NASA CASE NO.

PRINT FIG.

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 143, Hampton, Virginia 23681-0001.

Serial No." 08/250,141

05/20/94 LaRC

(NASA-Case-LAR-I5003-[) INTERNALLY

DAMPED, SELF-ARRESTING VERTICAL

DROP-WEIGHT APPARATUS Patent

Application (NASA. Langley

Research CenteF) 19 p

N94-36826

Uncl3s

G3/09 0019650
NASA Case No. LAR 15003-1 

v 

INTERNALLY DAMPED, SELF-ARRESTING 

VERTICAL DROP-WEIGHT APPARATUS 

The present invention relates to an internally damped, self-arresting vertically 

dropped-weight machine for impact testing of materials and structures. Referring to 

FIG. 1, a vertical dropped-weight impact test machine according to the invention 

comprises a dropped-weight barrel secured to a support structure via upper and lower 

brackets. The dropped-weight barrel is chambered to receive a dropped-weight 

assembly including a tup. The dropped-weight assembly is provided with a damping 

unit and a spring to attenuate the shocks from the dropped-weight assembly when 

the dropped weight activates the arrestor mechanism on descent and is arrested on 

its rebound from the test specimen. A self-contained arrestor mechanism is activated 

upon downward passage of the dropped-weight assembly and the arrestor jaws 

engage slots in the dropped-weight assembly upon its rebound from the test 

specimen. 

Inventor: Damodar R. Ambur Chunchu B. Prasad 

Home address: 108 Flag Creek Road 3 10 Gardenville Drive 

Yorktown, VA 23693 Yorktown, VA 23693 

Employer: 

- 

NASA LaRC 

- 

AS&M, Inc. 

Inventor: William A. Waters Robert W. Stockum 

Home address: 665 Harris Point Drive 128 Church Street 

Virginia Beach, VA 23455 Poquoson, VA 23662 

Employer: LESC Advex Corp. 

Inventor: Manfred A. Walter 

Home address: 744 Chatsworth Drive 

Newport News, VA 23601 

Employer: Advex Corporation 

Initial Evaluator: Charles J. Camarda 

Serial No.: 081250,141 

Filed: May 20, 1994 
LAR 15003-1 -1- PATENT APPLICATION

INTERNALLY DAMPED, SELF-ARRESTING VERTICAL

DROP-WEIGHT IMPACT TEST APPARATUS

10

Origin of the Invention

The invention described herein was jointly made by a NASA employee

and by a contractor employee in the performance of work under

NAS1-19000 and is subject to the provisions of Section 305 of the National

Aeronautics and Apace Act of 1958, as amended, Public Law 85-568

(72 Stat. 435; 42 USC 2457), and contractor employees in the performance

of work under NASA Contracts NAS1-19235 and NAS1-13317 and is

subject to the provisions of 35 U.S.C. 202. In accordance with

35 U.S.C. 202, the contractors elected not to retain title.

15 Background of the Invention

Field of the Invention

2O

This invention relates in general to an impact test apparatus, and

specifically to dropped-weight testing assembly for impact testing of

composite materials and structures by vertically dropping a weight from a

predetermined height.

25

Description of the Related Art

The use of composite materials for structural applications is

increasing due to cost and weight advantages provided by composites. For

example, composite materials find applications as structural parts of

aircrafts. However, test data have shown that the compression strength of
LAR 15003-1 -2- PATENT APPLICATION

certain composite structures can be significantly reduced by low speed

impact damage, e.g., tools dropped by maintenance and assembly

personnel. Such low speed impact damage is often undetectable by visual

inspection. The sensitivity of the compression strength of composite

5 structures to low speed impact damage has led to the development of more

damage tolerant materials and to the development of special damage

tolerance design criteria for composite structures.

In order to accurately determine the effect of low speed impacts on

composite structures and materials, dropped-weight testing apparatus and

10 procedures have been developed. These apparatus and procedures call for

the dropping of a weight, of given size and material, onto a specimen from

a given height to generate a certain impact response. In general,

investigators have used either a free-fall dropped-weight or a pendulum

apparatus to impact the specimen. The present invention relates to a

15 vertical free-fall dropped-weight testing apparatus.

