19176 

ECS-SS-3059 

SRM PROPELLANT, FRICTION/ESD TESTING 

12 May 1989 

Prepared for: 

NATIONAL AERONAUTICS AND SPACE ADMINISTRATION 

GEORGE C. MARSHALL SPACE FLIGHT CENTER 

MARSHALL SPACE FLIGHT CENTER, ALABAMA 358 12 

Contract No. NAS 8-30490 

DR.No. 3-5 

WBS.No. 4B102-10-04 

MORTON THIOKOL. INC. 

Aerospace Group 

Space Operations 

P.O. Box 707, Brigham City, Utah 84302-0707 (801 1 863-351 1 

FORM TC 4677 (REV 1 88) - 

(MASA-C3-183706) SBH PROPELLANT, %8 9 -278 64 

P€31CTION/ESD TESTING inorton Thiokol) 39 p 

CSCL 211 

Unclas 

G3/28 0224020 
MORTON THIOKOL. INC. 

Space Division 

ECS-SS-3 0 59 

SRM PRDPELLANT, FRICTIrn/EsD TESTIIG 

28 April 1989 

Prepared by: 

Ordnance Development 

Approved by: 

.A ~ 

',/ J. H. Stoker 

Project Enginvring 

Systems Safety 

,&< 4%&/ 

I. N. Black 

Test Plans and Reports 

J. R. Braithwaite 

Planning Certification 

Released By: 

Materials & Processes Data Management 

RESEARCH AM) DEvmxlEmENT LABORATORIES 

Ordnance Developnent Section 

REVISION 

FORM TC 7994-310 

i SEC I PAGE 
I I 

MORTON THIOKOL, INC. 

Space Division 

M3s-SS-3059 

SRM PROPELLANT, FRICTION/ESD TESTING 

In years past there was not much concern about electrostatic sensitivity of 

propellants. At Thiokol, testing was performed on solid propellants with 

the TCC Electrostatic Discharges (ESD) equipment, with upper limits of 

40,000 volts and 8 joules energy. With the acquisition of the Allegany 

Ballistics Lab (ABL) ESD equipment during a joint venture with Hercules, 

testing was also done at 5,000 volts at energy levels up to 6.25 joules. 

During standard hazards testing, most propellants were tested with one or 

both ESD systems and the sensitivity was usually reported as greater than 8 

joules or greater than 6.25 joules, depending on which system was used, 

since propellants rarely ignited. These energy levels are much higher than 

would be expected from normal electrostatic voltage build up in propellant 

handling or casting operations. Generally, however, some level of 

precaution was taken by grounding or shielding to prevent the possibility 

of an ignition by ESD. 

Following the Pershing I1 incident in 1985 and the Peacekeeper ignition 

during core removal on 29 December 1987, it was found that propellant can 

be much more sensitive to ESD than ever before realized. As a result of 

the Peacekeeper PK-303 motor near miss incident, a friction machine was 

designed and fabricated, and used to determine friction hazards during core 

removal. Friction tests on PK propellant produced no ignitions or 

indications of positive results, even to pressures on the sample of 13,000 

PSI. 

across the friction plates resulted in propellant ignitions at low friction 

pressures and extremely low ESD levels. This condition simulates friction, 

confinement, pressure and electrostatic voltage build up as a core is 

removed from a motor. 

Peacekeeper Propellant (TP-Hl207C) to determine the lowest energy levels at 

which it would ignite. Comparison tests were performed under this study on 

SRM propellant (TP-H1148), as specified in TEST PLAN, ETP-0359, "SPACE 

However, additional testing with an electrical charge being applied 

Testing was performed with this equipment on 

SHUTTLE SRM ELECTROSTATIC SENSITIVITY AND CHARGE GENERATION". 

OBJECTIVE 

The objective of this test series was to determine the sensitivity of 

TP-H1148 (SRM) propellant to combined friction pressure and electrostatic 

stimuli and to compare the sensitivity of the SRM propellant to Peacekeeper 

propellant (TP-H1207C). 

REVISION - 

FORM TC 7994.310 
1 I 

MORTON THIOKOL. INC. 

