Results of tensile, shear, fatigue and accelerated weathering tests are presented for the ram fastener, a reusable, single unit blind rivet. The effects of variations in hole size, grip length and sheet thickness on strength properties of the fastener were determined. The test results show these fasteners to have strength characteristics suitable for light structural applications. Exposure to accelerated weathering did not impair their performance

Dewalt, W. J.

English

NASA Technical Reports Server

"THE: ALCOA RAM .FASTENER - A REUSABLX BLIND RIVET" 
- 5  W. J. Dewalt 
' I  
Presented at the Symposium on Welding, Bonding 
and Fastening at Williamsburg, Virginia, on 
May 30 - June 1, 1972 
Alcoa Research Laboratories 
Aluminum Company of Ame'rica 
New Kensington, Pennsylvania 
J u l y  26, 1972 
https://ntrs.nasa.gov/search.jsp?R=19740022843 2020-03-17T15:11:22+00:00Z
."TE5 ALCOA RAM FASTENER - A REUSABLE ELIND FiIVF-" 
: ABSTRACT 
Results of tensile, shear, fatigue and accelerated 
weathering tests are presented f o r  the Alcoa Ran Fastener, a 
reusable, single-unit blind rivet. The effects of -7ariations 
in hole size, grip length and sheet thickness on strength 
properties of  the fastener were determined. 
show these fasteners to have strength characteristics suitable 
f o r  light structural applications. 
weathering did not impair their performance. 
I 
The test results 
Exposure to accelerated 
i 
"THE ALCOA RAM FASTENER - A REUSABLL; BLIND RIVE?* '  
,., -,- 
F ,  
I. In t roduc t ion  
The Alcoa R& Fas tene r  i s  a dr ive-pin o r  push-stem 
t y p e  of b l i n d  r i v e t  c o n s i s t i n g  of a nylon p l a s t i c  jacket and 
an  aluminum a l l o y  locking stem. 
t h i s  f a s t e n e r  i s  t h a t ,  a f t e r  being i n s t a l l e d ,  i t  can be e a s i l y  
removed w i t h  s i m p l e  tools. 
One outs tanding  f e a t u r e  of 
Another f e a t u r e ,  which i s  unique, 
i s  t h a t  i t  can be used over  and over aga in .  The f a s t e n e r ,  
t h e r e f o r e ,  should be idea l  f o r  a p p l i c a t i o n s  where f r equen t  
disassembly and reassembly of a u n i t  are necessary,  bu t  where 
h igh  s t r u c t u r a l  s t r e n g t h  i s  not  a requirement.  
This paper describes t h e  Alcoa Ram Fas t ene r  and 
recommends i n s t a l l a t i o n  procedures.  
d a t a  t o  ass is t  deslgners i n  t h e  cons ide ra t ion  and eva lua t ion  
It also provides  engineer ing  
1 
' o f  t h i s  fastener. Resu l t s  of t ens i l e ,  shear and f a t i g u e  tes ts  
of j o i n t s  a r e  shown. 
of acce le ra t ed  weathering t e s t s  an t h e  performance of t h e  f a s t e n e r .  
Data are also presented an t h e  e f f e c t s  
11. Descr ip t ion  of Fas tener  
Figure 1 shows t h e  two components of the  Alcoa Ram 
Fastener:  
The stem i s  made of aluminum a l l o y  2024-T4, a high-strength 
a l l o y  commonly used f o r  threaded fasteners. 
made of Dupont Z y t e l  71G, a 33% g l a s s  r e in fo rced  nylon. 
The aluminum locking  stem and t h e  nylon jacket .  
The j a c k e t  I s  
Figure 1 shows t h e  Alcoa Ram Fas tener  In both t h e  "open" and 
-2- 
" ins t a l l ed"  p o s i t i o n s .  It i s  supp l i ed  t o  t h e  u s e r  w i t k  '.he 
stem and j a c k e t  assembled, i n  t h e  open p o s i t i o n .  A t  . t h i s  
p o i n t  i t  i s .  a s i n g l e - u n i t  b l i n d  r i v e t ;  t h e  stem and jacket  
cannot b e  s e p a r a t e d  wi thout  d e s t r o y i n g  one o r  t h e  o t h e r .  I n  
t h e  open p o s i t i o n  t h e  f a s t e n e r  i s  e i the r  ready f o r  i n s t e l l a t i o n  
o r ,  a f t e r  i t  has been i n s t a l l e d ,  ready f o r  removal from t h e  . 
workpiece. ' .  
