Nomex® vs. Aluminum Honeycomb: The Right Core for Your Application

Selecting materials for aerospace manufacturing is not an exact science. Moreover, what constitutes the ‘best’ material isn’t a universal constant. Manufacturers face a balancing act as they consider everything from mechanical requirements to environmental exposure. Even something as benign as flooring needs to be carefully considered before materials are chosen.

Sandwich panel cores are ideal for aerospace interiors. They are utilized in floors, galley components, partitions, etc. The choice of core can be critical to the overall design of the interior. And currently, the two most utilized core options are Nomex® (aramid fiber) and aluminum. Which is the right choice for a given application?

Aluminum has been the preferred choice for structural applications for as long as most of us can remember. Still, Nomex honeycomb has found a place in aircraft cabin interiors. One might argue it has taken a dominant position over aluminum core products. Comparing Nomex with aluminum reveals why.

Superior Strength-to-Weight Ratio

In aerospace, weight and operational costs are intrinsically linked. Every ounce of total weight saved translates into a higher payload capacity and improved fuel efficiency. That being the case, Nomex honeycomb beats aluminum thanks to its superior strength-to-weight ratio.

Aluminum is no slouch. It offers exceptional stiffness and a high strength-to-weight ratio as well. It is a good choice for primary structures that designers expect to have to carry high localized loads. Aluminum is hard to beat in that regard. Still, Nomex outperforms aluminum in certain applications.

As a Nomex honeycomb core supplier, we can attest to the fact that this material is as strong as aluminum but still provides a softer failure mode and better fatigue resistance. It is preferred in low-density environments, like cabin interiors, because it allows for thin-walled cells that increase weight savings without compromising structural integrity.

Superior Corrosion Resistance

Aircraft cabin surfaces are routinely exposed to all sorts of things that can encourage corrosion. From spilled liquids to cleaning agents and atmospheric moisture, components need to resist their impacts as much as possible. How do aluminum and Nomex perform?

• Aluminum – All metallic cores are highly susceptible to corrosion. They can be treated with corrosion-resistant coatings, but they are still subject to galvanic corrosion when cores are exposed to moisture or come into contact with carbon fiber. When this happens, delamination becomes a problem.
• Nomex – Nomex is essentially a resin-impregnated aramid paper. It is immune to normal corrosion because it is chemically inert. Leading honeycomb core producers recommend it for airplane interiors since it is unaffected by changing humidity.

For the aircraft cabin, Nomex honeycomb panels are a set-and-forget solution. They require minimal maintenance thanks to their corrosion-resistant nature.

Moisture Absorption and Bond Integrity

Moisture is not just a concern in terms of corrosion. It also affects bond integrity. A panel’s ability to resist moisture is key to preventing internal material rot.

Aluminum is moisture-resistant because it is nonporous. Simply put, aluminum does not absorb water. But bond lines are a different matter. If a panel’s seal is broken, even slightly, moisture can make its way into the cells. Over time, repeated freeze-thaw cycles at high altitudes will lead to rot.

Nomex honeycomb cores are a better choice in this regard as well. As a fiber-based product, Nomex is manufactured with a high-grade phenolic resin that overwhelms the fibers. This prevents the fibers from absorbing moisture. So even if moisture does make its way in, Nomex is not subject to the same degradation. Panels will maintain their structural integrity throughout their serviceable life.

In this particular area, it is important for aerospace manufacturers to work with a trusted Nomex honeycomb core supplier with a good track record of insisting on the highest quality phenolic resins.

Nomex Cores Beyond Aircraft Interiors

While Nomex honeycomb core panels have taken a dominant position in aircraft interior design, they face more competition from aluminum in other areas of the aircraft. Still, Nomex is worthy of consideration for other applications. Here are just a few examples:

1. Control Surfaces and Secondary Structures

Nomex isn’t ideal for applications subject a high localized loads. But it is a good material for moving parts that must maintain stiffness but be as lightweight as possible. Nomex parts are stiff enough to handle typical aerodynamic loads. So it is often used in manufacturing:

• Ailerons, flaps, and rudders.
• Leading and trailing wing edges.
• Spoilers and slats.

One of the advantages Nomex offers for control surfaces and secondary structures is its ability to be formed into complex shapes. That makes the material suitable for modern aerodynamic profiles.

2. External Fairings and Cowlings

Even though aerodynamic skins do not carry primary loads, they must be able to withstand high-speed airflow and environmental exposure. Nomex is up to the task, making it suitable for:

• Engine cowlings and nacelles.
• Fuselage fairings.
• Radomes.

One of the more visible uses of Nomex honeycomb panels, outside the aircraft interior, is the nose cone (radome). Its superior dielectric properties prevent the material from interfering with radar signals. Nomex will not bother weather and navigation systems in flight.

3. More Specialized Applications

Nomex honeycomb products are even utilized for more specialized applications most people would not understand as being appropriate. For example, Nomex performs extremely well in space. It is utilized heavily in satellite structures, including antenna reflectors and solar arrays.

Nomex has applications in:

• Unmanned aerial vehicles (UAVs)
• Helicopter rotor blades.
• Helicopter tail booms.

Nomex honeycomb core proves it can’t replace aluminum for every application. It is certainly not suitable where high localized loads are a concern. But it is showing its worth in many low-load environments throughout different types of aircraft.

As an aerospace manufacturer, your search for the best Nomex honeycomb supplier ends with Axiom Materials. We invite you to contact us to learn more about this amazing material and its many applications. As a space-age composite, Nomex adds flexibility to your designs by giving you a lightweight but strong alternative to aluminum core products.

FAQs

What is Nomex honeycomb, exactly?

Nomex is a brand name. It is a product made with a synthetic aramid fiber, in the form of a honeycomb. The fibers themselves are formed into a paper-like sheet and then coated with a phenolic resin and cured.

How do aluminum and Nomex cores compare in terms of failure?

Aluminum is a more brittle material and can fail under extreme stress. Buckling and crinkling are not uncommon. Nomex offers better fatigue memory, making it more resilient. It does not permanently deform so easily.

Is galvanic corrosion a problem for Nomex?

No. Unlike aluminum-core products, Nomex is not subject to galvanic corrosion. This makes it a better choice when an application calls for carbon fiber skin.

How does cell size affect a honeycomb panel?

Cell size is defined as the distance across a hexagonal opening. Smaller cells offer more surface area for bonding, leading to a higher overall strength and a smoother surface finish. Larger cells offer less bonding surface but decrease panel weight.