Space Division 

Ecs-SS-3059 

The low rate, high load friction tester (AV-groove" test), used in the 

investigation of the Peacekeeper invqstigation of motors PK-303 and PK-322 

incident, was also used in the testing of SRM propellant. While running 

the friction test, a charged capacitor was discharged across the 

electrically isolated friction plates. 

to popping a motor core; that is friction, pressure, confinement, and an 

electrostatic charge. A 550 pF capacitor was charged and connected into 

the friction plate circuit at about one second intervals for a total of 

about 15 pulses; 4 pulses before, with the remaining pulses during and 

after movement of the friction plate. 

charge across a very thin film of propellant between two steel friction 

plates is more severe than is normally seen during normal core popping, and 

provides a worst case situation. 

This provided a condition similar 

The condition of an electrostatic 

During the initial phase of the testing, several items were held constant. 

They were a friction speed of 1/2 inch per second, friction pressure of 

1164 psi and the 550 picofarad discharge capacitor. 

voltage was changed during testing to provide a variable energy level. 

In the initial test series, the test equipment capability was limited to 

1000 volts, which, during preliminary testing, was not enough voltage to 

consistently ignite 0.03-inch thick sheets of first time (once-used) 

TP-H1148 propellant. 

energy of 44 microjoules, on the once-used propellant. 

The capacitor charging 

However one ignition did occur at 400 volts, with an 

Some of the propellant was re-used several times so that it was very thin, 

smashed, broken, and granulated. Under there conditions much less voltage 

was required for ignition. The lowest voltage that this re-used Sm 

propellant ignited at was 280 volts, or 22 microjoules. 

propellant, tested in a similar manner, ignited at 222 volts or 13.5 

microjoules, Table IX. 

352 volts or 34 microjoules, Table VIII. 

propellant appeared to be less sensitive to the combined friction/ESD 

stimuli than the PK TP-Hl207C propellant. 

The PK TP-H1207C 

The once-used PK single sheet propellant ignited at 

In general, the SRM TP-H1148 

Later testing, after the modification of the capacitor, "charge", 

"discharge" switching system and using a higher voltage power supply, was 

done on single sheets of 0.030-inch thick TP-H1148 propellant, a single 

sheet covered the entire contacting surfaces of the friction plates. 

the single sheets of 0.030-inch thick propellant resulted in much higher 

voltages and energy levels required to cause positive results. 

Using 

Approximately 1200 tests were performed using single sheets of TP-H1148 

propellant 0.030-inch thick. 

four pressures and 20 tests at each of five voltages. 

sheets are shown in Tables 1 to 6. 

These tests were at three friction speeds, 

The raw data summary 

REVISION - 

FORM TC 7994.310 
1 I 

MORTON THIOKOL. INC. 

Space Division 

Ecs-SS-3 0 59 

In general, most of the ignitions occurred before movement of the friction 

plates. 

cause of the sensitivity of propellants to ESD. 

coNcUIsI(MS 

This would indicate that pressure and not friction is the major 

SRM propellant (TP-Hl148) was tested on the combined friction/ESD 

V-groove" equipment. 

igniter probability curves shown in Figures 2 to 12. 

levels vs pressure are on Figures 13 to 14. 

The results are summarized in Tables 1 to 6 and 

The minimum ignition 

The data indicate that the TP-H1148 propellant is slightly less sensitive 

to the combined friction/ESD stimuli than the TP-H1207C propellant. 

However, the SRM propellant can be ignited with combined friction, pressure 

and an electrostatic discharge. There was no resolution for three of the 

probability curves, but the lower ignition levels are shown which is the 

most important information. 

As a comparison, results of previously tested Peacekeeper propellant, 

(TP-Hl207C) are shown in Tables VI1 and VIII, with the related ignition 

probability curves shown on Figure 15. 

Table 7 and 8 was the only Peacekeeper propellant that was tested using 

single sheets 0.030 inch thick and provides a better comparison than the 

other curves which were pieces of "core residue" propellant. The re-used 

TP-H1148 propellant ignited at the low level of 280 volts, and an energy of 

22 microjoules. 

voltage than the re-used propellant to ignite. .The once-used propellant 

ignited at 400 volts with an energy of 44 microjoules. As a comparison, 

the Peacekeeper TP-Hl207C propellant ignited at 352 volts at 34 microjoules 

for the once-used propellant (see Table VIII) and 222 volts at 13.5 

microjoules for the re-used propellant, (see Table IX). 

The testing that was tabulated in 

The once-used sheets of propellant required a higher 

. 

The once-used 0.030-inch thick single sheet propellant covered the entire 

llv-groove" friction plate surface and probably held the friction plate 

surfaces farther apart than when the propellant had been re-used several 

times. 

