As more airplane components are made from composite materials, adhesive bonding promises a better and safer way to join aircraft parts together.
Over the past 30 years, airplane manufacturers have gradually replaced metal aircraft parts with composite materials, making their planes lighter and therefore more fuel-efficient. And in 2010, the first airplane made of more composites than metals was launched. “That was a milestone from my perspective,” said Dr Sofia Teixeira de Freitas, Assistant Professor at TU Delft’s Faculty of Aerospace Engineering, “because new materials require new ways of joining aircraft parts, and to me that means adhesive bonding.”
Of course in the aircraft industry, the most streamlined technology for joining metals is riveting, but that involves making holes, which can be a problem. “When you drill a hole in metal, you make a weak point that has to be compensated for by using extra material around the hole,” explained Teixeira de Freitas. “And this makes the component heavier which is an important consideration in air-travel.”
Drilling a hole in composite materials is even worse because composites are made of carbon fibres, and drilling a hole cuts through the fibres, weakening the structure. “These weak points are significant”, said Teixeira de Freitas, “A carbon composite is a good material with a very high strength-to-weight ratio which is significantly reduced if it has a hole in it”; hence the need for a better joining technology such as adhesive bonding.
As the name suggests, adhesive bonding is basically glueing, and it’s already widely used within aircraft manufacturing albeit with so-called “chicken-rivets” acting as a back-up system in case adhesive bonding fails. But the air industry clearly sees great potential in adhesive bonding as Teixeira de Freitas has just won a prestigious grant from the Netherlands Organisation for Scientific Research (NWO) allowing her to investigate and optimise the use of this technology within the aircraft industry. “We’re currently working with composites using adhesive bonding solutions that were designed for metals. But composites behave differently,” said Teixeira de Freitas. “And if bonded structures are designed properly, the distribution of stresses within composite materials can be very even.” And that means more efficient aircraft design in future.
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