Researchers have developed a lightweight composite material suitable for use in the aerospace applications that changes colour as soon as it is deformed, effectively a material that inspects itself.
Lightweight composites are increasingly being used for load-bearing applications across transport industries including aerospace, in addition to traditional lightweight metals such as aluminium, magnesium or titanium. According to ETH Zurich, this is driving a need to develop new techniques and methods for the early detection of damage to or even the possible failure of such as yet understudied materials.
Mother of pearl
The researchers from the Complex Materials Group at ETH Zurich in Switzerland have created the lightweight material from plastic polymer and artificial nacre or mother-of-pearl. The material changes colour to indicate internal deformation and thus indicates possible material failure at an early stage.
Composed of alternating layers, their laminate is translucent, break-resistant and yet very lightweight.
Artificial nacre is a speciality of the Complex Materials Laboratory and is modelled on the biological example of the mussel shell. It consists of countless glass platelets arranged in parallel, which are compacted, sintered and solidified using an polymeric resin. This makes it extremely hard and break-resistant.
The second layer consists of a polymer to which the researchers have added an indicator molecule synthesised specifically for this application at the University of Fribourg, Switzerland. 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.
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,” said 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 identify overstressed areas within the composite material before fractures form. This allows early detection of vulnerable areas in a structure before catastrophic failure occurs.
Possible applications of the 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.
The next step for researchers is to assess if the material can be produced on an industrial scale. So far, it exists only at laboratory scale as a proof of concept.