Currently, two types of dropped-weight machines are used by

researchers for impacting test specimens. One is a sophisticated droppedweight system for screening materials in a manual or automated manner for

damage tolerance characteristics. In such systems, the weight is typically

20 guided by two or four guide bars and hoisted by a motor operated cable

system. Thereafter, the weight is released and descends to impact the test

specimen. To prevent multiple impacts, the dropped-weight is arrested by

means of a hydraulic or pneumatically actuated system after rebounding

from the test specimen. Such machines are typically very expensive and

25 can only test small specimens.

The second type of dropped-weight test apparatus is a basic machine

where the weight is moved manually up a frame to a predetermined height

and released by pulling a locking-pin mechanism. After impact, the weight

is manually caught as it rebounds from the test specimen. Not only is such
LAR 15003-1 -3- PATENT APPLICATION

an operating procedure unsafe, but the impact location cannot be accurately

controlled, making for wide discrepancies in the accuracy of acquired test

data.

U.S. Patent No. 3,106,834 to Parstorfer discloses a high acceleration

5 impact shock testing apparatus which comprises a tester carriage slidably

constrained for movement between parallel guide members. The tester

carriage includes a specimen carrier and an impact member. A slidably

disposed rebound stop member also carried by the carriage, is laterally

deflected upon impact to frictionally engage the stop member with the guide

10 members thereby terminating movement of the carriage at the peak of its

rebound from the impact. Shock, strain or impact registering transducers

may be carried by the specimen carrier for registering suitable outputs

indicating shock, strain, impact, etc. As the specimen travels with the

impact member, the size of the specimen is limited.

15 U.S. Patent No. 3,103,116 to Kohli discloses a shock testing machine

having a brake mechanism for preventing multiple rebounds of a droppedweight assembly. The brake mechanism comprises a pneumatic brake

which is actuated by a control circuit to prevent relative movement between

the weight assembly and guide rods.

20 U.S. Patent No. 3,209,580 to Colby discloses a device for preventing

multiple rebounds of an impacting mass of a free-falling shock testing

machine. The device for preventing multiple rebounds of the impacting

mass comprises an air cylinder including a reciprocative piston.

U.S. Patent No. 4,505,362 to Layotte et al. discloses a device for

25 avoiding multiple bounces of a vertically falling mass after a first impact.

The device comprises at least one deformable element secured to a guide

and a control is adapted to press the deformable element against a lateral

wall of the mass after its bounce and to secure the latter in position.

U.S. Patent No. 2,590,486 to Aubert discloses a scleroscope having
LAR 15003-1 -4- PATENT APPLICATION

a clutching mechanism for stopping a test plunger at a maximum height of

rebound. A movable hammer plunger of a magnetic material is slidably

positioned in a guide passage. The hammer plunger is dropped from a

predetermined height onto a surface to be tested. A magnetic wedge in the

5 frame acts as a clutching or braking mechanism to stop downward

movement of the plunger after it has reached its maximum rebound height.

U.S. Patent No. 2,496,420 to Stern discloses a drop weight test

apparatus having two parallel vertical guides, a top plate at the top of the

guides, a bottom plate, a weight slidably mounted on the guides, a

10 supporting plate slidably mounted on the guides and bearing a hydraulic

velocity reducer. A specimen is mounted for testing beneath the hydraulic

velocity reducer by applying a compressive force to it. Between the

specimen and the top plate is mounted a piezoelectric strain gage. The

weight is raised to a desired height by means of a line. The line is then

15 released so that weight falls, striking the top of the hydraulic velocity

reducer. The impact is transmitted through the velocity reducer to the test

specimen and the strain gage. The shock or concussion of the impact is

absorbed by a resilient layer.

