Introduction To Honeycomb Core Materials: Types And Properties

Introduction

Honeycomb core materials play a key role in panel construction, providing essential structural integrity and performance for many engineering applications. The unique strength stems primarily from the geometric design of the honeycomb structure itself, which optimizes the use of materials while maintaining lightweight properties. In this article, we will explore the various types of honeycomb core materials, delve into their properties, and discuss their wide range of applications in different industries. Let you wait for a better understanding when choosing the material for the honeycomb core.

Understanding Honeycomb Core

The honeycomb core combines strength and lightness, which can significantly improve the strength and durability of the panel. The unique honeycomb structure is similar to the hexagonal pattern in a honeycomb, which can evenly distribute the load while maintaining lightness. The honeycomb core can be made of a variety of materials. Its versatility and different characteristics enable the honeycomb core to be used in different fields.

How Is The Honeycomb Core Made?

——Material Selection
The first step in making a honeycomb core is to select the right material for the application. Common materials include aluminum, thermoplastics, aramid fibers, and paper. Each material has different properties and uses.

——Core Formation
Once the material is selected, it is processed into sheets or strips. For metal cores such as aluminum, the sheets may be treated to enhance properties such as corrosion resistance. The sheets are then cut into precise strips, stacked, and bonded together using adhesives. The stack is then pulled through a heated die during the extrusion process, which causes the adhesive to expand and form the unique hexagonal cells of the honeycomb. The expansion and stretching can be controlled to different cell sizes and densities depending on the specific strength and flexibility required.

——Cutting and Forming
After the honeycomb structure is formed, it is cut into specific sizes according to the application requirements. Large industrial cutting tools may be required for uniform, mass-produced panels, or more precise cuts for specialized custom applications. Honeycombs can also be further processed or treated to seamlessly integrate with other structural components in larger assemblies.

——Finishing
Finally, finishing is done to enhance the performance of the honeycomb core. For example, the aluminum core can be anodized for improved corrosion resistance, while the aramid and thermoplastic cores can be coated with heat-resistant or flame-retardant chemicals. In addition, edge sealing is used to prevent moisture and environmental factors, especially in applications exposed to harsh conditions.

Types Of Honeycomb Core Materials

There are many different materials that can be used for honeycomb cores, each with its own properties and applications, such as：

Aluminum: Aluminum honeycomb core is a lightweight, strong structural material that is typically made from multiple layers of aluminum foil that are bonded together and then spread out to form a regular hexagonal pattern. The shape resembles a honeycomb, which offers a range of advantages that make it ideal for applications across a wide range of industries.

Advantages of Aluminum Honeycomb Core:

• Lightweight and Strong: Aluminum itself is lightweight, which helps reduce the overall weight of the structure. Despite its light weight, it maintains high strength, providing the necessary support and stability when needed.

• Corrosion Resistant: Aluminum naturally resists corrosion, which can extend the life of products made with aluminum, especially in environments exposed to moisture or chemicals.

• Recyclable: Aluminum materials can be reused sustainably without sacrificing quality. It is also an environmentally friendly choice.

• Easy to Fabricate and Form: Aluminum’s ductility allows it to be used in a variety of forming and manufacturing techniques, making it suitable for complex designs and custom applications.

• Fire Resistance: Aluminum can withstand high temperatures and is non-flammable, adding a necessary layer of safety in flammable environments.

• Customizable: The flexibility of the manufacturing process allows the honeycomb structure to be customized to meet specific performance criteria, such as different thicknesses, cell sizes, and densities.

Application of Aluminum Honeycomb Core:

—— Furniture: Aluminum honeycomb core can be used to produce furniture that is easy to move and rearrange, strong and durable.

——Ceilings and floors: Aluminum honeycomb cores are used in ceilings and floors to help improve structural integrity and provide sound insulation, which can also reduce the noise level of buildings.

—— Building exterior curtain wall panels: The use of aluminum honeycomb cores in curtain walls can improve durability and help improve the aesthetics of building exterior walls. It can also improve thermal performance and help regulate indoor temperature.

—— Automotive interior panels: In automotive design, these cores are used to make lightweight interior panels that absorb energy in the event of an impact, thereby improving vehicle safety and improving fuel efficiency.

—— Aviation: Aluminum honeycomb cores can build aircraft structures. The strength and lightness of the material are crucial to the aviation industry, with stable performance and safety.

