Laminate changes color to highlight damage

One possible use for the new laminate is in components in the load-​bearing structures of buildings, aircraft, or vehicles. (Credit: Getty Images)

A new kind of laminate changes color as soon as the material is deformed, making it a lightweight composite material that inspects itself.

Lightweight construction is now part of industries like automotive manufacturing, shipbuilding, and aircraft construction. In addition to traditional lightweight metals such as aluminum, magnesium, or titanium, load-bearing applications increasingly feature composite materials. This is driving the need to develop new techniques and methods for the early detection of damage to—or even the possible failure of—these yet-understudied materials.

Researchers from the Complex Materials Group at ETH Zurich and collaborators created the lightweight material that uses a color 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.

The laminate is composed of alternating layers of a plastic polymer and artificial nacre (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. The molecule is activated as soon as the polymer experiences stretching forces, and this changes its fluorescence. The more the material stretches and the more of these molecules are activated, the more intense the fluorescence becomes.

“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 on the work in the journal ACS Applied Materials and Interfaces. The system could also have been set up to produce a color change that would be directly perceptible from the outside. However, Magrini says, “the perception of colors is subjective and it is difficult to draw conclusions about changes in the material.”

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 use for the new laminate is in components in the load-​bearing structures of buildings, aircraft, or vehicles, where it’s essential to detect their failure at an early stage.

However, it remains to be seen whether and how the material can be produced on an industrial scale. So far, it exists only at laboratory scale as a proof of concept.

Source: ETH Zurich