1. Metallic foam is a cellular metallic material with a porous structure and lower density than solid metal. 2. Metal foams are prepared using a liquid metallurgy route where a foaming agent is added to a metal melt, releasing gases during solidification to form pores. Common foaming agents include titanium hydride, zirconium hydride, calcium carbonate, and sodium carbonate. 3. An example process uses an aluminum alloy melt with 3.3% sodium carbonate as the foaming agent, producing a foam with 63% porosity and a density of 0.96 g/cc.

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