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International Journal of Science, Engineering and Technology Research (IJSETR), Volume 5, Issue 1, January 2016

ISSN: 2278 – 7798 All Rights Reserved © 2016 IJSETR 125

Abstract— Advanced Space Transportation systems involve

the reusable vehicles or modules which can be recovered from

orbits of Earth or outer planets. The major challenge in the

development of such modules is the design of the thermal

protection system (TPS) which should withstand the high

aerodynamic heating levels encountered during the

atmospheric re-entry. The objective of the study was to conduct

a thermo-structural analysis of the TPS of a re-entry module

called Crew module developed by Indian Space Research

Organisation (ISRO). Thermo-structural analysis consists of

heat transfer analysis to obtain temperature distribution with

its variation for the entire duration of the operation. It is

followed by structural analysis for thermal and mechanical

load to obtain structural deformations and stresses.

Index Terms— Aerodynamic heating, Re-entry vehicle,

Thermal protection system, Thermo-structural analysis.

I INTRODUCTION

The development of atmospheric re-entry vehicles began in

the late 1950's. Atmospheric re-entry refers to the movement

of human made objects as they enter the atmosphere of a

planet from outer space. The major challenge in the

development of re-entry vehicle is the design of Thermal

Protection System (TPS) which should withstand the high

aerodynamic heating levels encountered during the

atmospheric re-entry. Aerodynamic heating refers to the

heating of a body produced by the passage of air or other

gases over its surface. It is caused by friction and

compression process and significant chiefly at high speeds.

Due to aerodynamic heating external surfaces of the re-entry

vehicle gets heated. Thermal Protection Systems are

necessary in order to protect the internal structure of the

vehicle from the elevated heat fluxes occurring on the

external surfaces. The design of a Thermal Protection System

is based on the principle that the energy released by the

aerodynamic heating must be absorbed or rejected by the

Thermal Protection System.

Crew Module Atmospheric Re-entry Experiment

(CARE) is an experimental test vehicle for the Indian Space

Research Organisations future orbital vehicle. The TPS of

crew module is made up of carbon-phenolic tiles. Schematic

sketch of TPS for crew module is shown in Figure 1.1. The

forward heat shield will be the leading edge during the

re-entry; hence it will be subjected to maximum heat flux.

Manu J PG Scholar, Department of Mechanical Engg, Mar Athanasius

College of Engineering, Kothamangalam 9447706304

Figure 1.1: TPS of crew module

Finite element model of the TPS was designed using

ANSYS WORKBENCH. Transient thermal analysis has

been carried out up to 200s. The temperature distribution

corresponding 100s (which is the maximum heat flux

condition), 180s (which is the maximum temperature

condition) and 200s are obtained for thermo-structural

analysis. Thermo-structural analysis has been carried out at

all the above mentioned time instants by applying

temperature and pressure as loads.

II FINITE ELEMENT MODEL

Three dimensional CAD geometry was generated and

imported to the finite element software. Finite element

modelling is done in ANSYS WORKBENCH. Hexahedral

type of meshing is used for the forward heat shield, flare and

conical heat shield which contains 3459351 numbers of

nodes and 843069 numbers of elements. Tetrahedral type of

meshing is used for the inner metallic structure which

contains 2433560 numbers of nodes and 1283451 numbers of

elements

Figure 2.1: Finite element model of forward heat shield and

flare region

Thermo-Structural Analysis of Thermal

Protection System for Re-Entry Module of

Human Space Flight

Manu. Jˡ, G. Vinod2, Dr. Roy N Mathews

3



Figure 2.2: Finite element model of conical heat shield

Figure 2.3: Finite element model of inner metallic backup

structure

Fig. 2.1 shows the finite element model of forward heat

shield and flare region, Fig. 2.2 shows the finite element

model of conical heat shield and Fig. 2.3 shows the finite

element model of inner metallic backup structure.

III TRANSIENT THERMAL ANALYSIS

Transient thermal analysis determines temperatures and

other thermal quantities that vary over time. Engineers

commonly use temperatures that a transient thermal analysis

calculates as input to structural analysis for thermal stress

evaluations. A transient thermal analysis follows basically

the same procedures as a steady state thermal analysis. The

main difference is that most applied loads in a transient

thermal analysis are functions of time.

The transient temperature distribution T (x; y; z; t)

throughout the domain is obtained by solving the

three-dimensional heat conduction equation shown below in

the substrate along with appropriate initial and boundary

conditions.

