Shims strain

8/10/2019 Shims strain

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52

Figure 3-1: Flex Nozzle Configuration-D



53

3.2 DESIGN CONSIDERATIONS

The following are the considerations taken during the design of the

flex nozzle system

Thermal Boot : No stretch due to flexing

Convergent profile: Geometric tangency

Divergent : Conical with half angle of 17.5°

Submergence = 30 - 35%

Factor of safety on shims and pads ≥ 1.5

The configuration of the flex nozzle is configured to have fourmajor subassemblies viz.

Submerged subassembly (SSA)

Flex seal subassembly (FSA)

Convergent assembly (CA)

Divergent subassembly (DSA)

SSA consists of AFNOR 15CDV6 steel Intermediate dome with

Rocasin rubber as its thermal protection.

FSA consists of thermal boot and flex seal. Thermal boot is

suggested to have single bellow shape with Rocasin material. Flex seal

is assembled to Intermediate dome at its aft end and to throat housing

at its fore end.

Convergent assembly consists of throat housing hardware and

flex seal subassembly which is bonded with two numbers of Carbon

Phenolic liners (Nose entry and throat entry liners). Material chosen

for throat housing is AFNOR 15CDV6 steel. Nose entry liner can be



54

made from any one of tape winding, compression moulding or rosette

lay-up. Throat entry liner can be made of random fibre compression

moulding technique. Ply orientation and sizing of the convergent liners

are decided considering flow direction at different regions.

The gap between the movable and fixed part in the submerged

region is configured such that in null condition, there is minimum

radiation heat transfer to the thermal boot.

DSA consists of liner Carbon Phenolic bonded to divergent

hardware (AFNOR 15CDV6 steel). Compliance ring is proposed to be of

full ring with bosses projecting to take the actuator brackets and MI

sensors. DSA and CSA joints are assembled with fasteners.

3.3 FLEX SEAL DESIGN

The flex seal designed for configuration-D is depicted in

Figure 3-2.

Flex seal design consists of the following steps:

- Configuration of seal geometry

- Material selection

- Selection of thickness and No. of elastomer pads and

reinforcement shims.

- Design check

- Torque estimation



55

Figure 3-2: Flex seal design configuration-D



56

3.3.1 Configuration of Seal Geometry

The following features are to be firmed up for configuration of the flex

seal geometry:

- Selection of pivot point

- Selection of ID of the seal

- Selection of envelope and joint angles.

Aft pivot point configuration is preferred / selected for booster

stage. ID of the seal has to be kept minimum possible, considering the

requirement of throat insert, hardware backup thickness, clearance

for assembly and vectoring envelope. This is required to limit the

spring stiffness of the seal since the same is proportional to 4 th power

of the pivot radius (Rp).

ID = Dt + 2 (liner thickness + hardware thickness) + 2 (clearance for

assembly / vectoring envelope)

= 333 + 2(83.5) + 2(46)

= 592 mm

The joint angles are selected considering the tradeoff between

spring stiffness and elastomer shear strain. The joint angles selected

are given below:

β1 40 Deg

β2 50 Degβ 45 Deg

Φ 45 Deg



57

Cylindrical body configuration (Figure 3-2) is selected

considering stress levels in shims and space availability.

Reinforcement shim configuration can be either conical or concentric

spherical with a common centre. Spherical shims are suitable for

higher vectoring angle capability. Seals with conical shims are used

for limited of 2 to 3 deg. Table 3-2 gives comparison between conical

shims and spherical shims [40].

Table 3-2: Comparison between Conical and Spherical Shims

Sl.

No.Description Shim configuration

Conical Spherical

1Vectoring

capability

Limited to 3 Deg.

Max

Higher (5 to 8

degrees)

2 Pivot point

No single point.

Mean of each shim

pivot point is taken

as Geometric Pivot

Point. Higher pivot

point excursion

reported.

Single pivot point

since all the shims

are the segments of

concentric spheres

less pivot point

excursion.

3 Fabrication cost Less More

4Interchangeability

within shimsYes No

Considering the vectoring capability of 4 deg, the option is to

choose spherical shims only. The use of CNC machines will improve

the accuracy and minimize the tooling cost.



