ssc-367 - Ship Structure Committee

damage accumulation similar to that of structural steel. Gurney
(Reference 7.6) indicatesthat increased material tensile strength
does not increase fatigue resistance and implies that a fatigue
design approach incorporatingmaterial tensi1e strength is not valid
for welded marine structures.
The effect of initial flaw size on
affecting crack propagation should
size estimatingprocedureby Grover
in assessing fatigue crack growth.
fatigue life and the parameters
be understood. An initial flow
(Reference7.7) is quite helpful
Plate Thickness
Current S-N curves reconunended by DnV (Reference 1.7), DEn
(Reference 1.6) and AWS (Reference 4.13) incorporate a thickness
correction factor. DnV and DEn recommendations largely reflect
early work by Gurney (Reference 7.1) and many test programs
corroborating plate thickness effect corrections proposed by
Gurney. Class B, C, D, E, F, F2, G and N curves are applicable to
non-tubular (including tube-to-plate) joints based on detail
geometry, stressing pattern and method of fabrication/inspection.
While these eight classes are applicablewithout correctionto plate
thicknessupto7/8inch (22MM), class Tcurve (for tubular joints)
is applicable to 1-1/4 inch (32 mm) plate.
The UK DEn Guidance Notes recoimnendspecific size effect (i.e.,
plate thickness) correction factors in the following form:
S = Sb (32/t)l/4
7“1
where
s =
fatigue strength of a joint under consideration
(N/nun2)
7-6