ρCp(∂T/∂t) = ∂/∂x (kx ∂T/∂x) + ∂/∂y (ky ∂T/∂y) + ∂/∂z(kz∂T/∂z)

(1)

Where ρ – Density. Cp – Specific Heat.

kx, ky, kz – Thermal Conductivities in x, y, z directions.

All material properties are considered temperature

dependent. Initial conditions applied to solve Eq.(1) is

T (x; y; z; 0) = T0 (2)

Where T0 is the ambient temperature. In the analysis, T0 is

set as 300K.Boundary condition applied is the heat flux

experienced by the TPS during re-entry. Heat flux at any

point on outer surface of TPS follows a parabolic curve with

respect to time, being zero at the start and attaining a

maximum at time 100sec.

3.1 Material Properties

The material properties required for the thermal analysis are

thermal conductivity, specific heat and density.

Carbon-phenolic tiles used for TPS are orthotropic in nature

and the material properties are temperature dependent.

Table 3.1: Variation of thermal conductivity with

temperature

Temperature(T) Thermal Conductivity

[K] [W/mK]

X-dierction Y-dierction Z-dierction

300 0.67 0.67 0.26

600 1.36 1.36 0.62

900 2.09 2.09 1.02

1200 3.12 3.12 1.47

1500 4.69 4.69 2.01

1800 7.05 7.05 2.66

2100 10.45 10.45 3.46

2200 11.5 11.5 3.76

3000 11.5 11.5 3.76

Fig. 3.1: Temperature Vs Thermal Conductivity

The properties are evaluated at room temperature as well as

elevated temperatures. Table 3.1 gives the thermal

conductivity at elevated temperature. The variation of

thermal conductivity with temperature is shown in Fig.3.1. It

can be seen that the thermal conductivity of carbon-phenolic

composite increases with increase in temperature. Table 3.2

gives the specific heat at elevated temperature. The variation

of specific heat with temperature is shown in Fig.3.2. It can

be seen that specific heat initially increases with increase in

temperature and maintain a maximum value in the

temperature range of 700K to 1000K, after that specific heat

decreases with increase in temperature.



Table 3.2: Variation of Specific Heat with temperature

Temperature(T) Specific Heat(Cp)

[K] [J/kgK]

300 1074.31

500 1386.74

600 1520.5

700 18694

1000 18694

1010 1999.74

1100 1999.74

1400 2167.16

1700 2273.38

.

Fig. 3.2: Temperature Vs Specific heat

3.3 Transient Thermal Analysis Results

Transient thermal analysis has been carried out up to 200s.

Temperature distribution corresponding to 100s (which is

the maximum heat flux condition), 180s (which is the

maximum temperature condition) and 200s are considered

for structural analysis.

Fig. 3.3: Temperature distribution on TPS at 100s

Fig. 3.4: Temperature distribution on inner metallic backup

structure at 100s

Fig. 3.5: Temperature distribution on TPS at 180s




structure at 180s

Fig. 3.3 shows the temperature distribution on TPS at 100s

and the maximum temperature is 1842.9K, which is below

the maximum allowable design temperature. Fig. 3.4 shows

the temperature distribution on the inner metallic backup

structure at 100s, which is at room temperature throughout

100s. Therefore the function of TPS is satisfied. Fig. 3.5

shows the temperature distribution on TPS at 180s and the

maximum temperature is found to be 2303.4K, which is

below the maximum allowable design temperature. Fig. 3.6

shows the temperature distribution on the inner metallic

backup structure at 180s, which is at room temperature

throughout 180s. Therefore the function of TPS is satisfied.

Fig. 3.7: Temperature distribution TPS at 200s


structure at 200s

Fig. 3.7 shows the temperature distribution on TPS at 200s

and the maximum temperature is found to be 2278.7K, which

is below the maximum allowable design temperature. Fig.

3.8 shows the temperature distribution on the inner metallic

structure at 200s, which is at room temperature throughout

200s. . Therefore the function of TPS is satisfied.

IV THERMO-STRUCTURAL ANALYSIS

Structural analysis is probably the most common application

of the finite element method. It is the science, which ensures

safety of structures and fulfils the functions for which they

have been built. Here the temperature values obtained from

the transient thermal analysis is imported and applied as

load along with the pressure for carrying out

thermo-structural analysis at 100s ,180s and 200s.The

governing equation for the analysis are given below

Thermal-mechanical strain

x = αx ∆T + σx/ Ex – μxy σy/ Ex – μxz σz / Ex

(3)

y = αy ∆T + μxy σx/ Ex –σy/ Ey – μyz σz / Ey (4)

z = αz ∆T + μxz σx/ Ex –μyz σy/ Ey –σz / Ez (5)

xy = σxy / Gxy

(6)



yz = σyz / Gyz

(7)

xz = σxz / Gxz

(8)

Where typical terms are:

x - direct strain in x direction

xy - shear strain in the x-y plane

σx - direct stress in x direction

σxy - shear stress on x-y plane

4.1 Material Properties

The material properties needed for thermo-structural

analysis are coefficient of thermal expansion, Young's

modulus, and Shear modulus.

