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Early Warning Coating Makes Invisible Cracks Visible Before They Lead To Disaster

Damage indicating system uses color-changing indicators that automatically highlight cracked, corroded, or stressed areas in structural materials.

January 19, 2016

When cracks form, microbeads embedded in the material break open and cause a chemical reaction that highlights the damaged area.

Catch it before it grows. Whether they're on equipment, bridges or pipelines, even the tiniest of cracks can fast lead to catastrophic failures. Damage developing in a material can be difficult to see until something breaks or fails. A new polymer damage indication system automatically highlights areas that are cracked, scratched or stressed, allowing engineers to address problem areas before they become more problematic.

Scientists at the Beckman Institute for Advanced Science and Technology at the University of Illinois have created a new polymer coating that can be applied to a wide variety of structural materials. When those materials crack – even a little – the polymer changes color to let inspectors know that something's up.

Professors Nancy Sottos and Scott White created the polymer coating that contains epoxy resin microcapsules filled with a light-yellow pH-sensitive dye. As long as no damage occurs, those capsules remain intact. However, should a crack form (as small as 10 micrometers in width), the capsules in that area burst and release the dye. That dye chemically reacts with the epoxy, changing from yellow to bright red in color. The larger the crack, the greater the amount of dye reacts, and the more pronounced the color-change.

"Detecting damage before significant corrosion or other problems can occur provides increased safety and reliability for coated structures and composites,” White said.

According to the researchers, the polymer has been successfully tested on materials including metal, glass and other polymers. It's also reasonably inexpensive, as it only needs to be composed of five percent microcapsules in order to work effectively.

The damage indication system worked well for a variety of polymer materials that can be applied to coat different substrates including metals, polymers and glasses. The system has long-term stability – no microcapsule leaking to produce false positives, and no color fading.

White and Sottos are exploring further applications for the indicator system, such as applying it to fiber-reinforced composites.

Source: University of Illinois, Illinois News Bureau; Advanced Materials Journal

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