This study evaluated the materials utilized in the flexible joint for possible failure modes. Studies undertaken included effect of temperature on the strength of the system, effect of fatigue on the strength of the system, thermogravimetric analysis, thermochemical analysis, differential scanning calorimeter analysis, dynamic mechanical analysis, and peel test. These studies indicate that if the joint failed due to a materials deficiency, the most likely mode was excessive temperature in the joint. In addition, the joint material is susceptible to fatigue damage which could have been a contributing factor

Hall, W. B.

English

NASA Technical Reports Server

NASA/ASEE SUMMER FACULTY RESEARCH FELLOWSHIP PROGRAM 
MARSHALL SPACE FLIGHT CENTER 
THE UNIVERSITY OF ALABAMA IN HUNTSVILLE 
AN EVALUATION OF TECHROLL SEAL F'LEXIBLE JOTNT MATERIAL 
Prepared by: William E. Hall, Ph.D. 
Academic Rank: Professor 
University and Department: 
NASA/MSFC : 
Division: 
Branch: 
Mississippi State University 
Department of Chemical Engineering 
Non-Metallic 
Ceramics & Coatings 
MSFC Counterpart: Ron L. Nichols 
Date: August 12, 1983 
Contract No: NGT 01-008-321 
The University of Alabama in Huntsville 
https://ntrs.nasa.gov/search.jsp?R=19840007969 2020-03-22T08:12:11+00:00Z
ABSTRACT 
An Evaluation of Techroll  Seal Flexible  J o i n t  Material 
W i l l i a m  B. Hall 
Professor,  Chemical Engineering 
Mississ ippi  S t a t e  University 
ASEE-NASA Fellow 
L n  L. Nirhols 
Ceramics Unit, EH34 
Marshall Space F l igh t  Center 
ASEE-NASA Counterpart 
On A p r i l  7,  1983 a Tracking and Data Relay S a t e l l i t e  (TDRS) launched 
from Space Shu t t l e  6 f a i l e d  t o  reach geosynchronous o r b i t .  
reached from an in t ens ive  inves t iga t ion  was t h a t  t he  satel l i te  tumbled 
out of con t ro l  due t o  f a i l u r e  of an oii seal i n  the rocket system known 
as I n e r t i a l  Upper Stage (IUS). The o i l  3eal is a f l e x i b l e  j o i n t  pel lni t t ing 
swivel o r  gimbal of the rocket nozzle t o  con t ro l  d i r e c t i o n  of f l i g h t .  
The conrlusion 
This study evaluated the  materials u t i l i z e d  i n  the f l e x i b l e  j o i n t  f o r  
Studies  undertaken included e f f e c t  p i  remperature possible  f a i l u r e  modes. 
on the s t r eng th  of t he  system, e f f e c t  of f a t igue  on the s t r t n g t h .  of 
the system, thermgravimetr ic  ana lys i s ,  thennomechanical sna lys i s ,  dlf feren-  
t i a l  acanning calor imeter  ana lys i s ,  dynamic ,8.echanical ana lys i s ,  and pee l  
test. 
These s t u d i e s  ind ica t e  t h a t  i f  t h e  j o i n t  f a i l e d  due t o  a materials 
deficiency, the most l i k e l y  mode was excessive temperature i n  the j o i n t .  
In addi t ion,  the j o i n t  material is suscep t ib l e  t o  f a t igue  damage which 
could have been a contr ibut ing f ac to r .  
xv- 1 
In t roduct ion  
The A i r  Force Space Div is ion  I n e r t i a l  Upper S t a t e  (IUS) is a three-  
axis  s t ab i l i zed , two-s t age  v e h i c l e  used t o  t a k e  payloads from low e a r t h  
o r b i t s  t o  o t h e r  reg ions  of space  such as a geosynchronous o r b i t .  The 
primary propuls ion  system is composed of two s o l i d  rocke t  mc+,rs b u i l t  
by ChemLcal Systems Divis ion  (CSD) J f  United Technologies  Corporat ion.  
The first s t a g e  (SRM-1) c o n t a i n s  2 , ,400  l b  of p r o p e l l a n t  and i s  used 
as a pe r igee  k ick  motor t o  provide  t h e  energy r equ i r ed  t o  go from low 
e a r t h  o r b i t  t o  geosynchronous o r b i t .  The second s t a g e  (SRC-2) con ta ins  
6000 l b s  of p rope l l an t  and is used as an apogee k i ck  motor t o  provide  
the  energy t o  c i r c u l a r i z e  t h e  geosynchronous o r b i t .  On a t y p i c a l  s h u t t l e  
