The sky’s the limit for AMCs
As aerospace manufacturers continue to look for new ways to increase product capabilities and performance while simultaneously meeting ambitious goals for fuel efficiency and sustainability, Richard Thompson, commercial director of Alvant, looks at the growing benefits offered to the sector by Aluminium Matrix Composites (AMC).
Reducing weight without compromising on structural integrity is a must-have for most engineering projects, none more so than in the aerospace industry, where weight reductions can reduce fuel consumption and carbon emissions.
Typical modern commercial aircraft have a material mix (by weight) of 50% composites, 20% aluminium, 15% titanium, 10% steel, 5% other materials. As well as weight, the industry is also looking to reduce titanium content due to cost, the difficulty to machine and the environmental impact of mining and processing.
While the industry faces a huge challenge to meet wide criteria, there could be hope in the form of a solution thanks to AMCs. They are an advanced class of composite materials in which the aluminium is reinforced with a secondary high-performance material and are suitable for applications where conventional metals are expected to approach or exceed their performance limits. AMCs could also find use applications in high-pressure seals, aircraft landing gear and seats, where safety and reliability are essential.
Growing interest in AMCs has been affirmed by big-brand collaborative projects such as the one with high-technology group, Safran Landing Systems, which has recently partnered with Alvant on a two-year, £28m project, titled ‘Large Landing Gear of the Future’ with the aim to reduce landing gear weight by as much as 30%.
The project looks at how AMCs can challenge traditional materials in the design and manufacture of landing gear assemblies. Current landing gear systems are typically stronger and heavier than necessary, accounting for approximately three per cent of aircraft weight, with a corresponding effect on fuel consumption.
“The project aims to make use of new materials and manufacturing methods to develop and demonstrate technologies that will reduce landing gear weight, fuel burn and noise at the same time as improving reliability and lowering maintenance, repair and operating costs,” says Thompson.
Alvant’s contribution to the project is the design, manufacture and testing of an AMC brake rod, targeting a 30 per cent weight reduction over an equivalent titanium component whilst maintaining the same strength as steel.
“A key objective of the Large Landing Gear project is to test and demonstrate as many technology advances as possible,” adds Thompson. “Alvant’s AMCs are a sustainable solution that enhance product capabilities. This landing gear component is just one of the many ways in which AMCs can help.
Another innovation from Alvant is CorXal, a unique high-performance multi-phase AMC that is similar in concept to a sandwich material but made in a single shot process, providing ultra-high stiffness and a density similar to carbon composite.
Alvant is currently working with aerospace companies to explore potential applications of this material, one example including the incorporation of a single piece AMC in the leading edge of aircraft wings.
Aircraft wings are subject to large aerodynamic forces, huge changes in temperature and are susceptible to bird and lightning strikes.
The existing materials used in traditional wing manufacture have been found to be susceptible to bond degradation between the skin and core elements. This can be caused by environmental factors such as temperature, moisture ingress and contamination, which can negatively impact on the integrity of the bond. The result has been a tendency to design components with excessive safety factors to compensate for this potential degradation.
Due to the one-shot production process of CorXal there is no bond interface between the skin and core elements, instead a continuous aluminium matrix throughout the material provides a closed system. This means parts made from CorXal will not succumb to the environmental conditions, maintaining the necessary structural properties needed, increasing stiffness by up to four times compared to some grades of aluminium, and reducing weight by a target of 40 per cent compared to some steels. The reduction in aircraft weight will also have a corresponding effect on fuel consumption.
Benefits of AMCs
AMCs offer significant weight reductions compared to legacy materials, offering manufacturers the chance to meet the challenge of reduced weight and fuel burn, while maintaining reliability and lowering whole-life ownership costs.
AMCs are unique in that they are available in multiple variants (where the metallic material has been reinforced with a secondary high-performance material – typically, a long-fibre, short fibre or particulate) and properties, such as stiffness, strength and density can be tailored through particle-reinforcement with continuous-fibre-reinforcement (CFR). This method is preferred for applications where higher performance is needed.
According to Alvant, AMCs can have superior strength compared to steel at less than half the weight, meaning highly loaded components, usually made from traditional metals, such as steel, titanium and aluminium can be replaced by lightweight, low inertia parts without any increase in package size.
When used to engineer durable lightweight components for harsh environments, AMCs can have higher strength, greater stiffness, lower weight, superior wear resistance, lower coefficients of thermal expansion and superior electrical conductivity, when compared to unreinforced metals.
AMCs also boast multiple advantages over polymer fibre reinforced materials, such as higher transverse strength and stiffness, a higher thermal operating range, better wear resistance, superior damage tolerance, and more opportunity to recycle.
“These industries face the challenge of finding suitable materials that will decrease weight whilst maintaining reliability and reducing the costs whole-life ownership can bring,” adds Thompson. “AMCs offer an exciting potential to industries that need a step change in performance to meet ever stringent market and legislative demands. We are in the growth stages of an age of New Materials, now is the time for the aerospace industry to stop relying on traditional technologies and embrace change.”