58

3.3.2 Material Selection

Reinforcement shims and end rings:

The reinforcement provide rigidity to the joint against motor

pressure and ejection load due to pressure and constrain the joints to

vector instead of having pure radial deflection. The important

properties in selecting the reinforcement shim material are high yield

strength and modulus of elasticity. AFNOR 15CDV6 steel is selected

for reinforcement shims. The properties of the material are given

below.

Ultimate Tensile Strength (min) 100 kgf/mm2 (980 MPa)

0.2 % Proof stress (min) 85 kgf/mm2 (835 MPa)

Young’s Modulus (min) 21000 kgf/mm2 (206 GPa)

Elastomer pad:

The properties required for elastomer pad are low shear

modulus, high shear strength and high bulk modulus. These

properties are required to design a flex seal with low spring torque,

high shear stress capability and less axial compression. In addition,

compatibility with shims for bonding or vulcanizing and good ageing

properties are also required. The developed low modulus Natural

rubber compound (LMC/NR-1) is considered for the elastomer pad

which has the following nominal properties.

Tensile strength (min) : 100 kgf/cm2 (9.81 MPa)

Shear modulus at 3.5 kg/cm2 shear stress : 2.5 kgf/cm2 (0.245 MPa)

Ultimate shear strength (min) : 27 kgf/cm2 (2.65 MPa)

Ultimate shear strain (min) : 800%



59

Hardness shores A (Max) : 40

3.3.3 Stress Analysis on Elastomeric Pads and Shims

The ratio of shim thickness to elastomer pad thickness (tr / te)

found for most of the flex seal in the operational solid rocket motors

falls within the range of 1.25 to 2.0, whereas in the present design, t r

/ te of 2.0 has been considered.

Following are the formulae used to estimate the shims stress

and elastomer pad strain capability as given in NASA SP 8114 [40]

and a technical note on new formulas for design of flex bearing by

Gajbir singh & G.V.Rao [44].

Reinforcement shim stress:

It is observed that always the ID of the shims experiences high

hoop stress due to pressure load and vectoring loads. Stress due to

pressure load is predominant.

1n

ΩxKxPx4087

pσ r c

Eq-(3-1)

1n

ΩθK43950σ r

v

Eq-(3-2)

Where

}t3283)β(β{Rβcosxtt3283

βcosxRΩ

2r 2122p2r 3r

2.4

p

Eq-(3-3)

Gajbir Singh and Rao [44] have modified the formulae as:

1n

ΩxKxKxPx4370

pσ mr c

Eq-(3-4)



60

m

r v

1)xK(n

ΩθK184516σ

Eq-(3-5)

Where

2

12

21.9

p

0.5

r

22.4

r

2.4p

)β(ββcosRxtβsint3283

βcosxRΩ

Eq-(3-6)

σσT

σ vp Eq-(3-7)

Kr is taken from Figure 3-3

Figure 3-3: Stress correction factor related to cone angle [40]

The correction factor Km [44] is taken from the Figure 3-4.



61

Figure 3-4: Correction factor, Km related to motor chamber pressure

[44]

Buckling stress capability of shim:

Buckling stress in the shim is function of modulus of elasticity

(E) of shim material and thickness of shim (tr) and elastomer pad (te).

The following empirical relation is used for obtaining the buckling

stress (σb) capability of the shim from the Figure 3-5. The buckling

stress (σb) [40] from the Figure 3-5 should satisfy the condition:

b 1.5 T Eq- (3-8)

where T is the total hoop stress due to pressure load and vectoring

load.



62

Figure 3-5: Buckling stress of reinforcements as a function of

reinforcement dimensions and properties [40]

Elastomer pad shear strain:

Shear strain in the elastomer pad

100

et xn

Rp x

m

Eq-(3-8)

at the mid flex seal (Refer Figure 1-5)

Shear strain in the ith elastomer pad

100

iΔ β

Δ βx

R p i

3R p

xmγi

γ Eq-(3-9)

Shear strain in the elastomer pad due to vectoring is

predominant compared to pressure loading which induces

compressive ejection load. Considering both vectoring and pressure

loading, a factor of safety assumed is minimum 1.5 over the strain

due to vectoring. Hence, the failure shear strain of elastomer pad



63

should be greater than twice the shear strain at all elastomer pads.

i.e.,

5.1

i

f

Eq-(3-10)

3.3.4 Thickness and Number of Elastomer Pads

A computer program in `C’ language has been developed using

the formulae from Eq-(3-1) to Eq-(3-11) in section 3.3.3 to iterate the

number of elastomer pads (n) with its thickness te. Range of n selected

is 6 to 10 and te chosen is from 3 to 5 mm. The inputs for the flex seal

design are given in Table 3-3.

