US3602039A

US3602039A - Multirate compression test apparatus

Info

Publication number: US3602039A
Application number: US881361A
Authority: US
Inventors: Walter H Trask; Laverne H Gillette
Original assignee: US Department of Navy
Current assignee: US Department of Navy
Priority date: 1969-12-02
Filing date: 1969-12-02
Publication date: 1971-08-31
Anticipated expiration: 1988-08-31

Abstract

A heavy duty elongate beam carrying a multiple-contoured Tshaped rib is secured to a vertical carriage to reciprocally pass through an orthogonally disposed cam follower. The cam follower includes a cam follower portion having two sets of substantially opposed needle rollers mounted on laterally extending shafts to form a T-shaped passageway. The passageway receives the rib and imparts an orthogonal reciprocating motion to an elastomer sample secured on a relatively immovable bed. Multiple compressive shocks of selectively variable duration as to period and intensity are thusly transferred to the elastomer sample. Interchangeable elongate ribs having differently contoured surfaces are passed through the cam follower to deliver compressive and tensile shocks to the elastomer sample in accordance with varying conditions.

Description

United States Patent [72] inventors Walter H. Trask Joseph, Oreg.; Laverne H. Gillette, Walnut Creek, Calif. [21] AppLNo. 881,361 [22] Filed Dec. 2, 1969 [45] Patented Aug. 31, 19711 [73] Assignee The United States oil America as represented by the Secretary of the Navy [54] MULTKRATE COMPRESSION TEST APPARATUS 6 Claims, 5 Drawing Figs.

[52] US. Cl 73/94, 73/90 [51] lint. (II GOln 3/32 [50] FieldolSearch 73/11, 12, 94, 90, 83, 91, 92, 93

[56] References Cited UNITED STATES PATENTS 2,354,562 7/1944 Webb 73/92 2,904,994 9/1959 Cloxton 73/15.6

Primary Examiner-Richard C. Queisser Assistant Examinen-Marvin Smollar Attorneys-Justin P. Dunlavey, Ervin F. Johnston and Thomas G. Keough ABSTRACT: A heavy duty elongate beam carrying a multiplecontoured T-shaped rib' is secured to a vertical carriage to reciprocally pass through an orthogonally disposed cam follower. The cam follower includes a cam follower portion having two sets of substantially opposed needle rollers mounted on laterally extending shafts to form a T-shaped passageway. The passageway receives the rib and imparts an orthogonal reciprocating motion to an elastomer sample secured on a relatively immovable bed. Multiple compressive shocks of selectively variable duration as to period and intensity are thusly transferred to the elastomer sample. Interchangeable elongate ribs having differently contoured surfaces are passed through the cam follower to deliver compressive and tensile shocks to the elastomer sample in accordance with varying conditions.

PAIENIEn AUE31 I971 3,602,089

SHEET 2 BF 2 FIG. 4

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INVENTORS WALTER H. TRASK time BY LAVERNEH. GILLETTE Thomas G. Keough E rw'n F Johns/on ATTORNEYS MUL'IIJIRATE COMPRESSION TESTAlPlP The invention described herein may be manufactured and BACKGROUND OF THE INVENTION Extensive use of synthetic elastomer suspension systems in expanding space and military applications is required for cushioning and protecting missiles and their instrumentation during transportation, storage, and launching. A characteristic phenomenon of elastomers utilized during launching operations is that a rapid double-rate compression cycle is exerted on the elastomer cushioning and lining pads. Since elastomer modulus at any given instant is a function of the deformation rate at that instant in addition to the compression history" of the pad immediately prior to the instantaneous deformation rate, the modulus is particularly complex for elastomeric materials where damping and phase angle shifts are not simple functions of velocity but depend upon nonlinear functions of displacement, velocity, and material hysteresis.

