CASE FILE COPY...NASA SP-5944(01) UTMSATION. t^.t ~ "' "ft CASE FILE COPY TESTING METHODS AND TECHNIQUES: STRENGTH OF MATERIALS AND COMPONENTS A COMPILATION NATIONAL AERONAUTICS AND

NASA SP-5944(01)

UTMSATION

. t .̂t ~ "'

"ft

CASE FILECOPY

TESTING METHODS AND TECHNIQUES:STRENGTH OF MATERIALS

AND COMPONENTS

A COMPILATION

NATIONAL AERONAUTICS AND SPACE ADMINISTRATION

https://ntrs.nasa.gov/search.jsp?R=19720011249 2020-04-03T11:01:15+00:00Z

ForewordThe National Aeronautics and Space Administration and the Atomic Energy

Commission have established a Technology Utilization Program for the dissemina-tion of information on technological developments which have potential utilityoutside the aerospace community. By encouraging multiple application of theresults of their research and development, NASA and AEC earn for the publican increased return on the public investment in aerospace and nuclear R&Dprograms.

The methods, techniques, and devices presented in this compilation are usedin testing the mechanical properties of various materials. Although metals andmetal alloys are featured prominently, some of the items describe tests on avariety of other materials, from concrete to plastics. Many of the tests describedare modifications of standard testing procedures, intended either to adapt themto different materials and conditions, or to make them more rapid and accurate.In either case, the approaches presented can result in considerable cost savingsand improved quality control.

The compilation is presented in two sections. The first deals specificallywith material strength testing; the second treats the special category of fractureand fatigue testing.

This compilation is not a complete survey of the field of materials testing.Rather, its sampling of many diverse activities is intended for the interest ofmechanical engineers and materials testing technicians. At the same time, it mayserve as an introduction to the field for those unfamiliar with the principlesand practices of materials testing.

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 utility of the information in this compilation.

Technology Utilization OfficeNational Aeronautics and Space Administration

NOTICE • This document was prepared under the sponsorship of the National Aeronautics and SpaceAdministration. Neither the United States Government nor any person acting on behalf of the UnitedStates Government assumes any liability resulting from the use of the information contained in thisdocument, or warrants that such use will be free from privately owned rights.

For sale by the National Technical Informat ion Service, Springfield, Virginia 22151. $ 1-00

Table of ContentsSECTION 1. Material Strength Testing Page

Tensile Tester Accepts Multiple Coupons 1Portable Tensile Testing Unit 1Long Coupon Used for Evaluating Organic MaterialTensile Properties 2

Frictional Loading Device for TestingBrittle Materials 2

Tensile Testing Grips Ensure Uniform Loadingof Tubular Specimens 3

Testing Filamentary Composites 4Pin-Ended Column Loading Device 5Tensile Coupon Gage Length Scriber and Elongation

Measurement Device 6Modified Technique for Elongation Measurement

of Thin Metal Strips 7Tensile-Strength Apparatus Applies High Strain-Rate

Load with Minimum Shock 7Problems in High-Velocity Shock Testing Usinga Slingshot Shock Machine 8

Flexure Test Apparatus for Electrical Conductors 9Controlled Hydraulic Loading Device ; 9High-Accuracy Flexure Test Fixture 10Load Cell Calibrator 11Testing Weld Strength and Mechanical Properties

of 2219-T81 Aluminum Alloy -. 11Torsion System for Multiple-Stress-ReversalCreep Testing 12

Testing the Room-Temperature Aging Propertiesof Tens 50 (T4) Aluminum Alloy 12

SECTION 2. Fracture and Fatigue TestingFatigue Testing of 1100-H14 Aluminum Alloy - 13Low-Cycle Fatigue Tests on Nickel Alloys 625and Hastelloy C 13

