TESTING METHODS AND TECHNIQUES: ENVIRONMENTAL …

NASA SP-5945(01)

TECHNOLOGY UTILIZATION

SE F I L ECOPY

TESTING METHODS AND TECHNIQUES:ENVIRONMENTAL TESTING

A COMPILATION

NATIONAL AERONAUTICS AND SPACE ADMINISTRATION

ForewordThe National Aeronautics and Space Administration and the Atomic Energy

Commission have established a Technology Utilization Program for the dissem-ination of information on technological developments which have potentialuti l i ty outside the aerospace and nuclear communities. By encouraging multipleapplication of the results of their research and development, NASA and AECearn for the public an increased return on the investment in aerospace andnuclear research and development programs.

This compilation describes various devices and techniques for testing hard-ware and components in four special environments-low temperature, high tem-perature, high pressure, and vibration. Organized in four sections according .tothe type of environment in which the innovations are used, the compilationincludes items ranging from an automatic calibrator for pressure transducers toa f ix ture for testing the susceptibility of materials to igni t ion by electric spark.

This compilation is not intended as a complete survey of the field of environ-mental testing. Rather, it gives a sampling of many diverse activities. The innova-tions presented have been selected for their potential value, in terms of improvedquality control, cost savings, or more realistic simulation of actual environmentalconditions.

Readers interested in testing in related fields may f ind additional informationin NASA SP-5943(01) Testing Methods and Techniques: Testing Electrical andElectronic Devices, and in NASA SP-5944(01) Testing Methods and Techniques:Strength of Materials and Components.

Additional technical information on individual devices and techniques canbe requested by circling the appropriate number on the Reader Service Card en-closed in this compilation.

Unless otherwise stated, NASA and AEC contemplate no patent action onthe technology described.

We appreciate comment by readers and welcome hearing about the relevanceand ut i l i ty of the informat ion in this compilation.

Ronald J. Philips, DirectorTechnology Utilization OfficeNational Aeronautics and Space Administration

NOTICE • This document was prepared under the sponsorship of the Nat ional Aeronautics and SpaceAdministrat ion. Neither the United States Government nor any person acting on behalf of the UnitedStates Government assumes any l iabi l i ty resulting from the use of the information contained in thisdocument, or warrants that such use wi l l be free from privately owned rights.

For sale by the National Technical Informat ion Service, Springfield, Virginia 22151. $1.00

ContentsSECTION! . Cryogenic Testing . Page

Cryogenic Fluid Sampler Permits TestingUnder Hazardous Conditions : 1

Chamber for "Dry" Cryogenic Testing: A Concept 1Cryostat Simplifies Tensile Testing at Liquid

Nitrogen Temperatures 2Tensile Testing of Irradiated Metals .• . . 3Testing for Adhesive Debond Under Cryogenic

Conditions 4.Variable-Environment Chamber for Materials

Testing , 5Biaxial Test Fixture Has Cryogenic Applications 5Reducing the Hazar.1 in Testing Cryogenic

Pressure Vessels 6Elongation Limit of Strain Gages in Liquid

Nitrogen 6

SECTION 2. High-Temperature TestingHigh-Intensity, Sustained-Operation Heat Source 7Tester for Study of Roller Bearings 8Test-Specimen Heater '. 9Burn-Rate Testing Apparatus 9Portable Heater for Lap Shear Testing 10Testing Igni t ion Susceptibility of Materials 10

SECTIONS. Pressure TestingPressure-Sensing Diaphragm .11Automated Calibrator for Pressure Transducers 12Pneumatic Pressure-Wave Generator Used to Test

Transducers 12Remote-Controlled, Air-Driven Pump 13Tester for Cam-Operated Valves 13Tester Provides Variable Pressure-Wave Amplitudes

and Frequencies 14Portable Pressure Tester for-Instrumentat ion

Fittings , 15Abrasion Testing Under High-Pressure Hydrogen 15Adapter Prevents Damage to Tubing During High-

Pressure Tests 16Biaxial Stress Test Uses Ellipsoidal Pressure

Vessel: A Concept 16

SECTION 4. Vibration Testing PageSuspension System for Vibration Tester 17Mult iaxis Vibration Fixture 17Shaker Slip-Plate Adapter 18Transient Vibration Simulator . ., 19Mass-Load ing Effects on Structural Vibrations 19Analog Equalization for Mul t iaxis Vibration

Tester 20Measurement of Frequency Response to Vibrations 20Vibration Amplitude Measurement 21Analysis of Brinel l ing Failure in Bearings 21Vibration Testing of Vidicons 22

Section 1. Cryogenic Testing

CRYOGENIC FLUID SAMPLER PERMITS TESTINGUNDER HAZARDOUS CONDITIONS

A remotely controlled sampling device con-sisting of a calibrated container, a dewar, asolenoid valve, a pressure gage, and a manualbleed valve takes timed samples of cryogenic

Pressure Gage

SampleProbe

The pressure gage indicates the presence ofsample f lu id in the container and serves as awarning indicator if boil-off begins. The bleedvalve permits, slow evaporation for paniculate

Solenoid Valve, (Normally closed to preventyflow prior to actuation. May be remotely or

/ locally actuated.)

= j£ To Vent

Bleed Valve (Allows slow bleed off for par-•ticulate, moisture,or cryogenic dilution test-ing after the sample is procured.)

Sample Container (Constructed to force the'first fluid on through to vent.)

Test: Fluid Duct vacuum Jacketed Dewar

Cryogenic Bath

f lu ids during hazardous tests. This capabilitypermits accurately determining the f lu id proper-ties, knowledge of which is useful in analyzing thetest results.

The sampler is in i t i a l ly submerged in a dewarcontaining a liquid with a boiling point no higherthan that of the f lu id to be sampled. When theboiling in this chi l l ing bath ceases, the containeris ready for sampling. Samples are obtained byactivating the solenoid valve, thus in i t ia t ing flowfrom the duct into the sample probe pipe. Thefluid enters the sample container near the bot-tom, forcing any purging contents in the containerout through the vent.

moisture, or cryogenic dilution testing. To pre-vent spurious contamination of the sample,there is no valving between the test duct andthe sample container.

When a satisfactory sample is obtained, thesolenoid valve is closed. The sample containeris removed after the test is completed.

Source: J. A. Mitchell ofNorth American Rockwell Corp.

under contract toMarshall Space Flight Center

(MFS--1927)

Circle I on Reader Service Card.

CHAMBER FOR "DRY" CRYOGENIC TESTING: A CONCEPT

This test chamber design, for establishingand m a i n t a i n i n g a "dry" cryogenic environ-ment, would eliminate the need for complextemperature controls while providing a testenvironment vir tual ly free of temperaturegradients. The design, a diagram of which isshown in the figure, might be applied in any

testing situation which requires exposure to verylow temperatures wi thout immersion in cryo-genic liquids.

