee

should be carefully reviewed and the model calibrated to
ensure the reliability of data.
● ✍
The S-N curvesused indetennining fatiguedamage computations
should be compatiblewith structural details investigated.
●
Considering the effect of size, weld profile and undercut on
fatigue strengthand S-N curves, it may be prudent to reassess
the hot spot stress range concept. The definition of hot spot
stressrange can be modified to reflect the weld toe defects.
●
The use of Miner’s cumulativefatiguedamage rule with the S-N
curves is appropriate. Further research, especial1y on the
effects of stress sequence and counting of stress reversals,
is considered necessary.
9.5.1 Research Priorities
Whether designinga supertankeror an offshoreplatform, significant
fai1ure modes can be identified, environmental 1oads generated,
structure response characteristics determined, and stress
superpositionscompatiblewith the environmentand the failuremodes
computed. Although strength statistics for these structures can be
expressed in terms of means and variance, lack of sufficient
statistical data on loads, stresses and strength prevent full
probabilistic fatigue analyses. A development of a semiprobabilisticanalysisapproachapplicableto
various structuresand
that does not require a distribution shape is desirable.
While a typical fatigue damage assessment is based on fatigue
strength data yielding S-N curves, such an assessment can also be
made based on fracture mechanics and crack growth laws. While the
damage assessment is based on propagationof individual crack, work
carried out by Morgan (Reference 9.14) has indicated possible
interactionof multiple cracks. Thus, further work is necessary to
obtain data on interaction of cracks as well as interaction of
parameters affecting development of S-N curves.
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