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The report is arranged in four parts under the general subjects of Design, Fabrication, Materials, and Statistics. Under the first, Design, is recorded confirmation of theoretical formulas for the bending of the hull girder of a ship and demonstration by laboratory tests of the improvements to be gained by relatively simple changes in desgn details. The second part, on Materials summarizes the continuation of the basic work on steel hull plate, looking toward an understanding of the fundamental reasons for brittle fracture, and shows the progress being made toward improvements in specifications in an effort to lower the incidence of fractures. Methods of Fabrication, the third part, summarizes the effect of certain fabrication practices on structural performance. In the fourth part cumulative statistical data on ship casualties are brought up to date.
To date investigations have not established the relative degree to which residual stress is likely to contribute to the initiation or propagation of fracture in ships. Brittle fracture of mild steel can be obtained when the average tensile stress is smaller than the yield stress, provided there has been some prior compressive cold working of the steel in the direction of the tensile loading. Cleavage-type microcracks are associated with fracture of ship steel at low temperatures. Full-scale heats of semikilled steel can be made in thicknesses to 1 1/2 in. that have about the same notch toughness as ABS Class-B steel in thicknesses to about 1 in. Mill sampling methods have been developed for ABS Class-B and Class-C steel that should be of value to any group that wiches to take samples of these grades of steel. Iridium 192 provides the fastest method and best sensitivity for radiographic inspection of steel welds. A A limited comparison of riveted and welded crack arrestors has verified that for equal materials the riveted arrestor is better (because of the discontinuity of the plating), but that flush-welded strips of high notch-tough steel can stop running cracks under certain laboratory conditions. The required width of material and properties of the arrestor strip have not yet been determined. Flaws cannot yet be evaluated for their potential danger to a structure.

Report

United States. Ship Structure Committee. Ship Structure Subcommittee

Published: 1959

Total Pages: 80


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