U.S. Patent No. 2,475,614 to Hoppmann, II, et al. discloses an

20 apparatus for electrically measuring strain applied in testing strength of

materials by impact testing. The testing apparatus comprises a tower

extending upwardly from an anvil to a predetermined height. A specimen

assembly comprises a hammer or tup and a weight attached to respective

opposite sides of a specimen of a material being tested, the specimen being

25 enclosed inside a spacer. The specimen is dropped from a predetermined

height in the tower and is guided by rails of the tower toward the anvil with

the weight in advance and the hammer trailing. The weight is contoured to

enter an aperture of the anvil without interference and the hammer is

contoured to extend laterally and overhang the sides of the aperture,
LAR 15003-1 -5- PATENT APPLICATION

whereby it strikes the anvil. A weight bar couples the weight to the

specimen. A series of strain gages are fastened on the sides of the bar.

U.S. Patent No. 161,737 to Beardslee discloses a testing apparatus

comprising an iron hammer mounted between two vertical rods, an anvil

5 and a hoisting/release assembly. The hammer is raised by the hoisting

assembly. A specimen is then placed on the anvil and the hammer is

released to strike the specimen.

U.S. Patent No. 3,998,090 to Wislocki discloses a dropped hammer

soil compactor including a limit mechanism used to control the distance of

10 the hammer drop. The limit mechanism includes upper and lower limit

valves. The upper limit valve is fixed, but the lower limit valve is vertically

adjustable.

U.S. Patent No. 4,640,120 to Garritano et al. discloses an impact

testing apparatus including a weighted dart which is dropped from a

15 prescribed height to penetrate a test specimen. A force transducer is

located at the tip of the dart for providing impact force information as the

tip penetrates the test specimen.

U.S. Patent No. 1,901,460 to Lewis discloses testing apparatus

adapted to test the strength of the materials by subjecting the material to

20 a number of impacts imposed by a weight dropped from predetermined

heights. A mechanical inertial switch on the impacting weight is used to

prevent multiple strikes. Upon striking the test specimen, the switch is

propelled downward allowing lifting lugs to engage a central guide rod. The

lifting rod and latch pins form a ratchet mechanism which allows motion of

25 the weight upward, but restrains any motion downward.

Summary of the Invention

Accordingly, it is an object of the present invention to provide an
LAR 15003-1 -6- PATENT APPLICATION

impact test apparatus able to cause a single accurate impact by a droppedweight on a wide variety of test specimens.

It is another object of the present invention to provide an impact test

apparatus adapted to gently secure the dropped-weight on its first rebound

5 prior to reimpacting upon the test specimen, thereby reducing strain on the

testing apparatus.

It is a further object of the present invention to provide an economical

dropped-weight impact test apparatus able to accurately deliver a single

impact upon test specimens of various sizes.

10 These and other objects are accomplished by an internally damped,

self-arresting vertical dropped-weight impact test apparatus which

comprises an elongated barrel defining a descent path, support means for

holding the barrel vertically over a specimen to be tested, a dropped-weight

assembly adapted to move vertically through the barrel along the descent

15 path, the dropped-weight assembly having an internal damping structure,

and a tup for measuring the force of the impact, at least one jaw member

adapted to engage the dropped weight assembly to arrest its movement

upon rebound, the jaw member being engageable through a slot in the

elongated barrel, and means for causing the jaw member to engage the

20 dropped-weight assembly after the dropped-weight assembly has rebounded

subsequent to impacting the specimen.

Brief Description of the Drawings

25 The present invention and the objects achieved by it will be

understood from the description herein, with reference to the accompanying

drawings, in which:

FIG. 1 is a lateral sectional view of an embodiment of the present
LAR 15003-1 -7-

invention.

FIG.

PATENT APPLICATION

2 is a lateral view of an embodiment of a dropped-weight

assembly for use in the present invention.

FIG. 3 is an exploded view of the dropped-weight assembly for use

5 in the present invention.

FIG. 4 is a lateral view of the clasp mechanism for use in the present

invention.

FIG. 5 is a perspective view of the present invention.

FIG. 6 is a perspective view of the lower portion of the present

10 invention illustrating the bounce-back arrestor mechanism.

Detailed Description of the Preferred Embodiments

FIG. 1 shows a lateral sectional view of an internally damped, self15 arresting dropped-weight test apparatus for impact testing of various

structures according to a first preferred embodiment of the invention. FIG.

