This document discusses sandwich metallic thermal protection panels with periodic cellular core structures. It describes how such panels consist of high-strength facings bonded to a low-density core. The core provides shear rigidity while keeping the facings supported. Various fabrication methods are also summarized, including how the cores can be made through slotting together constituent elements or using triply periodic minimal surfaces to create repeating open-cell structures. Applications mentioned include using such panels for thermal insulation to maintain a 220C temperature difference on either side.

1. SANDWICH METALLIC THERMAL PROTECTION
PANELS WITH PERIODIC CELLULAR CORE
STRUCTURE

2. Hybrid Composites
• Hybrid Composites, wherein one uses more than one type of fiber.
• Cost- performance effectiveness can be increased by judiciously using
different reinforcement types and selectively placing them to get the
highest strength in highly stressed locations and directions.
• For example, in a hybrid composite laminate, the cost can be
minimized by reducing the carbon fiber content, while the
performance is maximized by optimal placement and orientation of
the fiber.

3. Possibilities of Hybridization

4. Part of the E–ρ property chart

5. Material-property chart of thermal conductivity and
Young’s modulus

6. Young’s modulus and density

7. Classification of Hybrid Composites
• Hybridisation is commonly used for improving the properties and for
lowering the cost of conventional composites. There are different types
of hybrid composites classified according to the way in which the
component materials are incorporated. Hybrids are designated as
i) Sandwich ii) Interply iii) Intraply iv) Intimately mixed
• Sandwich: one material is sandwiched between layers of another.
• Interply: alternate layers of two or more materials are stacked in
regular manner.
• Intraply: Rows of two or more constituents are arranged in a regular
or random manner.
• Intimately mixed: constituents are mixed as much as possible so that
no concentration of either type is present in the composite material.

8. Sandwich Structure
• Sandwich composites involve two or more layers of the same or
different materials.
• Fibrous form results mainly in fiber reinforcement direction.
• Of course one can arrange fibers in two dimensional or even three
dimensional arrays, but this still does not gainsay the fact that one is
not getting the full reinforcement effect in directions other than the
fiber axis.
• If a less anisotropic behavior is the objective, then perhaps sandwich
composites made of, say two different materials would be more
effective.

9. Sandwich Structure
• Sandwich structure, consists of high strength facings or skins, being
adhesively bonded to the low density core.
• Core: A centrally located layer of a sandwich construction, usually low
density, which separates and stabilizes the facings and transmits shear
between the facings and provides most of the shear rigidity of the
construction.
• Facing (skin/face/face sheet): The outermost layer, generally thin and
of high density, which resists of most of the edgewise loads and flatwise
bending moments.
• Adhesives: The adhesives are used to bind the Core and Facing.

10. Sandwich Structure
• Sandwich panels are used in bending and compression dominated
components.
• The face sheets carry the applied in-plane and bending loads.
• The core resist the transverse shear and transverse normal loads, as
well as keep the facings supported and working as a single unit.
face sheet
adhesive layer
honeycomb

11. Sandwich panels (broken line) extend the range of
flexural modulus

12. Selection of Materials for High
Temperature Applications ( T >7000c )

13. Materials for selection
• Metallic materials
• Polymeric materials
• Ceramic materials
• Composite materials
13

14. Properties for selection
• Thermal expansion coefficient
• Electrical conductivity
• Oxidation resistance
• Corrosion resistance
• Yield strength
• Elastic modulus
• Joinability
• Formability
• Cost
• Others, including resistance to hydrogen embrittlement,
and machinability
14

15. Maximum service temperature of common
Engineering Materials
Cont’d…
15

16. Maximum service temperature of common
Engineering Materials
Cont’d…
16

17. Maximum service temperature of common
Engineering Materials
17

18. T < 700OC
• Plain carbon steels (%C < 0.08 to 1.03 ) Normalizing
– Increase in carbon % improves the creep strength
– Aluminium used as deoxidizer produce fine grain and reduces creep strength
– Aluminium effects reduced by presence of Manganese and molybdenum
• Low alloy steels (Alloy %< 10)
– Molybdenum and vanadium raise the creep resistance
– %C<0.15 + 0.5% Mo~6000C (super heater tubes)
– Above this temperature spheroidization and graphitization takes place and reduces
creep strength
– %Cr=1 increases the resistance to graphitization
– Used for 7500c in boiler tubes
18

19. T > 700OC
• Chromium + molybdenum + vanadium + C% upto 0.5
– High yield strength and creep strength
– Bolts, steam turbine rotors operating at 7500c
– Chromium content will increase the resistance to corrosion and oxidation
Cr. Comp. Operat.
Applications
Steels (%) Temp.
410 7500C Steam valve, bolts, pump shaft
422 9000C Steam valve, bolts, pump shaft
Heat-exchange equipment, condensers, piping
430 16% Cr. 12500C
and furnace parts
Heat-exchange equipment, condensers, piping
446 25% Cr. 17000C
and furnace parts
19

20. Austenitic stainless steels
• Chromium+nickel+carbon
– Better creep properties than chromium steels
Austen Comp. Operat.
Applications
. Steels (%) Temp.
Furnace linings, boiler baffles, thermocouple
25% Cr
310 12000C wells, aircraft-cabin heaters and jet-engine
+20% Ni
burner liners
18% Cr steam liners, super heater tubes, gas turbines
347 +11% Ni 1350 C
0
and exhaust systems in reciprocating engines
+Cb& Ta
20

21. Chromium-nickel-molybdenum-iron alloys
• Small amount of titanium and aluminium added
Trade Comp. Operat.
Applications
Name (%) Temp.
A-286 Forgings for Turbine Wheels, Gas turbines,
9500C to
Discaloy sheet-metal casings, housings and exhaust
11500C
Incoloy equipments
21

22. Nickel alloys
– 50 to 70% nickel
– 20% chromium
– 10% molybedenum or tungsten
– upto 20% cobalt
– titanium and aluminium
• Applications
– Manifold, collector rings, exhaust valves of reciprocating engines, sheet form for
combustion liners, tail pipes, casings of gas turbines and jet engines
Cobalt+chromium+nickel alloys have lower strength
used for wheels and buckets of gas turbines
22

23. Conclusion
• Commercial Alloys lose their strength rapidly when heated above
17000C
• Allowable operating temperature can be raised by suitable base
elements
• MOLYBDENUM-47300F
• TUNGSTEN-61700F
23

24. FABRICATION

25. 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.

26. 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

27. 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

28. Preparation of Core Metallic structure

29. Pyramidal truss core fabrication process

30. Panel assembly unit cell

31. Fabricated Structure

32. Manufacturing Route of the Triangular Honeycomb
Slotting Together of the Constituent Elements
2 Shapes of Slotted Sheets Employed Assembled Triangular Honeycomb Core

33. Periodic cellular Core structure

34. Foams and micro-truss structures are hybrids of
material and space

35. APPLICATIONS

36. Sandwich Assembly

37. Sandwich Thermal Insulation Panels
• 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)

38. Comparison by varying the thickness
(Thermal Barrier Coating)

39. Questions

40. Thank you