Techniques for producing cryogenic environ-ments generally require the use of cryogenic'f luids . In most cases, cryogenic temperatureexposure may be accomplished by immersion in

TESTING METHODS AND TECHNIQUES:E N V I R O N M E N T A L TESTING

a l iquid cryogen. In other cases, for variousreasons, the part to be tested cannot be im-mersed.

Q Inner ChamberVent Tube| (^ Fabricated From

'Thin AluminumSheet

Fill Tube

FlexibleSS Tube

ChamberAccessDoor

ChamberDoorVent

Outer ChamberFabricated FromMetal-InsulationComposite

In such cases, the cryogenic environment mustbe generated by a system comprising a chamber,a temperature controller, and a liquid cryogen.Cooling is accomplished by flowing cryogenicfluid into the chamber. Fluid flow rate is deter-mined by the controller, which senses chambertemperature and adjusts flow rate accordingly.

This technique, however, has certain weak-nesses, among which are: (1) it requires the use

of expensive temperature control systems, (2)it cannot accurately control chamber tempera-ture fluctuations, and (3) it cannot eliminatetemperature gradients within the chamber.

The proposed double-chamber design wouldeliminate these weaknesses. As conceived, theinner chamber would be made from a cryogenic-temperature resistant, thermally conductivematerial such as a luminum. The outer chamberwould consist of a thermal insulator such as ametal-ceramic composite. The inner chamberwould be cooled by f i l l i ng the volume betweenit and the outer chamber with a cryogenicliquid. Because it would be surrounded by thecryogen, the inner chamber would be veryrapidly cooled to a temperature near that ofthe liquid. Once stabilized, the temperaturewould remain constant as long as the liquidlevel remained above the top of the innerchamber. And, since every boundary would becooled to the same temperature, there would bevir tual ly no thermal gradients within thechamber.

Source: P.M. Torre ofNorth American Rockwell Corp.


(MFS-16934)

Circle 2 on Reader Service Card.

CRYOSTAT SIMPLIFIES TENSILE TESTING AT LIQUIDNITROGEN TEMPERATURES

A lightweight cryostat made of expanded poly-styrene and attached directly to a tensiletesting mechanism by a special seal, can reducemisalignment effects due to cryostat weight,while faci l i tat ing viewing and loading ofspecimens. (In tests of irradiated tensilespecimens under l iquid nitrogen, a slight eccen-tricity in the tensile system will cause erroneousresults. A conventional metal-type cryostat notonly adds eccentricity to the system becauseof its weight, but also makes it d i f f i cu l t toassure that a test specimen is properly sealed.)

The cryostat, shown in the figure, is made

of expanded, nonporous polystyrene, and is muchlighter than conventional cryostats. The lowdensity material is not subject to damaging thermalstresses, and its light weight allows the cryostatto be attached directly to the bottom pull rodof the testing mechanism without causing ec-centricity problems. Thus, the need for com-plicated dynamic seals is eliminated. A th in layerof a room-temperature-curing silicone adhesive,painted on the interior and exterior of thecryostat, increases the resistance of the materialto l iquid nitrogen (LN2) and keeps moisture outof the foam.

CRYOGENIC TESTING

Wall thickness tapersfrom 2.5 cm at topto 5 cm at bottom.

Viewing Window

Pull Rod

Clamp•Washer

Cryostat Assembly

Pull Rod Assembly

Two acrylite windows are incorporated intoopposite walls of the cryostat, permitting anexcellent view of the specimen and grips. Thewindows and pull rod assembly are sealed with

silicone adhesive; O-rings are also used in seal-ing the pull rod. The sealant is effective whenused sparingly or when put on in separate layers.

The cryostat's design has many advantages. Itis simple in design, with no moving seals orcomplicated assemblies. It is light weight andeasy to fabricate, since polystyrene can be easilyshaped with a hot-wire cutter. It is economical,showing reduced boil-off and leakage lossesof LN2 because the cryostat is well sealed andmade of an insulating material. Finally, it iseasily converted for use with many other gripassemblies and materials.

Source: R. P. Shogan and R. J. Skalka ofWestinghouse Astronuclear Laboratory

under contract toA EC-NASA Space Nuclear Systems Office

(NUC-10522)

Circle 3 on Reader Service Card

TENSILE TESTING OF IRRADIATED METALS

A modified cryogenic tensile testing system im-proves the accuracy and uniformity of results intensile testing irradiated metal specimens atcryogenic temperatures. The modifications in-

Split-Screw

alignment defects, which had previously beencaused by the greater weight of conventionalmetal cryostats.

The system was developed for tensile testing

Lightweight Tensile TestingPolystyrene Acrylite MechanismCryostar Window

TensileSpecimen

Split-Screw Grips

Perforated GasFeeding Coil ^

Spl it-ScrewAssemblies"

BottomPull Rod-

New Uni versa UJoint

\ThermocoupleWires

Recorder-Controller

Heat ing -v.Coil

HeliumTank

New Universal Joint

elude: (1) the lightweight, expanded polystyrenecryostat described in the preceeding item; (2)split-screw grips; (3) a universal joint; and (4)a special temperature control system. Thesemo'difications have greatly reduced critical mis-

TensileSpecimenLN2 Dewar

of irradiated metal specimens, which had to bekept at liquid nitrogen temperatures from thetime of their irradiation un t i l after the test had-commenced. There was also a need for fast,accurate control of specimen temperature dur ing


testing to determine annealing effects at inter-mediate temperatures. Previous radiation-effectstensile testing of brittle-type metals indicatedlosses in strength and ductility after irradiationat liquid nitrogen temperatures. However,measurement accuracy was hampered by pre-mature failure, caused by eccentricity of thetensile tester's loading system.

The split-screw grips are precision machinedto the contour of the test specimen shouldersin order to reduce misalignment effects dueto' uneven loading. Unl ike conventional split-screw grips, which are threaded to the end ofthe unit, the new grips are made with a guideand a beveled edge to facilitate rapid andaccurate seating under LN2. Also, theheads contain precision-located holes that matchpins in a specially designed wrench; this pre-vents jamming, and permits fast attachment of thegrips to the specimen and rapid assembly ofthe split-screw grips into the main grippingbody.

To further reduce misalignment effects, auniversal joint with limited side travel is in-serted in the socket located on the movablecrosshead and is connected with the bottom pull

rod. Semielliptical design of the universal-joint head and socket seal l imits side travelto minimize any random stresses of spillage ofLN2 that might be caused by "flopping" of theuniversal joint before slack in the system is takenup.

In the temperature control system, thespecimen is surrounded by a coil containingholes, specially sized and located, through whicheither cold gaseous nitrogen or preheated gaseoushelium may be injected. These are suppliedthrough lines leading to the coil from an LN2dewar or a helium tank. Temperature is deter-mined by a calibrated thermocouple at a controlpoint near the specimen and is maintained atthe desired point for testing (after the precool-ing LN2 has been drained from the cryostat) by acontroller, which actuates solenoid valves asrequired.