Providing a method for testing elastomers to determine whether or not they hold up after a series of rapid compression shocks is necessary to provide scientists and designers accurate information from which elastomeric suspension systems can be constructed with the minimum possibility of failure. Although well known single compressive or tensile shock simulating systems exist, they do not produce a series of shocks or shock sequences having an intermediate intensity in accordance with actual launch conditions.

SUMMARY OF THE INVENTION The present invention is directed to providing an apparatus for testing an elastomer sample at multiple compression and tension rates and includes a solid bed assembly mounting the sample and a vertically displaceable carriage carrying an elongate cam having a multiple-contoured rib. The multiple-contoured rib is sized to fit within a follower member for orthogonal reciprocation when the rib is forced through it. The follower member abuts the elastomer sample and exerts a series of compressive and tensile motions as the hills and valleys formed by the multiple-contoured rib pass through the follower member. Appropriate monitoring circuitry, for example, electronic micrometers, etc., produces output signals representative of the series of motions and the responsive compression and expansion rates of the elastomer sample as it transcends one elastomer modulus to another.

Therefore, it is an object of the present invention to provide an apparatus for testing an elastomer sample.

Further object of the invention is to provide a testing apparatus having a longitudinal cam carrying a series of discretely shaped hills and valleys formed to simulate missile launch conditions.

The ultimate object of the instant invention is to provide a testing device having a multirate capability at extremely high impulse rates.

Theseand other objects of the instant invention will readily become apparent from the ensuing specification when taken with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a side view of the invention operatively associated with representative supporting machinery.

FIG. 2 shows an elongate camming member operatively engaging the follower member as taken generally along lines 2- 2 in FIG. 1.

FIG. 3 shows a plurality of camming means each carrying a different program.

FIG. 4 is a side view of the invention with the camming member longitudinally displaced.

FIG. 5 shows an interrelationship between stimulus and deformation.

DESCRIPTION OF THE PREFERRED EMBODIMENT The multirate compressional test machine is used in its primary application, to test elastomer materials dynamic characteristics. Such characteristics are particularly important when an elastomer is utilized as a liner or shock absorbing material within a missile launching launch tube or silo since failure or an intolerable rate of deformation can result in damage to the missile or its components during launch. An elastomer liner having the proper dynamic characteristics to reliably function when subjected to successive compressional shocks or a prolonged compressional deformation must be identified in the laboratory prior to launch since failure or improper operation results in costly misfires. The present invention provides a way by which the impacts created in a missiles launching sequence are simulated both as to the rate of impacts and magnitude of compressional forces encountered.

Referring to FIG. I, a heavy, immobile machine bed 10 supports a sample supporting structure llll bolted or welded together and including a vertically extending mounting plate 12, the surface of which has been coated with a bonding resin for holding an elastomer sample l5.

Operatively associated, a vertically extending drop tower fixture 20 is formed with a vertically extending rail section ll shaped with a longitudinal groove 22 on opposite sides to provide vertical, longitudinal guidance for a heavily weighted drop member 23 having a plurality of inwardly facing groove follower fingers 23a sized to fit into the longitudinal grooves to permit only upward or downward travel.

On the opposite side of the drop member, an elongate camming member 30 is bolted to securely anchor the camming member onto the drop member. The camming member is constructed and is formed with a rib 30a and a T- shaped cross-sectional area having discretely different hills and valleys, the purpose of which will be set out below.

The drop member is free to traverse the length of the rail section by free fall or a motor-powered drop and return assembly 24 attached to eyes 23b and 230 which control the drop member's rate of ascent and descent to simulate desired missile-launch conditions. At the bottom of the vertical drop, a shock arrestor 25 employs conventional springs or a water shock arresting device to halt the downward motion of the drop member.

