Page 35 - Curriculum Visions Dynamic Book

(Above and below) Cold bending metal will make a metal exceed its elastic limit and experience plastic change. Repeated bending of this kind may lead to metal fatigue.
Preventing metal fatigue
One serious problem that can develop in metals
is metal fatigue. It happens when a piece of metal is squashed, pulled, or twisted many times. A crack and then a break occur after some time
even though the force on the metal might be much lower than the force normally needed to break it.
Metal fatigue has been known for over a century, but it has become more of a problem with modern equipment. The
first spectacular crash of a Comet
aircraft in 1954 led to widespread
concern about metal fatigue.
It has not been easy to understand what causes metal
fatigue, although certain metal
alloys have been found that are
much less prone to this failure.
These alloys are used in modern aircraft, in replacement body
parts, and elsewhere. Another
way of reducing the chances of fatigue is to make sure that designs
do not cause the buildup of a force
in a small area, for example, where an engine is attached to an aircraft wing.
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