1 is simplified to show only those elements necessary for understanding the

invention. The vertical dropped-weight impact test apparatus, shown

generally at 10, is rigidly supported from a support structure 8 above a tilt

20 table 6 holding a specimen 12. Various conventional means may be used

to rigidly secure the vertical dropped-weight impact test apparatus 10 to the

support structure. However, in the preferred embodiment the vertical

dropped-weight impact test apparatus 10 is held in place by a lower support

bracket 14 and an upper support bracket 18 which are bolted to the support

25 structure 8. An elongated tube is used as a dropped-weight barrel 16.

Although a variety of cross-sectional configurations and materials may be

used for the tube, a square seamless metallic tube is particularly well suited

for use as a dropped-weight barrel. A dropped-weight assembly 22 is

guided by the dropped-weight barrel 16 towards specimen 12. A bounce-
LAR 15003-1 -8- PATENT APPLICATION

back arresting mechanism 29 engages the rebounding dropped weight

assembly after the specimen has been impacted once, thereby preventing

further impacts of the specimen 12.

FIG. 2 shows the dropped-weight assembly 22 which comprises an

5 instrumented tup 42 at the lower end of the dropped-weight assembly 22,

a guide cylinder 25 connected at one end to the instrumented tup 42, and

an upper weighted area which includes a weight cylinder 23 which is

connected to the other end of the guide cylinder 25. The materials and

dimensions of the weight cylinder 23 are selected to produce the desired

10 weight to impact the specimen 12. Variations in material and dimensions

for the weight cylinder can be made in order to adjust the total weight of

the dropped-weight assembly 22 as it impacts different specimens 12.

The upper end of the dropped-weight assembly is provided with a

latch pin 50 for engagement with a latch pin coupling assembly 40 as

15 shown in FIG. 1. Guide pins 52 operate in conjunction with guide wheels

56 to insure that the dropped-weight assembly 22 maintains its orientation

within the dropped-weight barrel 16. Slots 54 are provided in the guide

cylinder 25 of the dropped-weight assembly 22 for engagement with the

bounce-back arresting mechanism 29 shown in FIG. 1 in the engaged

20 position.

FIG. 3 shows an exploded view of the dropped-weight assembly 22.

The guide cylinder 25 of the dropped-weight assembly 22 has a cavity

which receives a damping unit 58. The damping unit 58 is further

comprised of a cylinder 59 with an internal cavity filled with a gel and a

25 piston rod 61 to create a dashpot. A helical spring 60 is securely positioned

on the piston rod 61 in a preloaded condition by means of an end plate 62.

The end cap 57 serves as an adapter between the damping unit 58 and the

weight cylinder 23. The damping unit 58 acts to absorb shocks on the

dropped-weight assembly 22 resulting from its activation of the arresting
LAR 15003-1 -9- PATENT APPLICATION

mechanism 29 and when it is caught by the arresting jaws 32 on rebound

from the test specimen 12. The damping unit 58 enables the bounce-back

arresting mechanism 29 to experience smaller shock forces when the

dropped-weight assembly 22 is engaged. The damping action also prevents

5 the dropped-weight assembly 22 from rebounding against the self-arresting

mechanism 29.

The instrumented tup 42, refering to FIG. 1, is a metallic impactor

which preferably incorporates a load cell adapted for measuring contact

forces in the range from 0 to 10,000 Ibs. For example, suitable 0 to 5,000

10 lb. and 0 to 10,000 lb. force transducers with model numbers 8496-1 and

8496-2, respectively, can be obtained from Dynatup, Inc., Santa Barbara,

CA. The tup 42 is connected to a tup cable 44 for collection of data during

the testing operation. The tup cable 44 extends through slot 20 in the

dropped-weight barrel 16 and is connected to a signal conditioning amplifier

15 100. A latch pin coupling assembly 40 is releasably attached to droppedweight assembly 22 through halyard 24. A drive motor 30 operates a

halyard winch 28 to raise and lower the latch pin coupling assembly 40 via

pulley 26.