In comparing TP-H1148 and TP-Hl207C propellants, the volumetric resistivity 

of each propellant should be discussed. The ability of a triboelectrically 

induced charge to build to a hazardous level in a dynamic propellanthardware system is a function of the propellant's volumetric resistivity. 

If the resistance is "low", the generated charge will bleed off as it is 

generated. 

and TP-H1207C propellants" tps volumetric resistivity for TP-H1148 is 5x10 

ohm-cm as compared to 2.5~10 

triboelectric charge build-up in SRM propellant is only 1/5000 of that for 

TP-Hl207C propellant. 

According to Dr. Ti Luong in TWR-40029, "ESD data for TP-H11489 

ohm-cm for TP-Hl207C. The potential for a 

REVISION __ 

FORM TC 1994-310 

VOL DOCNO TFJR-19176 

3 PACE SEC 
.. Q* 

MORTON THIOKOL. INC. 

SEC 

Space Division 

4 PAGE 

ECS-SS-3059 

Another item that should be considered is the pressure between the SRM core 

and propellant. Appendix A memo L222-FY89-802, to T. A. Berger, from L. M. 

Clark; subject: Cont act Pressure Across The Dovetail Region, indicates 

the SRM propellant contact pressure is 500 psi. According to the tests 

performed in this study, 1200 in all, using single sheets of 0.030-inch 

thick of TP-Hl148 propellant, a minim of 2000 volts was required for 

ignitions to occur at this pressure. Figures 19 and 20 show these data. 

Because of the lower resistivity of the propellant and with proper tool 

grounding, SRM operations can be performed safely. 

DISCUSSION 

Following the Pershing I1 incident in 1985 and the Peacekeeper ignition 

during core removal on 29 December 1987, it was found that propellant can 

be much more sensitive to ESD than ever before realized. As a result of 

the Peacekeeper PK-303 motor near miss incident, a friction machine was 

designed and fabricated, and used to determine friction hazards during core 

removal. 

Friction tests on PK propellant produced no ignitions or indications of 

positive results, even to pressures on the sample of 13,000 PSI. 

additional testing with an electrical charge being applied across the 

friction pressures and extremely low ESD levels. 

friction, confinement, pressure and electrostatic voltage build-up as a 

core is removed from a motor. 

circuit is in Figure 1. Bare steel "V-groove" friction plates, one plate 

sliding three inches on the other with propellant between, causes the 

propellant to become very thin. When the dielectric strength of the thin 

propellant is exceeded by the applied voltage, dielectric breakdown occurs. 

As this process is repeated several times, with the same propellant being 

re-used, the propellant becomes smashed, broken, and about the same as 

being granulated during tool removal operations. Some of the aluminum 

particles would have the oxide coating rubbed off and could be flattened to 

the point of acting like a very thin bridge wire. 

most sensitive condition that could occur. 

condition but the possibility for a condition like this to exist and cause 

an ignition in an actual propellant system always exists. 

testing provides a means of comparing the relative sensitivity of one 

propellant to another in a combined friction, pressure and ESD environment. 

However, 

This condition simulates 

A sketch of the equipment and the electrical 

This is probably the 

This may not be the normal 

This type of 

Test data indicates that this friction/ESD test may be more of a confined 

electrostatic test than a friction test. Previous small scale ESD tests 

would sometimes show an ignition but very seldom show a sustained flame. 

During the friction/ESD testing of re-used and smashed propellant under 

pressure, the sample would often continue to burn after a positive reaction 

indication. A point of interest is that the positive reactions during this 

testing were extremely loud. They sounded like high powered rifle shots. 

REVISION - 

FORM TC 7994-310 
MORTON THIOKOL. INC 

SEC 

Space Division 

5 PAGE 

ECS-SS-3059 

The test series in which single sheets of TP-HI148 propellant were used 

reacted differently than the early tests where smaller pieces of propellant 

and re-used propellant were used. The positive reactions were very seldom 

loud. Usually the sound was only a ''click" or a very small l'popll. 

times the indication of a positive reaction was only a "smoke" mark on the 

propellant. 

sustained burning. 

Many 

Of the 1200 tests performed for this matrix, there was - no 

REVISION - 

FORM TC 7994-310 
MORTON THIOKOL. INC. 