Source: P. J. Levine, R. J. Skalka, andE. F. Vandergrift of

Westinghouse Astronuclear Laboratoryunder contract to

AEC-NASA Space Nuclear Systems Office(NUC-10521)

Circle 4 on Reader's Service Card.

TESTING FOR ADHESIVE DEBOND UNDER CRYOGENIC CONDITIONS

The illustrated testing setup is used to deter-mine adhesive debond strength under cryogenicconditions. The test specimen is a standardwishbone tensile coupon made from 2014-T6aluminum alloy plate. Tabs are bonded to theplate by patches of the adhesive to be tested.After the coupon is inserted in a standard cryo-genic tensile testing machine, each bonded tab isconnected to a pair of spring-loaded electricalcontacts. Debonding of the tab permits thecontacts to close, and lights an indicator lamp.

Source: W. G. Boyd ofNorth American Rockwell Corp.


(MFS-16794)


Housings forElectrical Contacts

CRYOGENIC TESTING .5

VARIABLE-ENVIRONMENT CHAMBER FOR MATERIALS TESTING

The illustrated controlled-environment chamber, ram, attached to appropriate force-registeringwhich encloses both a test specimen and thedevices used to perform a variety of physicaltests, can continuously vary the test environment

ChamberAtmosphereConduit

Chamber

instrumentation, is mounted directly above thechamber and led into it through a collapsiblesealing bellows. In the chamber, the ram engages

Cavity GasConduits

Transducer

Vacuum Gauge

Test Stand

through a range of pressure, temperature, humid-,ity, and atmospheric composition. The chamberis used to determine the energy-absorbingcapacity of various crushable materials througha wide range of environments. Presently avail-able test chambers give data on specimen orassembly behavior in various fixed environments,but not on behavior during changing environ-mental conditions.

The chamber is f i rmly mounted on a statictest stand so that external forces or movementswill not affect it. The device is equipped withconduits to introduce heating or cooling gas,to raise or lower the pressure, or to introduceatmospheres of differing chemical makeup. A

Movable Upper PlateCubical.Cavity

the upper plate of a cubical cavity that contains'the test specimen.

The cavity is made up of fixed and movableplates configured so that the ram, pressing onthe upper movable plate, will deform the speci-men through lateral expansion. The movableplates, contiguous with the crushable specimen,are spring loaded to maintain intimate contactwith the specimen while permitting its deforma-tion underpressure.

Source: A.C. Knoell ofJet Propulsion Laboratory

(JPL-789)


BIAXIAL TEST FIXTURE HAS CRYOGENIC APPLICATIONS

A recently developed test f ixture can producebiaxial stress fields of sufficient magnitude tocause failure in large test specimens. This fix-ture permits determining the magnitude of a bi-axial stress by simply dividing the applied loadby the net cross section. With relatively minormodification, the same test f ixture can be used

for biaxial stress-field testing at cryogenictemperatures.

With the development of large pressurizedtanks has come a need for an inexpensive methodof testing critical tank areas to failure. In allpressurized tanks there are small areas ofdiscontinuity that require structural certification.


Since no previously existing facility had thecapability of testing just these small areas,a complete tank had to be built. Testing acomplete tank proved unsatisfactory, becausethe exact location of rupture was often diff icul tto pinpoint, and the design reserve of undamagedcritical areas could not be established. Numerousattempts to duplicate the stress fields experiencedin a pressurized tank have had limited success,and then only with very small test specimens.

The new biaxial test facility is capable ofproducing biaxial stress fields in panels as largeas 61 cm (2 ft) square. The test panel is,machined on both sides to form a frame aroundthe test area. Clamp-type grips are used totransfer load into the corners of the test panelthrough bolts loaded at the centroid of area.Load is applied by hydraulic actuators attachedto the grips and to load plates on the endsof the fixture. Load transmitted to the test panelis controlled by calibrated load rods between

the hydraulic actuators and the fixture framedSince the load can be controlled to apply auniform sttess to the test panel, failure loadcan be determined simply by dividing the totalapplied load at fai lure by the net cross sectionof the panel.

For cryogenic application, a metal tub isfabricated beneath the test panel and filledwith a liquid cryogen. Cryogenic liquid isalso sprayed from perforated tubing ontothe test panel and loading grips. A plasticthermal barrier is secured above the metal tubto control splash and air flows.Source: J. C. Helf, R. E. Kelly, D. A. Kerr, and

C. R. Waldron ofNorth American Rockwell Corp.


(MFS-14185and 14189)

Circle 7'on Reader Service Card.

REDUCING THE HAZARD IN TESTING CRYOGENIC PRESSURE VESSELS

In burst testing large-capacity cryogenic stor-age vessels, sudden ruptures can produce anexplosion of considerable magnitude. To enabletesting of larger vessels without incurring theexpense of installing additional safety barri-cades, it is necessary to reduce the internalvolume of the tank. This can be accomplishedsimply and inexpensively by partially fi l l ingthe tank with small pieces of scrap a luminum.This procedure will reduce explosive force inthree ways: (1) The net liquid contents arereduced, with a corresponding decrease in burstenergy. (2) The large mass and high specificheat of the a luminum scrap aid in achievingnearly isothermal compression of the liquid. This

results in a much smaller rate of energy increasewith compression, as compared with isen-tropic compression. (3) Most of. the gas formedby the sudden decompression of the super-critical liquid expends its energy relativelyslowly, by friction during passage through theinterstices between the a luminum chunks, andby accelerating the fragments themselves torelatively small radial velocities.

Source: H. E. Hubbard ofNorth American Rockwell Corp.


(MFS-13534)


ELONGATION LIMIT OF STRAIN GAGES IN LIQUID NITROGEN

A test program has yielded data on theuti l i ty of various strain gage and cement com-binations for cryogenic applications in which awide temperature range may be encountered.

A wide variety of strain gage types was tested,but no attempt was made to evaluate theeffects of minor differences within a singlegage type. Hence, the effects of such parameters

CRYOGENIC TESTING

as thermal-expansion compensation, gage length,and cement-curing procedure were not inves-tigated.

Each strain gage, 3.18 mm (1/8 in.) in length,was mounted on 3003-H14 aluminum beams, 23cm long by 2.5 cm wide by 3.2 mm thick. Afterstandard installation and curing, each beam wassupported horizontally at both ends and sub-jected to bending under a centrally applied load.

The strain gage output was recorded on theX-axis of an X-Y recorder, and the deflectionof the beam was recorded on the Y-axis; thismade it possible to determine the mode offailure of the gage. For tests conducted atroom temperature, the load was applied unt i lthe strain gage failed electrically because ofan open circuit in the grid, or mechanically dueto failure of the bond between the gage andthe beam. The mode of failure was easily deter-mined in most cases from the shape of the curveobtained on the X-Y recorder. Incipient bondfailure was indicated by a decrease in the slope

of the strain-deflection plot, and electricalfailure by an increase.

