Tensile strength testing device having pulley guides for exerting multiple forces on test specime

Hanson, R. N.

English

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https://ntrs.nasa.gov/search.jsp?R=19710015358 2020-03-17T02:59:56+00:00Z
Aug. 12, 1969 JAMES E. WEBB 394t609379 
A D M I N I S T R A T O R  OF T H E  N A T I O N A L  A E R O N A U T I C S  
A N D  S P A C E  A D M I N I S T R A T I O N  
G'I'H TESTING DEVICE 
INVENTOR. 
ROBERT N. HANSON 
3,460,379 U ~ t e d  States Patent O 6 c e  ,,,, ,,, , ,,,, 
1 2 
tional tensile testing machine to be used to obtain vai-ious 
3,460,379 force patterns for testing an object. 
TENSILE STRENGTH TES'JTmG DEVICE Briefly, the testing device of this invenion includes a 
James E. Webb, Administrator of the National Aeronau- fixture, and a plurality of guides in /he for111 of pulleys 
tics and Space Administration, with respect to an in- supported by the fixture. The fixtulc is positioned be- 
vention of Robert N. Nanson, Covina, Calif. tween the rams of the uniaxial tensile testing machine. 
Filed Dec. 27, 1966, Ser. No. 605,096 The test specimen is positioned betmeen the pul!eys. A 
Int. C1. GOPrn 3/28, 3/08 
U.S. en. 73-95 , flexible member, such as a cable, is connected to the ram of the testing machine. It is also connected by a clamp to 
the portion of the specimen where it is desired to apply 
the force. The pulleys act as guides for the cables. being 
ABSTRACT OF THE DISCLOSURE so positioned that they will essentizlly bend the cable 
This is a testing device that is usable with a conven- so it will apply a force in the desired direction on the 
tional uniaxial force tensile testing machine. It  converts specimen' When the tensile testing machines' rams are moved the tensile testing machine from one that produces a uni- 15 apart, they apply lension on cables and ,his 
axial force to one that exerts many forces on a test speci- will be transmitted to the test spccirrcn. ne entire Test- 
men from various selected directions. The testing device ing device is very simple, comprising generally the sin- inclndes flexible members that interconnect the rams of pie fixture, pulleys, cables, hnd clam,Js. These arc easily the tensile testing machine and the test specimen, and a fabricated. fixture carrying a number of guides. The guides position 20 
the flexible members in the it is desired to apply In line with the above, it is an object of this inven- 
the forces on the test specimen. Moving the rams of the tion to provide a testing device that can apply Eorccs from various directions on a test specimen. 
tensile testing machine apart causes the flexible members object of this invelltion is to provide a simple 
exert lorces in the desired directions On the test 2j mechanical structure that can be used in a conventional 
specimen. uniaxial force tensile testing machine to provide various 
force patterns on a test specimen. 
The invention described herein was made in the per- Another object of this invention in to grovide a test- 
formance of work under a NASA contract and is subject ing device that is simple in constru~tion, contains few 
to the provisions of Section 305 of the National Aeronau- 30 moving parts, and can be easily niodified for various 
tics and Space Act of 1958, Public Law 85-568 (72 Stat. test programs. 
435; 42 U.S.C. 2457). Other objects and advantages will appear fiom the 
This invention relates to testing devices, and more specifications and claims taken in connection with the 
particularly to a testing device that will exert forces on an drawings wherein: 
object from a number of directions so as to more realisti- 35 FIG. 1 is a view of an embodirncnt of an invention 
cally duplicate conditions the object will encounter in showing how the testing device can b-, used in a conven- 
actual use. tional tensile testing machine; 
Normally, many objects are tested in tension by a con- FIG. 2 is a sectional view of FIG. I taker? in the 
ventional tensile testing machine, This type of machine direction of arrows 11-11 showing a s-ction of the testing 
consists generally of two oppositely facing, spaced rams 40 device's fixture, clamp, and pulley; 
that carry jaws. The object to be tested in tension is usual- FIG. 3 is a sectional view of FIG. 1 taken in the dircc- 
ly made in the form of a rod or bar. Each end of the bar tion of 111-111 showing a portion of the tensile testing 
is gripped by a jaw, and the rams are then separated to machine's ram; 
place the object under tension. This provides an indication FIG. 4 is a sectional view of a porlion of FIG. 2 
of various characteristics of the object, such as yield 45 taken in the direction of arrows IV-IV showing a jaw of 
strength, or ultimate strength. It will be noted that in this the clamp, and the cable connection, and 
type of testing the object is subjected to a single uniaxial FIG. 5 is a sectional view of FIG. 4 taken in the direc- 
force. tion of arrows V-V showing a detail of the cable washes 
One of the problems in this type of testing is that it is and clamp jaws. 
not completely realistic. While these tests are very valu- Referring to FIG. 1, the testing device of the invention 
able, it is noted that few objects are subjected only to 50 is indicated generally by arrow 2. The testing device mill 
