Split HopkinsonPressure Bar

High Strain RateMaterial Testing

Split HopkinsonPressure Bar

High Strain RateMaterial Testing

SPLIT HOPKINSON PRESSURE BAROPERATION

SPLIT HOPKINSON PRESSURE BAROPERATION

The purpose of Split Hopkinson Pressure Bartesting is to obtain high strain rate materialproperties.

(A) To initiate high strain rate testing of amaterial, a specimen is loaded between theincident and transmission bars. (B ) Next,the striker bar launcher is pressurized withhelium or nitrogen. When fired, the launcherreleases the gas and propels a striker barinto the end of the incident bar. The collisioncreates a compression pulse, or stress wave,that propagates through the bar toward thespecimen. (C) The incident wave is recordedby the incident strain gauge. Once the wavereaches the specimen, it splits into twosmaller waves. (D) The transmitted wavetravels through the specimen and into thetransmission bar where the energy isrecorded by the transmission strain gauge.The second wave is reflected away fromthe specimen and travels back down theincident bar. (E) At the end of the Split Hop-kinson Pressure Bar, a stop bar absorbs theimpact of the transmission bar to completethe test. (F) Both strain gauges measure thestrain duration and amplification in the bars.The reflected (tensile pulse) recorded by theincidence strain gauge is used to calculatestrain. The portion of the compression pulsethat continues through the specimen isrecorded by the transmission gauge and is used to calculate stress. Data from thestrain gauges is routed through amplifiersand an oscilloscope to a laptop computerwhere it is stored.

OSCILLOSCOPE GRAPHFigure 1 shows how a typical oscilloscopeoutput graph is displayed on a computer.The incident wave, transmitted wave andreflected wave are simultaneously collectedand presented in a graph of Voltage (y-axis)versus Time (x-axis).

BAR SUPPORTThe incident, transmission and stop barsare precision aligned using a series of barsupports. Each bar support moves laterally along an alignment key and is secured to themounting rail using built-in screw clamps.To further assist with leveling, the supportsglide on top of a blanchard ground surface.Proper bar alignment is critical for obtainingaccurate test results and minimizes theamount of noise in your recorded data.

SAMPLE MATERIALSSAMPLE MATERIALS

A Split Hopkinson Pressure Bar (SHPB) is used to obtain highstrain rate material properties. The bar is used to impose a dynamicload on a material specimen akin to loads the material will experience inservice. Determining how the material properties change under service loadscan yield critical performance data.

REL's precision-made Split Hopkinson Pressure Bar includes sophisticatedyet intuitive technology to simplify the process for the operator. Use of thelatest data recording devices and strain gauges ensure accurate measure-ments of material properties at a variety of strain rates.

The Split Hopkinson Pressure Bar by REL, Inc.can be found throughout the world and under thedirection of research institutions, government labs,

private businesses and a wide variety of material testing agencies.

REL, Inc. has provided SHPB equipment or material testing to the following organizations:

Johns Hopkins University - Youngstown State University -

University of Florida - Oak Ridge National Laboratory -

Contact REL, Inc. at(906) 337-3018 to discuss your

material analysis requirements.

oIDirection

Positive x

i t

INCIDENT BAR TRANSMISSION BAR

i = initial pulse

r = reflected pulse oI = specimen length

t = transmitted pulse

SPECIMENSPECIMEN

r

REL, Inc. manufactures steel and polymer Split Hopkinson Pressure Barsystems that are configurable to test compression, tension and torsionsamples. Sample sizes can range in diameter from 0.125" up to 3.000"and consist of a variety of materials, including:

• Metal Alloys • Foams and Plastics • Composite and Ceramics • Bio-tissue

Deformed sample shown for comparative purposes. Deformation of tested samples will vary depending on the material.

*

COMPRESSION SPLIT HOPKINSONPRESSURE BARDESIGN

TENSILE SPECIMENAPPROXIMATELY:0.375"W x 2.50"L x 0.125"H

REL, Inc. offers a tensionSplit Hopkinson Pressure Bar designthat uses a machined tensile specimen forobtaining the most accurate test data.

OSCILLOSCOPE & BRIDGE AMPLIFIERSThe strain gauges are routed through bridgeamplifiers (shown in yellow) and an oscillo-scope. Data from each gauge is conditionedand amplified for multi-channel, simultaneousdynamic recording and display. The oscillo-

scope converts the measured data from an analog signal to digital. REL’s proprietary software further converts the signal into a dynamicstress versus strain curve (Fig. 2).

DYNAMIC STRAIN GAUGEREL uses high-precisionbonded resistance straingauges to capture energyfrom stress waves. Thegauges are adhered tothe surface of the incidentand transmission bars. Signals transmitted fromthe bar to the gauge arecaptured and converted by REL’s proprietary dataacquisition system.

STRIKER BARSStriker bars can be made from steel or polymers andsupplied at different diameters (0.25" up to 3" orcustom) and lengths (3" up to 24"). Various lengthstriker bars will produce different loading durations.

LAUNCHER CONTROLSThe striker bar launcher controls includea gas fill valve (yellow handle), gas re-lease valve (silver lever) and a breechload adjustment control (large black dial).Turning the dial moves a positioning rodinside of the launcher, which pushes thestriker bar forward in the breech.

STRIKER BAR LAUNCHERThe velocity of the striker bar projectile is con-trolled by pressurized helium or nitrogen thatis forced into the launch chamber. The type ofmaterial being tested and the construction ofthe striker bars in use generally determineoperating pressure.

STRESS -VS- STRAIN GRAPHData collected from the REL Split Hopkinson Pressure Bar (See Fig. 1) isprocessed through a series of formulas to obtain final data (shown above).REL includes an intuitive graphical user interface for the operator to quicklyacquire dynamic material properties.

EQUIPMENT SPECIFICATIONSEQUIPMENT SPECIFICATIONS

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MATERIAL TESTING AND ANALYSIS

REL, Inc. offers comprehensiveSplit Hopkinson Pressure Bar testing

with complete material analysis.

For more information, contact an REL material specialist at

(906) 337-3018 or visit the company web site at

www.relinc.net

SYSTEM FLEXIBILITY- System Type (Compression, Tension or Torsion)

- System Material Construction (Steel, Polymer, etc.)

- Total Length of System- Incident, Compression and Stop Bar Diameter- Incident, Compression and Stop Bar Length- Striker Bar Diameter and Length- Striker Bar Launcher Pressure Range Requirement

* REL Split Hopkinson Pressure Bar dimensions shown for example compression design only. Complete system build requirements will determine final dimensionsand equipment specifications.

REL, Inc. reserves the right, under its Continuous Improvement Policy, to changeconstruction or design details and furnish product when so altered without reference to illustrations or specifications used herein.

Copyright ©2012 REL, Inc. All rights reserved.Litho in U.S.A. Form No. 1000-06-12

*EXAMPLE COMPRESSION DESIGN

- Strain Gauge Type and Construction- Momentum Trap Inclusion- Acquisition System Inclusion

(Computer, Amplifiers & Oscilloscope)