This is from those enormously observant folks at Medgadget. Imagine using it on a protective lower extremity device? That said, smell doesn’t seem to stop folks from doing what they shouldn’t as regards wound healing…
Research scientists at the Fraunhofer Institute for Mechanics of Materials IWM in Freiburg, Germany have developed a helmet that will make you think twice about continuing to cycle with a damaged helmet. For maximum protection, safety helmets need to be damage-free, but It is often impossible to know if a helmet is actually flawed after it has been dropped or hit by something. The researchers have used polymers that start to smell if there are any small cracks, and will really stink in the case of any large cracks. From the press release:
The smell comes from odoriferous oils enclosed in microcapsules. “Cyclists often replace their helmets unnecessarily after dropping them on the ground, because they cannot tell whether they are damaged or not. The capsules eliminate this problem. If cracks form, smelly substances are released,” explains Dr.-Ing. Christof Koplin, research scientist at the IWM. The capsules are added to a polypropylene mass which is injection-molded to form the final component. In the case of the bicycle helmet, the microcapsules are inserted in a thick foil made of polypropylene, which is fastened to the head gear.
A layer of melamine formaldehyde resin encloses the capsules so that they are completely airtight and mechanically sealed. It also protects the tiny pods, which are subjected to temperatures of 200 to 300 degrees during injection molding as well as static pressures of up to 100 bar. “Melamine formaldehyde resin proved to be the most suitable encapsulation material in the comparison we conducted of the material systems,” explains Koplin. “Inside the capsule there is a porous, hardly deformable silicon oxide core which absorbs the odoriferous substance. This core produced the best results,” he adds.
To determine the loads at which the miniscule capsules measuring just 1 to 50 micrometers break open, the scientists test them at the IWM with a Vickers indenter. The engineers calculate the number of capsules required by means of numerical computer simulation. The finished component is then subjected to bending and drawing tests. The tests are only deemed to be successfully completed if the capsules are found to open and exude the odoriferous substances just before the component fails. Koplin: “Our method of detection by smell offers several advantages. It not only indicates when safety-critical polymer components need to be replaced. The exuding smells also enable damage outside the safety range to be detected.”