Table 4.1: Variation of Coefficient of thermal expansion with

Temperature

Temperature(T) Coefficient of thermal expansion(α )

[K] [K-1]

X-direction Y-direction Z-direction

373 1.97E-05 1.97E-05 1.60E-05

973 3.90E-06 3.90E-06 -0.000107

1473 -1.10E-06 -1.10E-06 -7.50E-05

1973 2.60E-06 2.60E-06 -5.20E-05

2173 4.90E-06 4.90E-06 -4.80E-05

2273 6.00E-06 6.00E-06 -4.70E-05

2373 7.20E-06 7.20E-06 -4.60E-05


elevated temperatures. Table 4.1 gives the coefficient of

thermal expansion at elevated temperature. The variation of

coefficient of thermal expansion with temperature is shown

in Fig.4. In x and y direction coefficient of thermal expansion

decreases with increase in temperature during initial stages

and reaches negative value at temperature 1473K, after that

it increases steadily and reaches a positive value. In z

direction the coefficient of thermal expansion have positive

value only during initial stages.

Fig. 4.1: Coefficient of thermal expansion Vs Temperature

Table 4.2: Variation of Young's Modulus with Temperature

Temperature(T) Young's Modulus(E)

[K] [MPa]

X-direction Y-direction Z-direction

300 16900 16900 11900

373 16500 16500 10900

473 15000 15000 6580

573 12700 12700 5520

873 14700 14700 5660

1273 11800 11800 2520

1773 11800 11800 2590

2273 10300 10300 2470

Fig. 4.2: Young's Modulus Vs Temperature


elevated temperatures. Table 4.2 gives the Young's Modulus

at elevated temperature. The variation of Young's Modulus

with temperature is shown in Fig.4.2 Young’s modulus in x

and y direction goes on decreasing with increase in

temperature but there is a sudden rise in the value when the

temperature is 873K, after that the value decreases with

increase in temperature. In z direction the value of Young’s

modulus decreases with increase in temperature

.

Table 4.3: Variation of Shear Modulus with Temperature

Temperature(T) Shear Modulus

[K]

300 4540

373 4270

473 4270

573 4270

873 4370

1273 4370

1773 4670

2273 4670



Fig. 4.3: Shear Modulus Vs Temperature

Table 4.3 gives the Shear Modulus at elevated temperature.

The variation of Shear Modulus with temperature is shown in

Fig.4.3. Fig.4.3 shows that with the increase in temperature

from 300K the value of shear modulus decreases but the

value remains constant for a temperature range of 373K to

573K and there after it increases with increase in

temperature.

4.1 Thermo-Structural Analysis Results

The finite element model is run for 200s with temperature

and pressure as loads. Total deformation, directional

deformation and equivalent stress are obtained

corresponding to 100s (which is the maximum heat flux


condition) and 200s.

Fig.4.4 to Fig.4.6 shows the radial deformation, hoop

deformation and axial deformation on TPS at 100s

respectively. The maximum radial deformation is 0.759mm,

where as the maximum hoop deformation is 0.237mm and

the maximum axial deformation is 1.7mm.Fig.4.7 shows the

radial stress on the forward heat shield at 100s and the

maximum radial stress is 147MPa. On the forward heat

shield for a thickness of 0.2mm the stress values exceeds the

allowable strength of 41MPa and that region will be eroded

in the subsequent time instant. Fig.4.8 shows the hoop stress

on the forward heat shield at 100s and the maximum hoop

stress is 78MPa. The stress values exceed the allowable

strength of 41MPa locally at the bolt hole. On all other

regions the stress values are within the allowable limit.

Fig.4.9 shows the axial stress on the forward heat shield at

100s and the maximum axial stress is 55MPa. The stress

values exceeds the allowable strength of 41MPa locally at the

bolt hole. On all other regions the stress values are within the

allowable limit.