Fatigue Data Obtained from Programmed HydraulicLoading System 14

Hydraulic Servo System Increases Fatigue-TestingAccuracy 15

Fatigue Tester with Flex Plates and Bars GivesTrue Axial Motion 16

Automatic, Nondestructive Monitoringof Fatigue-Crack Growth 16

Fatigue Cracks Detected and MeasuredWithout Test Interruption 17

Analysis of Flow-Induced Fatigue in Bellows 17Cryostat Modified for Rotating-Beam Fatigue Test 18Fatigue in Reinforced Concrete Beams

under Dynamic Load 19Survey of Fracture Testing Methods 19Cracks of Known Size Induced in Metal Samples

for Fracture Mechanics Studies 20Fracture Mechanics Test Method 20Accelerated Stress Corrosion Test for Steels

and Nickel Alloys 21Failure Modes in Polytetrafluoroethylene ExaminedUsing Fractography 21

Stress Crazing of Chlorotrifluoroethylene PolymerCaused by Halogenated Solvents 22

A Rapid Stress-Corrosion Test for Aluminum Alloys 22Chemical Milling Reveals Stress Corrosion Cracks

in Titanium Alloys 23

in

Section 1. Material Strength Testing

TENSILE TESTER ACCEPTS MULTIPLE COUPONS

A novel device permits rapid, sequential testingof up to 6 tensile coupons without interruptionfor manual alignment between tests. This feature

TensileForce

PI*-—Pull Rod

•Upper ClevisI»_J

cing Links

I

TensileTestCoupons

LowerClevis

is especially useful when testing is to be per-formed under controlled environmental condi-tions, where time would be lost in regainingthe proper environment after the interruption.

The device differs from a similar, commerciallyavailable system in that it provides positivecoupon alignment prior to test, and is much

less apt to jam and cause premature failure.As shown in the figure, the device consistsof radially arrayed tensile coupons, connectedat the upper end by high-strength spacing links(two links per gap) and mounted at the lowerend on a special shank. The upper end of thefirst coupon is attached to the upper mountingclevis, which is attached to the pull-rod of thetesting machine. The shank is retained in thelower clevis by keeper plates, and the lowerclevis is screwed into the base of the tester.Strain gages are bonded to each specimen,enabling separate stress-strain plots to be made.

As the pull-rod moves upward, the firstspecimen is stressed to the breaking point. Furthervertical movement of the rod causes the linkageconnecting the first and second specimensto rotate the lower mounting about the shankand align the second specimen. Tension isthen applied to the second coupon across thefirst pair of spacing links. Progressive rotationof the plate after each failure of a specimenallows complete testing of all specimens.

Source: R. T. Hartunian ofMcDonnell Douglas Co.

under contract toMarshall Space Flight Center

(MFS-2067)

Circle I on Reader Service Card. '

PORTABLE TENSILE TESTING UNIT

A commercially available, portable, tensiletesting unit has been improved by adding anhydraulic accumulator to the tester's hand-pumped load cell. The accumulator allowslest loads to be applied at a constant strain rate,

thereby improving the accuracy and repeata-bility of test results obtained.

The addition of the accumulator to the unitprovides two separate test systems. The operatorcan (1) bypass the accumulator and use the hand

MATERIAL STRENGTH TESTING

steel cylinder whose diameter and length areconsistent with the size of the specimensto be tested. Six equally spaced rows of

testing machine (not shown), with a compres-sion loading block supporting the friction load-ing bars. Lateral loading is provided through

Friction Loading BarsTest Specimen steel Cylinder

Backup Rectangular Bars

Specimen Assembly

radially tapped holes are cut into the walls ;ofthe cylinder. These holes accept either hydraulicactuators or alignment/reaction bolts. Thisarrangement permits six-faced loadings of speci-mens that have a hexagonal cross section.

The test specimen assembly is prepared bysurrounding the specimen proper with sixfrictional loading bars that are slightly longerin length than the test specimen. Backup rec-tangular bars are added to distribute the lateralloading uniformly. The mating faces ofloading bars are machined to provide a smallclearance, so that the full lateral load is carriedby the test specimen.

The bundled specimen is centered in the testchamber, which is then positioned on a universal

Al ignment/ReactionBolts

Hydraulic Actuators

Test Chamber

the hydraulic actuators. With a very lightlateral pressure applied, the frictional loadingbars are compressed by a predetermined amount.The hydraulic actuators are then pressurizedto a preset pressure and the compression onthe loading bars is released at a uniform rate.As the load is released, the test specimen isplaced in tension. Compression release con-tinues until the test specimen fractures.