A pair of vertically extending

parallel support elements

26 and 27 of rectangularly cross-sectional area is anchored to the machine bed and vertically supports a follower member 35. The support elements are spaced in parallel relation to ensure that when the follower member is longitudinally displaced, the follower member does not teter back and forth but transmits a uniform, horizontal force to the elastomer sample 15. At their opposite ends, both support elements are securely anchored to a pair of

anchoring blocks

28 and 29. By longitudinally, reciprocally camming the follower member, an identical angular displacement of each of the parallel support elements imparted and the follower member retains its perpendicular orientation with respect to test sample 15.

Follower member 35 includes as its principal components, a bearing portion 36 joined to a follower portion 37 by a follower arm 33. A plurality of bolts 38a connects the follower member to anchoring block 28 and a pair of triangularly shaped braces 38b helps transfer a uniform pushing force to the bearing portion 36.

The follower portion is formed of an essentially W-shaped block 39 welded onto the end of the follower arm. A lateral bore provided across the W-shaped block houses and journals a first laterally extending shaft 40 mounting a pair of high capacity

needle cam rollers

41 and 32 in a freely rotational relationship. A left and a right essentially U-shaped block 43 and 44 are bolted onto the W-shaped block by pairs of block bolts 45 and M5 extending through bores provided in the W- shaped lock to terminate in correspondingly tapped holes in the respective left and right U-shaped blocks. A pair of laterally extending bores are drilled, one in each of the U- shaped blocks, to each mount a journaled shaft carrying a separate high capacity needle cam roller 47 or 48. The lateral bores in the U-shaped blocks must obviously be located in a plane separate and distinct from the block bolt plane as well as being disposed to not interfere with the laterally extending bore mounting the high capacity needle cam rollers 41 and 42. Optionally, the follower member is cast as a single unit, that is to say, with the W-shaped portion and the U-shaped portion cast together to eliminate any block bolt and shaft location problems.

The high capacity needle cam rollers are sized and disposed to extend beyond the W-shaped block ends and also beyond the inner extensions of the U-shaped blocks to form a slot 49 having as retaining walls the surfaces of the four needle cam rollers. Adjacent walls of the two U-shaped blocks are sufficiently spaced to form a cut 50 communicating with the slot to form a T-shaped slot for accommodating an elongate camming member 30.

Each camming member has a flanged base portion 31 carrying a perpendicularly extending rib 32 terminating in an outwardly flaring bidirectional cam surface 33. The width of the rib 32 is smaller than the space provided across cut 50 to allow its free passage therethrough. The width of the bidirectional camming surface is sized to fit into the slot 49 formed between the

cam rollers

41 and 47 and 42 and 48 to ensure the follower member's following the lateral bidirectional displacement imparted by the bidirectional camming surface.

Three representative

elongate camming members

30a, 30b, and 30c exemplify three distinct and separate programs representing the shocks attendant three different launching sequences. From a side view, it is apparent that these shocks are readily simulated by shaping the separate camming members with differently arranged sequences of hills and valleys, i.e., portions having longer and shorter perpendicularly extending rib sections, note FIG. 3 showing a long rib section, valley 32a and 320 and a short rib section, hill 32b.

The rate at which these shocks are absorbed by the lining elastomers within a launch tube is easily changed by merely changing the velocity at which the camming member is forced through the follower portion of the follower member. The relatively heavy drop member 23 is of sufficient mass to force the camming member through the follower portion by itself. Precise speed control to identically simulate a launch sequence is optionally provided by a variable speed motor 24.

In the simulation of one launch sequence, cam 30a is preprogrammed with an arrangement of hills and valleys to compress the elastomer sample approximately 0.75 inches at a deformation rate of approximately 7,200 inches per minute. This rate of compression is altered as quickly as possible to 720 inches per minute for an additional 0.25 inch of elastomer compression, that is to say, the elastomer has been deformed a total distance of l inch but at two successive distinct rates. In simulating another launch sequence, camming member 30b is programmed to simulate an initial compression rate of 7,200 inches per minute for one inch of travel followed by a zero rate or holding condition. In another sequence carried on elongate camming member 30c, the center hill 320 represents an initial compression of 1 inch at 7,200 inches per minute followed as quickly as possible by a negative or unloading rate of 7,200 inches per minute. The high inertia of the weighty drop member 23-coupled with the weight of the camming member itself and the force of the variable speed motor 24 ensures that a constant rate of travel through the follower portion is guaranteed.