Space Division 

SEC 

ECS-SS-3059 

PACE 

DISTRIBUTION 

Recioient M/S 

I. N. Black 

T. A. Berger 

L. C. Bracken 

A. H. Brandt 

J. R. Braithwaite 

D. K. Coziar 

L. E. Davis 

G. W. Dixon 

M. R. Harper 

R. D. Larsen 

G. R. Lasley 

A. M. Neilson 

J. D. Overby 

P. C. Petty 

J. H. Stoker 

C. r.1. White 

J. J. Woodworth 

1-10 File 

Data Management 

Print Crib 

R. R. Bowman 

K. J. Spas 

REVISION 

FORM TC 7994-310 

136 

411 

800 

136 

841 

136 

811 

240C 

E12 

240C 

851 

110 

121 

K68 

110 

121 

110 

240C 

280 

240C 

280A 

280C 
t 

MORTON THIOKOL, INC. 

Space Division 

ECS-SS-3059 

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MORTON THIOKOL. INC. 

Space Division 

ECS-SS-3059 

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MORTON THIOKOL, INC,

Space Division 

ECS-SS-3059 

REVISION 

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DOC NO. TWR- 19 176 

SEC PAGE 9 
1 

MORTON THIOKOL. INC. 

Space Division 

ECS-SS-3059 

REVISION - 

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Space Division 

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MORTON THIOKOL. INC. 

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MORTON THIOKOL. INC, 

Space Division 

ECS-SS-3059 

1 

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PAGE 

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. MORTON THIOKOL. INC. 

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MORTON THIOKOL. 

Space Division 

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MORTON THIOKOL. INC. 

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MORTON THIOKOL. INC. 

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Space Division 

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MORTON THIOKOL. INC. 

Space Division 

ECS-SS-3059 

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REVISION __ 

FORM TC 7994.510 

VOL DOCNO. TWR-19176 

SEC PAGE 21 

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* ECS-SS-3059 

Table I 

MORTON THIOKOL. lNCl - - Space Division ti ' ropellant, Data Tabulation Sheets, 

Combined Friction-ESD Stimuli, 0.2 jn/,-ec:. Velocity ' 

Hydraulic Pressure S6 5 ,,: I 

Friction Speed 

V-Groove !/ Flat Plate 

Sample Thickness de 03 ,M~4 

sample Pressure /I6 '7' /pq/ 

Tempe r a tu r e 

/ 

&w3 

Voltage Reaction Comments * 

# of Go # of No Go 

93 p->r Hydraulic Pressure 100 A-, - r';/ Sample Pressure 2 

3- ZSOO 

* B = Before Friction Movement 

D = During Friction Movement 

- = After Frictiorl Movement Doc NO TWR- 19 1 7 6 VOL 

22 SEC PAGE 

FORM TC 7994-310 
ESD F'RICTICN !EST 

T-16 

Propellant rype Tpd/{//LJ/y Date 22 / tZ5%3/ ByHydraulic Pressure -- 435 F3f - Sample Pressure 8 73 $6- 

Temperature 14/n& M Friction Speed d.2 6 fC 

/, 

V-Groove / Flat Plate 

Sample Thickness O)U.c;, ,nrh 

Opera tors D,,,, J -- J 

Capacitor 6% I;.) 

f 

Voltage React ion Comen t s * 

# of Go # of No Go 

452 C 

ycl'b 

Hydraulic 

I 

Ill1 /YilcNN \ - -Mu--- 

!!! J it 

P re ssure 

REVISION - DOC NO VOL 

SEC TIJR-19176 I PAGE * B = Before Friction Movement 

L) = burin9 Friction Movement 

A = After Friction Movement 

23 FORM TC 7994. 10 
-. 

MORTON THIOKOL. INC. 

. .' Space Division Table I11 

ECS-SS-3059 

'I'P-Hl148 Propellant , Data Tabulation Sheets, 

Combined Friction-ESC Stimuli, 0.5 in/sec. Velocity 

Propellant 

Hydraulic Pressure ;I" I 

Friction Speed #S /y;.gLI. 