Source: T. F. Hengstenberg and G. Zibritosky ofWestinghouse Astronuclear Laboratory

under contract toAEC-NASA Space Nuclear Systems Office

(NUC-0051)

No further documentation is available.

TENSILE TESTING GRIPS ENSURE UNIFORM LOADINGOF TUBULAR SPECIMENS

A new design, double-grip fixture for attachingtubular specimens to a tensile testing machinesolves the problem of unequal stress dis-

tribution across the tube cross section.Standard grips used in the tensile testing of

bimetal tube specimens allow tensile loading


Tensile Force

FilamentaryComposite Ring

Tensile Force

Figure 1. Split-Dee Tensile Test

corners of the dees. This generates bendingmoments of a sufficient magnitude to throwdoubt on the validity of the test data.

A straight section was added, adjacentto the split in the dees, in an attempt to eliminatethe bending moment. Mathematical analysisof the resulting "racetrack" specimen andcomparison of test results achieved with it andthe ring specimen indicate that, while bendingis not eliminated by this addition, it is sub-stantially reduced. Even a relatively short (1 cm)section reduces the bending moment to lessthan one-half that of the circular ring.

A fur ther advantage of the "racetrack" speci-men is that strain gages may be readily attachedto the composite material in the center of thestraight section.

1 to 3 cm.

Gap

Figure 2 "Racetrack" Filament-Wound Tensile Specimen

The following documentation may beobtained from:

National Technical Information ServiceSpringfield, Virginia 22151Single document price $3.00(or microfiche $0.65)

Reference:NASA-CR-66518 (N68-13926), DesignCriteria and Concepts for Fibrous Com-posites Structures

Source: B. W. Rosen and N. F. Dow ofGeneral Electric Co.

under contract toNASA Headquarters

(HQN-10268)

PIN-ENDED COLUMN LOADING DEVICE

icimen

MobbedLoading Plates

V

Load

Specimen

Aligning DeviceAdapterPlate

Ball Bearing

Section of View A

An inexpensive, simple-to-make device canapply a load to a round- or pin-ended columnin a universal testing machine and can yield anend-fixture constant near unity. The deviceallows universal movement, has very lowfriction under heavy load, and has a maximumend-fixture constant of 1.08.

The device (see fig.) enables a specimen tobe loaded between two small steel ball bearings.


MODIFIED TECHNIQUE FOR ELONGATION MEASUREMENTOF THIN METAL STRIPS

The scribing technique discussed in the previousitem will not work reliably when very thinspecimens are to be tested, because the inscribedmarks themselves may act as points of stressconcentration in the specimen and causepremature fracture.

A solution to this problem is achievedby applying a thin gold plating to the testcoupons before scribing. After test, the specimenmay be pieced back together and photographed

along with an accurate scale. The specimenshould be obliquely lighted in order to revealthe scribe marks in the gold layer.

Source: I .M. RehnofAerojet-General Corp.

under contract toAEC-NASA Space Nuclear Systems Office

(NUC-10076)


TENSILE-STRENGTH APPARATUS APPLIES HIGH STRAIN-RATELOAD WITH MINIMUM SHOCK

Pump-Down Port

Valve ChamberQuick-Dump Valve.

Capillary Bundj£Overtravel Spring

PistonLoading Cylinde

telease ValveAccumulator

AccumulatorVent Valve

SecondaryNitrogen Valve

Valve Poppet

Quick-Dump ValveDetail

Piston RodPotentiometer-!}}ArmThermal PaneWindow'Potentiometer

Temperature/Control Box

Oscilloscope

PrimaryNitrogen Valve

N2 Pressure'Regulator

NitrogenBottle

Temperature-ControlAir Ducts

The apparatus shown in the diagram can applytensile test loads at relatively constant, veryhigh strain rates (up to 8.5 m/s), with minimalshock and vibration to the tensile specimen andapparatus.

