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Mechanical and Thermal Properties of ChiralHoneycombs
Alessandro Spadoni
Massimo Ruzzene
School of Aerospace EngineeringGeorgia Institute of Technology
Atlanta, GA
USNCTAM 06 25-30 June 2006, Boulder, CO
Thermal protection systems (TPS) must fulfill multiple requirements:
• thermal
• aeroelastic
• light-weight
• damage tolerance
• maintainability (current space shuttle TPS requires 40,000 man-hours for each flight) [1]
[1] Morris, W. D., White, N. H., Ebeling, C. E.: “Analysis of Shuttle Orbiter Reliability and Maintainability Data for Conceptual Studies,” 1996 AIAA Space Program andTechnology Conference, 1996, Huntsville, AL, AIAA 96-4245.
BACKGROUND
Stainless steel honeycomb used to hold leeward ablative material.
Apollo Capsule
Early concepts of metallic heat shielding configurations developed for shuttle program [2].
Shuttle Program TPS Concepts
[2] Groninger, B.V., Shideler, J. L., Rummler, D. R.: “Radiative Metallic Thermal Protection Systems: A Status Report,” Journal of Spacecraft and Rockets, Vol. 14, No. 10,October 1977, pp. 626-631.
BACKGROUND
[3] Bouslog, S. A.; Moore, B.; Lawson, I.; and Sawyer, J. W.: “X-33 Metallic TPS Tests in NASALaRC High Temperature Tunnel.” AIAA Paper 99-1045, 37th AIAA Aerospace Sciences Meeting and Exhibit, Jan. 1999.
Improved TPS Concepts Spawned by X 33 Program
Typical X-33 metallic TPS panels [3]
A prepackaged superalloy honeycomb TPS concept [4]Latest TPS concept [5]
[4] Blosser, M. L.: “Development of Metallic Thermal Protection Systems for the Reusable Launch Vehicle,” NASA Technical Memorandum 110296
[5] Blosser, M., Chen, R., Schmidt, I., Dorsey, J., Poteet, C., and Bird, K.: “Advanced Metallic Thermal Protection System Development”, AIAA-2002-0504, 40th AIAA Aerospace Sciences Meeting and Exhibit, January 14-17, 2002, Reno, NV.
OUTLINE
• Discussion of previous work on heat transfer through honeycombs
• Development of a geometrically explicit finite-element model (FEM) for transient heat transfer
• Compare initial FEM model with analytical solutions for problem at hand
• Discussion of heat transfer modes for a refined FEM model
• Parametric analysis and comparison of chiral and hexagonal honeycombs
• Eigenvalue analysis for the estimation of flat-wise compressive strength of considered honeycombs
COMPARISON OF DIFFERENT HONEYCOMB CORES BY NASA [6]
• Temperature input (as opposed to heat flux) external radiation is neglected.• Temperature input is comparable to heating rate from space re-entry [6].• Performance of honeycomb core investigated in terms of temperature
response history.• Core and face sheet material is Inconel 617 alloy.
[6] Ko, W. L.: “Heat Shielding Characteristics and Thermostructural Performance of a Superalloy Honeycomb Sandwich Thermal Protection System (TPS) ”, NASA/TP-2004-212024
q = 0
Best heat shielding performance, although cell geometry is found not to affect performance significantly[6].
d
b
L
tc/2
tc
tc/2
tc/2
tc/2
tc
Variation of hexagonal honeycomb geometry with angle
HEXAGONAL HONEYCOMB UNIT CELL GEOMETRY
= -27° = 0 ° = 30 °
r
θ
βR
Ltc
y
x
Variation of chiral geometry with L/R ratio
CHIRAL HONEYCOMB AND UNIT CELL GEOMETRY
( )
( )
( )R
2Rsin
Lr2tan
Rr2sin
=
=
=
θ
β
β
L/R = 0.60 L/R = 0.90
L/R = 0.95
Fourier’s Law: heat flux ,
Heat equation: Power generated per unit volume
Heat equation 1-D (no power generated):
thermal conductivity , [ W/m-k ]
thermal diffusivity [ m2/s] density , [ Kg/m3] Specific heat , [ J/Kg-K ]
a
x
Assumed solution:
Non-homogeneous boundary condition
Homogeneous b.c.’s: if and
homogeneous P.D.E
Resulting governing eq.: Non-homogeneous P.D.E
Separation of variables:
ANALYTICAL 1-D CONDUCTION MODEL
ANALYTICAL 1-D CONDUCTION MODEL (Cont’d)
Relative density
[6] Ko, W. L.: “Heat Shielding Characteristics and Thermostructural Performance of a Superalloy Honeycomb Sandwich Thermal Protection System (TPS) ”, NASA/TP-2004-212024
d
L
h
t /2
t
t /2
t /2
t /2
t
r
θ
βR
Lt
y
x
Face-sheet area imposed equal
CORRELATION OF HONEYCOMB GEMOETRIES
ANALYTICAL 1-D AND NUMERICAL CONDUCTION MODELS (NO FACE SHEETS)
980
1000
1020
1040
1060
1080
1100
1120
oK
Hexagonal honeycomb(ANSYS)
Chiral honeycomb(ANSYS)
Analyticalsolution
0 20 40 60 80 100200
300
400
500
600
700
800
900
1000
1100
1200
time, [sec]
T o, [ ° K
]
TiTo chiralTo analyticalTo hexagonal
Material: Inconel 617
• ρ 8360 Kg/m3
• c 419 J/Kg-oK• k 13.4 W/m-oK• Homogeneous isotropic• constant material properties
As temperature input is uniform at the bottom side,No gradients are expected in the x or y directions.