Cryogenic tests were performed by placingthe test fixture in a liquid nitrogen bath andallowing the temperature to stabilize. Althoughthe cessation of violent bubbling indicatedapproximate equilibrium, a more accurateindication of equilibrium was given by thestabilization of the X-Y plotter reading. Oncethe temperature stabilized, the bar was loadedunt i l the strain gage failed.

After the gage failed, it was examined undera microscope to determine the presence of cracksin the strain gage grid and backing, and to detectflaws in the solder joints used to connect leadsto the strain gage.

Source: D. W. NichollsofNorth American Rockwell Corp.


(MFS-18218)


Section 2. High-Temperature Testing

HIGH-INTENSITY, SUSTAINED-OPERATION HEAT SOURCE

A water-cooled, high-intensity radiation source,rated at 125 kW, with an efficiency of 31 to 34percent, can operate repeatedly at maximumrated power for periods of 10 to 20 minutes.

Argon Out Heat Exchanger

Argon In^

At lower power inputs it can be operated con-tinuously for periods as long as two .hours. Orig-inally designed for evaluating ablative materials

entry into planetary atmospheres, the sourcehad to be capable of high-reliability cyclic opera-tion at maximum power for extended periodsof time. Previously available sources capable

Plasma ArcAnode

Cathode

Inner Quartz EnvelopeOuter Quartz Envelope

of long-term operation were not capable ofsupplying the required radiant power output.

The radiation source used was a direct currentunder simulated conditions of high velocity device in which an argon plasma arc was created


between a tungsten-tipped copper cathode anda copper anode with a molybdenum ring dif-fuser. The envelope through which the radiationwas transmitted was formed of two concentricquartz cylinders. The inner cylinder served asa heat shield; the outer cylinder as the pressurecontainer.

Argon was fed in at the anode, and passedfrom the anode, through the annulus between thetwo quartz cylinders, into a gas vortex generatorat the cathode. The gas was then passed through

a diffuser, collected, and recirculated throughcooling coils back to the source. In passingthrough the annulus between the cylinders,the gas acted as a coolant for the outer quartzcylinder.

Source: W. A. Geideman and K. Muller ofTextron Electronics, Inc.,

under contract toAmes Research Center

(ARC-61)


TESTER FOR STUDY OF ROLLER BEARINGS

A novel, five-ball fatigue tester enables thestudy of rolling element phenomena, includingroller fatigue, ball-bearing kinematics, and elas-tohydrodynamic lubrication, over a wide

Choice of operating speed is made throughstepped pulleys driven by an electric motor. Amagnetic pickup feeding an electronic counterprovides precise speed measurement. Temperature

Load

Test Specimen

temperature range (88.7 to 1366.5 K). Thetester consists essentially of a driven test ballpyramided on four lower balls. The four ballsare positioned by a separator and are free torotate in an angular-contact raceway.

The upper test ball and the raceway areanalogous in operation to the inner and outerraces of a bearing. The separator and the lowerballs are similar in function to the cage and theballs of a bearing. Specimen loading and driveis supplied through a vertical shaft. By varyingthe pitch diameter of the four lower balls,bearing contact angle may be controlled. Witheach revolution of the drive shaft, the upperball receives three stress cycles.

Separator

is measured by a thermocouple in contact withthe raceway containing the freely rotating lowerballs. The test specimen is lubricated by meteringdroplets of f luid lubricant into an air streamthat is directed at the test specimen.

Various modifications of this apparatuspermit fatigue testing at temperatures rangingfrom 88.5 to 1366 K (-300° to 2000° F), andtesting of full-scale bearings. Automatic failuredetection and shutdown systems have enabledlong term, unmonitored testing.

Additional information concerning thisinnovation is given in NASA-TN-D-529. "Rol-ling-Contact Fatigue Life of a CrystallizedGlass Ceramic," Thomas L. Carter and Erwin

HIGH-TEMPERATURE TESTING

V. Zaretsky, and in NASA-TN-D-270, "Effect These documents are available from theof Hardness and Other Mechanical Propertieson Rolling-Contact Fatigue Life of Four HighTemperature Bearing Steels," Thomas L. Carter,Erwin V. Zaretsky and William J. Anderson.

National Technical Information Service, Spring-field, Virginia 22151. Price per document: $6.00.

Source: E. V. Zaretsky et a).Lewis Research Center

(LEW-305)

TEST-SPECIMEN HEATER

A novel graphite heater is used to hold andheat small, electrically nonconductive specimensin vacuum or other inaccessible environments.Heating is performed by passing dc currents of100 to 400 A through the graphite. The heater,

Graphite ResistanceHeater

Specimen

shown in the figure, gives the greatest specimencontact area and the most uniform specimentemperature of the several heater designs tested.

The heater was originally developed in conjunc-tion with a research project on the formationof tektites. Operated with a heating current of400 A, it has produced brightness temperaturesas high as 1300 K in the glassy specimens usedin the research.

Source: General Electric Co.under contract to

Goddard Space Flight Center(GSC-379)


BURN-RATE TESTING APPARATUS

The combustibility tester shown in the fig-ure incorporates several improvements overprevious designs. First, it has been designedto fit into a sealed chamber, so that tests maybe performed under controlled atmosphericpressure and composition. Second, the material

Burn-Rate Sensors.(Photocells) Chamber Flange

.Port

Test Frame

Test MaterialIgnition Sensor(Photocell)

Frame AngleAdjustment

Burner^

Fuel/Oxygen ,- . - .,Control Lines Shutter Control

•—MechanismEnvironmetalControl Line

support frame has been modified to allow rota-tion of the test sample, so that ignition andcombustion may be tested with the samplein various orientations from horizontal tovertical.

Third, a remote-controlled ignition systemhas been incorporated. The system consists ofa burner externally supplied with fuel andoxygen, a spark-gap igniter, a shutter whichmasks the flame from the sample until theflame reaches the desired intensity, and a calibra-tion thermocouple which senses the flame tempera-ture.

Finally, three photocells have been added, toallow automatic determination 'of the time re-quired for burn-through and of the rate offlame propagation along the sample. One cellis placed to sense the start of the test; i.e.,the application of flame to the sample as theshutter is removed. The other two photocells

10 TESTING METHODS AND TECHNIQUES:ENVIRONMENTAL TESTING

are mounted on the test frame above thesample. One cell responds to ignition of thatpart of the sample immediately over the pointof application of the flame; the other to ignitionof another part of the test material.

This invention is owned by NASA, and apatent application has been filed. Royalty-free,non-exclusive licenses for its commercial use

will be granted by NASA. Inquiries concerninglicense rights should be made to Patent Counsel,Mail Code AM, Manned Spacecraft Center,Houston, Texas 77058.