Table 3-3: Input for the flex seal design program

d 4 °

Throat diameter 333 mm

Action time 50 seconds

MEOP 70 kgf/cm2 (6.86 MPa)

1 40 degrees2 50 degrees

Young’s modulus of shim (15cdv6) 21000 (kgf/mm2) (206 GPa)

Shear modulus of elastomer pad 2.5 kgf/cm2 (0.245 MPa)

Output for all the cases of n and te

Hoop stress experienced by the shims due to pressure and

vectoring

Buckling stress capability

Shear strain in elastomer pad due to vectoring

FOS on strength



64

FOS Buckling

The selected case, is

n = 8

te = 4 mm

tr = 8 mm

which gives the following performance

Shim stress (p

σ ) : -545.1 MPa (Eq-3-1 )

Shim stress (v

σ ) : -23.5 MPa (Eq- 3-2)

Shim stress ( Tσ ) : -568.6 MPa (Eq-3-7)

Shim stress (p

σ ) : -426 MPa (Eq-3-4 )

Shim stress (v

σ ) : -147.4 MPa (Eq- 3-5)

Shim stress (T

σ ) : -573.4 MPa (Eq-3-7)

Buckling stress capability : 1028 MPa (Eq-3-8)

FOS on strength : 1.5

FOS on Buckling : 1.8 (min)

The shim dimensions arrived from the above equations are depicted in

Figure 3-6. The end rings of the flex seal are configured based on the

attachment requirements of the throat housing and the intermediate

dome. The configured fore end and aft end rings are depicted in Figure

3-7 and Figure 3-8.



65

Figure 3-6: Shims 1 to 7 - Configuration - D



66

Figure 3-7: Fore end Ring - Configuration - D



67

Figure 3-8: Aft end Ring - Configuration – D



68

3.3.5 Spring Stiffness and Total Torque Estimation

The computed total actuation torque is considered in the design of

actuation system. The actuation torque is defined as the actuation

force multiplied by the moment arm. Moment arm is the

perpendicular distance between the geometric pivot point and the line

of action of actuator force. The total actuation torque is the

summation of Joint spring torque (T SP), Thermal boot torque (T TB),

Nozzle offset torque (T OFF), Inertial Torque (T IN) and Gravitational

torque (T GR).

Joint spring torque is the major contribution of total torque. It is

a function of pivot radius, joint angles, shear modulus of elastomer

pad, number of pads and its thickness. Thermal boot torque is

assumed to be 30% of spring torque for bellow boot configuration.

Nozzle offset torque is estimated based on the throat offset permitted

with respect to the motor axis. The maximum nozzle offset is specified

as 2 mm and offset torque is specified as 8% of spring torque. The

gravitational torque is specified as 4% of spring torque. Gravitational

torque is because of the lateral and longitudinal accelerations imposed

on the movable mass of the nozzle caused by the vehicle. Inertial

torque is estimated based on the accelerations imposed on the

movable mass of the nozzle by the actuator. It is the product of

moment of inertia of movable mass and angular acceleration which is

specified as 7.75 rad/sec2. The MI of movable mass is worked out to

be 102 kg-m2 using Pro-E cad package.



69

Hence, the total torque = T SP+ T TB + T OFF + T GR+ T IN Eq-(3-11)

TOTTQ = (1+0.3+0.08+0.04) T SP + T IN

For a specified angular acceleration of 7.75 rad/sec2 , the inertial

torque works out to be 7756 N-m.

The spring torque (T SP) is estimated from the following two relations

[43, 40]:

e

21

24

P

4

dSP

tn

βββcos1sin βRG109.57θT

Eq-(3-12)

3

i

3

o

330

SPr r

r r 0.156GxθT i

12 -xEq-(3-13)

Where r0 = Rp + n x te/2 and ri = Rp – n x te/2

(Refer Figure 1-5 for nomenclature).

The spring torque calculated from Eq-(3-13) and Eq-(3-14) are

3.413 kN-m/degree and 426 kN-m/degree respectively.

The total torque estimated using Eq-(3-13) is

(1+0.3+0.08+0.04)*3.413*4 + 7.756 = 27.14 kN-m.

