Resin-infused metal foam may make for better airplane wings

Resin-infused metal foam may make for better airplane wings
A sample of the infused CMF, with a ruler for scale
A sample of the infused CMF, with a ruler for scale
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A sample of the infused CMF, with a ruler for scale
A sample of the infused CMF, with a ruler for scale

Scientists at North Carolina State University have already had success using composite metal foams (CMFs) to stop bullets and block radiation. Now, they've determined that a new one should also outperform aluminum when used in the construction of aircraft wings.

CMFs typically consist of hollow spheres made of one type of metal, contained within a solid matrix composed of either the same or a different metal. One of their biggest selling features is that they tend to be lighter than conventional solid metals, while offering comparable strength.

Developed by a team led by Prof. Afsaneh Rabiei, the new material is known as an infused CMF.

It's based around a steel-steel CMF, meaning that both the hollow spheres and the matrix are made of stainless steel. Utilizing a vacuum process, however, a hydrophobic (water-repelling) epoxy resin is pulled into the material – as a result, the resin fills the inside of the spheres, along with about 88 percent of the smaller pores within the matrix material.

The scientists tested the infused CMF alongside traditional aerospace aluminum, to see how both materials would fare when used on the leading edge of an aircraft wing. It was found that the CMF performed better, in three specific areas.

First of all, it was superior at causing water to bead up and roll off, as opposed to clinging in place. Technically-speaking, its contact angle was 130 percent higher than that of the aluminum – the lower a material's contact angle, the greater the amount of water that clings to its surface.

Secondly, when insects were blasted against both materials, less of their residue accumulated on the CMF. Numbers-wise, there was 60 percent less residue as measured by height of accumulation, and 30 percent less according to area covered.

Finally, although both materials were made rougher when subjected to grit blast tests, the CMF still came out on top, showing less degradation.

"Our results suggest that infused CMF may be a valuable replacement [for aluminum], offering better performance at the same weight," says Rabiei. "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."

A paper on the research was published this week in the journal Applied Surface Science.

Source: North Carolina State University

Why go to all the trouble of making the spheres porous so the resin can get inside?

Surely that will make no difference to the strength of the composite, but it will certainly increase weight.....
I'm wondering how this CFM is vulnerable to metal fatigue considering all the flexing an airplane wing has to endure.
Resin reinforcement might make the spheres stiffer without contributing as much weight as a solid metal sphere. I'm wondering more about the steel "matrix" -- is it a powder mixed with the resin?
Louis Richards
It's probably more like why go to the trouble of making the spheres perfectly smooth, when it would increase costs without making much difference to the strength.
The irregularities and pores are there on the metal particles. If they were air in them it would likely be weaker than being vacuum processed to fill those gaps with resin.
Sounds great. But will it be a recycling problem??
I dont like the word ''should'' when applied to an aircraft wing! I would very much prefer' ''will.'' However there are many more tests that need to be applied, like hot or cold temperatures, and also how it performs when flexed persistently, as well as shock loading, before the ''will'' can be applied. It will also need to be corrosion tested, as when moisture is present, electrolytic effects come into play.
I would guess the reviewer has mis-understood the process somewhat
Another angle- will using differing resins allow for a more flexible material? The idea or "morphing" wings has been around for a long time, the main holdup is finding a flexible matrix that is strong enough to do the job.