NASA CASE NO. LAR 15212-1CU

PRINT FIG. _L_

NOZJCE

The invention disclosed in this document resulted from research in aeronautical and

space activities performed under programs of the National Aeronautics and Space

Administration. The invention is owned by NASA and is, therefore, available for

licensing in accordance with the NASA Patent Licensing Regulation (14 Code of

Federal Regulations 1245.2).

To encourage commercial utilization of NASA-owned inventions, it is NASA policy to

grant licenses to commercial concerns. Although NASA encourages nonexclusive

licensing to promote competition and achieve the widest possible utilization, NASA

will provide the necessary incentive to the licensee to achieve early practical

application of the invention.

Address inquiries and all applications for license for this invention to NASA Patent

Counsel, Langley Research Center, Code 212, Hampton, Virginia 23681-0001.

Serial No.: 08/306,556

09/24/94 LaRC

(NASA-Case-LAR-15212-I-CU) TEST

FIXTURE FOR DETERMINATION OF ENERGY

ABSORBING CAPABILITIES OF COMPOSITE

MATERIALS Patent Application

(NASA. Ldng|ey Res()aFch Center)

17 p

G3/24

N95-21008

Unc|as

00_9295

/

/ / _/
NASA Case No. LAR 1521 2-1 -CU 

AWARDS ABSTRACT 

TEST FIXTURE FOR DETERMINATION OF 

ENERGY ABSORBING CAPABILITIES OF COMPOSITE MATERIALS 

The present invention relates generally to crush testing, and more particularly to a fixture for 

supporting a elongated specimen during crush testing to determine the energy absorption 

capability of the composite material and laminate. 

The present invention provides a fixture for supporting an elongated specimen for crush 

testing. The fixture comprises a base plate, four guiding rods, a sliding plate, four support 

rods and two collars. The guiding rods connect to the base plate and extend in a direction 

substantially perpendicular to the baseplate. The sliding plate has linear bearings which 

encircle the guiding rods and enable translation of the sliding plate along the axis of each 

guiding rod. The four supporting rods mount to the base plate and also extend in a direction 

substantially perpendicular to the baseplate. Each support rod has a keyway for a wedge 

which contacts the elongated specimen and holds the specimen in place during crushing. 

Each collar lies above the sliding plate and holds a pair of support rods on their ends 

opposite the ends connected to the base plate. A spherical bearing sits on top of the sliding 

plate and transfers an applied load to the sliding plate, which moves downward and crushes 

the elongated specimen. 

Technical areas for use of this invention include crush testing of composite materials. 

Inventor: J. Andre Lavoie 

Home Address: 61 1 Clay Street # 12 

Blacksburg, Virginia 24060 

Employer: Graduate Student 

Inventor: Karen E. Jackson 

Home address: 41 Charles Parish Road 

Poauoson. Virainia 23662 

Employer: 

ss#: 

U.S. Army Vehicle Structures Directorate 

Inventor: John Morton 

Home Address: Elmhurst 

Harcourt Hill 

Oxford OX 29 AS 

England 

SS#: 

Employer: VPI&SU 

Initial Evaluator: Gary L. Farley 

Serial No.: 081306,556 

c:t....I. 09/24/94 
LAR 15212-1 -CU -1 - PATENT APPLICATION

TEST FIXTURE FOR DETERMINATION OF

ENERGY ABSORBING CAPABILITIES OF COMPOSITE MATERIALS

10

Origin of the Invention

The invention described herein was jointly made by a graduate student,

a NASA employee and a grantee employee during the performance of work

under NASA Grant NAG-I-343. In accordance with 35 U.S.C. 202, the

grabtee elected not to retain title.

Background of the Invention

1. Field of the Invention

15 The invention relates generally to crush testing, and more particularly

to a fixture for supporting an elongated specimen during crush testing.