The total torque estimated using Eq-(3-14) is

(1+0.3+0.08+0.04)*426*4 + 7.756 = 2427 kN-m.

The above relations indicate no variation in seal torque with the

pressure. In general, the flex seal spring torque depends on the

pressure and the seal torque decreases with increasing chamber

pressure.



71

Figure 3-10: Flex seal sub-assembly - Configuration - D



73

Figure 3-11: Throat Housing - Configuration - D



74

Figure 3-12: Intermediate dome - Configuration - D



77

3.6 DYNAMIC ENVELOPE:

Flex nozzle assembly is configured with above seal design

parameters meeting the thermal requirements in convergent sub

assembly and divergent sub assembly. On vectoring 6.22 deg (4x1.1x

√2), dynamic envelope is given in Figure 3-13.

The clearances in vectoring condition are as below:

Minimum axial clearance of convergent with respect to

Counter bore of propellant : 39 mm

Radial clearance : 123 mm

3.7 PRESSURE DISTRIBUTION ALONG NOZZLE CONTOUR

The pressure distribution along the nozzle contour is calculated

using the following isentropic relations [109].

12/12 ]1/M11/2[M/1*A/A Eq-(3-16)

1/2 ]1/M11/2[P/*P Eq-(3-17)

A 'C' Language program has been developed using the above relations

to calculate pressure distribution at various locations iteratively.

Table 3-6 gives the pressure distribution along nozzle contour.

3.8 EJECTION LOAD CALCULATIONS

Ejection load is the net load acting on the flex seal.

Ejection load = PdA. Ejection load is calculated in convergent and

divergent portion. The pressure distribution [108] given in Table 3-6

is used to compute the ejection load on Convergent and Divergent

portions of the nozzle. The net ejection load on the nozzle = 1961 kN.



79

3.9 MASS PROPERTIES OF FLEX NOZZLE SYSTEM

Table 3-7 gives detailed component level mass properties of Flex

Nozzle System shown in Figure 3-1. Given below is the summary of

mass properties.

TOTAL MASS = 630.9 kg

TOTAL MI = 117.67 kg-m2

MOVABLE MASS = 495.6 kg

MI OF MOVABLE MASS = 102 kg-m2

C.G.OF TOTAL ASSY. W.R.T. PIVOT POINT TOWARDS FOREEND SIDE (mm) = 77.54

Properties are calculated using PRO-Engineer CAD package.

3.10 INTERFACE DESIGN

Interfaces Design comprises of

Flange design [110-114]

Fastener design including bolt stress calculations [115]

Seal / 'O' rings design

Thermal protection of metallic parts of seal.

All interfaces are shown in Figure 3-14

Flange Design calculations are carried out following the

procedures of Schneider [111] and Broadman [110]. Specifications are

made based on the conservative results.



80

3.10.1 Flange Design

The following two approaches are used to design the flanges.

Broadman Approach:

Thickness of The Flange tfl = 7 xRi x [ P (R -Ri) ]0.5 Eq-(3-18)

4x [R x allowable]0.5

Schneider Approach:

Thickness of The Flange tfl =1.1 x R_m x ( 3 x P x l) 0.5 Eq-(3-19)

(allowable x (1- N x db) (R_m +l)0.5

Where N = No. of bolts Eq-(3-20)

2 X π X Pitch circle radius

3.10.2 Fastener Design

The fasteners are designed for the pretension load and the load

due to internal pressure acting on the joint based on formulae given in

mechanical engineering hand books [115].

The design summary of flanges and fasteners are given in Table

3-8 and Table 3-9. 'O’ ring sizes arrived based on configuration and

space available is given in Table 3-10. The material chosen for `O’

rings is Viton (from Du Pont).



