Metallurgy & Materials Engineering

Liberty Ship Failures

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The following case study illustrates one role that materials scientists and engineers are called upon to assume in the area of materials performance: analyze mechanical failures, determine their causes, and then propose appropriate measures to guard against future incidents.

The failure of many of the World War II Liberty ships[1] is a well-known and dramatic example of the brittle fracture of steel that was thought to be ductile.[2] 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. Figure shown below is one of the ships that fractured the day after it was launched.

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.)

Subsequent investigations concluded one or more of the following factors contributed to each failure:

Remedial measures taken to correct these problems included the following:

In spite of these failures, the Liberty ship program was considered a success for several reasons, the primary reason being that ships that survived failure were able to supply Allied Forces in the theater of operations and in all likelihood shortened the war. In addition, structural steels were developed with vastly improved resistances to catastrophic brittle fractures. Detailed analyses of these failures advanced the understanding of crack formation and growth, which ultimately evolved into the discipline of fracture mechanics.

Source: Materials Science and Engineering – An Introduction — 9th Edition [Callister & Rethwisch]


References:

[1] During World War II, 2,710 Liberty cargo ships were mass-produced by the United States to supply food and materials to the combatants in Europe.

[2] Ductile metals fail after relatively large degrees of permanent deformation; however, very little if any permanent deformation accompanies the fracture of brittle materials. Brittle fractures can occur very suddenly as cracks spread rapidly; crack propagation is normally much slower in ductile materials, and the eventual fracture takes longer.

[3] This ductile-to-brittle transition phenomenon, as well as techniques that are used to measure and raise the critical temperature range.

[4] The reader may note that corners of windows and doors for all of today’s marine and aircraft structures are rounded.

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