The apparatus consists of two primary as-semblies, a strain generator and a specimencontainer, separated by a strain wall. The speci-men container is enclosed in a temperature-control box, and the specimen is connected

directly to the strain generator through a pistonrod.

To ready the system for test, oil is pumpedfrom the pump-down port to the top side of theloading-cylinder piston. This transfer of oil auto-matically seats the quick-dump valve poppetand also drives the loading-cylinder piston toits lower position. The primary nitrogen valveis opened to pressurize the underside of thispiston. The secondary -nitrogen valve is then


FLEXURE TEST APPARATUS FOR ELECTRICAL CONDUCTORS

A flexure testing machine simultaneously sub-jects up to four insulated electrical wire speci-mens to repeated bending stress, and positivelyindicates failure of the conductor. The wire isrepeatedly bent over mandrels at a controlledrate, through a bend angle of ±?r/4 rad (±45°).A relay-actuated control circuit stops themachine upon fracture of any single conductor.Indicator lamps are lighted to reveal the failedspecimen. The control and indicator circuitry isneeded because many present day insulationmaterials are capable of bearing the loadweights by themselves after conductor fracture.

An alternate mode of operation allows measur-ing and recording any change in conductorresistance during test. The machine may be pro-grammed to discontinue the test after any, re-sistance value or resistance change ratio isreached.

Source: E. U. Baker ofMcDonnell Douglas Corp.


(MFS-13572)

Circle 6. on Reader Service Card.

CONTROLLED HYDRAULIC LOADING DEVICE

Plug and Seal

High PressureGaseous Hydrogen —

Frame

Specimen

Test"Vessel

ThrustBearing

Motion Pacer

The hydraulic loading device shown in the fig-ure provides either load- or strain-rate control fortesting critical tensile specimens. Designed to

provide loading at linear strain rates from 0.1 to0.5 m/m/min, the device effectively paces bothload-application and strain-rate from zero toa maximum load of 26.6 kN (6000 Ib).

For load-rate control, a commercially avail-able, motion pacer unit is attached to the bot-tom spring plate of the static loading device.The pacer is used in conjunction with a manualhydraulic flow control valve, which controlsthe rate at which the hydraulic ram compressesthe spring of the static loading device. Forspecimen strain-rate control, the motion paceris attached to the top plate of the static loadingdevice. In this mode of operation, cross-headmotion is paced.

Source: R. D. Lloyd and G. V. Sneesby ofNorth American Rockwell Corp.


(MFS-2000)


MATERIAL STRENGTH TESTING 11

LOAD CELL CALIBRATOR

Proving Ring

Load Cell

ILJU

The illustrated device permits the use of astandard proving ring as a calibration transferdevice for calibrating load cells of 220 to 2200 N(50 to 500 Ib) capacity. Prior to the constructionof this device, such low-capacity load cells werecalibrated using weights as transfer standards.

Hydraulic Ram The device, similar, except in size, to a com-mercially available force calibrator, is smallenough to permit handling low-capacity loadcells conveniently.

Source: S. C. Stene and E. R. Lebs ofNorth American Rockwell Corp.

under contract toManned Spacecraft Center

(MSC-11865)

Circle 8 on Reader Service Card.

TESTING WELD STRENGTH AND MECHANICAL PROPERTIESOF 2219-T81 ALUMINUM ALLOY

Welding, fracture, tensile-strength, and fatiguetests performed on 2219-T81 aluminum alloyhave resulted in improved knowledge of themechanical properties of this alloy. Among theimportant results are the following: (1) Theyield strength of 2219-T81 sheet and platedecreases significantly when welded. The re-duction of yield strength is much greater thanthe corresponding reduction in ultimatestrength. (2) Toughness of base metal 2219-T81sheet and plate increases with a decrease in tem-perature. Plane stress and plane strain fracturetoughness of the heat-affected zone (HAZ) in-creases . with a decrease in temperature; theHAZ is less tough than the base metal buttougher than any other zone. The weld metalregion has the lowest fracture toughness ofany of the regions tested. (3) The weld areafracture toughness (plane stress or plane strain)of automatically welded 2219-T81 sheet orplate decreases significantly between 78 and 20

