To aid in the prediction of the dynamic behavior of the space station, a one-tenth scale dynamic test model is to be constructed of commercially available, small scale truss hardware. Tests have been performed to determine the axial stiffness characteristics and failure loads of the truss joint. A parametric study has shown that the stiffness of the joint increases as the attachment bolt torque value is increased. Furthermore, at torque values equal to or higher than 250 in-lbs, hysteresis in the load-deflection curve is essentially eliminated. Also, the joint stiffness remained relatively constant between specimens. The effective stiffness of a joint subassembly tested is 76 percent that of the strut. Tensile and compressive failure occurred in the region of the bonded plug, with lower failure loads corresponding to compressive loadings

Lake, Mark S.

Mcgowan, David M.

English

NASA Technical Reports Server

NASA Technical Memorandum 89068 
EXPERIMENTAL EVALUATION OF SMALL-SCALE ERECTABLE 
TRUSS HARDWARE 
(LASA-TIl-8906&) E X f E E I d E N I A L  EVALUATXGN CP 187-26CE5 
SFALL-SCALE E&EC!.€ABLE IFiUSS P E E E L A B E  ( N A S A )  
15 F A v a i l :  N I I 2  EC A02lBF A01 CSCL 228 
Unclas 
G3/18 OC85734 
DAVID M ,  MCGOWAN AND MARK S,  LAKE 
JUNE 1987 
NASA 
National Aeror.jutics arld 
Space Adminiwation 
Langley Research Center 
Hampton. Virginia 23665 
https://ntrs.nasa.gov/search.jsp?R=19870016652 2020-03-20T09:44:52+00:00Z
EVALIJATION OF SMALL-SCALE 
EREmABLE TRUSS "mm2 
David M. McGawan and Mark S. Lake 
NASA Langley Research Center 
Hampton, Virginia 23665 
To aid in the development of test and suspension techniques for ground testing 
of large space structures, a one-tenth scale dynamic test model of a Space 
station-size structye is to be constructed of cammercially-available, small- 
scale truss hardware . A finite element model of the test article is also 
being developed to allow for camparison between predicted and measured dynamic 
behavior. This paper swrmarizes the results of tests that have been performed 
to determine the axial stiffness characteristics and failure loads of the 
small-scale truss joints. An effective stiffness of a strut-joint cambination 
has also been determined to allow it to be properly represented in the finite 
element model. 
identification of commercial products in this report is used to describe 
adequately the test hardware. 
does not constitute official endorsement, expressed or implied, of such 
prcducts by the National Aeronautics and Space Administration. 
The identification of these commercial products 
TEST DESCRIPTION 
Test Hardware 
The truss to be constructed for the Space Station dynamic test model will be 
one-tenth scale only in bay size. ?he hardtware does not represent scaled Space 
Station hardware; however, it is functionally similar to structural concepts 
proposed for space station. 
interconnected at spherical nodes (see figure 1). The nodes are hollm aluminum 
spheres with eighteen threaded holes for strut attachment. 
bolt attached to each end by means of a bonded, interference fit aluminum plug. 
For the purpose of subsequent analysis, the inside end of this plug is 
considered to be the outer boundary of the joint. 
includes the plug, bolt and spherical node. In this study, two different types 
of specimens were tested: a joint subassembly consisting of a node with a strut 
half mounted on either side, and a segment of a strut having the same length as 
the joint subassembly. 
The truss hardware consists of aluminum struts 
They have a steel 
Therefore, the joint 
Test Set Up 
The Material Testing System ( M E )  material testing machine was used to provide 
