Large mechanical structures such as oil rigs, bridges, pipelines, chemical
plants, nuclear installations and aircraft may in the future be equipped
with 鈥榝uses鈥� which give early warnings of stresses in the structure that
could lead to catastrophic failures. Just as an electrical fuse cuts out
when a circuit is overloaded, the mechanical 鈥榝uses鈥� share the stresses
experienced by thestructure to which they are attached, and gradually snap
as preset stress levels are successively exceeded.
The so-called 鈥榝atigue fuse鈥� was launched earlier this month by Tensiodyne,
a company based at Sarasota in Florida. It is around the size and shape
of a book of matches and consists of a flat metal frame housing five parallel
strips of metal (the 鈥榤atches鈥�).
Each strip has different nicks, indentations and fissures cut into it,
which mimic the condition of the most stressed parts of any structural component.
So the strips reflect the stresses experienced by flaws in the structure,
such as miniature cracks, or by features where stresses are greatest, such
as boltholes. Using an epoxy resin, engineers stick the fuse to strategic
points on the structure, where it effectively records the 鈥榝atigue histories鈥�
of the components.
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Some of the strips have nicks in them which make them weaker than the
others, and these gradually snap, one by one. This gives the inspector an
鈥榟ourglass鈥�, showing how much longer the structure can be left before it
requires maintenance or complete replacement.
Raymond de la Veaux, the executive vice president of engineering at
Tensiodyne, says the fuses can be used alone and inspected regularly, or
connected to an electronic remote monitoring system which keeps anautomatic
check on the fuses. The monitoring system was developed by Hughes Aircraft
Company and is potentially useful for large structures such as bridges and
oil rigs, where access to remote components is difficult and sometimes dangerous.
De la Veaux says that while the fuses cost $400 each 鈥� which includes
calibration for a specific installation and the necessary adhesive 鈥� they
save money in that fewer inspections are required. Alan Clayton, head of
structural performance engineering at AEA Technology in Risley, Cheshire,
expects the fuses will be useful, but will only catch on once potential
users have confidence in their performance.
