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This report covers the examinations of samples from 8 fractured ships received between April 1, 1950, and March 1, 1951, and laboratory investigations of 13 plates selected from these samples. Preliminary examinations of these samples and preparation of test specimens are in progress, and results of some of these preliminary examinations are discussed briefly in connection with their similarity to previous failures. A different method of analysis of the accumulated data for transition temperatures of source, thru, and end plates, by the use of percentage frequency diagrams, is discussed and illustrated. The method of calculation of the probable maximum transition temperatures of the plates from their chemical compositions and fracture grain sizes is illustrated in a table, and the calculated maximum and the observed transition temperatures of the plates are compared. The method used for determinations of the fracture grain size is described.
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This report covers the examination of fractured plates selected from 60 ships in which structural failures occurred. The chemical compositions and ordinary mechanical properties of most of the plates were satisfactory and met the specification requirements under which they were purchased. However, Charpy notched bar tests indicated that the plates in which fractures originated were notch sensitive at the temperature of fracture, and plates in which the fractures ended were generally less notch sensitive. Most of the fractures occurred at low operating temperatures, and the origin of each of the fractures examined could be traced to a notch such as a hatch corner, ladder opening, or a faulty weld. Such notches and defects create regions of stress concentration which may start failures in steels that are notch sensitive at the operating temperatures. (Author).
Samples of fractured plates from 72 ships were examined, and various laboratory examinations and tests were made on 113 plates selected from these samples. Information regarding the structural failures involved was obtained from the cooperating agencies, and the failures were analyzed on the basis of this information combined with the results of the laboratory investigations. The failures usually occurred at low temperatures, and the origin of the fractures could be traced, invariably, to a point of stress concentration at a geometrical or metallurgical notch resulting from design details or welding defects. The fractures in the ships generally were of a brittle or cleavage type, showing little evidence of ductility, although the steels showed normal ductility in the usual type of tensile test. The chemical compositions and ordinary mechanical properties of the fractured plates indicated that the steels met the specification requirements under which they were purchased. However, Charpy V-notch bar tests showed that plates in which fractures originated were more notch sensitive than plates which did not contain a fracture source. Thus, both service experience and the results of the laboratory investigation indicate that the fractures resulted from stress concentration in steels which were notch sensitive at the operating temperature. (Author).