FIG. 4 shows a lateral view of the preferred embodiment of the latch

20 pin coupling assembly 40 engaging the dropped-weight assembly 22. An

enclosure 64 holds a scissors-like clasp mechanism 62. The clasp

mechanism 62 is actuable by a solenoid unit 66. An electrical cable 45 is

attached at one end to the solenoid unit 66. This cable 45 runs through the

take-up spool 46, see FIG. 1, which keeps the cable under constant tension

25 to prevent it from entangling with other components of the apparatus when

the dropped-weight assembly 22 is raised or lowered. The cable 45 is

connected at its other end to control box 68. Solenoid unit 66 is operable

to open clasp mechanism 62 thereby releasing the retaining latch pin 50 of

dropped-weight assembly 22. In the preferred embodiment, the clasp
LAR 15003-1 -10- PATENT APPLICATION

mechanism 62 is opened by the solenoid in order to release the droppedweight assembly 22 to impact a specimen 12. When it is desired to engage

the latch pin 50 in the clasping mechanism 62, the clasping operation is

accomplished mechanically by physically positioning the latch pin 50 in the

5 clasp mechanism 62.

Referring once again to FIG. 1, the dropped-weight barrel 16 is

provided with an adjustable upper limit switch 36 that determines the

maximum height of operation for the dropped-weight assembly 22.

Similarly, dropped-weight barrel 16 is provided with an adjustable lower

10 limit switch 34 that determines the minimum height of operation of the

dropped weight assembly 22. The limit switches act to shut off power to

the drive motor 30 and the solenoid unit 66, thereby ensuring that the

dropped-weight assembly 22 is not inadvertantly released. The latch pin

coupling assembly 40 is provided with a limit switch contact 38 to activate

15 the functions provided by the limit switches.

FIG. 5 shows an isometric view of the vertical dropped-weight impact

test apparatus 10 including the bounce-back arrestor mechanism 29 in its

cocked position. The bounce-back arresting mechanism 29 comprises a pair

of substantially Z-shaped arresting jaws 32. The arresting jaws 32 are

20 pivotally connected to the dropped-weight barrel 1 6 via a pair of pivot pins

31. A pair of opposed arrestor slots 21 are provided in the dropped weight

barrel 16 to receive the broad heads of arresting jaws 32. A pair of springs

37 bias the arresting jaws 32 towards slots 21.

FIG. 6 shows an isometric view of the lower portion of the vertical

25 dropped-weight impact test apparatus illustrating the bounce-back arrestor

mechanism 29. A pair of spring-loaded restraining pins 33 are connected

to a flexible plate 39 which is attached to the outside of the dropped-weight

barrel 16 such that the restraining pins 33 are biased towards the arresting

jaws 32. A cam (not shown) is in contact with and disposed behind the
LAR 15003-1 -11- PATENT APPLICATION

flexible plate 39 and extends through the dropped-weight barrel 16 such

that it minimally intrudes into the descent path of the dropped-weight

assembly 22. When the dropped-weight assembly 22 descends, it pushes

the cam outward causing the restraining pins 33 to disengage from the

5 arresting jaws 32. In the cocked position, the spring-loaded restraining pins

33 prevent the arresting jaws 32 from entering the dropped weight barrel

16 until the descending dropped-weight assembly 22 disengages the pins

33. When the spring-loaded pins disengage the arresting jaws 32, the

arresting jaws 32 are biased toward slots 21 by the helical springs 37. A

10 trigger switch 43 is in contact with the flexible plate 39, and movement of

the restraining pins 33 results in a corresponding movement of the flexible

plate to activate the trigger switch 43. The trigger switch 43 controls

power to switch 73, as shown in FIG. 5. Thus, the switch 73 that releases

the clasp mechanism 62 is rendered inoperable unless the restraining pins

15 are engaged with the cocked arresting jaws 32. The trigger switch 43 also

includes an electrical circuit that provides a triggering voltage to the data

recording unit when the restraining pins 33 are disengaged as a result of the

dropped weight assembly 22 passing the cam.

