Page 23 - T. Anderson-Fracture Mechanics - Fundamentals and Applns.-CRC (2005)

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1 History and Overview

Fracture is a problem that society has faced for as long as there have been man-made structures.
The problem may actually be worse today than in previous centuries, because more can go wrong
in our complex technological society. Major airline crashes, for instance, would not be possible
without modern aerospace technology.
Fortunately, advances in the field of fracture mechanics have helped to offset some of the
potential dangers posed by increasing technological complexity. Our understanding of how materials
fail and our ability to prevent such failures have increased considerably since World War II. Much
remains to be learned, however, and existing knowledge of fracture mechanics is not always applied
when appropriate.
While catastrophic failures provide income for attorneys and consulting engineers, such events
are detrimental to the economy as a whole. An economic study [1] estimated the annual cost of
fracture in the U.S. in 1978 at $119 billion (in 1982 dollars), about 4% of the gross national product.
Furthermore, this study estimated that the annual cost could be reduced by $35 billion if current
technology were applied, and that further fracture mechanics research could reduce this figure by
an additional $28 billion.

1.1 WHY STRUCTURES FAIL
The cause of most structural failures generally falls into one of the following categories:

1. Negligence during design, construction, or operation of the structure.
2. Application of a new design or material, which produces an unexpected (and undesirable)
result.

In the first instance, existing procedures are sufficient to avoid failure, but are not followed by
one or more of the parties involved, due to human error, ignorance, or willful misconduct. Poor
workmanship, inappropriate or substandard materials, errors in stress analysis, and operator error
are examples of where the appropriate technology and experience are available, but not applied.
The second type of failure is much more difficult to prevent. When an ‘‘improved” design is
introduced, invariably, there are factors that the designer does not anticipate. New materials can
offer tremendous advantages, but also potential problems. Consequently, a new design or material
should be placed into service only after extensive testing and analysis. Such an approach will reduce
the frequency of failures, but not eliminate them entirely; there may be important factors that are
overlooked during testing and analysis.
One of the most famous Type 2 failures is the brittle fracture of World War II Liberty ships
(see Section 1.2.2). These ships, which were the first to have all-welded hulls, could be fabricated
much faster and cheaper than earlier riveted designs, but a significant number of these vessels
sustained serious fractures as a result of the design change. Today, virtually all steel ships are
welded, but sufficient knowledge was gained from the Liberty ship failures to avoid similar problems
in present structures.
Knowledge must be applied in order to be useful, however. Figure 1.1 shows an example of a
Type 1 failure, where poor workmanship in a seemingly inconsequential structural detail caused a
more recent fracture in a welded ship. In 1979, the Kurdistan oil tanker broke completely in two

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