The Color Deformation

Eth Zurich researchers have established a new type of laminate that changes colour as soon as the material is deformed. This way, the materials researchers can kill two birds with one stone: a lightweight composite material that inspects itself.

Researchers from the Complex Materials Group at Eth Zurich, working in collaboration with researchers from the University of Fribourg, have now adopted an approach that has recently garnered attention in materials research: they have created a lightweight material that uses a colour change to indicate internal deformation and thus possible material failure at an early stage. Composed of individual layers, their laminate is translucent, break-resistant, and yet very lightweight.

Artificial mother-of-pearl combined with polymer

The laminate is composed of alternating layers of a plastic polymer and artificial nacre or mother-of-pearl. The latter is a specialty of the Complex Materials Laboratory and is modeled on the biological example of the mussel shell. It consists of countless glass platelets arranged in parallel, which are compacted, sintered and solidified using a polymeric resin. This makes it extremely hard and break-resistant.

The second layer consists of a polymer to which the researchers added an indicator molecule synthesized specifically for this application at the University of Fribourg.

Fluorescence indicates overstressed parts

“We used fluorescent molecules because you can measure the increase in fluorescence very well and you don’t have to rely on subjective perception,” says Tommaso Magrini, lead author of the study, which was recently published in the journal Acs Applied Materials and Interfaces. The system could also have been set up to produce a colour change that would be directly perceptible from the outside. But: “The perception of colours is subjective and it is difficult to draw conclusions about changes in the material,” Magrini says.

With the help of fluorescence, the researchers can now identify overstressed areas within the composite material even before fractures form. This allows early detection of vulnerable areas in a structure before catastrophic failure occurs. One possible application of the novel laminate is in components in the load-bearing structures found in buildings, aircraft or vehicles, where it is essential to detect their failure at an early stage.

Though, it remains to be understood whether and how the substantial can be produced on a manufacturing scale. So far, it occurs only at laboratory scale as a proof of impression.

For more details: www.ethz.ch