F i s s ion  t h e  IUS could p l ace  up t o  5100 l b s  i n t o  geosynchronous o r b i t .  
SRM-1 and SRM-2 were designed wi th  as much commonality as p r a c t i c a l  
t o  improve r e l i a b i l i C y  and minimize cos t .  Common items inc lude  case 
material and s t r e n g t h  l e v e l ,  i n s u l a t i o n  and l i n e r  ma te r i a l ,  nozz le  
material, t h r u s t  vec to r  c o n t r o l ,  t h r u s t  v e c t o r  c o n t r o l  a c t u a t o r s ,  
i g n i t i o n  system, f l e x i b l e  j o i n t  concept ,  and i d e n t i c a l  manufacturing 
procedures and techniques.  
The f l e x i b l e  j o i n t  concept (Techro l l  s e a l )  was developed t o  permit  
t he  use of a low-weig' e lec t romechanica l  a c t u s t i o n  system a s  requi red  
by the  s t r i n g e n t  use parameters  i n  t h e  s h u t t l e  program. The movable 
Techro l l  s e a l  is a cons t an t  volume, f l u i d - f i l l e d  bear ing  us ing  a s e a l  
configured with two r o l l i n g  convolu tes  which permit  omniaxial  d e f l e c t i o n  
o f  t h e  nozz le  assembly. The Techro l l  s e a l  c o n s i s t s  of two l a y e r s  of 
KevLir-24 f a b r i c  layered  between two sheets of neoprene rubber wi th  
s t ee l  cab le  bends f o r  s e a l  r e t e n t i o n .  One l a y e r  of t he  Kelvar-29 f a b r i c  
is s u f f i c i e n t  f o r  load ca r ry ing .  The second l a y e r  is redundant f o r  e x t r a  
xv- 2 
s a f e t y  . 
Typica l  o p e r a t i n g  temperature  f o r  t h e  motors ranges from 45'F t o  
82'F. These temperatures  are maintained a t  t h i s  l e v e l  by i n s u l a t i o n  
and hea te r s .  However, p r i o r  t o  use  t h e  motors are ex -osed  t o  o t h e r  
temperatures  i n  va r ious  t r a n s p o r t e t i o n  sequences.  
A Tracking and Data Relay S a t e l l i t e  (TDRS) launched from Space 
S h u t t l e  6 f a i l e d  t o  reach geosynchronous o r b i t .  The ensuing  i n v e s t i g a t i o n  
concluded t h a t  t h e  sa te l l i te  went o u t  of  c o n t r o l  due t o  t h e  f a i l u r e  of t h e  
Techrc l l  seal. This  s tudy  w a s  conducted to  i d e n t i f y  p o s s i b l e  f a i l u r e  
modes f o r  t h e  f l e x i b l e  j o i n t .  S p e c i f i c  materials p r o p e r t i e s  were de te r -  
mined r e g a r d l e s s  of p r o b a b i l i t y  of t h e  Techro l l  seal system being exposed 
t o  e x a c t l y  t h e  same phys ica l  varameters. 
Material Evalua t ion  
S e v e r a l t e s t s w e r e  canducted t o  determine p o s s i b l e  f a i l u r e  modes 
of t h e  composite Techro l l  s e a l  ma te r i a l .  These tests included:  
a .  S t r eng th  ve r sus  temperature  
Tes ts  were conducted u t i l i z i n g  a Model 1113 Ins t ron  Universal  
Tes t ing  machine wi th  a 5000 l b  capac i ty .  
Lrought up t o  temperature ,  he ld  f o r  f i v e  minutes,  and pu l l ed  
t o  f a i l u r e  i n  t ens ion ,  a t  a p u l l  rate of 10 inlmin.  
Specimens were 
b. S t r eng th  ve r sus  number of f a t i g u e  cyc le s  
F lexura l  f a t i g u e  c y c l e s  were obta ined  a t  room temperature  
on a MIT Folding Indurance Tes tor  p e r  ASTM D-2176-63T under 
an app l i ed  load of 1 kg. S t rength  was then determined a t  room 
temperature  by p u l l i n g  t h e  f l exed  specimens KO f a i l u r e  i n  t ens ion  
u t i l i z i n g  a Model 1113 I n s t r o n  Universa l  Tes t ing  Machine wi th  
a 5000 Lb capac i ty .  
' I ' herco~ravimet r ic  a n a l y s i s  i n  A i r  and N2 was conducted u t i l i z i n g  
the DuPont 1090 system w i t h  t h e  Model 951 TGA at tachment .  
Addi t iona l  TGAtestswere conducted i n  vacuum u t i l i z i n g  a 
Mettler Model TA-2. 
xv- 3 
d. 
e. 
f. 
R. 
h. 
Results 
TMA 