81

Figure 3-14: Flex nozzle interfaces - Configuration - D



82

FLEX NOZZLE SYSTEM FOR CONFIGURATION - D

CONDITIONS:

Maximum Expected Operating Pressure = 6.86 MPa (70 kgf/cm2)

Area Ratio = 7.8

Ratio of Specific Heats = 1.19

Table 3-6: Pressure distribution along the nozzle contour

Sl.No

x(mm)

y(mm)

Pressure(MPa)

Load(kN)

Sl.No

x(mm)

y(mm)

Pressure(MPa)

Load(kN)

1 -155.4 370.5 6 .81 77.01 23 -124.3 192.5 5.89 17.78

2 -160.4 36 5.6 6 .80 83.81 24 -119.3 190.0 5.82 16 .15

3 -165.4 36 0.2 6 .80 92.14 25 -114.3 187.7 5.75 14.6 8

4 -170.4 354.2 6 .79 102.85 26 -109.3 185.5 5.68 13.34

5 -175.4 347.3 6 .79 117.6 6 27 -104.3 183.4 5.60 12.11

6 -180.4 339.2 6 .78 140.81 28 -99.3 181.5 5.53 10.97

7 -185.4 329.3 6 .77 187.73 29 -94.3 179.8 5.45 9.93

8 -190.4 315.6 6 .75 347.03 30 -89.3 178.1 5.37 8.96

9 -194.3 288.5 6 .70 324.46 31 -84.3 176 .6 5.28 8.06

10 -189.3 26 0.2 6 .6 1 120.6 0 32 -79.3 175.2 5.20 7.23

11 -184.3 248.7 6 .56 86 .27 33 -74.3 1 74.0 5.11 6 .45

12 -179.3 240.1 6 .51 6 8.30 34 -69.3 172.8 5.02 5.72

13 -174.3 233.0 6 .46 56 .70 35 -64.3 171.7 4.93 5.03

14 -169.3 226.9 6 .41 48.40 36 -59.3 170.8 4.84 4.3915 -164.3 221.6 6 .36 42.07 37 -54.3 16 9.9 4.75 3.79

16 -159.3 216.7 6 .31 37.03 38 -49.3 16 9.2 4.65 3.22

17 -154.3 212.4 6 .25 32.89 39 -44.3 16 8.5 4.55 2.6 8

18 -149.3 208.4 6 .20 29.42 40 -39.3 16 7.9 4.46 2.18

19 -144.3 204.7 6 .14 26 .44 41 -34.3 1 6 7.5 4.36 1.70

20 -139.3 201.3 6 .08 23.86 42 -29.3 16 7.1 4.26 1.25

21 -134.3 198.2 6 .02 21.59 43 -24.3 16 6 .8 4.16 0.82

22 -129.3 195.3 5.96 19.58 44 -19.3 16 6 .6 4.05 0.42



84

Sl.No

x(mm)

y(mm)

Pressure(MPa)

Load(kN)

Sl.No

x(mm)

y(mm)

Pressure(MPa)

Load(kN)

141 476 .2 282.3 0.49 -1.15 188 711.2 345.3 0.28 -0.80

142 481.2 283.7 0.48 -1.14 189 716 .2 346.6 0.27 -0.79

143 486 .2 285.0 0.47 -1.13 190 721.2 348.0 0.27 -0.79

144 491.2 286 .4 0.47 -1.12 191 726.2 349.3 0.27 -0.78

145 496.2 287.7 0.46 -1.11 192 731.2 350.7 0.26 -0.78146 501.2 289.0 0.45 -1.10 193 736.2 352.0 0.26 -0.77