Analytical 1-D conduction model exactly describes conduction in both the chiral and hexagonal honeycombs
m 109.3 ,044.0 5*
−⋅== tsρ
ρ
a
ts
a
ts
NUMERICAL CONDUCTION MODEL
0 10 20 30 40 50 60 70 80 90 100200
300
400
500
600
700
800
900
1000
1100
1200
time, [sec]
T o(t), [
o K]
TiT0 analytical no face sheetsT0 chiral L/R = 0.95T0 chiral L/R = 0.60T0 hexagonal
65070075080085090095010001050110011500
0.002
0.004
0.006
0.008
0.01
0.012
0.014
T(x,t=100 sec), [°K]
x, [m
]
oKwithout face sheetswith face sheets
700
750
800
850
900
950
1000
1050
1100
• The temperature at the top face sheet is taken as the mean calculated temperature
• This is the reason for the discrepancy in output temperature history, even with same relative density
L/R = 0.95
oK
oK
L/R = 0.60
0 10 20 30 40 50 60 70 80 90 100200
300
400
500
600
700
800
900
1000
1100
1200
time, [sec]
T o(t), [
o K]
Ti(t)chiral L/R = 0.60chiral L/R = 0.95Hexagonal θ = 30°
Chiral honeycomb’sTemp. history deviatesFrom that of the Hexagonalhoneycomb
NUMERICAL CONDUCTION MODEL (CONT’D)
REFINED NUMERICAL MODEL
Heat transfer through solids
Conduction
Radiation
Convection
0 10 20 30 40 50 60 70 80 90 1000
0.1
0.2
0.3
0.4
0.5
0.6
0.7
time, [sec]G
r
ρ (air density) 1.0 Kg/m3
β (volume expansion coefficient) = 1/Tg (acc. gravity) = 9.82 m/sµ (air dynamic viscosity) = 2x10-5 Ns/m2
[7] Gibson J. L., Ashby F. M., Cellular Solids - Structures and Properties 2nd Edition, Pergamon Press, Oxford, 1998
According to [7], convection may be neglectedif the Grashof number is smaller than 1000.
Conduction and radiation are the onlyheat transfer modes considered.
ρ*/ρs =0.043
According to [7], radiation becomes dominant as the reltive density decreases.
REFINED NUMERICAL MODEL (Cont’d)
Material: Inconel 617
• ρ 8360 Kg/m3 (constant wrt T)• Homogeneous isotropic
T, [oK] c, [J/Kg-oK] k, [W/m-oK]
293.1 419 13.4
373.1 440 14.7
473.1 465 16.3
673.2 515 19.3
873.1 561 22.5
1073.2 611 25.5
1273.2 662 28.7
[8] ANSYS Inc, Theory Reference
N radiating surfacesδij Kronecker deltaεi effective emissivityFij radiation view factorsAi area of ith surfaceQi energy loss of ith surfaceσ Stafn Boltzmann constant
r distance between Ai Ajθ angle with unit normals
Air: ε = 0.009ρ = 1.23 Kg/m3
Face sheets (Inconel 617):ε = 0.85
Honeycomb core (Inconel 617):ε = 0.85
REFINED NUMERICAL MODEL (Cont’d)
0 10 20 30 40 50 60 70 80 90 100200
300
400
500
600
700
800
900
1000
1100
1200
time, [sec]
T o(t), [
o K]
TiL/R = 0.60L/R = 0.65L/R = 0.70L/R = 0.75L/R = 0.80L/R = 0.85L/R = 0.90L/R = 0.95
0 10 20 30 40 50 60 70 80 90 100200
300
400
500
600
700
800
900
1000
1100
1200
time, [sec]
T o(t), [
o K]
Ti
θ = -27.0°
θ = -18.9°
θ = -10.7°
θ = -2.6°
θ = 5.6°
θ = 13.7°
θ = 21.9°
θ = 30.0°
L/R = 0.60 L/R = 0.90 L/R = 0.95
= -27° = 0 ° = 30 °
= 0.044 , = 0.15 mm , = 12.4 mm [6]
[6] Ko, W. L.: “Heat Shielding Characteristics and Thermostructural Performance of a Superalloy Honeycomb Sandwich Thermal Protection System (TPS) ”, NASA/TP-2004-212024
0 10 20 30 40 50 60 70 80 90 100200
300
400
500
600
700
800
900
1000
1100
1200
time, [sec]
T o(t), [
o K]
Ti(t)chiral L/R = 0.60chiral L/R = 0.95Hexagonal θ = -27°
Increasing θ
Increasing L/R
REFINED NUMERICAL MODEL (Cont’d)
0 10 20 30 40 50 60 70 80 90 1000
0.5
1
1.5
2
2.5
3
3.5
4 x 105
time, [sec]
q z(t), [
W/m
]
L/R = 0.60L/R = 0.65L/R = 0.70L/R = 0.75L/R = 0.80L/R = 0.85L/R = 0.90L/R = 0.95
0 10 20 30 40 50 60 70 80 90 1000
0.5
1
1.5
2
2.5
3
3.5
4 x 105
time, [sec]
q z(t), [
W/m
2 ]
θ = -27.0°
θ = -18.9°
θ = -10.7°
θ = -2.6°
θ = 5.6°
θ = 13.7°
θ = 21.9°
θ = 30.0°
qz = average elemental heat flux
k0 solid conductivity: interpolated givenand Inconel 617 material properties.