Thermomechanical analysts was conducted utilizing the DuPont 
1090 system in conjuction with the Model 943 TMA attachment. 
DSC 
Differential scanning calorimetertestswere conducted utilizing 
the DuPont 1090 system with the Model 910 DSC attachment. 
DMA 
Dynamic mechanical analysis was performed utilizing the 
DuPont 1090 system in conjunction with the Model 982 DMA 
attachment. 
Peel Test 
Bond strength of the various layers of the Techroll seal 
composite was determined utilizing the Model 1113 Instron 
Universal Testing Machine. 
SEM Evaluation 
Scanningelectronmicroscope analysis was conducted 
utilizing a Cambridge Stereoscan Model 250 MK2. 
Strength of the Techroll seal composite at various temperatures 
is shown in Fiqire 1. This data indicates the strength deteriorates 
rapidly at temperatures in excess of 200°F with only 54% of the 
original room temperature strength remaining at 5 O O O F .  
The slight increase in strength from 75°F to Z O O O F  is attributed 
to increase in ductility of the Kevlar fibers, whereby a greater load 
stinring capacity overides the decrease in individual f i b e r  strength. 
The decrease in strength of the composite material as it is subjected 
to flexure cycles is shown in Figure 2. 
with number of flexure cycles up to 1000 cycles, where the rate of 
decline in strength decreases. 
The strength decreases rapidly 
The differences in rate of strength deterioration between flat shret 
material and Techroll seal material is attributed to the difference in 
xv-4 
t he  lay-up c o c f i g u r a t i o n  and bond s t r e n g t h  between l a y e r s .  The f l a t  
s h e e t  material had 47% of  non-flexed s t r e n g t h  l e f t  a f t e r  1000 c y c l e s  
while  t h e  Techro l l  seal had 57% a f t e r  1000 cyc le s .  
Thermogravimetric a n a l y s i s  (TGA) r e s u l t s  as shown i n  F igures  3,4,5 
and Table  1 show t h a t  t h e  material is s t a b l e  over  t h e  a n t i c i p a t e d  
ope ra t ing  temperature  range. However, i f  t h e  temperature  should exceed 
75"C, t h e  neoprene begins  t o  decompose, v f t h  r ap id  decomposition occur r ing  
above 285°C. 
dependent upon environment. 
l o s s  of weight up t o  t h e  350°F range, whi le  a i r  causes  t h e  g r e a t e s t  l o s s  
of weight above t h a t  temperature .  This  lat ter weight l o s s  is a t t r i b u t e d  
t o  an ox ida t ion  process .  
The Kevlar f i b e r s  begin t o  d e t e r i o r a t e  a t  350"F, wi th  t h e  r a t e  
The vacuum environment causes  t h e  g r e a t e s t  
TMA r e s u l t s  shown i n  F igure  6 i n d i c a t e  uniEorm p r o p e r t i e s  i n  t h e  
range of -33°C up t o  100°C. 
a n t i c i p a t e d  u n t i l  decomposition temperatures  are reached The ab rup t  
change i n  t h e  s l o p e  o f  t h e  curve shown a t  -33.3"C is connected to  t h e  
Tg of t h e  system. 
No change i n  t h e s e  p r o p e r t i e s  would be 
DSC r e s u l t s  shown i n  F igure  7 i n d i c a t e  no r e a c t i o n s  i n  t h e  range 
of 0-100°C, wi th  two minor indothermic r e a c t i o n s  occur r ing  between -45OC 
and O°C, wi th  t h e  first r e a c t i o n  occur r ing  a t  t h e  Tg of  neoprene. 
DMA r e s u l t s  shown i n  F igure  8 i n d i c a t e  s t a b l e  cond i t ions  i n  t h e  
a n t i c i p a t e d  use temperature  range of 7°C up t o  28°C. No f u r t h e r  
change would be a n t i c i p a t e d  u n t i l  decomposition temperatures  are reached. 
The l a r g e  decrease  i n  E and i n c r e a s e  i n  damping capac i ty  a t  approximately 
-30°C is connected t o  t h e  Tg of t h e  system. 
Peel test r e s u l t s  shown i n  Table 2 i n d i c a t e  t h a t  bonding between 
l a y e r s  i n  t h e  composite i s  very  weak, a known problem wi th  Kevlar  