Thermoplastic: Thermoplastic honeycomb core is also a structurally strong but lightweight material, a polymer that becomes flexible or pliable at a certain high temperature and solidifies when cooled. Unlike thermoset plastics, thermoplastics can be reheated and reshaped many times without significant chemical changes, making them versatile and recyclable.

Thermoplastic honeycomb cores are typically manufactured using various types of thermoplastic polymers, such as:

• Polypropylene (PP): has excellent chemical resistance and fatigue properties, and is more suitable for automotive and aerospace applications.

• Polyethylene (PE): has high impact resistance and flexibility.

• Polycarbonate (PC): has high impact strength and clarity, suitable for protective applications and where visual inspection is required.

• Nylon (polyamide): has abrasion resistance and strength, used in more demanding mechanical applications.

Advantages of Thermoplastic Honeycomb Cores：

—— Lightweight: Thermoplastic honeycomb cores are extremely light, which can significantly improve fuel efficiency and performance for industries such as automotive and aerospace.

—— High Strength: Despite their light weight, these cores are very strong, with excellent stiffness.

—— Impact Resistance: Thermoplastics are generally good at absorbing and dissipating energy.

—— Corrosion Resistance: Unlike metal cores, thermoplastics do not corrode. Ideal for use in harsh or high-humidity environments.

—— Chemical Resistance: Thermoplastics can withstand attack from a wide range of chemicals, making honeycomb cores suitable for use in chemical processing environments or areas where materials may be exposed to contaminants.

—— Thermal Insulation: Thermoplastic cores have good thermal insulation properties. This helps the construction and automotive industries maintain energy efficiency.

—— Recyclability: Many thermoplastic materials can be recycled, supporting environmental sustainability.

—— Easy to Process: Thermoplastic honeycomb cores are easy to shape and cut, and can be heat welded without adhesives.

Specific Applications of Thermoplastic Honeycomb Cores：

1. Automotive: Used in interior panels, trunk floors, and other structural components.
2. Aerospace: Applied to cabin partitions, floors, and luggage compartments.
3. Marine: Used to build bulkheads, decks, and hull components. It is moisture-resistant and corrosion-resistant.
4. Sports Equipment: Used to make lightweight but strong sports goods such as skis, snowboards, and protective gear.
5. Building and Construction: Used in doors, walls, and partitions that require insulation, strength, and lightness.

Steel: Stainless steel honeycomb cores offer exceptional strength and durability, allowing the core to withstand significant mechanical stress and impact. They are suitable for applications such as façade panels, roof structures and decorative elements where structural integrity and aesthetics are important, strength to weight ratio and resistance to wind pressure.

They are also heat and corrosion resistant, making them ideal for use in thermally exposed and environments susceptible to moisture, chemicals and salt. Stainless steel honeycomb panels can also be used in components such as floors, panels and energy absorbing structures.

Kraft Paper: Kraft paper honeycomb core is made of multiple layers of kraft paper bonded together and expanded into a honeycomb structure. It is a natural brown paper produced through a sulfate pulping process. This paper has higher tensile strength than other papers.

Kraft paper is relatively cheap to make, biodegradable, and made from renewable resources. The honeycomb design enables it to absorb and distribute loads evenly, providing good compressive strength and stiffness. It has good thermal and acoustic insulation properties and can be used in a variety of construction and packaging applications. It can also be easily cut and formed.

It is commonly used in interlayer pads in pallets, crates and stacked packaging, or as a lightweight filling material for doors, partitions and floors, providing structural strength and insulation, and automotive door panels and trunk partitions.

Aramid Paper: Aramid paper honeycomb cores are made from aramid fiber paper that is infused with a synthetic polymer. Aramid fibers are heat resistant and have strong synthetic properties. These cores take advantage of the superior strength and thermal stability of aramid fibers in the honeycomb structure to provide a unique combination of lightness, strength, and resilience.

Aramid paper honeycomb cores are thermally stable, can withstand high temperatures, and have low thermal conductivity. They also have excellent fatigue resistance and can maintain their shape and size even under pressure or heat, making them ideal for fire protection applications and extremely hot environments.

Aramid paper honeycomb cores are generally used in:

• In floors, bulkheads, and partitions in aviation;
• In military vehicles and protective equipment in defense;
• Interior panels and floors in railways, etc.