Source: F. S. Dawn andW. L. Gill

Manned Spacecraft Center(MSC-10947)

PORTABLE HEATER FOR LAP SHEAR TESTING

The photograph shows a newly developed in-tegrated heater-clamp, used for elevated lapshear testing of adhesives. The clamp allowstesting to be performed on inexpensiveequipment, rather than on the expensive shear-testing machines formerly used. The heater iscapable of attaining test temperatures as highas 590 K (600° F).

Source: W. M.Zinsley,W. A. Edwards, Jr. and

C. O. McAdams ofNorth American Rockwell Corp.

under contract toManned Spacecraft Center

(MSC-17114)


TESTING IGNITION SUSCEPTIBILITY OF MATERIALS

The recently designed circuit shown in thefigure is used to test the ignition characteristicsand flammabili ty of specific materials in air-or

oxygen-rich atmospheres. Materials used inclose proximity to electrical equipment maybe subjected to incandescent metal fragments

HIGH-TEMPERATURE TESTING 11

or spalls ejected from intermittent short-circuitarcs. The apparatus simulates this real situation,in which an exposed live wire intermittentlycontacts a grounded structural member

ChamberFeed-through Solenoid #2.

Switch forSolenoid #1

Switch forSolenoid #2

in an area containing organic materials. Thedevice consists of a solenoid actuator, wire, andaluminum alloy angle, contained in an environ-mental chamber in which a controlled oxidizingatmosphere can be maintained.

The desired arcing condition is produced byrapidly shorting a live wire (e.g., no. 12 AWG),carrying current from a 28Vdc, 0-500A source,

against a grounded a l u m i n u m alloy angle.Specimens to be tested are placed in the chamberat various distances from the arc-forming mech-anism.

As shown in the schematic, the solenoid isused to raise and lower the bared live wirerelative to the grounded angle. The solenoid iscontrolled by a normally closed pushbuttonswitch. The solenoid, normally en~rgized (fromthe 28 Vdc source), holds the wire away fromthe shorting angle. When the pushbutton isdepressed, the solenoid is deenergized. Thisallows the wire to drop onto the shorting angle,causing arcing and spalling.

Two arc generators are installed in thechamber, enabling two tests to be run withoutdisturbing the chamber. The effects of theintermittent arcing on the test material areobserved through a window in the chamberwall.

Source: B. J. Hamlett andA. L. Krupski of

North American Rockwell Corp.under contract to

Manned Spacecraft Center(MSC-15225)

No further documentation is available.

Section 3. Pressure Testing

PRESSURE-SENSING DIAPHRAGM

A thin , metal ring-type diaphragm seal, similarto those used on pneumatic or hydraulic sensors,is welded to the outer diameter of a sphericaldisk spring and to a housing in which thedisk spring is enclosed. This configuration resultsin lower hysteresis than does the conventionalseal, in which the periphery of a solid diaphragmis welded directly to the housing, with thediaphragm lying across the entire face of the

disk spring. The configuration, with its reducededge effects, allows more precise pressuresensing than previous designs.

Source: C. W. Seltzer ofAmetek-Calmec


(MFS-20769)


12 TESTING METHODS AND TECHNIQUES:E N V I R O N M E N T A L TESTING

AUTOMATED CALIBRATOR FOR PRESSURE TRANSDUCERS

ComponentTransducersUndergoingTest

QuickDisconnects

TransducerExcitation andReadout Device

FlexibleHoses

ConsolePressureStations

ServoControlValve

ControlTransducers

SummingNetwork "*

n

i !III nieaauie V^UIIOUIG

Electrical SignalsPneumatic Lines

HeliumGasCylinder

An automated, portable, transducer checkercan be used to calibrate pressure transducers inthe range of 207kN/m2 to 7.45MN/m2 (15 to1065 psig) with an accuracy of ±0.05%. Thechecker consists of a pressure console and equip-ment for producing the test pressures. The

console is connected to other devices for measur-ing and visually displaying the electrical outputsof transducers being calibrated.

The transducers are connected by flexiblehoses to quick-disconnect pressure stationsmounted on the rear of the console. The consoleis connected to a 13.8 MN/m 2 (2000 psig)helium gas cylinder. A servo control valve anda summing network reduce the output of thecylinder to provide the exact desired test pres-sure. The outputs of the transducers under-going test can be shown on a strip recorder orother types of display equipment.

Source: J. Brinda, J. Shaw, L. Kristoff, andM. Vuckovich of

Westinghouse Astronuclear Laboratoryunder contract to

AEC-NASA Space Nuclear Systems Office(NUC-10067)


Input(BIAS) Pneumatic Output Port

PNEUMATIC PRESSURE-WAVE GENERATOR USED TO TEST TRANSDUCERSGas Pressure

accuracy. Standard pressure-wave generatorshave elaborate controls, consume enormousquantities of gas, and are severely limited inoperating range by either pressure or frequency.

The generator, shown in the figure, is pre-pressurized to any desired static level (biaspressure) and is coupled to a shaker table. Thetransducer or system undergoing test is connectedto the output port of the generator. The fre-quency and amplitude of the generator's pneu-matic output are controlled by the movement ofthe piston, which is directly linked to the drivefork. The fork in turn is driven by the vibrationof the shaker table. The pneumatic output of thegenerator is a direct function of the displacementamplitude and frequency of the shaker table.Sinusoidal or other wave shapes may be generated

Center Driven Piston

• Drive Fork

L

Shaker TableCoupling

Translation Input ForceProvided by Shaker Table

Pressure fluctuations about a bias or referencepressure level, produced by displacement of acenter-driven piston in a closed cylinder, providea means of testing pressure transducers andsystems to determine their reliability or

by controlling the operation of the shaker table.Source: A. E. Gaal and T. P. Weldon ofWestinghouse Astronuclear Laboratory

under contract toAEC-NASA Space Nuclear Systems Office

(NUC-10024)


. PRESSURE TESTING 13

REMOTE-CONTROLLED, AIR-DRIVEN PUMP

An air-driven pump, together with a controlvalve and a remote controller, combines in onedevice functions previously performed by two

Low-PressureWater Inlet

As shown in the figure, the control valveis placed in the pump's air supply. A pressureregulator assures a high pressure, high capacityair source. As the control valve opens, slightly,the pump turns over slowly, providing a lowcapacity, high pressure supply of liquid. Whenthe valve is opened further, the pump provides

Air

^£j

High Pressure.Water Outlet

i r

Control Valve

pumps. Pressure testing of large systems pre-viously required both a low capacity, high pres-sure pump and a very high capacity pump de-signed primarily for f i l l ing and draining opera-tions. The controllable features of the newsystem provide either high or low capacityas required, with a sufficient pressure headfor most test purposes.

Turbine Pump

higher capacity at the same high pressure level;when it is completely shut, the pump stops.

Source: C. W. Kenyon ofNorth American Rockwell Corp.


