SHPB SHTB TEST APPARATUS0 pages

Advance Instrument Inc.

Split Hopkinson Bar

High Strain Rata Material Testing

Materials undergo high strain rates deformation in various applications, e.g. accidental events such as explosions

and penetrations, and engineering applications such as crash worthiness of vehicles, bullet proof armors, impact

resistant pressure vessel and shipping cask for transport of nuclear materials. In addition to this, forming processes like

extrusion, rolling and high speed machining can also result in high strain rate deformation. For the optimal design and

safety analysis of components seeing high strain rates of loading the constitutive behavior of materials at high strain

rates is required.

Dynamic testing of material is becoming more important due to the need for more optimized crashworthiness and

impact analysis. Positive strain rate sensitivity, i.e. the strength increases with strain rate, offers a potential for improved

energy absorption during a crash event. The load can be an instant load wave used for very high strain rate. The

machine will also have the proper measurement systems to measure and record the important parameters, such as

strain, displacement and load.

Split Hopkinson Bar system, Single Bar (SB) system is the systems commonly used.

The systems has been developed by Adavnce Instrument Inc. in recent years to meet the increasing demand for

dynamic testing.

Loading Device

Gas Gun Striker^)

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Bar Components

Incident bar

Specimen Transmitter bar Momentum Bar

Stain Gages

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Principle of Split-Hopkinson Pressure Bar

Split-Hopkinson bar (SHB) works on the principle of one dimensional wave propagation, its main

components are a gas gun, a striker bar, an incident bar and a transmission bar. The striker bar sits in

the barrel at the gas gun chamber. The incident bar, transmission bar and striker bar are all made of same

material and same cross-section area. At all times during the test the striker, incident and transmission bar

should remain elastic. The sample to be tested is sandwiched between the incident and transmission bar.

The striker bar is propelled by gas pressure towards the incident bar.

On impact, an elastic compression wave propagates down the incident bar toward the sample. On

reaching the sample, repeated wave propagation within it deforms it plastically. Part of the wave goes

through to the transmission bar (transmitted pulse) and part is reflected back into the incident bar (reflected

pulse), each of which is picked up by the strain gauges mounted on the corresponding bars. Strain gauges

on each bar are mounted to the axial strain. Elastic strain generated in incident and transmission bar are

used to calculate the stress-strain in the sample.

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