K. (4) The behavior of welded 2219-T81 alu-minum plate is quite erratic after three repairwelds have been made. The toughness valuesof repair welded 2219-T81 aluminum can besubstantially lower than those of the new welds.(5) Cyclic flaw growth rates are generallyhigher on the weld metal than on any otherregion tested. (6) At normal operating stresses,the critical flaw size for 2219-T81 parentmetal and welds is quite large, given the standard2:1 weld land buildup. (7) Due to the Verylow possible toughness of repair welds, it isrecommended that repair welding be kept to aminimum with 2219-T81 aluminum, becauseserious material property degradation ispossible. All repair welds (except for the flawsimulation tests) on this program meet allgovernment specifications for welds. (8) Tungsteninclusions considerably reduce the fracturetoughness of the welds. Such inclusions shouldbe removed wherever possible.

MATERIAL STRENGTH TESTING 13

Strength—Grade 1" castings. The castings wereall produced with the same mold design andfrom the same ladle of metal. The machinedtest bars were solution heat treated for 12 hoursat 865 K and then oil quenched. Two test barswere used for each test. The first two bars weretested after 30 minutes and the last two bars weretested after 24 hours.

The results indicated that room temperature

aging of Tens 50 alloy is a slow process, prob-ably requiring several days before minimumstrength requirements are met or exceeded.

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


(MFS-18931)


Section 2. Fracture and Fatigue Testing

FATIGUE TESTING OF 11QO-H14 ALUMINUM ALLOY

An investigation of the fatigue properties ofpure (1100) aluminum in various gaseous en-vironments has shown that the fatigue life ofthe metal is greater in vacuum than it is inair, by a factor of about 3:2. The effects ofresidual, concentrations of oxygen, water vapor,and hydrogen on fatigue life have also beeninvestigated.

Fatigue tests were conducted in partialpressure and vacuum environments, using modi-fied ASTM constant stress bend specimens inthe cantilever mode of reverse bending. Thefatigue life data were plotted as a function of sur-face strain amplitude calculated from fixeddeflection amplitudes. Outer surface stress

amplitudes were calculated from the elasticstrain levels, assuming negligible fatiguehardening. Preliminary studies have shownthat the 1100-H14 aluminum used in thisseries of fatigue tests exhibits very little strainhardening and maintains an essentially elasticstress-strain response in bending.

Source: M. J. Hordon, M. A. Wright andM.E. Reed of

National Research Corp.under contract to

NASA Headquarters(HQN-10197)


LOW-CYCLE FATIGUE TESTS ON NICKEL ALLOYS 625AND HASTELLOY C

Low-temperature, low cycle, flexural fatiguetests have been performed on two prominentnickel alloys to determine short-term de-formation and change in load-carrying ability.Flexural reverse-bending fatigue tests wereconducted on Alloy 625 .and Hastelloy C atspeeds up to 30 cycles per minute, with maxi-mum deflections of ±2.41 cm in a total specimenlength of 12.7cm.

For each alloy, two strain gages were cementedto each of two specimens, at 8.1 cm and 3.45 cmfrom the moving end of the specimen. With thefirst specimen of each pair, the gages were con-nected to an X-Y recorder; the second set ofgages was .connected to an oscilloscope.A standard tensile testing machine was usedto deflect each specimen 2.41 cm in tension andin compression.

FRACTURE AND FATIGUE TESTING 15

and a calibration readout unit, together with thesignal from a second strain-gage bridge. The.section also includes readout instrumentationneeded to calibrate and monitor performance.

- Source: W. T. DavisLangley Research Center

(L A R-10042)

Circle 12 on Reader's Service Card.

HYDRAULIC SERVO SYSTEM INCREASES FATIGUE-TESTING ACCURACY

+E

h—Command SignalGenerator

Proportional Loop

LimitComparatorErrorDetection

Signal GeneratorFor Solid StateSingle-Pole. Double-Throw Switches

The fatigue testing system shown in the figurehas improved the accuracy of loads applied toa standard fatigue specimen. The system con-sists of a proportional loop hydraulic system andan error-sensing electronic control loop.