V-Groove - J Flat Plate - 

Sample Thickness 0.03 irlc/f 

Date 09 / AX?/ 89 

sample Pressure &&' as/ 

- 

Temperature pus, I, 

Capacitor 55l3 /{' 

Voltage Reaction Comments * # of Go # of No Go 

FORM TC 7994-310 TWR-19176 * 24 B = Before Friction Plovement 

D = During Friction Elovement 

A = After Friction Movement 
Table IV 

ECS-SS-3059 

MORTON THIOKOL, INC, 

Space Division 

TP-€111.48 Propellant, Data Tabula+-, I Sheets, 

Combined Friction-ESD Stimuli, 0. .,ec. Velocity 

ESD FRICTICN TEST 

T-16 

Hydraulic Pressure 5-G >- ps,' 

Friction Speed J. 5- //CL-~[ 

V-Groove Flat Plate 

Sample Thickness 3 C' (~~4 

Voltage React ion 

# of Go # of No Go 

Temperature Am& 

Capacitor ~5a pf 

Comments * 

Hydraulic Pressure 

A / 

Sample. Pressure 

Hydraulic Pressure Sample Pressure 

. 

- vo L -AE"'Wm - DOC NO 

* FOR TC 799 SEC TIJR-19176 PAGE % = ¶%!'fore Friction Movement 

D = During Friction Yovement 

A = After ri ''? Movement 

25 

ORM'VAL PAGE 1s 

OF POOR QUALITY 
._ 

__ -- -------- - 

- ,- MORTON THIOKOL. INC. ECS-SS-3059 

Table V Space Division 

TP-H1148 Propellant,, Data Tabulation Sheets. 

Combined Friction-ESD Stimuli, 1.0 in/sec. Velocity 

ESD FRIWCN TEST 

T-16 

Hydraulic Pressure s 6s ,n5/ 

Friction Speed /,o %e=- 

V-Groove Flat Plate 

Sample Thickness 0103 /nc& 

Voltage Reaction 

# of Go # of No Go 

sample Pressure //~q n 4 '7 

Temperature 

Operators 

Capacitor 

I 

Comments * 

Hydraulic Pressure Sample Pressure 

Hydraulic Pressure Sample Pressure 

DOL IIV 

SEC PAGE 

REVISION - ""L 

~odrn~cB94=oBefore Friction Movement 

D = Durinq Friction Movement 

A = After Friction Movement 

TWR-191 76 ' 

26 
ECS-SS-3059 ,..-A' 

f - MORTON THIOKOL. INC. 

Space Division 

Table VI 

TP-H1158 Propellant, DATA Tabulation Sheets, 

Combined Fr,iction-ESD, Stimuli, 1.0 in/sec. Velocity 

ESD FRicrIq TEST 

T-16 

Propellant .-ff-//46 Date G /MM/ 87 

Hydraulic Pressure /uz) 85/ Sample Pressure tt3 H/ 

Friction Speed 1. d Temperature hp 

/ 

V-Groove / Flat Plate I 

Sample Thickness 0.03 ,fl clr 

Operators , OdkLI 

0- J 

Capacitor .5sc\ / 

1- 

voltage Reaction Comments* 

# of Go # of No Go 

REVISION - DOC NO VOL 

TWR-19176 I PAGE 

27 

* p =. pefare Friction Movement 

D = During Friction Movement 

A = After Friction Movement 

FORMT 799431 
MORTON THIOKOL, INC, 

SEC 

Space Division 

PAGE 28 

ECS-SS-3059 

c MOR"TX THIOKOL "V" GEEOOVE 

OXBINED ESE/FRICl!ICN TESTS 

BARE STEEL FRICTICN PLATES 

Date: 08-17-88 

Sample: PK-323 Motor Propellant, Baseline 

Capacitor 550 pF 

Friction Speed 0.5 in./second 

Hydraulic Pressure 100 psi 

Sample Pressure 1164 psi 

Propellant N;rmber 

0.03-in. Thick 1 512 N 

1 51 2 72 G After Stroke 

1 456 57.2 G Before Movement 

1 400 N 

Sample of Tests Volts Microjoules Results Camnents 

11 

II 

I1 

Reused Propellant 1 11 

11 

11 

II 

II 

11 

II 

11 

I1 

II 

1 

2 

1 

7 

1 

1 

2 

1 

10 

1 

REVlSlOtr __ 

FORM TC 7394.310 

400 

400 

376 

376 

3 50 

350 

328 

312 

312 

304 

296 

N 

N 

N 

44 G During Stroke 

38.9 G During Stroke 

33.7 G During Stroke 

29.6 G During Stroke 

26.8 G During Stroke 

N 

N 

N 
MORTON THIOKOL. INC. 