Figure 4.4: Radial deformation on TPS at 100s

Figure 4.5: Hoop deformation on TPS at 100s

Figure 4.6: Axial deformation on TPS at 100s

Figure 4.7: Radial stress on forward heat shield at 100s



Figure 4.8: Hoop stress on forward heat shield at 100s

Figure 4.9: Axial stress on forward heat shield at 100s

Fig.4.10 shows the radial stress on flare region at 100s and

the maximum radial stress is 90MPa. On the flare region for

a thickness of 0.2mm the stress values exceeds the allowable

strength of 41MPa and that region will be eroded in the

subsequent time instant.Fig.4.11 shows the hoop stress on

the flare region at 100s and the maximum hoop stress is

300MPa. The stress values exceed the allowable strength of

41MPa locally at some regions. On all other regions the

stress values are within the allowable limit. Fig.4.12 shows

the axial stress on flare region at 100s and the maximum

axial stress is 138MPa. On the flare region for a thickness of

0.2mm the stress values exceeds the allowable strength of

41MPa and that region will be eroded in the subsequent time

instant.

Figure 4.10: Radial stress on flare region at 100s

Figure 4.11: Hoop stress on flare region at 100s

Figure 4.12: Axial stress on flare region at 100s



Figure 4.13: Radial stress on conical heat shield at 100s

Fig.4.13 shows the radial stress on conical heat shield at 100s

and the maximum radial stress is 188MPa. The stress values

exceed the allowable strength of 41MPa locally at the bolt

hole. On all other regions the stress values are within the

allowable limit. Fig.4.14 shows the hoop stress on the conical

heat shield at 100s and the maximum hoop stress is 136MPa.

On the conical heat shield for a thickness of 0.2mm the stress

values exceeds the allowable strength of 41MPa and that

region will be eroded in the subsequent time instant. Fig.4.15

shows the axial stress on conical heat shield at 100s and the

maximum axial stress is 109MPa. The stress values exceed

the allowable strength of 41MPa locally at the bolt hole. On

all other regions the stress values are within the allowable

limit.Fig.4.16 shows the equivalent stress on inner metallic

backup structure at 100s and the maximum value is found to

be 263.03MPa which is below the allowable strength of

375MPa.

Figure 4.14: Hoop stress on conical heat shield at 100s

Figure 4.15: Axial stress on conical heat shield at 100s

Figure 4.16: Equivalent stress on inner metallic backup

structure at 100s




where as the maximum hoop deformation is 0.379mm and

the maximum axial deformation is 1.96mm. Fig.4.20 shows

the radial stress on the forward heat shield at 180s and the

maximum radial stress is 110MPa. On the forward heat



in the subsequent time instant. Fig.4.21 shows the hoop

stress on the forward heat shield at 180s and the maximum

hoop stress is 86MPa. The stress values exceed the allowable




180s and the maximum axial stress is 55MPa The stress



allowable limit.







the maximum radial stress is 178MPa. On the flare region for

a thickness of 0.5mm the stress values exceeds the allowable

strength of 41MPa and that region will be eroded in the

subsequent time instant.Fig.4.24 shows the hoop stress on

the flare region at 180s and the maximum hoop stress is

384MPa. The stress values exceed the allowable strength of

41MPa locally at some regions. On all other regions the

stress values are within the allowable limit. Fig.4.25 shows

the axial stress on flare region at 180s and the maximum

axial stress is 322MPa. On the flare region for a thickness of

0.5mm the stress values exceeds the allowable strength of

41MPa and that region will be eroded in the subsequent time

instant.




Fig.4.26 shows the radial stress on conical heat shield at 180s

and the maximum radial stress is 238MPa. The stress values

exceed the allowable strength of 41MPa locally at some

regions. On all other regions the stress values are within the

allowable limit. Fig.4.27 shows the hoop stress on the conical

heat shield at 180s and the maximum hoop stress is 395MPa.

On the conical heat shield for a thickness of 0.5mm the stress

values exceeds the allowable strength of 41MPa and that

region will be eroded in the subsequent time instant. Fig.4.28

shows the axial stress on conical heat shield at 180s and the

maximum axial stress is 290MPa. On the conical heat





in the subsequent time instant.










structure at 180s

Fig.4.29 shows the equivalent stress on inner metallic backup

structure at 180s and the maximum value is found to be

316.03MPa which is below the allowable strength of

375MPa.







where as the maximum hoop deformation is 0.39mm and the

maximum axial deformation is 2.04mm.

