Liberty ship

The early study of brittle failures, notably those of the Liberty ships, indicated a temperature dependence. This can be illustrated by plotting both fracture stress (of) and yield stress (Oy) against temperature (Fig. 8.81). Below a certain temperature some materials exhibit a transition from ductile to brittle fracture mode. This temperature is known as the ductile-brittle transition temperature DBTT. 

Local stress caused by discontinuities result in zones which encourage brittle-fracture failure. Brittle-fractures have caused failure in a variety of equipment items, from the Liberty ships of World War II to stor e tanks, and the designer should try to minimize local stresses as much as possible, especially if the design calculations do not specifically take them into account. 

Work-study, including time and motion studies, looked at efficient ways to design production. Tayloristic production-line methods paid too little attention to the whole person and their needs and, although they are now recognized as a mistake, they may have been the best approach in, for example, the World War II production of Liberty ships. 

But when steel is cooled below the reference temperature, brittle fracture can occur. This phenomenon was partly responsible for the sudden collapse in winter of some early welded bridge designs and for the spectacular breakup of Liberty ships during World War II. A typical ship failure occurred on January 16,... 

Old Liberty ships were filled with nerve gas (some encased in conCTete) and mustard gas ordnance and sunk in deep water off the coast as part of Operation CHASE (Cut Holes And Sink Em). 

It was mentioned in Chapter 4 that the lower atomic density slip systems in bcc materials become inactive at low temperatures and a ductile-to-brittle transition occurs. From Figure 9.6 it is seen that for some high-carbon steels, this transition occurs well above the freezing point of water. A number of the early Liberty ships that operated in the North Atlantic during World War II were apparently made from the wrong kind of steel and broke apart without warning. 

Explosion of US liberty ship carrying mustard gas shells in Bari harbour, Italy... 

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. Figure 1.3 shows one of the ships that fractured the day after it was launched. 

When some normally ductile metal alloys are cooled to relatively low temperatures, they become susceptible to brittle fracture—that is, they experience a ductile-to-brittle transition upon cooling through a critical range of temperatures. These Liberty ships were constructed of steel that... 

Figure 1.3 The Liberty ship S.S. Schenectady, which, in 1943, failed before leaving the shipyard.

In spite of these failures, the Liberty ship program was considered a success for several reasons, the primary reason being that ships that snrvived 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 fractiu-e mechanics. 

Two new case studies Liberty Ship Failures (Chapter 1) and Use of Composites in the Boeing 787 Dreamliner (Chapter 16)... 

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