147 506.2 290.4 0.45 -1.09 194 741.2 353.3 0.26 -0.77

148 511.2 291.7 0.44 -1.08 195 746 .2 354.7 0.26 -0.76

149 516.2 293.1 0.44 -1.07 196 751.2 356.0 0.25 -0.76

150 521.2 294.4 0.43 -1.06 197 756.2 357.4 0.25 -0.75

151 526.2 295.7 0.43 -1.06 198 76 1.2 358.7 0.25 -0.75

152 531.2 297.1 0.42 -1.05 199 76 6 .2 36 0.0 0.25 -0.74

153 536.2 298.4 0.42 -1.04 200 771.2 36 1.4 0.24 -0.74

154 541.2 299.8 0.41 -1.03 201 776 .2 36 2.7 0.24 -0.73

155 546.2 301.1 0.40 -1.02 202 781.2 36 4.1 0.24 -0.73

156 551.2 302.4 0.40 -1.01 203 786 .2 36 5.4 0.24 -0.72

157 556.2 303.8 0.39 -1.00 204 791.2 36 6 .7 0.23 -0.72

158 561.2 305.1 0.39 -1.00 205 796.2 36 8.1 0.23 -0.71

159 566 .2 306 .5 0.38 -0.99 206 801.2 36 9.4 0.23 -0.71

160 571.2 307.8 0.38 -0.98 207 806 .2 370.8 0.23 -0.70

161 576.2 309.1 0.38 -0.97 208 811.2 372.1 0.22 -0.70

162 581.2 310.5 0.37 -0.97 209 816 .2 373.4 0.22 -0.70

163 586.2 311.8 0.37 -0.96 210 821.2 374.8 0.22 -0.69

164 591.2 313.2 0.36 -0.95 211 826.2 376.1 0.22 -0.69

165 596.2 314.5 0.36 -0.94 212 831.2 377.5 0.22 -0.68

166 6 01.2 315.8 0.35 -0.94 213 836.2 378.8 0.21 -0.68

167 606 .2 317.2 0.35 -0.93 214 841.2 380.1 0.21 -0.67

168 611.2 318.5 0.35 -0.92 215 846 .2 381.5 0.21 -0.67

169 616 .2 319.9 0.34 -0.91 216 851.2 382.8 0.21 -0.67

170 6 21.2 321.2 0.34 -0.91 217 856.2 384.2 0.21 -0.66

171 6 26.2 322.5 0.33 -0.90 218 86 1.2 385.5 0.20 -0.66

172 631.2 323.9 0.33 -0.89 219 86 6 .2 386.8 0.20 -0.65

173 636.2 325.2 0.33 -0.89 220 871.2 388.2 0.20 -0.65

174 641.2 326 .6 0.32 -0.88 221 876 .2 389.5 0.20 -0.65

175 646 .2 327.9 0.32 -0.87 222 881.2 390.9 0.20 -0.64

176 6 51.2 329.2 0.31 -0.87 223 886 .2 392.2 0.19 -0.64

177 656.2 330.6 0.31 -0.86 224 891.2 393.5 0.19 -0.64

178 661.2 331.9 0.31 -0.86 225 896.2 394.9 0.19 -0.63

179 666 .2 333.3 0.30 -0.85 226 901.2 396.2 0.19 -0.63

180 671.2 334.6 0.30 -0.84 227 906.2 397.6 0.19 -0.62

181 6 76 .2 335.9 0.30 -0.84 228 911.2 398.9 0.19 -0.62

182 681.2 337.3 0.29 -0.83 229 916.2 400.2 0.18 -0.62183 686 .2 338.6 0.29 -0.83 230 921.2 401.6 0.18 -0.61

184 6 91.2 340.0 0.29 -0.82 231 926.2 402.9 0.18 -0.61

185 696.2 341.3 0.28 -0.81 232 931.2 404.3 0.18 -0.61

186 701.2 342.6 0.28 -0.81 233 936.2 405.6 0.18 -0.60

187 706 .2 344.0 0.28 -0.80 234 941.2 406 .9 0.18 -0.60



85

Sl.No

x(mm)

y(mm)

Pressure(MPa)

Load(kN)

Sl.No x (m m) y (m m)

Pressure(MPa)

Load(kN)

235 946.2 4 08.3 0.17 -0.60 255 1046 .2 435.1 0.15 -0.54

236 951.2 4 09.6 0.17 -0.59 256 1051.2 436.4 0.15 -0.53

237 956.2 4 11.0 0.17 -0.59 257 1056 .2 437.7 0.14 -0.53238 961.2 4 12.3 0.17 -0.59 258 1061.2 439.1 0.14 -0.53

239 966 .2 4 13.6 0.17 -0.58 259 1066 .2 440.4 0.14 -0.53

240 971.2 4 15.0 0.17 -0.58 260 1071.2 441.8 0.14 -0.52

241 976.2 416 .3 0.17 -0.58 261 1076 .2 443.1 0.14 -0.52

242 981.2 4 17.7 0.16 -0.57 262 1081.2 444.4 0.14 -0.52

243 986.2 4 19.0 0.16 -0.57 263 1086 .2 445.8 0.14 -0.51

244 991.2 4 20.3 0.16 -0.57 264 1091.2 447.1 0.14 -0.51

245 996.2 4 21.7 0.16 -0.57 265 1096 .2 448.5 0.14 -0.51

246 1001.2 423.0 0.16 -0.56 266 1101.2 449.8 0.13 -0.51

247 1006 .2 424.4 0.16 -0.56 267 1106 .2 451.1 0.13 -0.50

248 1011.2 425.7 0.16 -0.56 268 1111.2 452.5 0.13 -0.50

249 1016 .2 427.0 0.15 -0.55 269 1116 .2 453.8 0.13 -0.50250 1021.2 428.4 0.15 -0.55 270 1121.2 455.2 0.13 -0.50

