Here are the different types of core materials and their advantages and disadvantages.
Honeycomb
The most common core material used for aircraft honeycomb structures is aramid paper. Fiberglass is used for higher strength applications.
Advantages
- Can be made to conform to compound curves without excessive mechanical force
Disadvantages
- Low strength and stiffness
- Lightweight
Thermoplastics
It has a high-temperature mechanical property that is used in aircraft engines and other hot section areas.
Advantages
- Good insulating properties and energy absorption
- Moisture and chemical resistance
- Low cost
Disadvantages
- Relatively low strength
Note that thermoplastic resins are different from thermosetting resins.
Aluminum
Aluminum core materials have electromagnetic shielding properties.
Advantages
- Best strength-to-weight ratio
- Energy absorption
- Good heat transfer properties
- Machinable
- Low cost
Disadvantages
- Flammable core
- Steel
- Used For high-frequency application
Titanium
Welded by gas-tungsten arc or plasma-arc techniques
Advantages
- Relatively high strength-to-weight ratio
- Good heat transfer properties
- Chemical resistance
- Heat resistant
Disadvantages
- Expensive
- Poor wear characteristics
Kraft Paper
It is made by the sulphate pulping process. Natural kraft paper is a stronger type.
Advantages
- Good insulating properties
- Available in large quantities
- Low cost
Disadvantage
- Relatively low strength
Aramid Paper
Molded by a four-layered shell with two central fiber mat plies
Advantages
- Flame resistant
- Good insulating properties
- Low dielectric properties
- Good formability
Disadvantages
- Absorbs moisture
- Poor compressive properties
Fiberglass
For high compression strength requirements
Advantages
- Tailorable shear properties by a layup
- Low dielectric properties
- Good insulating properties
- Good formability
Disadvantage
- Ultraviolet sensitive unless coated or pigments are in gel coat
Ceramics
Used for leading-edge and nose structures to withstand up to 1800-degree Celsius
Advantages
Heat resistant to very high temperatures
- Good insulating properties
- Available in very small cell sizes
Disadvantage
- Very expensive
Balsa Wood
Balsa is a natural wood product with elongated closed cells. it is available in a variety of grades that correlate to structural, cosmetic, and physical characteristics.
Advantage
- It has a considerably higher density than the other types of structural cores.
Disadvantage
- The density of balsa is less than one-half of the density of conventional wood products.
Foam
Foam cores are used on homebuilt and lighter aircraft to give strength and shape to wingtips, flight controls, fuselage sections, wings, and wing ribs.
Advantage
- Gives shape with strength advantage
Disadvantage
- Not commonly used on commercial type aircraft because it is heavy
Examples:
POLYSTYRENE (STYROFOAM)
Aircraft-grade Styrofoam with a tightly closed-cell
Advantages
High compressive strength and good resistance to water penetration
Can be cut with a hot wire to make airfoil shapes
Disadvantages
Flammable and toxic
POLYPROPYLENE
Used to make airfoil shapes
Advantages
Can be cut with a hot wire
Compatible with most adhesives and epoxy resins
Disadvantages
Not for use with polyester resins
Dissolves in fuels and solvents
PHENOLIC
It can be easily contoured with a large knife and sanding equipment
Advantages
Can be cut with a hot wire
Compatible with most adhesives and epoxy resins
Disadvantage
Can’t be used with a hot wire to cut polyurethane foam
Polyvinyl chloride (PVC) (Divinycell, Klegecell, and Airex)
A closed-cell medium- to high-density foam.