0 10 20 30 40 50 60 70 80 90 1001
1.02
1.04
1.06
1.08
1.1
1.12
time, [sec]
k* (t) /
k o(t)
chiral L/R = 0.60chiral L/R = 0.95Hexagonal θ = -27°
[9] Zenkert, D., The Handbook of Sandwich Construction, Engineering Materials Advisory Services , Cradley Heath, West Midlands , 1997
k* As suggested by [9]
REFINED NUMERICAL MODEL (Cont’d)
0 10 20 30 40 50 60 70 80 90 100200
300
400
500
600
700
800
900
1000
1100
1200
time, [sec]
T o(t),
[ o K
]
ts = 7.6e-005, a= 0.0062 [m]
ts = 3.0e-004, a= 0.0248 [m]
ts = 5.3e-004, a= 0.0434 [m]
ts = 7.6e-004, a= 0.0620 [m]
Chiral
Hexagonal
a
ts
a
ts
a
ts
a
ts
REFINED NUMERICAL MODEL (Cont’d)
= 0.044
EIGENVALUE BUCKLING MODEL
-25 -20 -15 -10 -5 0 5 10 15 20 250
0.5
1
1.5
2
2.5
θ, [deg]
σz,
el 1
07 , [Pa
]
0.6 0.65 0.7 0.75 0.8 0.85 0.9
0
0.5
1
1.5
2
2.5
L/R
σz,
el 1
07 , [P
a]
-25 -20 -15 -10 -5 0 5 10 15 20 250
0.5
1
1.5
2
2.5
θ, [deg]
σz,
el 1
07 , [P
a]
0.6 0.65 0.7 0.75 0.8 0.85 0.9
0
0.5
1
1.5
2
2.5
L/R
σz,
el 1
07 , [P
a]
a= 0.0062 [m]
a= 0.0248 [m]
Hexagonal
Chiral
[7] Gibson J. L., Ashby F. M., Cellular Solids - Structures and Properties 2nd Edition, Pergamon Press, Oxford, 1998
λ
Analytical chiral
FEM chiral
Analytical hexagonal
FEM hexagonal
= 0.044
-25 -20 -15 -10 -5 0 5 10 15 20 250
0.5
1
1.5
θ, [deg]
σz,
el 1
07 , [P
a]
0.6 0.65 0.7 0.75 0.8 0.85 0.9
0
0.5
1
1.5
L/R
σz,
el 1
07 , [P
a]
EIGENVALUE BUCKLING MODEL
-25 -20 -15 -10 -5 0 5 10 15 20 250
0.1
0.2
0.3
0.4
0.5
0.6
0.7
θ, [deg]
σz,
el 1
07 , [P
a]
0.6 0.65 0.7 0.75 0.8 0.85 0.9
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
L/R
σz,
el 1
07 , [P
a]
a= 0.0434 [m]
a= 0.0620 [m]
Analytical chiral
FEM chiral
Analytical hexagonal
FEM hexagonal
= 0.044
SUMMARY
• Developed a numerical model that predicts the transient heat transfer through the core of chiral and hexagonal honeycombs;
• Imposing same relative density and same occupied volume results in similar heat transfer behavior;
• Chiral honeycombs seem to provide a slightly better thermal performance;
• Developed a model to predict linear, flat-wise compression strength of chiral and hexagonal honeycombs
• Chiral honeycomb show significantly better flat-wise strength than the hexagonal honeycombs
• The chiral honeycomb may offer enhanced performance for thermal-protection applications
FUTURE WORK
• Investigation of postbuckling behavior of the chiral honeycomb