ssc-367 - Ship Structure Committee

structures. A comprehensive discussion of strength
improvementtechniquesby Booth (Reference9.7) is recotmnended
for further review of compressive overstressing.
Peening is a cold working process intended to produce surface
deformations to develop residual compressive stresses. When
impact loading on the material surface would otherwise cause
the surface layer to expand laterally, the layer underneath
prevents such surface layer expansion, creating the
compressiveresidualstressesat the surface. Typical peening
methods are hamer peening, shot peening and needle peening.
Further discussion on peening techniques and their relative
benefits is provided by Maddox (Reference 9.8).
9.3.3
Comt)arisonof StrenctthImrirovementStratecties
Strength improvement techniques are time consuming and costly and
they should be applied selectively. Comparison of different
techniques allows assessment of their effectiveness and cost. The
recommended strength improvement strategy depends on the
characteristics of the structure (global and local) and the
preference for one technique over others based on effectiveness,
cost and fabricationyard characteristics.
Some of the more important comparisons of various approaches
available to improve fatigue strength of weld details subjected to
a wide range of stresses are as follows:
●
Full profile burr grinding is preferable to toe burr grinding
only, or disc-grinding only, because it results in higher
fatigue strength even at a substantial cost penalty.
Disc grinding requires the least time and cost. However, it
produces score marks perpendicular to the principal stress
direction, making this technique less effective than others.
9-13