DYNAMIC TEST

SPLIT HOPKINSON PRESSURE BAR

A split Hopkinson pressure bar (SHPB), is a test apparatus used to characterize the mechanical response of materials deforming at high strain rates (102 – 104 s-1). Comparison of strain rate regimes for SHPB to some other classes of testing facilities, the SHPB has evolved from the original version of dynamic compression loading to various versions of other loading states, including tension, torsion, triaxial and axial/shear combination. The principles for all these methods are similar. The major differences are in loading mechanisms and specimen gripping methods.

Although there are various setups and techniques currently in use for the Split-Hopkinson pressure bar, the underlying principles for the test and measurement are the same. The specimen is placed between the ends of two straight bars, called the incident bar and the transmitted bar. At the end of the incident bar, a stress wave is created which propagates through the bar toward the specimen. This wave is referred to as the incident wave, and upon reaching the specimen, splits into two smaller waves. One of which, the transmitted wave, travels through the specimen and into the transmitted bar, causing plastic deformation in the specimen. The other wave, called the reflected wave, is reflected away from the specimen and travels back down the incident bar. Strains caused by the waves are measured using strain gauges on the bars. Then the stress and strain can be calculated from the amplitudes of the incident, transmitted, and reflected waves based on the assumption that the deformation in the specimen is uniform.

THE COMPONENT

The system shown is a generic compression type.

FUNCTIONAL SECTIONS

	Driving Section Using the compressed gas, with the pressure vessel containing emission gas pressurized at 0.8-5 MPa. The operating system is provided with a pressure fine-tune structure and control system. Projectile velocity up to 50 ms-1 and is readily customizable to higher values.
	Speed measurement The velocity of the striker bar is measured using optical sensors, with the digital display gives the reading in m/s up to 4 decimal places.
	Bar system Bars made of heat treated high strength alloy steel with yield strength ≥ 1500 MPa and super-hard aluminum with yield strength ≥ 400 MPa. Other materials include high strength spring steel, 18% Ni steel and polymers. Diameter ranging from 8 mm to 100 mm, can custom-made.
	Centre supporting and aligning devices Constructed of a fixed base, opening upper bracket, triaxial adjustment mechanism, high-precision bearings. Adaptable to various bar diameter sizes.
	Test section The test specimen is located in between incident bar and transmission bar with the use of test specimen protection box.
	Buffer means  Combination of steel structure, double buffer and slippable. Effectively absorb impact energy without damage, and can be installed at the arbitrary location along the rail.
	Base Combined Guiding rail A combination of multiple rails that forms a unified base, with ≧ 10 meters in length. Support part of the launch system and pressure bar can work under the same basis.

SHPB SOFTWARE & MEASUREMENT

- Data analysis software package features
- Preset measurement parameters
- Measurement range, sensitivity, trigger parameters , sampling rate,
- Direct control to hardware
- Channel clearing and balancing, start and stop sampling,real-time data transmitting
- Robust and powerful real-time features
- Manipulations of the channels and setting of display modes can be done dynamically
- Real-time data and waveform simultaneous display
- Powerful processing and analysis functions in time domain
- Maximum, minimum and average values, standard deviation, curve fitting, etc
- Intuitive GUI and simple guided steps to produce strain, stress, strain rate, and stress-strain curves
- Dedicated module for SHPB data analysis
- Incident-reflected, incident-transmitted, incident-reflect-transmitted methods
- Direct conversion into text, spreadsheet and image files

RESULT OUTPUT

DAQ: 6-channel dynamic strain gauge system, frequency response 1MHz, amplification 3000; data processing software with built-in Hopkinson principle to quickly obtain the stress-strain curve of the specimens.

SPLIT HOPKINSON TENSILE BAR

In many structural design applications, engineers are not only concern with the stress-strain response of materials but also the associated failure criteria at various strain rates. A more relevant and critical in tensile loading. The typical SHPB with compressive mode of loading inherently limits the meaningful investigation of failure criteria for practical usage. The tensile version of Splittek split Hopkinson bar system has been designed to provide the solution to overcome such shortcoming by allowing the characterisation of specimen material properties in terms of stress-strain curves coupled with failure criteria.

FEATURES

• Versatile modular structure to facilitate overall system modification and expansion
• Three-way adjustable bearing blocks to facilitate adjustment and alignment of bar system
• Solenoid actuated valve system with electric control panel for effective and efficient operation
• Options of plain or threaded type of specimen
• Impedance matched collets and grips calibrated for each bar material and size
• Precision electric discharge machined slot with a serrated surface finish for better specimen grips
• Precision slip fit tubular striker provides full contact impact and balanced load distribution

DYNAMIC TEST SERVICES

The dynamic mechanical testing of a product comprises a critical part of the product and development process. Applied physical force such as high strain rate shock stresses and strain can reveal the inelastic behavior of the material. Dynamic mechanical testing allows the product developers to understand the product better, identify vulnerabilities, and establish stronger quality control. Dynamic mechanical testing employs a variety of strength tests that can determine the suitability of a material or component for the intended application. We can perform dynamic mechanical testing as an independent analysis or in combination with environmental stimulation, including:

HIGH STRAIN RATE MATERIAL TEST

We are using split Hopkinson pressure bar (SHPB), is a test apparatus used to characterize the mechanical response of materials deforming at high strain rates (102 – 104 s-1). Comparison of strain rate regimes for Split Hopkinson Pressure Bar to some other classes of testing facilities, the Split Hopkinson Pressure Bar has evolved from the original version of dynamic compression loading to various versions of other loading states, including tension, torsion, triaxial and axial/shear combination.

FINITE ELEMENT ANALYSIS

It is a numerical method for solving problems of engineering and mathematical physics. Useful for problems with complicated geometries, loadings, and material properties where analytical solutions can not be obtained. This process is at the core of mechanical engineering, as well as a variety of other disciplines. It also is one of the key principles used in the development of simulation software. Engineers can use these FEM to reduce the number of physical prototypes and run virtual experiments to optimize their designs.

Complex mathematics is required in order to understand the physical phenomena that occur all around us. These include things like fluid dynamics, wave propagation, and thermal analysis. Analyzing most of these phenomena can be done using partial differential equations, but in complex situations where multiple highly variable equations are needed, Finite Element Analysis is the leading mathematical technique.