A DAB of paint could soon warn engineers when bridges are in danger of
shaking themselves to pieces. A researcher at the University of Newcastle upon
Tyne says that the 鈥渟mart paint鈥� will allow engineers to build lighter, cheaper
and more elegant structures.
Vibrations can produce fatigue cracks in structures like bridges and oil rigs
that can lead to catastrophic failure. So engineers tend to make their
structures more robust than they need to be. 鈥淓specially where failure could
mean lives are lost, engineers over-design to ensure they don鈥檛 get failures,鈥�
says Jack Hale, who developed the paint.
Hale鈥檚 paint is able to sense vibrations because it is loaded with a fine
powder of a piezoelectric material called lead zirconate titanate (PZT). When
PZT crystals are stretched or squeezed they produce an electrical signal that is
proportional to the force.
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To test the idea, Hale sprayed a patch of smart paint 5 centimetres square
onto a metal beam and coated it with a second layer of an electrically
conductive paint. He then applied a voltage to the paint to align the crystals
at right angles to the surface. This ensures the PZT crystals produce a signal
whatever direction the beam is stressed: stretching it makes the paint layer
thinner and squeezes the crystals; compressing the beam does the reverse.
Hale then attached electrodes to the beam and the conductive paint. Tapping
the beam made it vibrate, which stretched and compressed the patch of paint. The
harder he hit the beam the larger the voltage he recorded.
Hale says engineers could use the paint to monitor vibrations throughout the
lifetime of a structure, allowing them to calculate much more accurately when
fatigue is becoming a problem. 鈥淭hey鈥檇 be able to design lighter, more elegant
and cheaper structures, because they鈥檇 know if they were getting towards the end
of its life,鈥� he says.
The new paint is a much easier way of measuring vibrations than conventional
strain gauges, says Hale. 鈥淚f they鈥檙e not on right, you get false readings.鈥�
However, Derek Smith of the Dynamics and Vibration Group at Cambridge University
warns that Hale鈥檚 system would be unable to tell in which direction a vibration
is strongest because it measures strains in all directions at once.
鈥淵ou might get a muddled signal out and not be certain what was going on,鈥� he
says. 鈥淚t could still be useful, though, because an awful lot of strain patterns
are unidirectional.鈥� Hale will test the paint on the Gateshead Millennium Bridge
across the Tyne later this month.