Refering again to FIG. 5, an isometric view of the vertical dropped20 weight impact test apparatus 10 coupled to a control apparatus 68 is

shown. The control apparatus 68 is powered through switch 70. The

control apparatus 68 communicates with the drive motor 30, and latch pin

coupling assembly 40, see FIG. 4. A dropped-weight positioning switch 71

on the control apparatus 68 activates a motor 30 which causes winch 28

25 to raise and lower the latch pin coupling assembly 40. The speed with

which the assembly can be raised or lowered can be selected by setting the

position of dial 72. A switch 73 is provided on the control apparatus 68 for

activating the solenoid unit 66 on clasp mechanism 62 to release the

dropped-weight assembly 22.
LAR 15003-1 -12- PATENT APPLICATION

In operation, the height of the latch pin coupling assembly 40 is

indicated by a measuring device 48. Upon raising the dropped-weight

assembly to the desired height, the arresting jaws 32 are placed in their

cocked position to engage the restraining pins with the arresting jaws 32

5 and to make the switch 73 operable. The solenoid unit 66 in the latch pin

coupling assembly 40 is then activated through switch 73 to release the

clasp mechanism 62. Dropped-weight assembly 22 then drops vertically

through the dropped-weight barrel 16 towards the specimen 12. When the

dropped-weight assembly 22 passes by the self-arresting mechanism 29 it

10 trips the cam to move the flexible plate 39 and the restraining pins and thus

release the arresting jaws 32. The arresting jaws 32 are forced toward the

dropped-weight barrel 16, through arrestor slots 21, by springs 37. After

the dropped-weight assembly 22 rebounds from specimen 12, the slots 54

on the dropped-weight assembly 22 are engaged by the arresting jaws 32.

15 The damping unit 58, in conjunction with the spring 60, acts to absorb most

of the shock from the dropped-weight assembly 22 when it trips the cam

and engages with the arresting jaws 32 and prevents it from rebounding

from the now engaged self-arresting mechanism 29. Thereafter, the vertical

dropped-weight impacting test apparatus 10 is reset by lowering the latch

20 pin coupling assembly 40 onto latch pin 50 of dropped-weight assembly 22.

After the clasp mechanism 62 has engaged latch pin 50, halyard winch 28

is activated to raise the dropped-weight assembly 22. Thereafter, the selfarresting mechanism 29 is once again cocked to prepare the dropped-weight

impact testing apparatus 10 for another impact test.

25 Looking once again at FIG. 1, a data collection system is shown

therein. Three data leads: a specimen data cable 108, a trigger data cable

110, and tup cable 44 are used to control and monitor all data output of the

vertical dropped-weight impact test apparatus 10. A signal conditioning

amplifier 100 receives data from the tup cable 44 and the specimen data
LAR 15003-1 -13- PATENT APPLICATION

cable 108. The signal conditioning amplifier 100 amplifies the signals which

are then recorded on a digital storage oscilloscope 102. A data storage

system 104 and a computer 106 operate to store and process the data from

the specimen data cable 108 and tup cable 44. Trigger data cable 110

5 feeds to the data storage oscilloscope 102.

Numerous modifications and adaptations of the present invention will

be apparent to those skilled in the art. Thus, the following claims and their

equivalents are intended to cover all such modifications and adaptations

which fall within the true spirit and scope of the present invention.

10 WHAT IS CLAIMED IS:

65535
LAR 15003-1 PATENT APPLICATION

INTERNALLY DAMPED, SELF-ARRESTING VERTICAL

DROP-WEIGHT IMPACT TEST APPARATUS

Abstract of the Disclosure

5

10

15

A vertical dropped-weight impact test machine has a dropped-weight

barrel vertically supported on upper and lower support brackets. The

dropped-weight barrel is chambered to receive a dropped-weight assembly

having a latch pin at its upper end, a damping unit in the middle, and a tup

at its lower end. The tup is adapted for gathering data during impact

testing. The latch pin releasably engages a latch pin coupling assembly.

The latch pin coupling assembly is attached to a winch via a halyard for

raising and lowering the dropped-weight assembly. The lower end of the

dropped-weight barrel is provided with a bounce-back arresting mechanism

which is activated by the descending passage of the dropped-weight

assembly. After striking the specimen, the dropped-weight assembly

rebounds vertically and is caught by the bounce-back arresting mechanism.

The damping unit of the dropped-weight assembly serves to dissipate

energy from the rebounding dropped-weight assembly and prevents the

dropped-weight assembly from rebounding from the self-arresting

mechanism.
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