Space Division 

ECS-SS-3059 

c NOEMON THIOKOL "V" 

-1- ESE/F'RICI'ION TESTS 

BARE STEEL FRImoN PLATES 

Date: 09-09-88 

Sample: PK-324 Motor TP-H1207C Baseline 

Capacitor 550 pF 

Friction Speed 0.5 in./second 

Hydraulic Pressure 100 psi 

Sample Pressure 1164 psi 

Carton Mix F380128 

Propellant Number 

New Propellant 1 480 N 

6 352 N 

11 304 N 

Sample of Tests Volts Microjoules Results ComPents 

1 480 63.4 G After Movement 

1 352 34.1 G After Movement 

Reused 

I1 

I1 

II 

I1 

11 

II 

II 

P rope1 lant II 

II 

II 

II 

II 

I1 

II 

11 11 

It I1 

REVISION - 

FORM TC 7994.310 

1 

1 

3 

1 

5 

1 

16 

9 

408 

408 

352 

352 

304 

304 

256 

272 

N 

45.8 G 

N 

34.1 G Before Stroke 

N 

25.4 G During Stroke 

N 

N 

1 272 20.3 G During Stroke 

12 264 N 

vo L DOC NO TWR- 19 176 

SEC I PAGE 29 .. 
e 

MORTON THIOKOL. INC. 

Space Division TABLE IX 

~ ~- 

ECS-SS-3059 

MOR" THIOKOL "V" 

COkIBINED ESE/FRICTION TESTS 

BARE STEEL FRIcrIau PLATES 

Date: 08-18-88 to 08-19-88 

Sample: PK Motor 323, TP-Hl207C 

Core Insert No. 8, Ribbons 

Capacitor 550 pF 

Friction Speed 0.5 in./second 

Hydraulic Pressure 100 psi 

Sample Pressure 1164 psi 

Propellant Number 

New Propellant, 

Sample of Tests Volts Microjoules Results Camnents 

. During Stroke II 

I1 

II 

G Thin Ribbons 1 352 34.1 

1 304 25.4 G 

4 256 N 

1 272 N 

Before Movement 

I1 

11 

1 272 20.3 G During Stroke 

5 26 4 N 

Reused, Thin Ribbons 6 272 II 1 304 25.4 

1 II 272 

Reused II 

II 

II 

11 

II 

11 

II 

REVISION 

FORM TC 7994.310 

1 

4 

1 

7 

1 

7 

1 

18 

272 

256 

256 

232 

232 

232 

222 

200 

N 

G During Stroke 

N 

20.3 G Before Movement 

N 

N 

N 

G 

N 

G 

N 

14.8 

13.5 

During Stroke 

After Movement 

DOCNO TWR-19176 VOL 

SEC PAGE 

30 
APPENDIX A 

Aerospace Group 

Space Operations 

29 Harch 1989 

L222:FY89:802 

TO : T.A. Bcrger 

Manufacturing Engineering 

Propellant and Adhesive Structures 

FROM : L.H. Clark 

SUBJECT: Contact Pressures across the Doveta 

INTRODUCTION 

This memo provides predictions for contact pressures that occur across 

the dovetail region of the forward segment tooling. Contact pressures 

in this region were requested to assist in assessing the BSD hazards 

associated with the forward segment casting operation. 

During the forward segment casting operation, propellant can intrude 

into the interface between the tip fin and the stub fin. Problems 

may occur because of the inverse relationship between pressure and 

the dielectric breakdown voltage of propellant. The dielectric 

breakdown of propellant has been shown to occur at lower voltages as 

the pressure on the propellant is increased. 

Structural analysis predicted average contact pressures of 

approximately 50 psi in the dovetails. Uaximum pressures reached 

local values exceeding 500 psi. These maximum pressures cause concern 

for two rtasons: 

o The maximum contact pressures indicate that propellant in the 

dovetails would have a dangerously low dielectric breakdown 

volt age. 

o The maximum contact pressures are nonconservative because 

geometric simplifications of the dovetail were required 

for the analysis. 
T.A. Bcrger 

L222:PY89:802 

Page 2 

FINITE ELEMENT ANALYSIS 

Modelling. 

dimensional forward segment model using the ABAQUS finite element 

code, The model consisted of a 16.4' slice of the segment with an 

unpopped fin former incorporated into the model. (See Figure 1). The 

dovetail interface region of the fin former was not explicitly 

modelled, but simplified to assume full radial contact with the core. 