Fig.4.33 shows the radial stress on the forward heat shield at

200s and the maximum radial stress is 110MPa. On the

forward heat shield the stress values exceeds the allowable

strength of 41MP for a thickness of 0.75mm, which is only

1.5% of total thickness 50mm. Therefore the forward heat

shield configuration is safe. Fig.4.34 shows the hoop stress

on the forward heat shield at 200s and the maximum hoop

stress is 85MPa. The stress values exceed the allowable




200s and the maximum axial stress is 61MPa The stress



allowable limit.





the maximum radial stress is 173MPa. On the flare region he

stress values exceeds the allowable strength of 41MP for a

thickness of 0.75mm, which is only 1.5% of total thickness

50mm. Therefore the flare region is safe. Fig.4.37 shows the

hoop stress on the flare region at 200s and the maximum

hoop stress is 380MPa. The stress values exceed the

allowable strength of 41MPa locally at some regions. On all

other regions the stress values are within the allowable limit.

Fig.4.38 shows the axial stress on flare region at 200s and the

maximum axial stress is 316MPa. On the flare region he

stress values exceeds the allowable strength of 41MP for a

thickness of 0.75mm, which is only 1.5% of total thickness

50mm. Therefore the flare region is safe.

Fig.4.39 shows the radial stress on conical heat shield at

200s and the maximum radial stress is 246MPa. The stress



values exceed the allowable strength of 41MPa locally at

some regions. On all other regions the stress values are

within the allowable limit. Fig.4.40 shows the hoop stress on

the conical heat shield at 200s and the maximum hoop stress

is 392MPa. On the conical heat shield the stress values

exceeds the allowable strength of 41MP for a thickness of

0.75mm, which is only 1.5% of total thickness 50mm.

Therefore the conical heat shield configuration is safe.

Fig.4.41 shows the axial stress on conical heat shield at 200s

and the maximum axial stress is 298MPa. On the conical

heat shield the stress values exceeds the allowable strength of

41MP for a thickness of 0.75mm, which is only 1.5% of total

thickness 50mm. Therefore the conical heat shield

configuration is safe.









Fig.4.42 shows the equivalent stress on inner metallic backup

structure at 100s and the maximum value is found to be

353MPa which is below the allowable strength of 375MPa.


structure at 200s

V CONCLUSION

Transient thermal analysis was carried out to obtain

temperature distribution in a TPS of re-entry module

called Crew module which is developed by ISRO. The

flight duration was 200s and temperature distribution

corresponding 100s (which is the maximum heat flux


condition) and 200s are obtained for structural analysis.

The maximum temperature obtained is 2303.5 (at

180s) and is found to be below maximum allowable

design temperature of the carbon-phenolic composite

with which the TPS is made, also the inner metallic

structure is maintained at room temperature during the

entire flight duration. Therefore the function of the TPS

is satisfied.

Thermo-structural analysis was carried out at 100s

(which is the maximum heat flux condition), 180s

(which is the maximum temperature condition) and

200s to assess the deformations and stresses. The

maximum radial deformation, hoop deformation and

axial deformations are 1.57mm, 0.39mm and 2.04mm

respectively (at 200s) which are within the desired limit.

At 200s the stress values on the TPS exceeds the

allowable strength of 41MPa for a thickness of 0.75mm

which is only 1.5% of total thickness 50mm.On all other


Therefore the carbon-phenolic TPS configuration is

safe. Also the equivalent stress on inner metallic backup

structure is below the allowable strength of 375MPa for

the entire flight duration.

REFERENCES

[1] Santhosh,B., ―Thermo-Structural Analysis of 3D Composites for

Reusable Applications‖, Proceedings of 2nd International

Conference on Materials for the Future(ICMF),2011.

[2] Roberto,Silva., ―Direct Coupled Thermo- Structural analysis in

ANSYS‖, Proceedings of ESSS Conference, Bourbon

Atibaia,2013.

[3] Thirapat,Kitinirunkul., ―Affecting Factors of the Mechanical

Properties to Phenolic Fibre Composite, World Academy of

Science, Engineering and Technology, International Journal of

Chemical, Nuclear, Metallurgical and Materials Engineering Vol

: 7 No: 10, 2013.

[4] Zinchengo,V. I., ―Thermal degradation of a carbon phenolic

composite in a high-temperature gas flow”, January–February,

1995, Volume 31, Issue 1,pp 79-86.

[5] Suneeth,Sukumaran., ―Design and Analysis of Metallic Thermal

Protection Systems‖,International Journal of Scientific and

Research Publications, Volume 1 ISSN 2250-3, Issue 2, February

2013.

http://link.springer.com/journal/10573/31/1/page/1

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Thermo-Structural Analysis of Thermal Protection System ...ijsetr.org/wp-content/uploads/2016/01/IJSETR-VOL-5-ISSUE-1-125-137.pdfANSYS WORKBENCH. Transient thermal analysis has been