case study
Could stainless steel have saved the Liberty Ships during WW2?
The Liberty Ship S.S. Schenectady, which, in 1943, failed before leaving the shipyard.
(Reprinted with permission of Earl R. Parker, Brittle Behavior of Engineering Structures, National Academy of Sciences, National Research Council, John Wiley & Sons, New York, 1957.)
By executive order of President Roosevelt, the United States started the production of all-welded cargo vessels (DWT 11000 Liberty Ships) in 1942 to meet the demands of the Pacific War. These cargo vessels were used as troop ships or carriers for large amounts of military logistics to ensure eventual US victory in the Pacific and were therefore named ‘Liberty Ships’.
T he general aim was to build ships faster than the enemy could sink them. Nineteen pre-existing shipyards and eighteen newly built shipyards were set aside for the exclusive construction of the Liberty Ships. A total of 37 factories worked night and day on an assembly line to produce the Liberty Ships. The use of welded structures instead of the more traditional riveted construction for a ship design enabled the fast continuous block manufacturing method. This manufacturing method of cargo ships was similar to that used in Japan during the same period. The scale involved in the Liberty Ship construction was astounding. Between 1939 and 1945, 37 shipyards produced 5 777 ships of which 2 708 were Liberty Ships. Cracks in the system The failure of many of the World War II Liberty Ships is a well- known and dramatic example of the brittle fracture of steel that
was thought to be ductile. Some of the early ships experienced structural damage when cracks developed in their decks and hulls. Three of them catastrophically split in half when cracks formed, grew to critical lengths, and then rapidly propagated completely around the ships’ girths. The picture shown above is one of the ships that fractured the day after it was launched. Subsequent investigations concluded one or more of the following factors contributed to each failure: • The Liberty Ships were built of steel that experienced a ductile-to-brittle transition. When certain metal alloys, that are ductile at ambient temperatures, are cooled to relatively low temperatures, they become susceptible to brittle fracture. Some Liberty Ships were deployed to the frigid North Atlantic, where the once ductile metal experienced brittle fracture when temperatures dropped to below the transition temperature. This meant that their steel frame transformed from a ductile
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