2. Related Art of the Invention

20 One of the goals of manufacturers of rotorcraft and light, fixed wing

aircraft is to design crashworthy structures, i.e., structures which protect

their occupants against injury and which also minimize damage to

equipment in the event of a crash. Designing for crashworthiness requires

a total systems approach which means each part of the structure should

25 dissipate a portion of the energy from a crash. Accordingly, manufacturers

of rotorcraft and light fixed wing aircraft need test methods for studying the

energy-absorbing capability of materials used to construct rotorcraft and

aircraft. Typically, these materials are lightweight, high-strength composite

materials.
LAR 15212-1 -CU -2- PATENT APPLICATION

Examples of related methods for determining the energy-absorbing

potential of composite materials includes the tube crushing method. The

tube crushing method involves the fabrication of a cylindrical tube which

has a trigger mechanism machined on one end to serve as a site for

5 crushing initiation. A compressive load is applied until the desired stroke is

obtained. The energy absorbed in the tube crushing process is the area

under the load deflection curve. Shortcomings of the tube crushing method

include: (1) tubes are expensive to fabricate and difficult to manufacture in

a reliable manner especially when using a hand-layup technique; (2) the

10 energy absorption values measured from tube crushing tests are idealized

because of the self-stabilizing nature of the tube structure, and (3) tubes are

not practical structural elements for realistic designs of aircraft subfloors,

making the data obtained from tube tests inapplicable to structural designs

which incorporate plates.

15 Another example of a test fixture for composite plates comprises four

vertical rods fixed at one end in a steel base plate. The four rods provide

lateral support for an elongate specimen and also serve as a guide for

motion of a sliding plate. A compressive load is applied to the sliding plate,

which in turn applies a crushing load to the specimen. Shortcomings of this

20 method include global buckling, binding of the support rods with the sliding

plate, and inaccurate test data because the frictional loads between the

support rods and the sliding plate are a major fraction of the measured load.

Other related art includes U.S. Patent No. 5,297,441 by Smith et aL

Smith et aL disclose an apparatus for stabilizing an elongated specimen in

25 a compression testing machine. The apparatus supports the test piece

along its lengthwise edge or edges to prevent unwanted Euler buckling, yet

the device allows sublaminate buckling to occur. The apparatus includes

grip plates which are mounted to the test machine and which engage a

portion of the elongated specimen while the remainder of the specimen is
LAR 15212-1 -CU -3- PATENT APPLICATION

supported along its lengthwise edges by its stabilizing plates. Shortcomings

of this art include: (1) limited range of deformation, which is insufficient

for obtaining energy absorption data, (2) capability of testing only one size

of an elongated specimen, and (3) an elaborate design which does not

allow for crushed debris to escape.

Summary of the Invention

Accordingly, an object of the present invention is to perform crush

10 tests on flat plate or elongated specimens. Another object is to allow

crush testing of specimens of different sizes.

Another object is to promote crushing rather than global buckling of

compressively-loaded plates.

Another object of the invention is to examine the effect of alternate

15 trigger mechanism geometries, used to initiate crushing, on crushing

characteristics.

Yet another object is to enable crush testing with dynamic loads.

The present invention obtains the foregoing and additional objects by

providing a fixture for supporting an elongated specimen for crush testing.

20 The fixture comprises a base plate, four guiding rods, a sliding plate, four

support rods, a spherical bearing and two collars. The guiding rods connect

to the base plate and extend in a direction substantially perpendicular to the

base plate. The sliding plate has four linear bearings which encircle the

guiding rods and enable translation of the sliding plate along the axis of the

25 guiding rods. The four supporting rods mount to the base plate and also

extend in a direction substantially perpendicular to the base plate. Each

support rod has a keyway which receives a wedge. Each wedge contacts

the elongated specimen and holds the specimen in place. The wedge is

adjustable to accommodate specimens of different thicknesses. Each collar
LAR 15212-1 -CU -4- PATENT APPLICATION

lies above the sliding plate and holds a pair of support rods on their ends

opposite the ends connected to the base plate. A spherical bearing sits in

a centering dimple on top of the sliding plate and transfers an applied load

to the sliding plate while eliminating the possibility of applied bending

moments. The sliding plate then moves downward and crushes the

elongated specimen.