tensile/campressive load cycling in all of the tests (see figure 2) .  The M'rs 
1. Meroform M 12: Trade name of MERo-Raumstruktur W H  & Co., Wurzbury, 
west Germany. 
2 
machine employs a hydraulic gripping system t o  hold the test specimen. 
Toaccammodate this system, the end of each strut t o  be placed in  the machine 
w a s  fitted w i t h  a solid aluminum plug, (see figure 3) .  
prevent the strut fram being crushed. Three differential current displacement 
transltucers (mls )  w e r e  mounted around the test specimens and their 
deflections averaged t o  COmpeTlsate for any bending that occurred in the 
specimens (see figwe 4 ) .  
s t r u t 4  plugs to measure to t a l  displacement of the joint  and s t r u t  ends. 
This w a s  done t o  
Mounting plates w e r e  placed two inches inside of the 
T e s t  Matrix 
Table 1 outlines the s p e c k  designations and tests performed. 
segment (specimen #1) w a s  tested f i r s t  t o  determine its stiffness and t o  
calibrate the system t o  ensure the test set-up was operating properly. 
strut w a s  cycled, quasi-statically, through tensile and campressive loads of 
approximately 200 lb. for five cycles. 
The s t ru t  
me 
After verifying the test procedure, a joint  subassembly ( s p e c k  #2) was 
loaded in tension t o  determine its failure load and thus determine a desirable 
upper load limit  for testing the remaining joints (1000 lb. was chosen). 
A parametric study was conducted on the next joint  subassembly ( s p e c k  #3) t o  
determine the effect of the attachment bolt torque value on joint  stiffness. 
To accmplish this, tests using four torque values (50 h.-lb., 150 in.-&., 
250 h - l b .  and 300 in.-lb.) w e r e  conducted. 
specimen was cycled through +/- 200 lb. for five cycles. Similarly, it was 
cycled through +/- 1000 lb. for  f ive cycles to  detennine i f  the torque value 
effects would change a t  higher loads. 
For each torque value, the 
The remaining two specinens (#4 and #5) w e r e  tested through the same  load 
cycles as spechen #3,  each a t  the torque value of 250 in.-=. 
t o  determine the stiffness variation between joints. Furthermore, each 
specimen w a s  failed t o  obtain data on the failure loads and corresponding 
failure d e s  of the joint. 
This was done 
St ru t  Stiffness 
The load-deflection curve for the s t r u t  (specimen #1) is shown in figure 5. 
E!ecause the strut segment should behave linearly, the anomaly present a t  the 
origin (change in slope) is believed t o  be due t o  a problem in the test machine 
that has not yet been determined. As expect&, the slope of the tensile and 
conpressive portions of the curve are very nearly equal, differ- only by 0.86 
5 Fram this curve, the experimentally detennined s t i f fness  is 9.37 x 10 lb. 
This is computed by multiply- the slope of the load-deflection curve by the 
test article length (16.0 in.) whiq yields the stiffness,  EA. Assmirig a 
maserial Young's modulus of 10 x 10 psi. and a cross sectional area of .0976 
in. (.868 in. outer d i p t e r ,  .0374 in. wall thickness), the predicted 
s t i f fness  is 9.76 x 10 lb. This represents a difference of only 4.16 percent 
3 
fmm the experimentally determind value, and, thus, ver i f ies  the test 
P-. 
Joint Stiffness 
The parametric study performed on specimen #3 sham that the structural 
performance of the joint does improve as the attachment bolt torque value is 
increased. As shown in the load-deflection plots in fiqures 6a and 6b, the 
hysteresis that is present in the test  conducted w i t h  50 in.-lb. of torque is 
nearly nonexistent in the test conducted w i t h  250 in.-&. of torque. 