Figure  1 shows s e v e r a l  a d d i t i o n a l  f e a t u r e s  of t h e  
Alcoa Ram F a s t e n e r .  The contour8 of t h e  s p l i t  o r  expansion end  
of the  j a c k e t ,  and t h e  bulb  machined on t h e  end of  t k e  stem, 
are designed t o  f a c i l i t a t e  i n s e r t i o n  i n t o  t h e  h o l e .  After 
t h e  f a s t e n e r  i s  p l aced  i n  a h o l e ,  i t  i s  d r i v e n  by push1r.g t he  
stem w i . t h  e i ther  thumb p r e s s u r e  o r  a hammer. 
the d i s c  on the  head of the  stem i s  seated i n  a r e c e s s  r-olded 
i n  t h e  head of the  jacke t ,  and t h e  s lo t t ed  end o f  t he  j a c k e t  has 
been expanded t o  form t h e  b l i n d  head. 
I n  t h i s  p G s i t i o n  
3 
The purpose of  t h e  d i s c  
on the 's tem is  t o  remove t h e  f a s t e n e r  from i t s  I n s t a l l e d  p o s i t i o n .  
The groove molded i n t o  the  head o f  the  jacke t  p r o v i c e s  a c c e s s  f o r  
a p l i e r - l i k e  t o o l  ( o r  even a small sc rewdr ive r )  t o  grasp the  d i s c  
and pull t h e  stem u n t i l  t h e  f a s t e n e r  i s  i n  t h e  open p o s i t i o n .  
The f a s t e n e r  can now be removed, i n t a c t  and ready f o r  r e u s e ,  s i n c e  
w i t h  a s l i g h t  t i m e  .delay the  nylon jacket  r ecove r s  its i n i t i a l  
shape. 
Currant  p roduc t ion  of the Alcoa Ram F a s t e n e r  i s  
confined t o  two diameters, 3/16 and 1/4-in. ,  and, for bo th  
s i z e s ,  l e n g t h s  t o  accommodate g r i p s  ranging  from 0..100 t o  
-3- 
0.503 i n . ,  Tn i r c r e n e r t s  sr' 0.050-in. 
i t  i s  recozmende5 t h a t  e "rstener made : 3  accrrziodate a 
noz ina l  g i p  thicl>:ness te :sed i n  j o i n t  :hic%zcsses  w i t k L z  
- + 0.025 i n .  of t k e  norr.ir.al va lue .  For  t ? e  t e s t s  d e s c r i b e ?  
h e r e i n ,  f a s t e n e r s  d e s i g x e t  nor g r i p  t h i c h e s s z s  considere:  as 
shoFt  (0 .150  i n . ) ,  m e d i T i m  IO.350 i n . )  ar.2 10r.g (0.600 i K . )  
were used. 
.;s i f i Z c z t e d  i n  F'g. I, 
n i h e  sugges ted  01' "recommended" h o l e  2 i a n e t e r s  f z r  
t h e  Alcoa Ram FasteneTs ET'?: 0.187 t o  C.192 iz. f o r  t h e  3/16-in. 
s i z e  and 0 .250  t c  0.255 ir.. f o r  t h e  1/4-'n. sLze.  The 1 r . F t i a l  
development work end evalLEtions i n d i c a t a d  t k z f  best over s11  
performance, f ro -  t h e  s t e c l g o i n t s  of c h z p i n g  a c t i o n  and s t r e n g t h ,  
was ob ta ined  when these h o l e  sizes were x e d .  
of ho le  diameter 3n t e n s i l t  and shear s t r e n g t h ,  tes'ts were made 
w i t h  "oversize1'  k o l e s  , m r ' n a l l y  O.OlO-ir,. lzrger t h a n  t k e  
To show t k ?  effect 
I 
f a s t e n e r  nominal diameter. Actual. d i a n e z e r s  o f  t h e  o v e r s i z e  
ho le s  were from 0 .197  t o  0 .202  i n .  f o r  t k e  3/16-in. s i z e  2nd 
0.260 t o  0.265 ir.. f o r  t h e  1/4-in. size. 
