SHAPE FORMING
due to the reaction between oxygen molecules, which enter a crack, and silicon carbide in the ceramic. This reaction forms silicon dioxide, which reacts with another ceramic component, alumina, to form a material that fills the gap and crystallises into a hardened form. Research conducted in 2018
found that adding trace amounts of manganese oxide to alumina grains allowed the ceramic to heal in under 60 seconds at 1,000°C. This was noted as the operating temperature of the aircraft engines where this ceramic might be used as turbine material. However, most of these materials
are not at a stage where they are suitable for the rigorous conditions of transport. Similarly, these non- autonomic healing processes make them ineffective for transport applications, where the biggest value comes from materials that heal in immediate response to damage during operation.
APPLICATIONS These materials might promise an exciting prospect for design engineers, but most have not yet been scaled- up to a commercial stage. Although brands such as Lamborghini and Goodyear have teased self-healing cars and tyres, respectively, in recent years, these applications remain largely conceptual. However, that doesn’t stop us from imagining where self-healing materials might lead or conceiving of how they will fit into future designs. Decades from now, it’s possible that cars constructed of lightweight, self-healing CFRP chassis will travel on concrete roads that autonomically repair potholes using embedded limestone- producing bacteria. Any minor punctures or cracks in the tyres could also be healed by hybrid rubber tyres. Until this becomes reality, however, the best step that design engineers can take is to select materials that adequately meet the strenuous demands of transport applications. To this end, design engineers should use material databases such as Matmatch to research materials with ideal characteristics, and compare those which are best suited for the task ahead.
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www.engineerlive.com Render of a self-healing composite
For example, molybdenum copper
alloy (MoCu30) is ideally suited to demanding automotive and aerospace applications. This material is lightweight with high thermal conductivity – 205 Watts per metre-Kelvin at 20°C – and good performance across a wide range of temperatures, with a low thermal expansion. Likewise, an aluminium-copper metal matrix composite, such as AL427915 as offered by Goodfellow, makes an ideal choice for low- stress applications that still require stiffness, good strength and fatigue levels, and a high tensile modulus. Its characteristics make it suitable for automotive pistons, chassis components and even aircraft structural components and brakes. For protecting materials during demanding applications, one of the current best courses of action is to support materials with specialist coatings. This is another area where developments are being made to achieve self-healing coatings that can reinforce existing structures. Yet it is
another area in which there are limited commercial offerings. Until that changes, design engineers should consider coatings that can protect surfaces against wear and corrosion. As with material selection, choosing a coating with the right properties is invaluable. On Matmatch’s online materials database, there is a selection of alloy powders for coatings that help protect applications against corrosion, while offering a desirable strength-to-weight ratio. The developments in self- healing materials are exciting and are undoubtedly picking up pace. However, as with most things, it’s important to establish the facts and reality of the current situation. Specifically, that until these materials begin scaling up, it might be best that transport engineers design for longevity by choosing materials that can go the distance. ●
The author is head of growth at materials search engine Matmatch.
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