Liberty ship failures

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

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. 

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,... 

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. 

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. 

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