111. Engineering Proper:ies 
F igu re  2 i l l u s t r s t e s  some t y p e s  of e g p l i c a t l o n s  
envis ioned  f o r  tk3 A l c o a  ~ L Z I  F a s t e n e r .  Gxite  o f t e n  there is  a 
s t r e n g t h  requireKent  at';er,lant t o  such a c g l i c s 2 i o n s .  The tests 
conducted a t  the  Alcoa ?;.tsigrch Laborato-Fes ;:'ere made t o  3 r o v i d e  
basic in fo rma t ion  t h a t  x o u l d  be  h e l p f u l  :3  a n  eng inee r  o r  
des igne r .  . 
The r e s u l t s  of t e s t s  t o  de te rmine  t h e  t e n s i l e  l oad  
c a r r y i n g  capac i ty  of 3/16 and 1/4-in.  diameter Alcoa .Ram 
F a s t e n e r s  a r e  summarized i n  F i g s .  3, 4 and 5.  A t  least  
f i v e  t e s t s  were made f o r  each t e s t  c o n d i t i o n  p l o t t e d  i n  these  
f i g u r e s .  I n  a l l  of t he  t e n s i l e  t es t s  f a i l u r e  occurred  i n  t h e  
nylon j a c k e t ,  no t  i n  t h e  aluminum stem. Two k inds  of f a i l u r e s  
occurred.  I n  some cases  t h e  expanded, s l o t t e d  end of t h e  nylon 
I 
j a c k e t  was sheared o f f  by t h e  t e s t  f i x t u r e .  I n  o t h e r  cases  
t h e  f a i l u r e  was a t  t h e  j u n c t u r e  of t h e  head and t h e  body of 
t h e  j a c k e t .  
The r e s u l t s  p l o t t e d  i n  F ig .  3 are  f o r  t e n s i l e  t es t s  
made us ing  recommended h o l e  d i ame te r s .  The average  t e n s i l e  
breaking  l o a d s  f o r  t h e  3/16 and 1/4-in. diameter Alcoa R a m  
F a s t e n e r s  were about 100  l b  and 180 lb, r e s p e c t i v e l y .  For 
both  d i ame te r s  t h e  f a s t e n e r s  w i t h  the s h o r t e s t  (0.150 i n . )  g r i p  
l e n g t h  gave the lowest  t e n s i l e  breaking  l o a d s .  Inc luded  i n  
the resu l t s  shown i n  F ig .  4 are  tests of f a s t e n e r s  that  were 
reused f i f t y  times be fo re  t e s t i n g .  No d i f f e r e n c e  was observed 
i n  the  s t r e n g t h  o f  t h e s e  fasteners and of  those used only’once .  
F igu res  4 and 5 compare t h e . t e n s i l e  s t r e n g t h s  of  
f a s t e n e r s  t es ted  w i t h  recommended and o v e r s i z e  h o l e s .  For 
both  s i z e s  t he  use of o v e r s i z e  holes  tended t o  dec rease  t e n s i l e  
s t r e n g t h .  The average  loss, however, was much greater f o r  the  
3/16-in. s i z e  t h a n  f o r  the  1/4-in. size, 43.1b o r  43 p e r  c e n t  
ve r sus  only 15 l b  o r  8 p e r  c e n t ,  r e s p e c t i v e l y .  
-5- . 
Resul ts  of t h e  shear t e s t s  made of Alcoa Ram Fas t ene r s  
u s i n g . s t e e 1  f i x t u r e s  are s u i q a r i z e d  i n  F i g s .  6 ,  7,  8 'and 9. N o t .  
l ess  t h a n  f i v e  tes ts  were made for each cond i t ion  shown i n  
these  f i g u r e s .  A l l  f a i l u r e s  were by shear ing  of t h e  nylon 
j a c k e t .  \!hen t h i s  occurred,  t h e  compressive clamping a c t i o n  
was r e l eased  and t h e  jo ined  members spread a p a r t .  There were 
no shear  f a i l u r e s  of t h e  aluminum stem. 
