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AIRCRAFT COMPOSITE STRUCTURE REPAIR
Constituents – Core Materials
Introduction to Composite Materials 1 ATA 51 - Aircraft Composite Repair
AIRCRAFT COMPOSITE STRUCTURE REPAIR AIRCRAFT COMPOSITE STRUCTURE REPAIR
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
AIRCRAFT COMPOSITE STRUCTURE REPAIR AIRCRAFT COMPOSITE STRUCTURE REPAIR
• 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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Introduction to Composite Materials 5
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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Introduction to Composite Materials 11
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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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