uniaxial tension. Usually an object is exposed to a num- be described as it would be used to produce biaxial forces 
ber of forces from various directions. in a relatively rectangular test specimen 4. Such a test i s  
In line with the above, it would be a distinct advantage useful to approximate conditions that an object will en- 
to be able to more realistically test an object by sub- 55 counter when used as a wall of a pressure vessel. 
jecting it to forces from more than one direction. This To  produce a biaxial force pattern 3n test specimen 4. 
would provide a more accurate indication of how it would it is necessary to apply the forces on test specimen 4, 
perform in actual use. along axes 6, 7 so the forces are at right angles to each 
To  amplify the above, it would be very useful to be able other. 
to subject a material to conditions that would approximate Testing device 2 is set up between rams 8 and 9 of a 
the forces encountered in the vessel. This would permit 60 conventional uniaxial tensile testing machine. Only the 
a more efficient design to be developed without going rams are shown since tensile testing machines arc well 
through the expense of building a pressure vessel and per- known in the art. Generally, the tensiie testing machine's 
forming an actual pressure test. It  would also be desirable upper ram 8 and lower ram 9 are vertically movable rela- 
to  learn how a flexible material, such as rubber, would tive to one another. While both will be refelred to as 
perform when stretched by forces from a number of 65 "rams" for convenience, generally only one i s  actually 
directions. made movable. 
In order to test an object before this invention, it would Referring to FIG. 1, the testing device includes a Bat, 
have been expensive and complicated to construct a de- plate-like fixture 14 positioned between rams 8 and 9. 
vice, or devices, to apply forces in various directions on Fixture 14 carries a plurality of guide means in the form 
the object. This invention, however, teaches how to con- 70 of four pulleys 16, one positioned in each corner portion 
struct a simple testing device that permits a conven- of fixture 14. Fixture 1 4  may also be plovided with vari- 
3,460,379 
3 4 
011s individual grooves or openings 24 to permit each While only a relatively simple force pattern is shown 
pulley 16 to be adjustably positioned. and described, it will be apparznt to those skilled in the 
Referring .to FIG. 2, there is shown a cross-section of art that various force patterns can be devised by posi- 
pulley I6 and. fixtures 14. Each pulley 16 includes a roller tioning any selected number of pulleys, and cables, in vari- 
ball bearing portior 26 that is carried on shaft 28. Shaft ous positions to provide selected folces in either tension 
28 is threaded at one end and extends through opening or compression on the test specimen. 
24 in fixture 14. Fastening means in the form of a nut 32 It  is noted that the test device is simple in construc- 
and washer 33, proiiided on each side of fixture 14, may tion, contains few moving parts, and enables a conven- 
be used to secure each pulley in adjusted position. tional uniaxial tensile testing machine t o  be used to pro- 
Flexible force means, including cables 34, 36, and vide forces on a test specimen from a number of direc- 
clamp me~ins 58, ate provided to transmit the force of tions. 
rams 8 and 9 to test specimen 4. Referring to FIGS. 1 and What is claimed is: 
3, the cable's center portion passes over pulley 40 that is 1. In a testing device for applying forces from more 
rotatably mounted in the bifurcated end of each ram g than one direction on a test specimen, said testing device 
(9). The free end cf each cable then passes over a guide 15 being adapted for use in a tensile testing machine that 
pulley I6 on the fixture and is connected to the adjacent has relatively movable opposed rams that apply a uni- 
clamp means 38. axial force to a test specimen, the combination com- 
An advantage in using a single cable is that it balances prising: 
the forces on both of its ends. If one cable was used for individual flexible means for connecting each of said 
each clamp means 38, it can be seen there might be a 20 rams to spaced locations on opposite sides of said 
problem in equaliziilg the forces on the test specimen due test specimen which are diagonally opposite to  one 
to slight differences in cable length that would occur. another so as to apply tensile forces to said test 
As shown in FIGS. 1 and 2, there are four clamp means specimen when said rams are relatively separated; 
38. Each clamp means 38 is connected to an end of test a fixture; and 
specimen 4 on eithi-r axis 7 or 8. Clamp means 38 has 25 guide means adjustably carried by said fixture to po- 
spaced plate-like seFrated jaws 42, 42 that engage oppo- sition each of said flexible means so that it will exert 
site surfaces of specimen 4. Each clamp means contains a force from a desired direction on said test speci- 
a plurality of bolts 44 and a spacer member 46 positioned men as determined by the placement of said guide 
between the jaws. When bolts 44 are tightened, it causes means. 
the jaws to rock about spacer member 46 and move into 30 2. A testing device, as Set forth in claim 1, wherein 
grippipg engagement with the surfaces of the test speci- said flexible means includes a plurality of cables, and 
