Not long ago, the website of North Carolina State University in the United States published a report entitled "Composite Metal Foam Outperforms Aluminum for Use in Aircraft Wings" (Composite Metal Foam Outperforms Aluminum for Use in Aircraft Wings) English original): The leading edge of the aircraft wing must meet very stringent performance indicators. The latest research shows that, compared with the aluminum alloy widely used in aircraft wings, the new material made of steel-containing composite metal foam (CMF) combined with epoxy resin has more ideal application characteristics.
Dr. Afsaneh Rabiei, the corresponding author of the research paper and a professor in the School of Mechanical and Aerospace Engineering at North Carolina State University, said that this new hybrid material is called "infused composite metal foam" ( infused CMF). Although the weight of CMF and aluminum alloy is about the same, from the perspective of actual flight performance, safety and fuel efficiency of the aircraft, the new material has higher strength and other excellent characteristics, which makes this new material more attractive force.
Professor of the School of Mechanical and Aerospace Engineering of the University of North Carolina, Dr. Afsan Rabbi, and her advanced materials laboratory (AMRL) and the main direction of work (Photo of North Carolina State University, USA)
CMF is a kind of foam, which consists of hollow metal balls (such as stainless steel or titanium alloy) and is embedded in a metal matrix made of steel, aluminum or other metal alloys. In this study, the CMF made by the researchers consists of a steel metal sphere and a steel substrate. Through previous research, it has been found that this metal foam is very hard, can withstand the impact of .50 caliber (12.7 mm caliber) ammunition, can withstand high temperatures, and can withstand the energy released by high explosive bombs.
The preparation process of this infusion CMF: firstly, the steel CMF is immersed in hydrophobic epoxy resin, and then the resin is poured into the hollow metal sphere and the small holes of the steel substrate by vacuum force, and finally "infused CMF" is made. This makes about 88% of the space in the hole of this CMF filled with epoxy resin.
New composite metal foam CMF (Photo of North Carolina State University, USA)
The researchers tested the perfusion CMF and aviation-grade aluminum alloys, and observed their performance in three aspects:
One is the contact angle. The contact angle is the angle produced when a liquid contacts a solid, and it is a measure of the degree of water accumulation on the surface of the structure. It determines how fast the water flows from the surface of the material-the smaller the contact angle of the material, the more water adheres to the surface. This is closely related to the structure of the aircraft wing, because the accumulation of water on the wing will affect the performance of the aircraft. The researchers found that the contact angle of infused CMF is 43% higher than that of stainless steel and 130% higher than that of aluminum alloy, which significantly improves the hydrophobicity of the material surface.
The second is insect adhesion. It determines the extent to which insects attach to the surface of the material; there are two ways to measure insect adhesion: one is to measure the maximum height of insect residues on the material; the other is to measure the area covered by insect residues on the surface of the material. Similarly, infusion CMF is better than aluminum alloy in this index-the maximum height of the residue is reduced by 60%, and the residue coverage area is reduced by 30%.
The third is the degree of particle loss. That is, the degree of erosion of the material. Researchers conducted sandblasting tests to simulate the corrosion caused by wear and tear of aircraft wings over time during flight. The researchers found that although sandblasting did cause damage to the surface of the infused CMF, the degree of damage was still better than that of aluminum alloy; even under the most severe corrosion conditions, the contact angle of the surface of the infused CMF could still be higher than that of aluminum alloy 50 %. In other words, the perfusion CMF can still maintain its characteristics after erosion and wear, which shows that it can make the leading edge components of the wing have a longer service life, while also reducing maintenance and replacement costs.
Aluminum alloy is still the material of choice for the leading edge of fixed-wing and rotary-wing aircraft wing, but the research results of North Carolina State University indicate that perfusion CMF may be a very valuable substitute, which can be provided under the same weight. Better performance. In addition, if the metal material used in the substrate or the metal sphere is replaced, it is possible to create a CMF with performance equivalent to that of traditional aluminum alloy but greatly reduced weight. No matter which method is adopted, the aircraft performance and fuel efficiency can be improved.
The research paper "Polymer Infused Composite Metal Foam as a Potential Aircraft Leading Edge Material" (Polymer Infused Composite Metal Foam as a Potential Aircraft Leading Edge Material) has been published in the Dutch Journal of Applied Surface Science.