ssc-367 - Ship Structure Committee

While API S-N curves are applicableto stationarymarine structures,
other S-N curves by DEn and Det norske Veritas (DnV - Ref. 1.7) may
be equally applicableto stationaryand mobile vessels with tubular
and orthogonally stiffened plate construction. The preferred S-N
curve should be defined in the design criteria. Typical S-N curves
applicableformarine structuresare illustratedon Figure3-7. S-N
curves are discussed further in Section 5.
Cumulative Damacle
The calculation of cumulative damage is typically performed using
the Palmgren-Minerdamage rule. In this approach fatigue damage is
calculated by dividing stress range distribution into constant
amplitude stress range blocks, assuming that the damage per load
cycle is constant at a given stress range and equal to:
Dti = l/N
where,
Dtiis the damage, and
N is the constant-amplitudenumber of cycles to
given stress range.
failure at a
Another key assumption of the Palmgren-Miner damage rule is that
damage is independent of order in which loads are applied.
Accordingly, for the case of a stress history with multiple stress
blocks, Sti,each block having n cycles, the cumulative damage is
defined by:
This is the Miner-Palmgren formula, where:
3-17