Helmets may save lives, but they become less effective when they develop even small cracks. So in an attempt to alert bicyclists, motorcyclists, and construction workers when their helmets should retire, researchers in Germany are developing helmets made of polymer materials that start to smell foul when they crack. The bigger the crack, the fouler the odor.
How foul? Think formaldehyde. Which is somehow both absurd and brilliant--absurd because no one wants to reek of formaldehyde, and brilliant because, well, no one wants to reek of formaldehyde.
"Cyclists often replace their helmets unnecessarily after dropping them on the ground, because they cannot tell whether they are damaged or not," says Christof Koplin, a research scientist at the Fraunhofer Institute for Mechanics of Materials IWM in Freiburg, Germany. "The capsules eliminate this problem. If cracks form, smelly substances are released."
The researchers enclosed the capsules in a layer of melamine formaldehyde resin to make for an airtight, mechanical seal. And the formaldehyde does double duty as a layer of protection against extreme heat during injection molding.
The capsules are tiny, measuring 1 to 50 micrometers in diameter. To determine the load at which they break, the team tested the helmets at the IWM with the Vickers indenter method for gauging the hardness of materials and calculated the number of capsules required to open and release the odor just before the component fails.
Koplin says the results could be useful not only for all sorts of helmets, but also for checking hard-to-reach pressure hoses in, say, washing machines, as well as detecting cracks in, say, gas supply pipes:
Smell detection is already in use for coated metal components. We are applying the process for the first time to polymer materials. The cycle helmet is being used as a demonstrator. Work on the capsules has finished and we are now completing characterizing tests on individual configurations.
No word yet on what a helmet with these capsules would cost, but I predict wide adoption among elite cyclists, a gear-hungry breed not known to complain about outrageously priced components.