Composite materials that ‘report’ before they fail
Researchers in Germany have developed a composite that is capable of alerting engineers when it is approaching the point of failing. This has the potential to avoid huge costs from inflicted damage but more importantly could save lives.
Early detection of material failure is difficult for a huge number of materials, but poses particular problems regarding composites. The fact that they are lightweight, durable and inexpensive makes them an attractive material for use in many situations, but the issue of them failing under stress without due warning has meant that employing them must be done with care.
Scientists from Kiel University, University of Erlangen-Nuremberg and Technical University Munich (TUM) have tackled this issue by developing a way of designing composites so that they ‘self-report’. This new approach will hopefully address numerous problems in industry, as there is a thirst for composite materials suited to high-strain applications.
In the researchers’ process, zinc oxide tetrapod crystals are used as a filler material within the composite. The luminescence of these crystals reveals any inner damage within the material if subjected to UV light. Dr Yogendra Mishra of Kiel University’s Technical Faculty explains: “The luminescent features of zinc oxide tetrapod crystals are well established. According to our work hypothesis, these characteristics showed pronounced variations under a mechanical load, and we realised that it could help to detect internal damages of composite materials.”
One of their experiments involved adding the crystals to a silicone polymer (polydimethylsiloxane). The addition of the crystals actually increased the strength of the material but also caused different-coloured light to be emitted (under UV) when subjected to mechanical stress, giving a visual warning that it was about to fail.
TUM’s Professor Cordt Zollfranck states: “The alteration of the luminescent characteristics of defined semiconductor microstructures under load – as we could show for zinc oxide tetrapods – might be also interesting for many other phosphor material systems. We expect further developments in this emerging field on self-reporting materials.”