Brief Description of the Drawings

10 For a more complete understanding of the present invention and for

further objects and advantages thereof, reference is now made to the

following description taken in conjunction with the accompanying drawings

in which:

FIG. 1 is a perspective view of a test fixture for supporting an

15 elongated specimen during crush testing in accordance with the present

invention;

FIG. 2 is a top view of a base plate in accordance with the present

invention;

FIG. 3 is a top view of a sliding plate in accordance with the present

20 invention;

FIGS. 4 and 5 are overhead views of supporting rods with wedges

in accordance with the present invention;

FIGS. 6A and 6B are top views of two collars in accordance with the

present invention; and

25 FIG. 7 is a perspective view of the test fixture placed under a loading

machine just before crush testing in accordance with the present invention.
LAR 15212-1-CU -5- PATENT APPLICATION

Detailed Description of the Invention

Referring now to FIGS. 1-3, a fixture for supporting an elongated

5 specimen for crush testing, shown generally as reference numeral 100,

comprises a base plate 110, four guiding rods 130, 132, 134, and 136, a

sliding plate 150, four supporting rods 170, 172, 174 and 176, two

supporting rod collars 190 and 196, and a spherical bearing 210. The base

plate 110 has two sets of four circular holes machined to receive and

20 support the four guiding rods and the four support rods. The circular holes

112, 114, 116 and 118 for the guiding rods are each located near a

different corner of the plate 110. The guiding rods 130, 132, 134 and 136

fixedly attach to the plate within the holes 112, 114, 116, and 118,

respectively, located in the corners of the base plate 110 and extend in a

15 direction substantially perpendicular to the plate.

The supporting rods 170, 172, 174 and 176 fixedly attach to the

plate 110 within the holes 122a, 124a, 126a and 128a, respectively,

located within the middle of the base plate 110. Alternatively, the

supporting rods 170, 172, 174 and 176 may fixedly attach to the plate 110

20 within the holes 122b, 124b, 126b, and 128b, respectively. The position

of the holes for receiving the supporting rods depends on the size of the

elongated specimen 50. Varying the dimensions of the specimen enables

one to study the effects of specimen size on energy-absorbing capabilities.

The holes for the supporting rods 122a-128a and 122b-128b shown in FIG.

25 2 are for a 2 x 3 specimen and a 4 x 6 specimen, respectively.

The base plate 110 may have an additional pair of bores 111a and

111b tapped at 90 ° angles from each hole 112-118 for receiving the guiding

rods. The bores 11 la and 11 lb each receive a setting screw for securing

the guide rod into its upright position. Each guide rod accordingly has two
LAR 15212-1 -CU -6- PATENT APPLICATION

small indentations to receive the two setting screws. The guiding rods, the

supporting rods, and the base plate may be made of steel.

The sliding plate 150 is preferably rectangular and similar in size to

the base plate 110. The sliding plate 150 has two sets of pass-through

5 holes. One set of four holes 152, 154, 156 and 158 is for receiving the

four guiding rods, while the second set of four holes 162a, 164a, 166a,

168a, or 162b, 164b, 166b and 168b, is for receiving the support rods. As

with the base plate, the set of holes 152-158 for the guiding rods are

located near a different corner of the sliding plate 150. The position of the

10 set of holes for the supporting rods depends on the size of the elongated

specimen. The two sets of holes for the supporting rods, 162a-168a and

162b-168b, shown in FIG. 3 are for a 2 x 3 specimen and a 4 x 6

specimen, respectively. The holes 162a-168a or 162b-168b in the sliding

plate for the support rods are not completely circular but instead have a

15 semi-circular notch in opposite facing directions along the inner portion of

the plate 150 near where the elongated specimen 50 is located. The sliding

plate 150 also has a dimple 160 for centering the load transferred to the

sliding plate. The sliding plate may be made of steel.

Referring to FIGS. 1 and 3, the sliding plate 150 includes four linear

20 bearings 151, 153, 155 and 157 which fit within the holes 152-158,

respectively. Each linear bearing 151-157 is a ball bushing which encircles

a different guiding rod 130-136, respectively, and enables nearly frictionless

travel of the sliding plate along the guiding rods.

Referring now to FIGS. 4 and 5, each supporting rod 170, 172, 174

25 and 176 has a keyway 171, 173, 175 and 177, respectively, notched along

the axis of the rod. Four wedges 180, 182, 184and 186each having a

knife-edge fit within a different keyway of each support rod. The wedges

180-186 extend from the support rod and contact the elongated specimen

50 to stabilize the specimen during crushing. The wedges are adjustable to
LAR 15212-1 -CU -7- PATENT APPLICATION

accommodate specimens of different thicknesses.