reduction is a result of the increased pre-load in the threaded connections 
between the node and strut a t  the higher torque values. 
the origin in these curves is similar t o  that shown for specimen #1 (figure 5) 
and m y  be due to  thread play as w e l l  as the aforementioned load machine 
problem. 
This 
?he a n m l y  present a t  
Furthermorg, as shown in tab18 2 ,  the stiffness of the joint  increases fram 
1.385 x 10 lb. t o  1.846 x 10 lb. (33.3 percent increase) when the torque 
value was raised from 50 in.-&. t o  300 in.-=. Hawever, in the tests run w i t h  
the higher load l i m i t s  of +/- 1000 Ib. (see figure 7 ) ,  there w a s  a s l ight  shift 
in the zero-load deflection on eap subsequent load qcle. As seen i n  table 2, 
this sh i f t  was between 1.18 x 10- in. and 2.12 x 10- 
threads on the node, or  it may be due t o  slippage in  the bonded plug. 
in. for  the various 
?tt3mh-nt h l t  t m r m r h  r , 3 l , l n c  mL:-  -l..:c+ --.. L- ---..-I& .--I--&'-.:&-- - 
u L u - u h = A L  u u I b  LuLyuG VUAUW. AAALD ~ L L L L  iiuy u= L-UL VI Y i a s L i L i L y  i i i  
The jo in t  st iffness remained relatively constant between specimens #3, #4 and 
#5 as shuwn in table 3. 
torque value of 250 in.-&. The maximum difference between any two values is 
10.93 percent. 
is 183 percent. 
The data shown is for the +/- 200 lb. loadings w i t h  a 
The average joint  stiffness as a percentage of s t r u t  st iffness 
It is of interest to  determine the change in s t i f f n e s s  of the strut-joint 
cambination due t o  the pmsenp of the joint. mom table 3, the s t i f fness  of 
the strut (EA ) is g.937 x 10 lb., and the average s t i f f n e s s  of the joint  
(EA.) is 1.717 x 10 lb. For the joint subassembly tested L = 8.0 in. and L 
effective st iffness (EA,) results in a value of 1.162 x 10 This 
represents a 24 percent increase in stiffness over that  of the strut. 
= 6?0 in. (see figure 8 ) ,  using the follming expression (ge?. 1) for the j 
Ib. 
Joint Failures 
The joint subassemblies failed in the area of the bonded plug i n  both tension 
and compression. The plug was pulled out of the tube when loaded in tension, 
while it was forced into the tube when loaded in campression. Two specimens 
w e r e  failed in tension, and two in campression. T e n s i l e  failures OccUzTed a t  
3123.75 lb. and 2806.25 lb., and the campressive failures occurred a t  2596.25 
lb. and 2221.25 lb. 
Poisson Ratio effect. 
constricts slightly. 
The lower failure load in campression is due t o  the 
As the specimen is loaded i n  tension, the tube 
This increases the normal force acting on the bonded 
4 
plug, and increases the failure load. The opposite is true for the cmpressive 
cases. 
CONCLUSIONS 
Tests have been performed to determine the axial stiffness characteristics and 
failure loads of a small scale truss hardware joint. 
shuwn that the s t i f fness  of the joint increases as the attachment bolt torque 
value is increased. 
in.-lb., hysteresis in the load deflection cuwe is essentially eliminated. 
Also, the joint stiffness remained relatively constant between specimens. 
effective cross sectional stiffness (EA ) of the strut-joint subassembly tested 
is 124 percent that of the strut. 
the region of the bonded plug, with lower failure loads corresponding to 
compressive loadings. 
A parametric study has 
F'urthemre, at torque values equal to or higher than 250 
The 
Tensyle and campressive failure occurred in 
REFERENCE 
1. Timoshenko, S. P.; Young, D. H.: Theory of Structures. McGraw-Hill, Inc., 
1965. 
5 
TABLE 1.- SUMMARY OF "E3 PERFQFUvIED 
# 3  
JOINT 
SUBASSEMBLY 
# 4  I JOINT 
SUBRSSEMBLY 
I # 5  LZL SUBASSEMBLY 
+/- 200 LBS 