251 1026 .2 429.7 0.15 -0.55 271 1126 .2 456.5 0.13 -0.49

252 1031.2 431.0 0.15 -0.54 272 1131.2 457.8 0.13 -0.49

253 1036 .2 432.4 0.15 -0.54 273 1136 .2 459.2 0.13 -0.49

254 1041.2 433.7 0.15 -0.54 274 1141.2 46 0.5 0.13 -0.49

Load on Convergent(CA) 2243.59 kNLoad on Divergen t(DSA) -282.6 1 kN

T otal Load 1960.98 kN



86

Table 3-7: Mass properties of the flex nozzle (Configuration-D)

Table 3-8: Flange thickness calculations

INTER- FACES

THICKNESS OF FLANGE(mm)

FLANGES THICKNESS

CHOSENBROADMANAPPROACH

SCHNEIDERAPPROACH

Intermediate dome-

motor 19.9 26.7 28*Intermediate dome – aft end ring

11.8 14 18.6**

Throat housing –foreend ring

11.6 16.2 16.5**

Throat housing -divergent

11.5 16.3 25**

Sl.No

DESCRIPTIONDENSITY(kg/m3)

MASS(kg)

C.G (mm)FROM PIVOT

POINT

MI (kg-m2)W.R.TPIVOT

POINT1 Outer Convergent 1400 28.72 -416.8 7.192 Inner Convergent 1400 16.68 -476.97 4.483 Throat 1800 31.65 -322.41 4.114 Throat Backup 1200 12.73 -302.02 1.595 Throat Housing 7800 51.96 -350.24 8.906 Aft End Ring 7800 38.53 -228.36 4.127 Fore End Ring 7800 24.59 -391.33 5.238 Shims 7800 72.09 -320.84 11.369 Pads 1200 5.83 -319.88 0.9210 Thermal Boot 1200 19.14 -294.52 3.22

11 e-Glass 1400 0.79 -292.45 0.1312 Putti 1100 8.33 -286.78 1.3213 Divergent 7800 132.38 323.38 32.12

14Divergent Liner-AE 1400 50.68 479.26 17.19

15Divergent Liner-FE 1400 33.34 0.35 1.49

16StructuralBackup 1400 3.66 719.63 2.28

17IntermediateDome 7800 87.34 -138.67 10.34

18IntermediateDome Liner 1200 10.3 -178.49 1.23

19 Retainer Strip 7800 2.18 -292.8 0.35



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* - Flange thickness of 28 mm is arrived based on 3D analysis of the

bolted joint [116].

**- Thicknesses are finalized based on configurational requirements to

accommodate O Rings and fasteners meeting the minimum design

requirements.

Table 3-9: Interface Fasteners

Table 3-10: O-ring details

INTERFACE SIZENo. OFBOLTS

NOMINAL DIA.(mm)

OPENINGDIA

(mm)

PITCH(mm)

STRESSAREA

(A)(mm2)

INITIAL TENSION

(kgf)

TORQUE(kgf-m)

INT.DOME-MOTORFLANGE

M20x1.5 72 20 918 1.5 272 14688 35

INT.DOME-AER

M12x1.25 60 12 646.8 1.25 92.10 4973.4 9

THROAT HOUSING-

FERM8x1.0 60 8 338 1.0 39.20 2116.8 3

THROAT HOUSING-

DIVERGENT M10x1.25 72 10 487 1.25 61.2 3304.8 5

INTERFACESEAL

C/SDIA

GROOVE DETAILS

TYPE (mm)Depth(mm)

Width(mm)

SealingID (mm)

Intermediatedome

Axial 7 5.6 8.5 925

to motor Radial 5 3.75 6.5 918Intermediatedome to AER

Axial 5 4.0 6 830

Throathousing toFER

Axial 5 3.9 6.7 550

Throathousing todivergent

Axial 3 2.3 4.0 487



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3.11 CONFIGURATIONS DESIGNED

Three conical and three cylindrical configurations have been

designed for specific requirements. Configuration A, B & C are conical

body and D, E, & F are cylindrical body flex seals. The configuration

parameters of all the six configurations are given in Table 3-11.