FIGS. 6A and 6B illustrate the collars 190 and 196 each having a pair

of holes 191, 193 and 197, 199, respectively, for receiving the other end

of the supporting rods. The collars 190 and 196 also each have a semi5 circular notch 192 and 198, respectively, for receiving the spherical bearing.

The collars may be made of steel.

Referring now to FIGS. 1, 3, 6A and 6B, the collars 190 and 196

each lie above the sliding plate 150 and attach to a different pair of

supporting rods. The direction in which each collar attaches to the pair of

10 supporting rods is substantially perpendicular to the direction in which the

elongated specimen extends. The collars 190 and 196 ensure that the

elongated specimen is supported along its entire length by controlling any

spreading of the supporting rods which may occur during crushing. The

collars also ensure the supporting rods do not contact the sliding plate.

15 The spherical bearing 210, which may be made of steel, sits on top

of the sliding plate in the dimple 160 and between the two semi-circular

notches 192 and 198 of the collars. The spherical bearing receives an

applied load and eliminates any bending moments by providing a point load

to the sliding plate.

20 The novel features of this invention include an outer set of guiding

rods whose only function is to guide the sliding plate and linear bearings

which provide nearly frictionless travel along the guiding rods. Other novel

features include supporting rods which have no contact with the sliding

plate, wedges which fit into the keyways of the supporting rods, and a

25 spherical bearing to receive the applied load.

The advantages of the present invention include the capability of

testing different sizes of specimens with the same test fixture, no

interference of the fixture with the load measurements, no interference of

the support rods with the free travel of the sliding plate, adjustable wedges
LAR 15212-1 -CU -8- PATENT APPLICATION

which accommodate elongated specimens having slightly different

thicknesses, reduction in the likelihood of global buckling, and lower costs

of fabrication of materials to perform crush testing. Another advantage

includes the capability of this fixture to be used for dynamic loading.

Operation of the Invention

As illustrated in FIG. 7, the procedure for conducting a crush test

with the fixture 100 includes the following steps: 1) center the elongated

10 specimen between the support rods; 2) obtain line support along the

elongated specimen by using set screws to adjust the wedges; 3) engage

the sliding plate with the guiding rods; 4) install the collars over the other

end of the supporting rods; 5) place the spherical bearing on the centering

dimple located on the sliding plate; 6) position a loading rod of a loading

15 machine over the spherical bearing; 7) set the testing machine to the proper

cross-head displacement rate and begin loading; and, 8) stop the test when

the desired displacement or stroke is achieved.

Although the invention has been described relative to a specific

embodiment thereof, there are numerous variations and modifications that

20 will be readily apparent to those skilled in the art in the light of the above

teachings. It is therefore to be understood that, within the scope of the

appended claims, the invention may be practiced other than as specifically

described.

What is claimed as new and desired to be secured by Letters Patent

25 of the United States is:
LAR 15212-1 -CU _ PATENT APPLICATION

TEST FIXTUREFOR DETERMINATIONOF

ENERGYABSORBINGCAPABILITIES OF COMPOSITE MATERIALS

10

15

Abstract of the Invention

The present invention provides a fixture for supporting an elongated

specimen for crush testing. The fixture comprises a base plate, four guiding

rods, a sliding plate, four support rods and two collars. The guiding rods

connect to the base plate and extend in a direction substantially

perpendicular to the base plate. The sliding plate has linear bearings which

encircle the guiding rods and enable translation of the sliding plate along the

axis of each guiding rod. The four supporting rods mount to the base plate

and also extend in a direction substantially perpendicular to the base plate.

Each support rod has a keyway for a wedge which contacts the elongated

specimen and holds the specimen in place during crushing. Each collar lies

above the sliding plate and holds a pair of support rods on their ends

opposite the ends connected to the base plate. A spherical bearing sits on

top of the sliding plate and transfers an applied load to the sliding plate,

which moves downward and crushes the elongated specimen.
i

155

134

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i

153

196

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210

76

136

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151

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150

190

130

170

5O

172

FIG. 1
118

128B

128A __

126A-_ I_

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116

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124A

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___ 114

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FIG. 2
157

158_

168B

168A_

166A_

166B ---_..

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162A

164A

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154

153

FIG. 3
171

170

FIG. 4

176 170

175

172

FIG. 5
193

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FIG. 6A 192

190

191

199

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196

197

FIG. 6B

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FIG. "7