Electronic micrometers

51 and 52 are carried on the follower member and the sample itself to produce output signals which represent the motion of the follower and the deformation of the sample. These two output signals are fed to an oscillograph 53 or similar device for providing a visual representation of the two signals. The oscillogram shown in FIG. 5 recording a comparison between camming member's compression 54 and samples deformation 55 wt respect to time shows the lag between deformation and recovery of the sample when compared to the stimulus, the compressional shock, that represents approximately l20gs of acceleration.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings and it is therefore to be understood that within the scopeof the disclosed inventive concept, the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. An apparatus for testing a sample at multiple rates comprising: 4

a bed assembly supporting said sample;

elongate camming means having a longitudinal multiplecontoured rib;

a follower member carried on said bed assembly .for permitting reciprocal movement thereof having,

a bearing portion abutting said sample, and, a follower portion secured to said bearing portion having opposed spaced follower surfaces receiving said multiple-contoured rib therebetween; and

linear displacement means securing said camming means thereto disposed to align said rib with said spaced follower surfaces for forcing said multiple-contoured rib against the spaced follower surfaces as said rib passes therethrough to impart reciprocal forces against said sample.

2. An apparatusaccording to claim 1 in which said spaced follower surfaces are the peripheral surfaces of two sets of rollers mounted on lateral shafts disposed to form a T-shaped passageway and said multiple-contoured rib has a T-shaped cross-sectional area sized to permit longitudinal roller contacting travel through said T-shaped passageway.

3. An apparatus according to claim 2 in which said multiplecontoured rib is formed with a plurality of discretely shaped successive hills and valleys to provide said multiple rates.

4. An apparatus according to claim 3 further including:

a pair of parallel spring-bars supporting sad follower member a distance from said bed assembly to ensure unimpeded said reciprocal motion orthogonally from said roller contacting travel.

5. An apparatus according to claim 4 in which said follower member is constructed of a lightweight metal to minimize inertial resistance to said reciprocal motions.

6. An apparatus according to claim 5 further including:

means for monitoring said reciprocal motion and the physical response of said sample; and

means for providing a visual representation of said reciprocal motion and said physical response.

Claims

1. An apparatus for testing a sample at multiple rates comprising: a bed assembly supporting said sample; elongate camming means having a longitudinal multiple-contoured rib; a follower member carried on said bed assembly for permitting reciprocal movement thereof having, a bearing portion abutting said sample, and, a follower portion secured to said bearing portion having opposed spaced follower surfaces receiving said multiplecontoured rib therebetween; and linear displacement means securing said camming means thereto disposed to align said rib with said spaced follower surfaces for forcing said multiple-contoured rib against the spaced follower surfaces as said rib passes therethrough to impart reciprocal forces against said sample.

2. An apparatus according to claim 1 in which said spaced follower surfaces are the peripheral surfaces of two sets of rollers mounted on lateral shafts disposed to form a T-shaped passageway and said multiple-contoured rib has a T-shaped cross-sectional area sized to permit longitudinal roller contacting travel through said T-shaped passageway.

3. An apparatus according to claim 2 in which said multiple-contoured rib is formed with a plurality of discretely shaped successive hills and valleys to provide said multiple rates.

4. An apparatus according to claim 3 further including: a pair of parallel spring-bars supporting sad follower member a distance from said bed assembly to ensure unimpeded said reciprocal motion orthogonally from said roller contacting travel.

6. An apparatus according to claim 5 further including: means for monitoring said reciprocal motion and the physical response of said sAmple; and means for providing a visual representation of said reciprocal motion and said physical response.