(See Figure 2). The fin former was assumed to fully adhere to the 

propellant throughout the core popping operation and was modelled as a 

uniformly bonded component. 

Finite element analysis was performed on a threeMaterial Properties. Material properties used in the analysis for 

grain components are summarized in Tables 1 and 2. These properties 

have been excerpted from TWR-18011, Rev. A, Supplement B,. "RSRM 

Structural Mechanical Properties Databook, Propellant, Liner, 

Insulation and Inhibitor". 

Loads. Loads on the model included slump loads and thermal cooldown 

to 90 OF. An equivalent body force was used to assess effects due to 

the weight of the fin former. The body force used in the analysis 

assumed a fin former density based on fin volume and the actual weight 

of the fin former, 2100 lbf. 

Boundary Conditions. The model was fixed axially at the aft end of 

the case. Theta fixes were applied along both symmetry boundaries at 

the zero degree location and the 16.36 degree location. A radially 

fixed sliding boundary condition was applied to the stub fin/tip fin 

interface region. 

Results. Analytical results included the contact pressure 

distributions over the surface of dovetail and reaction forces at the 

boundary. Radial stresses on the surface range from -470 psi to 525 

psi. The radially compressive stress (-470 psi) on the surface is 

interpreted as the maximum contact pressure across regions A and B of 

the dovetails. The radially tensile stress (525 psi) must be 

interpreted as the maximum contact pressure across region C of the 

dovetails. However, this area of the dovetail is much smaller than 

the area across which analytical stresses were obtained, and stresses 

could increase to several times the analytical stress prediction. 
T.A. Berger 

L222:FY89:802 

Page 3 

VERIFICATION OF THE ANALYSIS 

The results of the finite element analysis were validated for order of 

magnitude accuracy with a simple hand calculation. Once the core is 

popped, lifting forces to remove it total 89000 lbf. Core weight 

(39180 lbf) accounts for just part of this lifting force. A 

conservative assumption is that the remainder of this force is 

required to overcome friction in the dovetails. Therefore 

approximately 50000 lbs is needed to overcome friction. The contact 

force normal to the dovetail is obtained by applying the following 

relationship: 

Ff 9 P x Fn 

where: Ff = force to overcome friction 

u = 0.09 (coefficient of friction for a 

Fn 

TeflonITeflon interface) = normal force 

The coefficient of friction for the Teflon/Teflon interface is taken 

from the CRC Handbook of Tables for Applied Engineering Science, 

Second Edition. 

The calculated normal force is 555,555 lbf. When this normal force is 

distributed over the width of the dovetail and the length of the fin, 

the resulting average contact pressure is 136 psi. The results of 

this conservative hand calculation show contact pressures 2.6 times 

higher than the finite element results, indicating that the finite 

element predictions are in the appropriate range. 

If there are any questions regarding this analysis, I can be reached 

at extension 6465. 

.M. Clark 

Propellant and Adhesive Structures 

Concurrence: 

A.R. Thompson, Acting Manager 

Propellant and Adhesive Structures Applied Mechanics 

cc: G.W. Dixon, R.A. Guthie, J.R. Kapp, D.A. Sebahar, J.H. Stoker, 

R.B. Thue, R.E. Wynn, L.E. Davis 
Table 1. Propellant Material Properties. 

Equivalent Modulus E 130 

Poisson Ratio V 0.4999 

Coefficient of 

Thermal Expansion a 6.06~10-5 

PS i 

--- 

in/in OF 

Table 2. NBR Material Properties 

i 

El = 1230 

ORTH 

Equivalent E2 = 460 

Modulus 

G12 = 274 

~12 = 0.4348 

~21 = 0.1626 

~~ ~ ~ 

Shear 

Modulus 

G13 = 165 

v13 = 0.5552 

~31 = 0.1986 

Poisson 

Ratio 

a3 = 21.05 

Coefficient 

of Thermal 

Expansion 

(1.0 x 10-5 

in/in OF) 

OTROPIC NBR' INSULATION* I 

a1 = 1.33 a2 = 8.05 

I 

E3 = 71 440 

G23 = 155 

v23 = 0.8274 

v32 = 0.7914 

* Haterial Directions for Orthotropic NBR Insulation 

(1) Parallel to Fiber (2) Perpendicular to Fiber (3) Across the Ply 
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