The shear  s t r e n g t h  r e s u l t s  shown i n  F igs .  6 and 7 were 
obtained using s t e e l  t e s t  f i x t u r e s  prepared  w i t h  recommended 
hole  diameters .  Average s ingle-shear  values  obtained at t h e  
t h r e e  g r i p  l eng ths  ranged from 185 lb to 370 lb f o r  t h e  
3/16-in. s i z e  and from 265 l b  t o  560 l b  f o r  t h e  1/4-in. s i z e  
f a s t e n e r .  The wide var iance  i n  s ing le-shear  s t r e n g t h s  f o r  b o t h  
s izes  i s  the  r e s u l t  of  having t o  use d i f f e r e n t  t h i cknesses  of 
p l a t e  f o r  t h e  d i f f e r e n t  f a s t e n e r  g r i p  l eng ths .  F igure  7 shows 
t ha t  t h e  e f fec t  was no t  nea r ly  s o  d r a s t i c  In tests where t h e  
,. 
f a s t e n e r  was i n  d o u b l e  shear. 
The data p l o t t e d  i n  Figs. 9 and 10  show t ha t  over- 
s i z e  holes  a l s o  t e n d  to reduce shear s t r e n g t h  of  Alcoa R a m  
Fas t ene r s .  On t h e  average, t h e  l o s s ' f r o m  the shear s t r e n g t h  
values  obtained using recommended ho le  s i z e s  f o r  both f a s t e n e r  
diameters was about 1 0  per  cent  f o r  the 0.150-in. g r i p  length  
f a s t e n e r s  and about 20 p e r  cent  for t h e  0.600-in. g r i p  l eng th  
f a s t e n e r s .  
F a t i g u e  s t r e n g t h  data were obta ined  
specimens jo ined  w i t h  3116-in. diameter A l c o a  
?> 
5 SI  
&ing s ing le - l ap  
R a m  Fas t ene r s .  The 
specimens were made of 0.080-in. t h i c k  aluminum a l l o y  3003-Hl4 
s h e e t  and employed t h e  recommended h o l e  s i z e .  
were designed t o  accomoda te  a nominal 0.150-in. g r i p  t h i c k n e s s .  
The tes t  s e t u p  and j o i n t  dimensions are shown i n  F i g s .  
The f a s t e n e r s  
10 and 11. 
Fa t igue  t es t s  were made of t e n  specimens,  two of which were 
s u b j e c t e d  t o  500 hours  o f  cont inuous s a l t  spray  p r i o r  t o  t e s t i n g .  
The t e s t s  were made i n  a 5 k i p  Krouse f a t i g u e  t e s t i n g  machine. 
I n  these t e s t s ,  a specimen was cons idered  t o  have fa i led ,  even 
though s t i l l  i n t a c t ,  when i t  could  n o t  ma in ta in  t h e  i n i t i a l  
t e s t  l o a d  because of wear of t h e  nylon j a c k e t .  
p i o t t e d  i n  Fig. 11 show t h a t  t h e  specimens loaded t o  h a l f  t h e  
The r e s u l t s  
s t a t i c  f a i l u r e  l o a d  gave f a t i g u e  l i ves  on t h e  o r d e r  of  5 m i l l i o n  
c y c l e s .  
Research L a b o r a t o r i e s  f o r  o t h e r  t y p e s  of f a s t e n e r s  under 
similar c o n d i t i o n s  o f  t e s t .  It should  b e  no ted  t h a t  the  
exposure t o  salt  s p r a y  p r i o r  t o  t e s t i n g  had no adve r se  e f f e c t  
on f a t i g u e  s t r e n g t h .  
T h i s  compares f avorab ly  w i t h  data ob ta ined  a t  Alcoa 
Both a c c e l e r a t e d  and long-time c o r r o s i o n  t e s t  programs 
are be ing  employed t o  determine t h e  effects  of  "weathering" on 
the performance o f  Alcoa Ram F a s t e n e r s .  Fo r  t h e  a c c e l e r a t e d  
tests,  t w o  k inds  of exposures were used. 
Meter and t h e  o t h e r  a S a l t  Spray Tes t .  
exp.osures w i l l  b e  ou tdoors  for s e v e r a l  years a t  two l o c a t i o n s :  
N e w  Kensington, Pa. ( i n d u s t r i a l  a tnosphe re )  and Po in t  J u d i t h ,  R .  I. 
( seacoas t  a tmosphere) .  