(MFS-13615)


TESTER FOR CAM-OPERATED VALVES

A tool used for high pressure functional test-ing of cam-operated valves can measure the actua-tion displacement of a valve while it is underworking pressure. Previously, actuation dis-placement was measured by clamping the valveonto the round surface of a cam-operated roller,but this did not provide a stable reference point.Further, any rotation of the roller during pres-surized operation often dislodged the clamp,resulting in loss of high pressure fluid anddamage to surrounding equipment.

The tool is composed of two basic parts, acircular disk and a shank. The clamping deviceis positively retained in the disk by a circulardepression. Welded to the bottom of the disk isa shank containing a lateral hole for the freepassage of an assembly pin. The width, thick-ness, and depth of this shank must be such thatit can freely pass into the depression in the actua-tor shaft. Shank height above the shaft con-straints can be any convenient amount.

At each end of the assembly pin is a cross


hole for accepting a retaining pin. Adjust-ment so that the tool can be firmly kept in placeis provided by a set screw passing through athreaded hole running between the disk andshank.

Source: R. W. Grindle, Jr. ofThe Boeing Co.

under contract toKennedy Space Center

(KSC-10468)


TESTER PROVIDES VARIABLE PRESSURE-WAVE AMPLITUDESAND FREQUENCIES

A pulsating pressure, obtained from a hydraulicactuator driven by a vibration exciter, formsthe heart of a device used to test hydraulic sys-

center of their strokes by trapping the appro-priate balancing pressure on the back side ofthe hydraulic actuator. The actuator is bolted

High Shutoff ValvePressureInput

Shutoff Valve

Drain

Accumulator

tem components to high vabration pressure orfrequency requirements. The device can alsobe used to test pressure transducers, switches,and other hydraulic components. The pressurelevels and pulsation frequencies can be variedas test requirements dictate.

As shown in the figure, the rod of a hydraulicactuator is attached to the exciter head. Therod-end port of the actuator cylinder is connectedto the test specimen and pressurized to the levelrequired by the test item. The shaker headand hydraulic actuator are maintained in the

to a lead mass for stability. A pressure trans-ducer and a direct-writing oscillograph are usedto indicate the pulsation magnitude, and theinput to the exciter is adjusted accordingly. Themotion of the actuator piston provides thecompressive force necessary to vary the pressure.

Source: J. W. Routson ofGeneral Dynamics Corp.

under contract toLewis Research Center

(LEW-10205)


PRESSURE TESTING 15

PORTABLE PRESSURE TESTER FOR INSTRUMENTATION FITTINGS

A fixture incorporating a vacuum cup, whichseals a pressure regulator adapter around oneside of a f i t t ing to be pressure tested, facilitatesleak testing in instrumentation fi t t ings mounted

Test Gas Inlet

in the bulkhead of a large tank. Use of thisdevice eliminates the need for leak testing in acompletely closed vessel.

As shown in the figure, the vacuum cup of thefixture is held against the tank bulkhead at theposition of the plugged fitting, and a vacuumis drawn. Test gas is slowly introduced throughthe pressure regulator adapter until the pressurereaches 207 kN/m2 (15 psig). Leakage is detectedwith a gas sniffer at the opposite side of thebulkhead, or by the bubbling of a leak-checkfluid previously applied at the junction of thefi t t ing with that side of the bulkhead.

Pressure Regulator Adapter

Vacuum Cup

Fitting

Plug

Vacuum Line Bulkhead

Source: G. A. Olson ofThe Boeing Company


(MFS-2032)


ABRASION TESTING UNDER HIGH PRESSURE HYDROGEN

The device shown in cross section in the fig-ure is used for abrasion testing in a high pressurehydrogen atmosphere. Constructed during a

Electrical FeedThrough

Specimen

SlidingSeal

Abrading f wire Coil for Resistance/ T i p / Measurement

Bolt Hole for Gas InletMounting Bracket

materials evaluation program for long-term, high-pressure, hydrogen storage vessels, the deviceis capable of abrading cylindrical tensile speci-

mens in hydrogen atmospheres at pressures upto 103.4 MN/m 2 (15,000) psi). While its sur-face is being abraded, the specimen can be placedunder tensile load and tested to failure.

Electrical isolation between the specimen andthe vessel, and special feedthroughs to passwires through the vessel wall, permit measure-ment of the electrical resistivity of the specimenwhile it is being abraded or tensile tested.The abrader has two interchangeable tips,one for abrading a strip approximately 6 mmwide on an unnotched specimen, and theother for scratching the root of a notch (25 Mmnotch radius).

Source: G. V. Sneesby and R. J. Walker ofNorth American Rockwell Corp.


(MFS-18480, 18488)



ADAPTER PREVENTS DAMAGE TO TUBING DURING HIGH PRESSURE TESTS

The portable adapter assembly shown in thefigure can prevent damage to tubing and in-jury to personnel during high pressure tests.

Triangular Plate

tubing immediately behind the brazed collar,and the triangular plate is positioned in frontof it. A rubber O-ring, which serves as a seal

To PressureSource Brazed Collar

Tubing Stub EndBoss (with fittingsfor attachment topressure source)

Spacer

Capable of withstanding high pressure whilesecurely attached, to a tubing stub end, theadapter can be removed without debrazing orcutting the tubing. Tube ends often have beendamaged by the use of an unsatisfactory methodof attaching the tube to the pressure source,and connecting devices have often blown offthe tube ends while under pressure.

The tubing stub end has a brazed collar formechanical attachment to the adapter. The splithalves of the clamp assembly are secured to the

Clamp Assembly Collar

when compressed, is slipped over the tubing.The boss plate, with fittings for attachment tothe pressure source, receives the stub end tubing,and the adapter assembly is then tightened withthe spacer nuts and bolts.

Source: L. L. StinettofNorth American Rockwell Corp.


(MSC-563)


BIAXIAL STRESS TEST USES ELLIPSOIDAL PRESSURE VESSEL:A CONCEPT

Reliable determinations of weld-joint biaxialstress-strain characteristics could be providedby a conceptual, ellipsoidal pressure vessel. Theellipsoidal configuration, fabricated with weldedjoints in any appropriate orientation, wouldprovide simple biaxial load control, and couldyield data for several stress-strain ratios fromeach specimen. The vessel would be loadedby internal pressurization only, .and strain gageswould be used to collect the data.

The ellipsoidal test specimen would thusprovide an alternate to the cylindrical or cruci-

form specimens commonly used in' biaxialstress testing. Although the cost per specimenwould be higher, multi-point instrumentation andsimplified load control would give a lower costper increment of data.

Source: W. H. Armstrong ofThe Boeing Co.