The proportional loop contains a servoamplifier with a limit control, a servo valve whichdrives a piston, a velocity sensor, a force sensor,and the fatigue specimen. Frequency controlis obtained by setting the limits on the servoamplifier. This is the normal assembly used forfatigue loading of a specimen.

To increase the accuracy of the system, anerror-sensing electronic control loop is added tothe proportional loop. This control loop con-sists of a signal generator, a force voltage trackerand storer, an error detection comparator,an error integrator, SPOT switches, and a com-mand signal generator.

The electronic error sensor tracks and storesthe force sensor's output voltage to the point

where the velocity changes sign (i.e., the pointof maximum force). The stored output voltagesare then compared with the desired commandreference voltages in the error detection com-parator. An error signal generated for each peakis integrated and added to the appropriate com-mand voltage level, and the composite commandsignal is fed to the proportional loop hydraulicsystem.

The velocity sensor of the proportional loopsystem triggers the signal generator which drivesthe SPOT switches! These switches, SI and S2,appropriately channel the inputs and outputs ofthe error sensing electronic control loop toachieve two proper feedback voltages. One ofthese is selected by switch S3 and fed into theproportional loop.

Source: G. V. Dixon and K. S. KiblerLangley Research Center

(LAR-217)



a flexible shaft, guides the transducer across thespecimen.

Tests were conducted on a specimen intowhich a slot was being machined to simulatethe propagation of a fatigue crack. Incrementsas small as 0.003 cm were detected and auto-matically tracked. The repeatability of thesystem was ±0.013 cm for a number of speci-mens tested.

Source: F. Hoppeand N. S.Jnman ofFairchild Miller Corp.

under contract toLangley Research Center

(LAR-10091)


FATIGUE CRACKS DETECTED AND MEASUREDWITHOUT TEST INTERRUPTION

An ultrasonic flaw detector, involving modifiedtransducers clamped to the. specimens, non-destructively detects fatigue cracks. The systemprovides a permanent, continuous record ofcracks encountered throughout fatigue tests,without any need to interrupt or interfere withthe tests.

Detecting fatigue cracks by the reflection ofultrasonic energy is similar to detecting distantobjects by using radar. Acoustic energy generatedby an ultrasonic transducer is transmitted intothe test specimen in the form of pulsed en-velopes of high-frequency waves. After the pulseis transmitted, the same transducer acts as areceiver for energy reflected from any dis-

continuity, such as that formed by the metal-airinterface of a fatigue crack. The amount ofenergy reflected from a crack is related to thecrack area, the intensity of the incident ultra-sonic wave, and the orientation of the crack.

The oscillograph readout is coupled to a gat-ing circuit, permitting a permanent record to bemade of signals received from flaws in a selectedportion of the specimen while the test isrunning.

Source: S. J. Klima, D. J. Lesco, andJ. C. Freche

Lewis Research Center(LEW-266)


ANALYSIS OF FLOW-INDUCED FATIGUE IN BELLOWS

An investigation of bellows failure caused byflow-induced fatigue has yielded increased under-standing of the mechanism of vibration genera-tion and amplification in bellows, and has pointedthe way toward a solution to the problem ofbellows fatigue.

Fatigue failures are experienced in bellowscarrying fluids at high speed. Such failurescommonly occur when bellows are subjectedto flow speeds around Mach 0.3, but theprinciples governing this behavior are not wellunderstood. Although a rigorous analysis ofthis problem is difficult, much insight can beobtained qualitatively.

It can be assumed that flow through a bellowsgenerates random sound waves in the - f lu idfrom repeated sources. For example, soundgenerated by the disturbance in flow past aconvolution root will be generated at repeatedintervals, corresponding to the convolutionspacing, along the bellows. Under these condi-tions, certain wavelengths of sound will beamplified and others cancelled. Because thesound travels along the bellows in both direc-tions, standing waves can be produced.

Because convolutions are essentially springs,they must be affected to some extent by anyvarying force such as sound waves. The extent


load the specimen during test. Automatic controlof liquid level in the Dewar, and a shut-offswitch actuated by test specimen failure, permitunattended operation for considerable periods.

