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AIRCRAFT COMPOSITE STRUCTURE REPAIR

Constituents – Core Materials

Introduction to Composite Materials 1 ATA 51 - Aircraft Composite Repair

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Core Material Properties

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Introduction to Composite Materials 2

Core materials

Metallic

Aluminum

Non metallic

Honeycomb Foam Wood

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Introduction to Composite Materials 3

LAMINATES

LAMINATE/

MONOLITHIC

STRUCTURE

LAMINA LAMINA

CORE

SANDWICH

STRUCTURE

Core Material Properties

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Core Material Properties

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Introduction to Composite Materials 4

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• First used in 1940’s. – Nomex honeycomb – Typically Hexcel

HRH 10 • Meta aramid fiber with phenolic resin

– Kevlar N636 reinforced honeycomb • Para amid fiber with phenolic resin

– Glass fiber reinforced plastic honeycomb • Glass fiber with phenolic resin

– Aluminum honeycomb

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Core Material Properties

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U.O.M

Nomex HRH

GFRP Core

Kevlar N636

Aluminum Alloy 5052

Density Kg/m3

72 72 72 72

Compressive Strength MPa 2.8 3.86 4.2 2.79

Shear Strength in L Direction

MPa 1.7 1.72 1.9 1.97

Shear modulus in L-Direction

MPa 54 65.5 120 354

Shear strength in W direction

MPa 0.86 0.97 1.2 1.16

Shear modulus in W direction

MPa 29 36 65 173

Absorption in humidity % 4.4 1.7 <5 N/A

In use temp range 0C -55 ~ 135 -55 ~ 135 -55 ~ 135 -55 ~ 175 ATA 51 - Aircraft Composite Repair

Modulus to Composite Materials 6

Core Material Properties

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Introduction to Composite Materials 7

Nomex HRH HRP Glass Kevlar N636

Advantages

Available with small cell size and low density High shear properties

+/-450 Fiber orientation

Good fatigue & impact strength

Tough Dimensioanl stability

Easy to Bond when dry Higher modulus and strength than NOMEX ®

2X modulus

Easy to form Higher strength

Formadable Low moisture

absorption Better hot wets

Fire resistant, self extinguish Good thermal and electrical insulation up

to 1750C

25% weight reduction over GFRP

core

Good thermal and electrical insulation up to 1300C

Low CTE up to 1500C

Drawbacks High Prices

Water migration

Core Material Properties

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Introduction to Composite Materials 8

Core Material Properties

Manufacturing honeycomb core

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Core material properties

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Introduction to Composite Materials 9

HRH10 – 1/8 – 3.0

ECA – 3.2 - 48

Material Designation

Cell Diameter

Density

Expanding direction

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Introduction to Composite Materials 10

Core Material Properties

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Core Material Properties

• Rigid • Curvature is

perpendicular to the ribbon direction

• Easy to form complex curve.

• Provide higher shear strength.

• Facilitate curving in L direction.

• Have higher ‘W’ shear properties and decrease ‘L’ shear properties.

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Introduction to Composite Materials 12

Core Material Properties Lowly

loaded part

Sandwich Structure

Highly loaded part

Monolithic Structure

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• Saving in the maintenance of the aircraft

• Higher energy impact resistant

• No fluid ingress problem

• Bolted repair possible in panel area

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Introduction to Composite Materials 13

Core Material Properties

• Best stiffness versus weight ratio

• Good twisting stiffness

• Excellent thermal insulation

• Excellent acoustic damping properties

Monolithic Structure Sandwich Structure

Advantages

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• Heavy if compared to sandwich structure

• Heavy weight ratio to stiffness

• Necessity of stiffening structure for twisting and compression resistance

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Introduction to Composite Materials 14

Core Material Properties

• Sensitive to water ingress and various liquid agent

• Impact sensitive compared to monolithic

• Bolted repair are not recommended

Monolithic Structure Sandwich Structure

Drawbacks

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Introduction to Composite Materials 15

Core Material Properties