One was a Weather-O- 
For  t he  long-time tests,  
-7- 
The Weather-0-Kster t e s t  c o n s i s t s  of t e n  txo -how , 
: j  
exposure c y c l e s  p e r  24-hour p e r i o d .  I n  each c y c l e  t h e  s p e c i z e n s ’  
are exposed t o  u l t r a v i o l e t  l i g h t  f c r  t h e  txo-hour pe,-iod, :.rith 
a de- ionized water spray  dur ing  the  las t  18 ziinutes.  The t e s t  
temperature  i s  a cons t an t  145*?. I n  this t e s t  i n d i v i d u a l  
f a s t e n e r s  ( i n  both  t h e  open 2r.d i n s t a l l e d  p o s i t i o n s )  and f a s t e n e r s  
i n s t a l l e d  i n  l a p  j o i n t s  o r  alur inum a l lcy  3393-Hlb skeet x e r e  
exposed f o r  t o t a l  p e r i o d s  of 10; and 500 k o w s .  After excosare  
f o r  up t o  500 hours ,  t he  ind iv26ua l  f a s t e n e r s  !:)ere i n s t a l l e d  
and removed 50 times wi thout  an:: i n d i c a t i c r .  of  f a i l u r e .  Cnlzr a 
s l i g h t  whi ten ing  of t h e  b l ack  Rglon p l a s t i c  i n d i c a t e d  soKe n i l d  
s u r f a c e  deg rada t ion ,  b u t  t h i s  h2.d no adverse  e f f e c t  on performance. 
The sa l t  sp ray  t e s t  c o n s i s t s  of a cont inuous spray 
i of 5 per c e n t  NaCl s o l u t i o n  a t  55OF f o r  500 o r  1000 hours. 
I n  t h i s  t e s t  t h e  f a s t e n e r s  were i n s t a l l e c i  i n  l a p  joints of  
e i t h e r  aluminum a l l o y  3003-Hl4 o r  paintee.  s t ee l  sheet. 
Examination of specimens a f te r  590 and 1000 hours  exposure 
revealed only m i l d  c o r r o s i v e  a t t z c k  on t k e  2024-T4 lock ing  sterns 
i n s i d e  t h e  nylon s l e e v e s ,  which :vere .unaffected.  As mentioned 
p rev ious ly ,  500 hours  exposure time had n o . a d v e r s e  e f f ec t  on t h e  
f a t i g u e  s t r e n g t h  of l a p  j o i n t s  r a d e  w t t h  alloy.3003-314 sheet. 
I V .  Summary 
The in fo rma t ion  i n  this papcr shcxs that t h e  Alcoa 
R a m  F a s t e n e r  has  ‘ s t r e n g t h  c h a r a c t e r i s t i c s  s u i t a b l e  f o r  
light s t r u c t u r a l  a p p l i c a t i o n s .  The t e n s i l e  and shear s t r e n g t h  
va lues  g iven  s h o u l d  s e r v e  as a gu ide  t o  t h e  d e s i g n e r ' f o r  h i s  
p a r t i c u l a r  s t r e n g t h  requi rements .  Qtimum s t r e n g t h s ,  as 
would b e  expected,  are obta ined  when 3 o l e  c l e a r a n c e  i s  kept  t o  
a minixum and t h e  r a t i o  of t he  f a s t e n e r  diameter t o  t h e  least 
t h i c k n e s s  of  sheet  being j o i n e d  i s  about 1. E x c e l l e n t  
r e s i s t a n c e  t o  loosening  by v i b r a t i o n  xas  demonstrated by t h e  
long f a t i g u e  l i v e s  ob ta ined  i n  t h e  lac, j o i n t s  tested a t  a 
maximum load  e q u a l  t o  ha l f  t h e  s t a t i c  s t r e n g t h .  The a c c e l e r a t e d  
c o r r o s i o n  tes t  r e s u l t s  confirmed the r e - u s a b i l i t y  f e a t u r e ,  even 
a f t e r  exposure t o  rather seve re  envi-onments. 
Fig. 1 
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EFFECT OF 
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GRlP LENGTH, IN. 
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. GRIP LENGTH, 1N. 
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GRIP LENGTH, G, IN. 
SINGLE -SHEAR STRENGTH OF ALCOA RAM FASTENERS 
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The Alcoa ram fastener: A reusable blind rivet

Abstract

Similar works

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