Fiberglass：Fiberglass honeycomb cores are made from fiberglass sheets or woven fiberglass materials that are then formed into a honeycomb structure. This type of core combines the inherent strengths of fiberglass (such as high tensile strength, chemical resistance, and thermal stability) with the geometric efficiency of the honeycomb design to provide a strong yet lightweight composite material.

Fiberglass honeycomb structures provide excellent thermal and acoustic insulation, and unlike metals, fiberglass does not absorb water, which helps maintain structural properties and prevents degradation in humid conditions. It is also naturally flame retardant, which can be enhanced with special coatings, and has good fatigue resistance and the ability to withstand a variety of environmental conditions, making it very durable.

Fiberglass honeycomb cores are generally suitable for interior panels, floors, and cargo compartment linings. And for the construction of wind turbine blades.

Carbon Fiber: Carbon fiber honeycomb core is a high-performance composite material that combines the strength and stiffness of carbon fiber with the efficient, lightweight geometry of a honeycomb structure. It is made by bonding carbon fiber layers in an adhesive matrix and then expanding them to form a honeycomb grid.

Carbon fiber is one of the hardest and strongest materials available, and these properties are enhanced when configured into a honeycomb structure, providing excellent stiffness and load-bearing capacity. It is also fatigue-resistant, maintaining its integrity over multiple load cycles and can be used with frequent or cyclic loads. In addition, carbon fiber has low thermal expansion and high thermal conductivity, and remains stable over a wide range of temperatures. It is also not easily corroded, so it can maintain its performance in harsh environments.

Carbon fiber honeycomb cores are generally suitable for aircraft fuselage panels, wing assemblies, and floor panels. It can also be used in automotive structural components, chassis components, and body panels.

Foam Core: A lightweight core material used in composite structures, usually sandwiched between two rigid skins to form a "sandwich panel". This core material is made from various types of foam, including polyurethane, polystyrene, PVC (polyvinyl chloride) and PET (polyethylene terephthalate), each with different properties to meet specific needs.

Although foam core is light, it has considerable structural strength and is easy to manufacture and can be easily cut and shaped. It is also very good at insulation, which can maintain temperature control in buildings, vehicles and other enclosed structures. And it has sound insulation function, which can reduce the transmission of noise.

Foam core is also moisture-resistant and suitable for environments exposed to water.For example:

• It is suitable for hulls, decks and superstructures;
• For the manufacture of wind turbine blades;
• For building panels, doors and roof systems;
• For the production of lightweight sports boards such as surfboards, snowboards and structural cores for artificial turf.

Properties Of Honeycomb Core Materials

—— Structural Properties

• Compressive Strength: Due to its honeycomb structure, honeycomb cores are able to withstand significant compressive forces.

• Shear Strength: Honeycomb cores have excellent shear strength, which is the ability to resist sliding forces in a plane.

—— Physical Properties

• Low density and lightweight.

• Thermal Conductivity: Honeycomb cores have low thermal conductivity, making them excellent insulators.

• Moisture Resistance: While moisture resistance can vary depending on the material used (such as aramid, aluminum, or fiberglass), many honeycomb cores are designed to resist moisture intrusion and maintain their structural integrity.

—— Durability and Environmental Resistance

• Chemical Resistance: Due to its chemical resistance, honeycomb cores are often selected for environments exposed to harsh chemicals.

• Temperature Resistance: The ability to withstand extreme temperatures is another important property of honeycomb cores.

What Are The Core Shapes Of Honeycomb Cores

Honeycomb cores come in a variety of shapes, including hexagonal, over-expanded core, flexible core, square and rectangular, with the most widely used shape being the hexagonal core, which offers the best balance of strength and density, high efficiency in load distribution and light weight. Over-expanded cores have larger cells and are more flexible, making them suitable for curved surfaces such as aircraft fuselages and boat hulls. Flexible cores are designed for applications that require high formability. While each shape has its advantages, the hexagonal configuration remains the most commonly used due to its versatility and effectiveness in a wide range of applications.

Conclusion

In summary, honeycomb core materials are indispensable in modern engineering due to their diverse types and advantageous properties. Their ability to provide strength, lightweight, and other critical features ensures their continued use and development across various high-performance industries.

Related references

Introduction to Honeycomb Core from HEXCEL
Information about honeycomb types and materials from GlobalSpec