f i b e r s .  A good bond s t r e n g t h  would be i n  t h e  range of 15 l b l i n .  
xv- 5 
SEM a n a l y s i s  i n d i c a t e s  t h e  primary mode of  damage t o  t h e  f i b e r  
dur ing  f l e x u r e  is s p l i t t i n g  o f  f i b e r  i n t o  many o t h e r  f i b e r s  of  much 
smaller diameter ,  and breakage of t h e s e  sma l l e r  f i b e r s .  This  type 
of damage is shown i n  F igure  9 .  
Discussion of R e s u l t s  
The eva lua t ion  of t h e  f l e x i b l e  j o i n t  materials revea led  t h e  
fol lowing:  
a .  
b. 
C. 
d. 
The s t r e n g t h  o f  t h e  composite degrades r a p i d l y  a t  t empera tures  
above 200°F. 
The Kevlar f i b e r s  are very s u s c e p t i b l e  t o  f l e x u r a l  c y c l i c  
damage. 
Bonding rubber  t o  Kevlar ,  and Kevlar t o  Kevlar produces a 
very  weak bond which perc ludes  much load-sharing a b i l i t y  
of  t h e  system. 
Neoprene begins  t o  decompose a t  7SoC with  r a p i d  decomposition 
above 285OC i n  vacuum. This would permit  t h e  f l u i d  t o  escape  
from t h e  seal, causes  loss of  swive l  a b i l i t y  and thereby  l o s s  
of  c o n t r o l .  
The most l i k e l y  mode of f a i l u r e  of t h e  Techro l l  s e a l  would be 
excess ive  temperature  wi th  f l e x u r e  damage being a c o n t r i b u t i n g  f a c t o r .  
XV- 6 
- n 
2 
0 U
c z 
W 
t 
L 
x c 
(3 z 
W 
m 
W 
-I 
c( 
z 
W c 
E 
m 
120 
I00 
eo 
60 
- 
- 
- 
- 
0 100 200 300 400 500 
Figure 1. Per cent room temperature tensile strength retained 
versus test temperature. 
m- 7
ORIGINAL PAGE S 
OF POOR QUALITY 
A TECHROLL SEAL 
p FLAT SHEET 
41 
21 
2000 4000 6000 
NUMBER OF CYCLES 
Figure 2. Per cent unflexed tensile strength retained 
versus number of flexed cycles. 
XV- 8 
ORIGINAL PAGE Is 
OF POOR QUALIW 
140.. 
120.- 
100.. 
A 
00.- 
e 
4 z m 
e 
" 
* 88.. 
40.. 
20.- 
0 
Ootu 12-May-83 f s r r  al7e33 
Oprroton HUMILM 
T G A  
Sompln 2ND STAGE TECHROLL SEAL 
Sizes 
Rote: 20OEG/WIN 50MLA41N GN2 
a : :  z : : : : : : : : : : : : : : : : : : : .  
(6il.P.F) 
29.84 I ~ I f l O N  
*. 
e r : : : : : : : : : : : : : : : : : : : : : : +  
100 200 300 400 588 600 700 800 900 1008 1100 
Figure 3. Thermogravimetric analysis of Techroll seal material in N2 atmosphere 
xv-9 
ORIGINAL PAW II 
OF POOR QUALITY 
Figure 4. Thmnogravimetrlc analysis of Techroll seal material in a ir  atmosphere. 
xv- 10 
ORlGlNAL PAGE Is 
OF POOR QUALW 
: 40- 
- 
T G A  wmsn .WWL TA-I 
Somplat 2ND STAGE TECHROLL SEAL 
y : '  . . , Y I I  V A i  (lUn 
Figure 5 .  Thermogravirnetric analysis of Techroll seal material i n  vacuum. 
xv- 11 
ORIGINAL PAQE IN 
OF POOR QUALlW 
Figure 6. Thermomechanical analysis of Techroll seal material. 
xv- 12 
ORIGINAL PAGE 
OF POOR QUALlW 
-5.. 
~ : : . : 1 : : : : : : : : : : : : . : . . .  
a 68 86 16B B 28 -128 -168 -60 -60 -48 -2B 
Temperature <OW OuPont l0g0 
T 
Figure 7. Differential scanning calorimeter analysis of tleoprene. 
XV-13 
Figuce 8. Dynamic mechanical analysis of Techroll seal material 
XV- 14 

Temperature of Neoprene Decomposition Total 
Atmosphere first weight loss Temperature weight loss 
("0 ("C) (93 
Vacuum 75 285 57 I 
1 
Air 150 314 95 
N2 200 328 52 
- 
Table 1. Comparison of Thermalgravimetric analysis of Techroll seal 
material in different environments. 
XV- 16 
ItD D E R =  P.?EL TEST 
FLAT SHtCT PEEL STRENGTH. LES. tmcn 
0.010" RUBBER TO KEVLAR 2 . 0  
0.010~~ KEVWR TO K E V U R  4.5 
0.035" RUBBER TO KPVLAR 4.0 
T m  ROLL 
0.013" RUBBER TO KEVLAR 3.0 
" 
0.013" KEVLAR TO KEVLAR 
5 
0 - 4.0 
0.040'' RUBBER TO REV- 4.0 
m m L Y  UIIlr BONO STR- BETWEEN KEVLAR AND NEOPRENE OBSERVED 
LARGE AREAS OF Dl?LAMINATDON PRCFUUT M TRS 
Table 2. Peel strength of Techroll seal composite. 
XV-17 


An Evaluation of Techroll Seal Flexible Joint Material

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