1. Metallic Foam

2. Metallic Foams
• Metallic foam can be defined as a metallic
material with a cellular structure.
• Metal foams have plenty of pores inside
and their density is much lower than the
solid one.
• Cellular materials are multifunctional
materials with porous structure.
Sandwich Composites- An Overview 2

3. Preparation of Metal Foam
• Liquid Metallurgy Route
 Aluminium is melt in stir casting furnace
 The foaming agent is added to Aluminium melt
 Aluminium and foaming agent decompose and release the gases
 When trapped gases in the solidifying metal convert it into a closed-
cell foam
• Foaming Agent
– Titanium hydride - Effective Foaming Agent
– Zirconium hydride - High Cost
– Calcium carbonate - Low Cost ,Easily Available
– Sodium Carbonate - Low Cost , Easily available

4. Preparation of Metal Foam
• First stage
• 1.1 kg of Aluminium alloy is melt in stir casting furnace
• The melt reaches 650 ºc, the furnace is turned off
• Start the stirrer until the temperature reaches 635 ºC
• Add the 3.3 wt % of foaming agent to the molten metal
• Continue stirring up to 60sec
• When the temperature reaches 580ºC,the rotating stirrer is stopped
• After that crucible with foam can be taken out from the furnace
• The metallic Foam is cooled by air
• Second Stage
• Insert the precursor into sintering furnace
• Bake the precursor for 15min at 650ºc
• Precursor (Foam) can be left cool in air
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5. Experimental Results
Sample Material Proportion Density of Relative %
&foaming Foam density Porosity
agent
1. LM6 with 1.1kg 0.36 63
0.96g/cm3
Na Co 3.3wt%
2 3
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6. Macrostructure Image Results
Macro structure Materials Pore size Micro Vickers
image hardness
Value(load
Minimum pore
size 2mm
0.3kg)
67
LM6 with Na CO
2 3
Maximum
poresize
8mm 6

7. The micro-structural analysis of the Al-33wt % of Na CO is carried out. The
2 3
microstructure is shown in Figure
The areal porosity was found to be 63%.
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8. S.No: Material Specification
Face Aluminium 6061 Density 2.71g/cm3
(same material for both
side)
Foam (Core) LM6 added with Na Co Density 0.96/cm3
2 3 The resin and
Adhesive Epoxy / Hardener hardener mixing
Redux 322 ratio 10 : 1 Curing
time is 7-10hrs.
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9. Summary of case study
1 The density of the Al alloy+CaCo3 and Al alloy+Na2Co3
was found to be 1.65g/cc and 0.96g/cc respectively.
2. The porosity of the Al alloy+CaCo3 and Al alloy+ Na2Co3
was found to be 36 % and 63% respectively.
3. A sandwich panel is developed with dimensions of ASTM
standards to conduct three point loading test. The
maximum deflection for al alloy+ Na2co3 foam at a load of
2300N is found to be 1.61mm. The values obtained were
compared with theoretical formula at load of 2300N is found
to be 2.22mm.

10. Comparison of Foam core
• PVC (closed cell)
- ‘linear’ – High ductility, low properties
- ‘cross-linked’ – High strength and stiffness but brittle
- ~ 50% Reduction of properties at 40-60oC
- chemical breakdown (HCl vapour) at 200oC
• PU
- inferior to PVC at ambient temperatures
- better property retention (max. 100oC)
• Phenolic
- Poor mechanical properties
- Good fire resistance
- Strength retention to 150oC
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11. Polyurethane Foam

12. Comparison of Foam Core
• Syntactic Foam
- Glass or polymer microspheres
- Used as sandwich core or buoyant filler
- High compressive strength
• Balsa
- Efficient and low cost
- Absorbs water (swelling and rot)
- Not advisable for primary hull and deck structures
- OK for internal bulkheads
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13. Mechanical Thermal Protection System(for Skin)
(For a hypersonic aircraft - 5 Mach Number)
Requirement : To withstand surface temperature of 1100oC
Facing sheet – Ni alloy of 0.08
- .1mm
Core - Ni alloy of 4mm cell
size honeycomb structure
Ceramic wool of
thickness 40mm
Core - Ti alloy of 4mm cell
size honeycomb structure
Facing sheet – Ti alloy of 0.3
- .4mm
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14. Sandwich Panel with Thermal Barrier Coating
• Exposed surface temperature found under such conditions was 5240C
• Temperature of the air outside the colder (inner) surface of the
sandwich panel was sustained at 210C (room temperature)
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15. High Strength Applications
• Diamond orientation 304 stainless steel textile sandwich panel with
relative core density (12.6%).
• Tetrahedral structures are stacked node to node with an interleaved
planar hexagonal perforated layer
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16. SMA Composite