Table 3-11: Design details of six configurations of flex seals designed

PARAMETER/TYPE

CONF-

A

CONF-

B

CONF-

C

CONF-

D

CONF-

E

CONF-

F

Design inputs

MEOP (MPa) 5.88 5.39 5.88 6.86 7.84 5.88Ejection Load (kN) 3137 735 735 1961 1200 470

Vectoring angle

(Degree)± 50 ± 40 ± 40 ± 40 ± 30 ± 20

Geometric parameters

Seal OD (mm) 968 470 487 705 512 368

No of pads 8 8 8 8 8 6

tr (mm) 7.3 4.5 4.8 8 6 4.5

te (mm) 4 3 3 4 3 3

1 (deg) 45 45 45 40 40 40

2 (deg) 55 55 55 50 52 50

(deg) 50 50 50 45 46 45

(deg) 30 35 40 55 45 45

Rp (mm) 570 274 289 460 325 240

Spring Torque

(kgf-m)/deg

(kN-m/deg)

855

(8.38)

63

(0.618)

74.8

(0.734)

348

(3.413)

142.3

(1.395)

46.75

(0.458)Moment arm (mm) 757 398 507 494 530 381



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3.12 PROCESS PLAN

Following are the methods adopted for the manufacturing of flex

seal [117]

Secondary bonding

Injection moulding

Compression moulding

Secondary bonding technique is normally followed for the seals

with conical shims where the cured elastomer pads are bonded with

metal shims. Each bond line quality can be checked through NDT. For

the seals with spherical shims, secondary bonding technique is not

suitable because,

Separate mould is required for each elastomer pad for procuring

since pads are with different radii.

There is a difficulty in matching the radii of adjacent shim and

cured pad. Mismatch in radii will result in inferior bond.

More processing time is required. Since procured elastomer

pads are to be bonded with shims and at a time only one bond

line can be processed at a time.

Normally for processing of the seals with spherical shims, either

injection moulding or compression moulding is followed. These

moulding techniques being a single shot operations, are not amenable

to NDT (X-ray or thermograph). However quality of bond lines can be

examined by subjecting the seal to leak test under tensile load. For

large size seals, injection moulding is not adopted due to large surface



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area of the bond in which the elastomer flow will not be effective

resulting in voids. Compression moulding technique, which is widely

followed for large size seals, is adopted.

3.13 DEVELOPMENT PLAN

Development plan essentially consists of the following tests in

specimen level and flex seal level.

3.13.1 Specimen Level Tests

Quadruple lap shear specimen (QLSS) and tensile bond strength

(TBS) specimen of ASTM standards are utilized to evaluate the

following elastomer pad material properties:

Secant shear modulus

Ultimate shear strength

Ultimate shear strain

Bond strength

Specimen are processed by simulating the moulding process. In

addition, the following properties are also evaluated for quality control

applications:

Tensile strength

Tensile modulus of elasticity

Hardness To determine the aging characteristics of the elastomer material,

QLSS specimens are to be stored for testing at specified time intervals.



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3.14 TRIAL MOULDING

Trial mouldings are required to achieve the following objectives.

Validation of mould design

To freeze the size of the uncured elastomer pad for lay-up

To determine the size and No. of the steel spacers to be

positioned to control the thickness of pads during moulding

To freeze the process parameters; cure temperature, pressure

and duration of curing

To firm up the handling and assembly procedures during the

moulding operation

Trial mouldings should be carried out without the adhesive so

that the elastomer pad after curing can be removed separately and

inspected for its quality. QLSS properties should also be evaluated to

confirm the elastomer pad properties in full scale moulding

conditions. The realized flex seal and flex nozzle are shown in Figure

3-15 and Figure 3-16.

3.15 CONCLUDING REMARKS

The chapter presents the design details of flex seal,

configuration of nozzle with envelope clearances, interfaces design and

actuator requirements. Summary of design details of six

configurations are also presented. The processing and developemental

plan of specimen and flex seals are discussed in brief. The

characterisation of materials used in flex seal design, selection of



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material models and validation of models are dealt in detail in the next

chapter.

Figure 3-15: Realised Flex seal

Figure 3-16: Realised Flex nozzle



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Figure 3-17: Flex nozzle system development methodology

Shims strain

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