(MFS-13803)


17

Section 4. Vibration Testing

SUSPENSION SYSTEM FOR VIBRATION TESTER

Special1 thrusters, air suspension springs, andsupport columns are used to eliminate theneed for large reaction masses and hydraulic

Test Article

Air Springand Base

Added Rod

slip tables in the vibration testing of massiveassemblies. The special thrusters are isolatedso that damaging force levels are not transmittedto the supporting floor. The weight of the testarticle is supported by air suspension springs

positioned between the thrusters. These springsare used instead of the standard hydraulicslip tables, since the tables would limit theapparatus to motion in one direction, andwould in addition, be undesirably loaded by thedead weight of the test article.

The high tensile loads generated by thehorizontal testing of large articles are normallyabsorbed by a large reaction mass. To replacethe mass in this application, four concrete columnsare added to the apparatus support structure.High strength steel rods, equipped with sphericalend bearings, are used to transfer the static loadof the test article to the four columns. The rodsdo not limit the motion to one plane (con-sidering the relatively small displacements en-countered in vibration testing), but allowmultidirectional vibrational testing without rota-tion of the test article.

Source: T. C. Martin ofLockheed Electronics Co.


(MSC-11001)


MULTI^XIS VIBRATION FIXTURE

A modified attachment fixture for a standardvibration tester enables three-dimensionaltesting with only one setup.

The usual method of vibration testing alongthree axes has been as follows: (1) The shakeris positioned vertically and the test specimenis mounted on a plate attached to the movingelement. Instruments are installed and the testperformed on the first axis. (2) The shaker ispositioned horizontally and its moving elementconnected to a "slip" plate which rideson an oiled granite block. The item is mounted

on this plate, instruments are installed, and thetest performed on the second axis. (3) Theslip plate is unfastened, the item rotated n/2rad (90°), and the plate reinstalled. The instru-mentation is changed to the new orientation, andthe test is performed on the f inal axis. This pro-cedure is both time-consuming and expensive.

The attachment fixture is modified by addinga wedge and a pyramid to the shaker head.The triangular pyramid, constructed with threemutually orthogonal, equal-length edges inter-secting at its apex, has sides that make an angle

18 TESTING METHODS AND TECHNIQUES:ENVIRONMENTAL TESTING

of about 0.96 rad (54°54-) with its base. Thewedge is constructed with the complementaryangle, about 0.615 rad (35° 16').

The wedge is fixed on the shaker table so thatthe vibrations are parallel to its base, the pyramidis installed on the face of the wedge, and thetest object is attached to one face of the pyramid.With this setup, transfer from one test axisto the next is made by merely rotating the pyr-amid 2i"/3 rad (120°) about the line that runsfrom its apex perpendicular to its base.

Source: C. R. SimsMarshall Space Flight Center and

R.C.Taylor ofThe Bendix Corp.under contract to

Marshall Space Flight Center(MFS-20242)


SHAKER SLIP-PLATE ADAPTER

Specimens subjected to vibration tests are casting was selected as the means of fabrication,commonly mounted on a horizontal slip table in order to provide a structure with greaterand associated plate, which is driven by an rigidity and superior damping characteristics.

ShakerTest Specimen

DrivingForce

Shaker Head Coupled Directlyto Slip Plate

electrodynamic shaker. To attach the edgeof the horizontal plate directly to the shakerhead would result in ineffective dissipation of thedriving force, which is usually stronger aroundthe outer bolt circle. A recently developed hori-zontal adapter ties in all of the shaker's attach-ment bosses and makes a rigid coupling whichterminates in a single row of attachment bossesat the edge of the plate.

The adapter is made of a lightweight magnesiumalloy and weighs approximately 18 kg. Sand

Improved Technique UsingHorizontal Adapter

This adapter allows the entire driving force ofthe electrodynamic shaker to be transmittedwith minimum loss, at all frequencies up to3000 Hz.

Source: O. S. Holm ofMcDonnell-Douglas Corp.


(MFS-14063)


VIBRATION TESTING 19

TRANSIENT VIBRATION SIMULATOR

A new method of vibration testing, in whichthe object is excited with short duration, highintensity, shaped random vibrations, has provento be a more realistic test for certain applicationsthan conventional tests using sinusoidal sweepexcitation. The improved method was devisedafter sinusoidal sweep testing produced repeatedfatigue failures in components that had per-formed successfully in actual use. Investigationrevealed that the sinusoidal sweep test wastoo severe by a factor of almost 200:1, in termsof the number of high-acceleration fatigue cyclesexperienced during test, with respect to thoseencountered in actual use.

The improved method was based on the observa-tion that the statistical behavior of vibrationstimulants in the test system approximatelyconformed to a Gaussian distribution. Because

of this, the probability of very high accelerationlevels (at the three sigma level) is only 0.27percent. For this reason, actual (in use) systemresponse can be accurately stimulated by shortduration random vibration.

The peak acceleration level for each octavefrequency band in the random vibration isdetermined in advance, in a manner similarto that used to derive the requirements for thesinusoidal sweep test.

Source: L. C. Kula and T. E. Fitzgerald ofThe Boeing Co.


(MFS-14800)

Circle '25 on Reader Service Card.

MASS-LOADING EFFECTS ON STRUCTURAL VIBRATIONS

A report on the effects of mass loading onshock and vibration in beams, plates, honey-combs, rings, and cylindrical shells presentsexperimental and analytical data that may beuseful in the dynamic analysis 'of radial andaxial structural vibration (transmission andattenuation) characteristics.

No general technique is presently knownfor analyzing the dynamic transmissibilitycharacteristics of complex structures. Some in-formation is available for predicting the , res,-onance. and modal response of an unloadedshell, but all practical methods for computingthe transmissibility characteristics of complexstructures require some arbitrary assumptions.As a result, most current designs, even of simplestructures, rely on guessed transmissibilities oron arbitrarily assumed dampings. In either case,substantial errors, sometimes as high as severalthousand percent, may result.

Analysis of mass-loaded shell structures iseven more diff icul t , requiring the investigationof response-attenuation characteristics, modeshape changes, resonance disappearance, fre-

quency shift , and resonance coupling andamplification, as well as shock-spectrumresponse.

In the report, results of a combined theoret-ical and experimental investigation of the mass-loading effect on shell vibrations are presented.Essentially, a typical primary structure is rep-resented by a cylindrical shell; auxiliarycomponents appear as discrete masses. Non-contact-type vibrators and shock excitersare used to generate the forcing functions.For shock tests, a shock-synthesis device and anelectromechanical shaker are coupled longi-tudinally to the specimen to determine bothaxial and radial transmissibility characteristics.

Test results indicate significant mass-loadingeffects upon the vibration response of asystem. These effects include some resonancefrequency shifts, many resonance el iminations,substantial response-amplitude at tenuation, somechanges in mode shape, and general amplifica-tion of response at resonance points. Shockresponse is little affected.

The effective forcing areas of mass loading


may be defined by the vibratory patterns,which change in accordance with resonanceattenuation and disappearance characteristics.The transmissibility characteristics indicate somedifferences for beams, plates, honeycomb panels,rings, and shells.

Source: S. Y. Lee ofNorth American Rockwell Corp.