Source: T. F. Durham ofNorth American Rockwell Corp.


(MFS-435)


FATIGUE IN REINFORCED CONCRETE BEAMS UNDER DYNAMIC LOAD

Investigation of the strength properties ofreinforced concrete beams subjected to vibra-tional stresses has led to increased knowledgeof the dynamic properties of concrete. Suchknowledge is needed for the design of buildingsfrequently subjected to high-intensity vibra-tions. Buildings located near missile launchingpads and jet air fields are obvious examples.

One hundred specially designed, scaled, rein-forced concrete beams were tested. Fifteen weretested to determine their static strengths. Theremaining beams were tested under sinusoidaland random vibrations to determine theirdynamic fatigue characteristics. The beams weremounted, one at a time, on an electromagneticshaker and were vibrated at their supports.Desired stress levels were maintained by moni-toring the input signal to the shaker. The num-ber of vibration cycles was established up tothe moment of the specimen's failure. The rein-forcing wires imbedded in the concrete beams

were also tested by a tensile machine to deter-mine their yield and ultimate tensile strengthsand to obtain a better analytical understandingof the strength of the reinforced concrete speci-mens.The following documentation may be obtainedfrom:

National Technical Information ServiceSpringfield, Virginia 22151Single document price $3.00(or microfiche $0.65)

Reference:NASA-CR-79530 (N67-11684) Fatigueof Reinforced Concrete Due to Sinus-oidal and Random Loadings

Source: G. C. Chan ofWyle Laboratories


(MFS-14980)

SURVEY OF FRACTURE TESTING METHODS

A comprehensive survey has been preparedon current fracture-toughness testing methodsthat are based on linear-elastic fracture mechanics.General principles of the basic, two-dimensionalcrack, stress-field model are discussed in rela-tion to real three-dimensional specimens. Thedesigns and necessary dimensions of specimensfor mixed mode and opening mode (planestrain) crack-toughness measurements are con-sidered in detail. Test procedures and instru-

mentation methods are described, and expres-sions for the calculation of crack-toughnessvalues are given for the common types ofspecimens.

Source: J. E. Srawley, M. H. Jones, andW. F. Brown, Jr.

Lewis Research Center(LEW-10379)



spanning the machined crack, and knife-edgeclips on the bracket engage the notched arms ofthe holders. When the precracked joint is placedunder load, the gage measures displacementswhich are primarily due to the behaviorof the crack, with the parent metal acting es-sentially as rigid material.

Source: J. E. Collipriest and D. E. Kizer ofNorth American Rockwell Corp.


(MFS-16786)


ACCELERATED STRESS CORROSION TEST FOR STEELSAND NICKEL ALLOYS

The stress corrosion susceptibility of a widevariety of steels and nickel alloys can berapidly evaluated using a new laboratory testprocedure.

Single-edge-notched specimens are fatigue-cracked, loaded in plane tension, and immersedin 20% by weight NaCl solution at room tem-perature. A computer program is used to calcu-late approximate loading parameters, and requiredtesting time is limited to a maximum of 1000hours. Times as short as 100 hours may be usedunder some circumstances.

The test can be used to determine: (1) thestress-corrosion susceptibility of many commonhigh-strength alloys; (2) the effects of processingparameters on the susceptibility of these alloys;and (3) the acceptance level for stress corrosion

resistance of the alloys. Preliminary seacoasttrials have verified the validity of the test.

The same basic approach to the developmentof a stress-corrosion test has been used before.However, earlier tests were based on the use offatigue-cracked cantilever bend specimens, whichrequired individual loading fixtures. Using edge-notched tensile specimens allows a large numberof specimens to be loaded in series and testedsimultaneously in a single, dead-weight, lever-armloading system.

Source: A. H. Freedman ofNorthrop Corp.


(MFS-13701)


FAILURE MODES IN POLYTETRAFLUOROETHYLENE EXAMINEDUSING FRACTOGRAPHY

Fractographic principles, long used in metal-lurgy, can now be applied to the analysisof the microstructure and fracture characteristicsof polytetrafluoroethylene (PTFE). Fractographyis a common analytical technique for studyingthe fracture face of a failed metal by means ofboth macro- and microphotography. The minutetopographical features revealed in the fracto-graphs are then compared with standards pre-pared from specimens fractured under controlledconditions. Similarity between a standard and a.fractograph that represents an actual service fail-ure is used to determine the failure mode.