men. each cable has its center portion adapted to be con- 
me of each :able is connected to clamp means 38 nected to a ram and its ends to be connected to said 
by washer member 40. The washer member is welded specimen. 
to the end, ,has shown in FIG. 5, washer member 3!, 3 A testing device, as Set forth in claim 2, wherein said 
48 is received in an over-size groove 50 provided in each guide means are a plurality of pulleys that can be ad- 
jaw 42. Groove 50 permits the washer to be held by each justably positioned in selected positions on said fixture 
jaw, w ~ l e  permitting the jaws to pivot up or down about SO as to rotatably guide said cables as they exert the forces 
spacer member 46. from the selected directions. 
40 4. In a testing device for converting a uniaxial force OPERATION tensile testing machine, having opposed rams for exerting 
A~~~~~~~~ eaik, 16 has been fixed in selected a uniaxial force on a test specinlen into a multiple force 
grool,e 24 in fixtLtre B4. Pulleys 16 are ar- t ende  testing machine, the combination comprising: 
idngeii on fixture 1 4  so the forces applied by cables 34, a each ram, each having its center 
36 will be applied fiom the desired direction to test 4.3 portion adapted be to its ram and its 
men 4. cable ends connected to said test specimen; 
AS Sh63M,n in F 1 ~ .  each clamp means 38 is clamped a fixture adapted to be positioned between said rams; 
by bolts 44 to an end of test specimen cable 34 will a plurality of pulleys carried by said fixture, said pul- 
be connected by the clamp means to the upper adjacent leys positioning said cable ends so they are tangent 
sides of test specimen 4, while cable 36 will be connected 50 said pulley's outer surface and directed toward 
to its lower adjacenq sides. It will be noted that test speci- the center of said test specimen; and 
men is not connected to fixture 14. It is supported in clamp means to  connect the end of each cable to said test specimen. position 'lamp lneans 38, each pulley l6 and 5. In a testing device, for converting a tensile testing 34 and 36 It  is not restrained from movement by fixture 
machine having opposed rams for a uniaxial force 14. 
Bn tile embodiment described in FIG. 1, cables s4 and into a machine for applying a biaxial force on a rela- 
36 are gPlided by p,llleys 16 so the forces applied by the tively rectang~~lar test specimen, the combination com- 
cables ate coincident with the testing axes 7 and 8 of the prising: 
lest That is, each pulley 16 is positioned so a a flat fixture adapted to be positioned be- 
line drawn from the center of test specimen 4 will be 60 tween said rms; 
to the outer surface of each pulley, and so lines a pair of cables, each cable having its center portion 
drawn through the adjacent ends of one cable will be per- adapted to be movably connected to one of said 
pendictilar to each other. rams and its ends connected to adjacent ends of said 
To place test specimen 4 under load, it is only neces- rectangular test specimen; 
sary to separate rams 8 and 9. This in turn ap- 65 a plurality of pulleys adjustably carried by said fixture, 
plies a force to the test specimen equal to  the tension said pnlleys positioning said cable ends so they are 
force in cables 34 and 36 that are connected to the vari- tangent to said pulley's outer surface and directed 
ous portions of test specimen 4. toward the center of said test specimen, and also 
The applied forca can be calculated from the tensile at right angles to each other; and 
testing machine's readings. Additionally, if desired, de- 70 clamp means to  connect the end of each cable to said 
flection can be measured with strain gauges, dial indica- test specimen. 
tors or extensometers. The measurements taken would 6. A testing device, as set forth in claim 5, wherein 
depend upon the test specimen, and parameters it is de- said fixture is provided with a plurality of grooves and 
\ired to monitor, as, for example, ultimate strength, yield a pulley is adjustably carried within a groove. 
strength or elongation. 7 6  7. In a testing device, for converting a uniaxial force 
3,460,379 
5 6 
tensile testing machine having opposed rams for exerting of each cable at right angles to its other end; and 
a uniaxial force into a machine for applying a biaxial clamp means to connect the ends of each cable to the 
force on a relatively rectangular test specimen, the com- ends of said test specimen. 
bination comprising: 
a cable for each ram, each cable having its center References Ciited 
portion movably connected to  its ram and its cable UNITED STATES 13ATENTS 
ends connected to adjacent sides of said test speci- 1,326,505 12/1919 Bull -------------- 38-102.5 
men; 
a relatively flat, rectangular fixture adapted to be po- 1,343,611 6/1920 Berger --- 73-95 X 
sitioned between said rams; 1,726,254 8/1929 Allen et a1. 69----I9 3 10 four pulleys carried by said fixture, each pulley acting CHARLES A. RUEHL, Primary Exminer 
as an individual guide for the end of each cable, 
each of said pulleys being positioned in a corner por- U.S. C1. X.R . 
tion of said fixture so their cable will be tangent 73-159 
to said pulley's outer surface and directed toward 15 
the center of said test specimen, and with the end 


Tensile strength testing device Patent

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