Engineers have proposed an alternative to aluminium for the leading edges of aircraft wings after the material demonstrated encouraging aerospace-grade qualities in tests.
The material combines steel composite metal foam (CMF) and epoxy resin to form a hybrid material dubbed ‘infused CMF’ by the team that developed it at North Carolina State University (NC State).
“While infused CMF is about the same weight as aluminium, it is tougher and has other characteristics that make it more appealing from a flight performance, safety and fuel efficiency standpoint,” said Afsaneh Rabiei, corresponding author of a paper on the work and a professor of mechanical and aerospace engineering at NC State.
CMF consists of hollow, metallic spheres made of materials including stainless steel or titanium that are embedded in a metallic matrix made of steel, aluminium or metallic alloys.
For their latest CMF study, the researchers used so-called steel-steel CMF, where the spheres and the matrix were made of steel. Previous work has found the metal foam can withstand .50 calibre rounds, resist high temperatures, and block blast pressure from high explosive incendiary rounds.
The infused CMF is made by immersing the steel-steel CMF in a hydrophobic epoxy resin and using vacuum forces to pull the resin into the hollow spheres and into much smaller pores found in the steel matrix. According to NC State, this results in about 88 per cent of the CMF’s pores being filled with epoxy resin.
The researchers then tested infused CMF and aerospace-grade aluminium to see how they performed in three areas that affect the performance of a wing’s leading edge: contact angle, insect adhesion, and particle wear.
Contact angle is a measure of how well water beads up on a surface. The lower a material’s contact angle, the more the water clings to the surface, which can affect aircraft performance. The researchers found that infused CMF had a contact angle 130 per cent higher than aluminium.
Insect adhesion is measured in two ways: by the maximum height of insect residue that builds up on a material, and by the amount of area covered by insect residue on a material’s surface. Infused CMF reportedly outperformed aluminium by 60 per cent in terms of maximum height, and 30 per cent in regard to the surface area covered.
The researchers also conducted grit blast experiments to simulate the erosion caused by the wear and tear that occurs over time when aircraft wings are in use. The researchers found that, while grit blast did increase surface roughness for infused CMF, it still fared better than aluminium; at its worst, infused CMF still had a contact angle 50 per cent higher than that of aluminium.
“Aluminium is currently the material of choice for making the leading edge of fixed-wing and rotary-wing aircraft wings,” Rabiei said in a statement. “Our results suggest that infused CMF may be a valuable replacement, offering better performance at the same weight.
“By the same token, the results suggest that we could use different materials for the matrix or spheres to create a combination that performs as well as conventional aluminium at a fraction of the weight. Either way, you’re improving performance and fuel efficiency.”
The paper, “Polymer Infused Composite Metal Foam as a Potential Aircraft Leading Edge Material,” is published in Applied Surface Science.