A combination of steel composite metal foam and epoxy resin could be a better leading-edge material in airplane wings than aluminum, tests show.
“We call our hybrid material ‘infused CMF,'” says corresponding author Afsaneh Rabiei, a professor of mechanical and aerospace engineering at North Carolina State University. “And while infused CMF is about the same weight as aluminum, it is tougher and has other characteristics that make it more appealing from a flight performance, safety, and fuel efficiency standpoint.”
Composite metal foam (CMF) consists of hollow, metallic spheres—made of materials such as stainless steel or titanium—embedded in a metallic matrix made of steel, aluminum, or metallic alloys. For this study, the researchers used steel-steel CMF, meaning that both the spheres and the matrix were made of steel. Previous work has found the metal foam is remarkably tough: it can withstand .50 caliber rounds, resist high temperatures, and block blast pressure from high explosive incendiary rounds.
Researchers made the infused CMF by immersing the steel-steel CMF in a hydrophobic epoxy resin and using vacuum forces to pull the resin into both the hollow spheres and into much smaller pores found in the steel matrix itself. This results in about 88% of the CMF’s pores being filled with epoxy resin.
The researchers then tested both infused CMF and aerospace grade aluminum to see how they performed in three areas: contact angle, which determines how quickly water streams off of a material; insect adhesion, or how well bug parts stuck to the material; and particle wear, or how well the material stands up to erosion. All of these factors affect the performance of an aircraft wing’s leading edge, which have to meet a very demanding set of characteristics.
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. This is relevant for aircraft wings because water buildup on a wing can affect aircraft performance. The researchers found that infused CMF had a contact angle 130% higher than aluminum—a significant improvement.
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 insect residue covers on a material’s surface. Again, infused CMF outperformed aluminum—by 60% in regard to maximum height, and by 30% in regard to the surface area covered.
The researchers also conducted grit blast experiments to simulate the erosion that the wear and tear that occurs over time when aircraft wings are in use causes. The researchers found that, while grit blast did increase surface roughness for infused CMF, it still fared better than aluminum. For example, at its worst, infused CMF still had a contact angle 50% higher than that of aluminum.
In other words, the infused CMF retained its properties through erosion and wear, which indicates that it would give leading-edge wing components a longer lifetime—and reduce the costs associated with maintenance and replacement.
“Aluminum is currently the material of choice for making the leading edge of fixed-wing and rotary-wing aircraft wings,” Rabiei says. “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 aluminum at a fraction of the weight. Either way, you’re improving performance and fuel efficiency.”
The paper appears in the journal Applied Surface Science. Additional coauthors are from NC State and NASA Langley Research Center. Support for the research came from NASA.
Source: NC State