5 CYCLES 
4 TORQUES 
5 CYCLES 
250 IN-LBS 
5 CYCLES 
250 IN-LBS 
5 CYCLES 
+/- 1000 LIES 
4 TORQUES 
5 CYCLES 
250 IN-LBS 
5 CYCLES 
250 IN-LBS 
5 CYCLES 
FAIUTRE 
TENSION 
CCMPRESSION 
TENSION 
CX=MPRESSION 
6 
TABLE 2. - DEPENDENCE OF JOINT STIFFNESS ON ATTACHMEKC BOI-IT TORQUE VAUTE 
specimen #3 
TABLE 3.- STI- VARIATION BEIWEEN JOINT SPECIMENS 
s r I m 2 *  % D I F " C E  WITH % of s7rFaJT 
(lbs x 10 ) SPECIMEN: STIFFNESS 
- m 0.937 3 4 5 
SPEclMEN 3 1.698 - 6.42 4.24 18 1 
SPECIMEN 4 1.807 6.42 - 10.93 193 
SPECIMEN 5 1.629 4.24 10.93 - 174 
* Stiffness nuthers given for specimens 3,4 and 5 are the s t i f f n e s s  of 
the joint sections only of those specimens. 
* 
7 
A T T A C U M F N T  RAI T . . . . . ... . * a -  rn Y V k  m 
THREADED NODE 0 0 
BONDED PLUG 
STRUT 
- JOINT 
STRUT 
Figure 1.- Joint Subassembly 
CONTR 
ORIGINAL PAGE IS 
OF: POOR QUALITY 8 
Figure 2. - MTS Test Machine 
MOUNTING 
PLATES 
Figure 3. - Plugged Strut End 
DCD 
'EST 
T's 
SPE 
9 
Figure 4. - Test Set-Up 
10 
Load 
-.0024 0.0012 0 .0012 .0024 
Deflection (in) 
(Strut) 
Figure 5. - Load-Deflection Curve for Specime 
. 
1 6 0  
80 
Load (Ibs) 0 
-80 
- 1 6 0  
-.0024 -.OO 1 2 0 .0012 .0024 
Deflection (in) 
Figure 6a. - Load-Deflection Curve for Specimen # 3 
with 50 in-lbs Torque 
Load 
Deflection (in) 
Figure 6b. - Load-Deflection Curve for Specimen # 3 
with 250 in-lbs Torque 
11 
12 
Load 
Figure 7.- Load-Deflection Curve for Specimen + 3 
With Zero-Load Shift 
(250 in-lbs Torque) 
-.016/ 0.008 0 .008 ,016 
Deflection (in) 
b 
1 
r 
2 
1 
i 
P I 
I 
L-, 
- 
L 
Figure 8. - Definition of Length Terms 
Standard Bibliographic Page 
1. Report No. 
NASA TM-89068 
2. Government Accession No. 
~~ ~ 
7. Author(s) 
19. Security Classif.(of this report) 
Unclassified 
David M. McGowan and Mark S .  Lake 
3. Performing Organization Name and Address 
NASA Langley Research Center 
Hampton, VA 23665 
20. Security Classif.(of this page) 21. No. of Pages 22. Price 
Unclassified 14 A02 
12. Sponsoring Agency Name and Address 
National Aeronautics and Space Administration 
Washington, DC 20546 
15. Supplementary Notes 
3. Recipient’s Catalog NO. 
5. Report Date 
June 1987 
6. Performing Organization Code 
8. Performing Organization Report No. 
10. Work Unit No. 
506-43-41-02 
11. Contract or Grant No. 
13. Type of Report and Period Covered 
Technical Memorandum 
14. Sponsoring Agency Code 
16. -Abstract 
To aid in the prediction of the dynamic behavior of the Space Station, a 
one-tenth scale dynamic test model is to be constructed of commercially- 
available, small-scale truss hardware. Tests have been performed to 
determine the axial stiffness characteristics and failure loads of the truss 
joint. A parametric study has shown that the stiffness of the joint 
increases as the attachment bolt torque value is increased. Furthermore, at 
torque values equal to or higher than 250 in-lbs, hysteresis in the load- 
deflection curve is essentially eliminated. Also, the joint stiffness 
remained relatively constant between specimens. 
a joint subassembly tested is 76 percent that of the strut. 
compressive failure occurred in the region of the bonded plug, with lower 
failure loads corresponding to compressive loadings. 
The effective stiffness of 
Tensile and 
17. Key Words (Suggested by Authors(s)) 7 8 .  Distribution Statement 
Small-scale truss hardware 
Load-deflection behavior 
Stiffness 
Unclassified - Unlimited 
I 
For sale by the National Technical Information Service, Springfield, Virginia 22161 
N A S A  Langley Form 63 (June  1985) 
~~ 


Experimental evaluation of small-scale erectable truss hardware

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