Advantages
High compression strength
Durability
Excellent fire resistance
Can be vacuum formed to compound shapes and be bent using heat
Disadvantage
Emits toxic fumes when melted
Polymethacrylimide (Rohacell)
A closed-cell foam used for lightweight sandwich construction
Advantages
Excellent mechanical properties
High dimensional stability under heat
Good solvent resistance
Creep compression resistance
Mechanical properties
Disadvantage
More expensive than the other types of foams
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| Types of Core Materials | Description | Advantages | Disadvantages |
| Honeycomb | The most common core material used for aircraft honeycomb structures is aramid paper. Fiberglass is used for higher strength applications. | Can be made to conform to compound curves without excessive mechanical force | Low strength and stiffnessLightweight |
| Kraft Paper | It is made by the sulfate pulping process. Natural kraft paper is a stronger type. | Good insulating propertiesAvailable in large quantitiesLow cost | Relatively low strength |
| Thermoplastics | It has a high-temperature mechanical property that is used in aircraft engines and other hot section areas. | Good insulating properties and energy absorptionMoisture and chemical resistanceLow cost | Have a limited temperature spectrum for applications |
| Aluminum | Aluminum core materials have electromagnetic shielding properties. | Best strength-to-weight ratioEnergy absorptionGood heat transfer propertiesMachinableLow cost | Flammable core |
| Steel | Used For high-frequency application | Good heat transfer propertiesElectromagnetic shielding propertiesHeat resistant | High cost |
| Specialty metals (titanium) | Welded by gas-tungsten arc or plasma-arc techniques | Relatively high strength-to-weight ratioGood heat transfer propertiesChemical resistanceHeat resistant | ExpensivePoor wear characteristics |
| Aramid Paper | Molded by a four-layered shell with two central fiber mat plies | Flame resistantGood insulating propertiesLow dielectric propertiesGood formability | Absorbs moisturePoor compressive properties |
| Fiberglass | For high compression strength requirements | Tailorable shear properties by a layupLow dielectric propertiesGood insulating propertiesGood formability | Ultraviolet sensitive unless coated or pigments are in gel coat |
| Carbon | For stringent strength and rigidity requirements CarbonFor stringent strength and rigidity requirements AdvantagesGood dimensional stabilityHigh-temperature property retentionHigh stiffnessVery low coefficient of thermal expansionTailorable thermal conductivityHigh shear modulus DisadvantagesVery expensive | Good dimensional stabilityHigh-temperature property retentionHigh stiffnessVery low coefficient of thermal expansionTailorable thermal conductivityHigh shear modulus | Very expensive |
| Ceramics | Used for leading-edge and nose structures to withstand up to 1800-degree Celsius | Heat resistant to very high temperaturesGood insulating propertiesAvailable in very small cell sizes | Very expensive |
| Foam | Foam cores are used on homebuilt and lighter aircraft to give strength and shape to wingtips, flight controls, fuselage sections, wings, and wing ribs. | Gives shape with strength advantage | Not commonly used on commercial type aircraft because it is heavy |
| POLYSTYRENE (STYROFOAM) | |||
| Aircraft-grade Styrofoam with a tightly closed-cell structure & no voids between cells | High compressive strength and good resistance to water penetrationCan be cut with a hot wire to make airfoil shapes | Flammable and toxic | |
| POLYPROPYLENE | |||
| Used to make airfoil shapes | Can be cut with a hot wireCompatible with most adhesives and epoxy resins | Not for use with polyester resinsDissolves in fuels and solvents | |
| PHENOLIC | |||
| It can be easily contoured with a large knife and sanding equipment | Very good fire-resistant properties and can have very low densityRelatively low mechanical properties | Can’t be used with a hot wire to cut polyurethane foam | |
| Polyvinyl chloride (PVC) (Divinycell, Klegecell, and Airex) | |||
| A closed-cell medium- to high-density foam. | High compression strength, and durabilityExcellent fire resistanceCan be vacuum formed to compound shapes and be bent using heat Compatible with polyester, vinyl ester, and epoxy resins | Emits toxic fumes when melted | |
| Polymethacrylimide (Rohacell) | |||
| A closed-cell foam used for lightweight sandwich construction; | Excellent mechanical propertiesHigh dimensional stability under heatGood solvent resistanceCreep compression resistanceMechanical properties | More expensive than the other types of foams | |
| Balsa Wood | Balsa is a natural wood product with elongated closed cells. it is available in a variety of grades that correlate to structural, cosmetic, and physical characteristics. | It has a considerably higher density than the other types of structural cores. | The density of balsa is less than one-half of the density of conventional wood products. |