(MFS-20897)


ANALOG EQUALIZATION FOR MULTIAXIS VIBRATION TESTER

A new method of real time equalization,using a special analog computer, achievesmore effective vibration testing by realisticallys imu la t ing the v ibra t ional forces which an objectwi l l actually experience in use. The analogcomputer is programmed to simulate the equa-tions of motion of the electromechanical systemmade up of the test structure and the multipleshakers. The input to the computer is an electri-cal signal representing the acceleration timehistories which it is desired to be reproducedfor the vibration test. The output of the com-puter drives separate power amplifier-shakermechanisms which apply distinctive drivingforces at different locations. The forces produceresponses which correspond to the desired accelera-tion time histories.

Structural qualification, in particular of aspacecraft, requires that it be designed and'constructed with sufficient strength to with-

stand large dynamic forces while in poweredflight. However, because of the extremelyhigh ratio of thrust energy to payload, a space-craft must also be designed for min imum weight.Therefore, the more realistically the actual forcesexperienced by the spacecraft can be simulatedduring qualification testing, the more adequatelyits structure can be designed. When such simula-tions are only approximate, prudence dictatesthe use of large safety factors. When the simula-tions approach reality the safety factor can bereduced and considerable savings in weightand thrust energy requirements can be realized.

Source: M. R. P. Trubert ofCaltech/JPL

under contract toNASA Pasadena Office

(NPO-10544)

Circle .27on Reader Service Card.

MEASUREMENT OF FREQUENCY RESPONSE TO VIBRATIONS

The frequency response characteristics of alarge volume fluid system has been accuratelydetermined by using a small, pulsating, bleed-off flowrate to perturb the system. Because of thehigh system flowrate, application of the conven-tional testing technique, involving interruptionof the main flow stream, would have been verydiff icul t and economically prohibitive.

Instead, a small valve was modified for connec-tion to a pulsating bleedoff exciter. With thevalve actuator modified so that it could bedriven cyclically by a small motor, the bleedoffvolume and pulsation frequency could be remotelycontrolled. The small bleedoff was found capable

Variable Speed Drive

LOX Suction LineFlowrate 1800 kg/sec

Approximately 3Mto LOX Pump Inlet

FlowModified ValvePulse Capability 2-15 Hz,36 kg/sec 10 cm Sh'utoff Valve

VIBRATION TESTING 21

of exciting the resonant response of the muchlarger system. Hence, it was found possible tomeasure the response of the overall system veryrapidly, using existing hardware with verylittle modification.

Although the technique was originally devel-oped for use with the propellant system for theSaturn V launch vehicle, potential applicationsexist wherever the resonant response of a largefluid system must be measured. Such situations

may be found, for example, in the fields ofhydroelectric power generation, jet engines, andpipelines.

Source: R. E. Biggs ofNorth American Rockwell Corp.


(MFS-18445)


VIBRATION AMPLITUDE MEASUREMENT

The vibration frequency response of adhesivelybonded structures may be accurately and non-destructively measured by a recently developedinstrument. The instrument, which combinesa modified commercially available micro'dis-placement meter, a fiber-optic probe, andany of several standard display or recording de-vices (oscilloscope, VTVM, X-Y recorder, etc.),can measure local displacements as small as0.12 Mm (5M in.) in response to vibrationalexcitation in the frequency range from 10 Hz to10 kHz, with an output sensitivity of 0.12 ^M/mVp-p.

The commercial displacement meter wasdesigned to read static displacement. An acamplifier-demodulator circuit was developed

to convert the instrument to read dynamicdisplacement. The basic circuit was modified byadding an emitter follower circuit to lower theoutput impedance to a value more suitable fordriving other high impedance loads. Two opera-tional amplifiers and associated circuitry wereadded to demodulate signals from the meterand provide a dc signal suitable for an X-Yrecorder.

Source: J. F. Moore and D. S. Weinstein ofNorth American Rockwell Corp.


(MFS-20396)


ANALYSIS OF BRINELLING FAILURE IN BEARINGS

Noisy operation of certain fans after exposuretoihigh intensity;random'vibration has been;foundto,be caused by brinel l ing of the fan bearings.

Assuming a maximum Hertz stress of 3.17GN/m 2 (460,000 psi) to produce brinelling,the maximum axial load for the fan bearingwas calculated as 190 N(43 Ib). Dynamic analysisof the rotor-bearing spring system revealedthat, with one preload spring, the maximumaxial load would be 1320 N (297 Ib).

Maximum vibratory bearing loads werereduced by decreasing the rotor's natural fre-quency and by increasing the damping through

use of a soft spring system. This required us-ing multiple springs at both ends of the shaft.When a system of five springs at each end ofthe rotor was considered, the bearing loadpredicted was 258 N (58 Ib). Actual vibrationtests using this configuration showed a reduc-tion in bearing damage. Use of belleville springswith this particular rotor-bearing configurationwas found undesirable, because the collapseload of such springs would be exceeded duringoperation.

A bearing load-capacity computer programhas been written so that, given the bearing

22 VIBRATION TESTING

parameters—inner race diameter, ball diameter,diametral clearance, total curvature of the racegroove and number of ^alls—the limiting axialload can be determined, using maximumHertz stress and overriding of the race landas the failure criteria.

Source: W. A. Glaeser, S. K. Batra, andR. H. Prause, of

Battelle Memorial Instituteunder contract to

Marshall Space Flight Center(MFS-20968)


VIBRATION TESTING OF VIDICONS

A method for checking the performance ofvidicons during mechanical vibration testsuses an external signal to modulate the vidiconelectron beam during the "write" period,thereby storing the image on the vidicon face.No optical test pattern or lens system isemployed.

Previously, performance was tested by storinga fine-detail test pattern on the photosensitivesurface of the vidicon, using a light source andlens system. The vidicon with the stored imagewas then placed on a vibration table andthe reading beam turned on while the tube wasbeing vibrated. This method, however, requiredthe tube to be moved for each test, and gaveonly limited resolution, due to the distancebetween the overlay used to produce the imageand the photosensitive surface.

In the new method, the photosensitive surfaceof the vidicon is first primed by exposing it tolight. The test 'pat tern is then stored on theprimed surface by picking the pattern up on anauxiliary camera tube and transferring it, after

amplification, into the tube under test as videomodulation of the control grid during scanning.A second method involves producing black andwhite bar patterns, which are generated by usingvariable frequency scan generators with no videomodulation.

The photosurface is then scanned in thenormal manner and the video informationis displayed on a cathode ray tube or datastorage tube. Depending on the test require-ments, the desired mechanical vibration may beapplied during the storage period or thereadout period, or during the entire sequence.Comparison of results obtained during a stillcondition and during various modes of vibrationthen yields the performance capabilities of thevidicon.

Source: B. R. Corson ofHughes Aircraft Company

under contract toJet Propulsion Laboratory

(JPL-SC-113)


NASA-Langley, 1971

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