Notched and unnotched samples of 0.65 cmthick PTFE were tested in tensile and fatiguetesting machines, both at room temperature andat the temperature of liquid nitrogen. Thetest conditions approximated the most extremestress and cryogenic environments to which thePTFE would be exposed during use. Replicasof the fractured surfaces were prepared by thecommonly used, two-stage, acetate replicatechnique. All fractures were studied in twomagnification ranges: the macrorange, from 1 tol O x ; and the microrange, from 3500 to 15,000x(with the. electron microscope). The various


rosion of the specimens. Failure of highlystressed susceptible alloys and tempers generallyoccurs during the first few hours of testing.Therefore, specimens should be inspected atleast once during the first four hours' exposure,and twice a day thereafter.

Source: W. J. Helfrich ofKaiser Aluminum and Chemical Corp.


(MFS-20175)


CHEMICAL MILLING REVEALS STRESS CORROSION CRACKSIN TITANIUM ALLOYS

A solution of the type used for the chemicalmilling of titanium alloys may be used to re-veal stress corrosion cracks, without specialsurface preparation. The solution consists of 10parts HF (concentrated), 60 parts H2O2

(30% concentration), and 30 parts H2O, byvolume. The surface is simply rinsed in waterand dried, swabbed with the solution for 10 to30 seconds, and rinsed again in water. The crackscan then be observed by the naked eye or atlow magnification. The technique is especially

useful with large specimens or hardware,where polishing would be impractical. The solu-tion may also be useful in revealing smallmachining cracks or fatigue cracks,but should notbe used when the examination must betotally nondestructive.

Source: D. N. BraskiLangley Research Center

(LA R-10077)


NASA-Langley, 1971

NATIONAL AERONAUTICS AND SPACE ADMINISTRATIONWASHINGTON, D. C. 20546

OFFICIAL BUSINESSPENALTY FOR PRIVATE USE S300

FIRST CLASS MAIL

POSTAGE AND FEES RAIDNATIONAL AERONAUTICS AND

SPACE ADMINISTRATION

POSTMASTER: If Undeliverable (Section 158Postal Manual) Do Not Return

"The aeronautical and space activities of the United States shall beconducted so as to contribute . . . to the expansion of human knowl-edge of phenomena in the atmosphere and space. The Administrationshall provide for the widest practicable and appropriate disseminationof information concerning its activities and the results thereof."

— NATIONAL AERONAUTICS AND SPACE ACT OF 1958

NASA TECHNOLOGY UTILIZATION PUBLICATIONSThese describe science or technology derived from NASA's activities that may be of particularinterest in commercial and other non-aerospace applications. Publications include: '

TECH BRIEFS: Single-page descriptions ofindividual innovations, devices, methods, orconcepts.

TECHNOLOGY SURVEYS: Selected surveysof NASA contributions to entire areas oftechnology.

OTHER TU PUBLICATIONS: These includehandbooks, reports, conference proceedings,special studies, and selected bibliographies.

Details on the availability of thesepublications may be obtained from:

, National Aeronautics and

Space Administration

Code KT

Washington, D.C. 20546

Technology Utilization publications are part

of NASA's formal series of scientific and

technical publications. Others include Tech-

nical Reports, Technical Notes, Technical

Memorandums, Contractor Reports, Technical

Translations, and Special Publications.

Details on their availability may beobtained from:

National Aeronautics and

Space Administration

Code KS

Washington, D.C. 20546

NATIONAL AERONAUTICS AND SPACE ADMINISTRATIONWashington, D.C. 20546

Documents

CASE FILE COPY...NASA SP-5944(01) UTMSATION. t^.t ~ "' "ft CASE FILE COPY TESTING METHODS AND TECHNIQUES: STRENGTH OF MATERIALS AND COMPONENTS A COMPILATION NATIONAL AERONAUTICS AND