International. 
Damage in the development of a material can be difficult to see until something breaks or fails. Now, a new polymer damage indication system automatically highlights areas that are cracked, scratched or stressed, allowing engineers to tackle problem areas before they become much more complicated.
The early warning system would be particularly useful in applications such as pipelines, air transport and space, and automobiles — applications where a one-part failure could have costly ramifications that are difficult to repair. The project was led by Nancy Sottos of the University of Illinois (Champaign, Illinois) and aerospace engineering professor Scott White, the researchers published their work in the journal Advanced Materials.
"Polymers are susceptible to damage in the form of small cracks that are often difficult to detect. Even on a small scale, crack damage can significantly compromise the integrity and functionality of polymer materials," says Sottos. "We developed a very simple but elegant material to autonomously indicate mechanical damage."
The researchers incorporated tiny microcapsules of a pH-sensitive dye into an epoxy resin. If the polymer forms cracks or suffers a scratch, stress or fracture, the capsules open. The dye reacts with the epoxy resin, causing a dramatic color change from light yellow to a bright red color—with no chemical additives or activators required.
The deeper the scratch or crack, the microcapsules break the more, and the more intense the color. This helps to assess the extent of the damage. Even so, small microscopic cracks of only 10 micrometers are enough to cause a color change, letting the user know that the material has lost some of its structural integrity.
Source: https://news.illinois.edu
