Using Controlled Impulses of Energy for High Strain Rate Material Testing
A car crash, a ballistic event, a volcano, an IED explosion, football players’ helmets colliding, and high speed machining. What do these events have in common? The materials in all of these circumstances are subject to a high rate of deformation. The performance of materials under a high strain rate can be significantly different than the performance under quasi-static loading conditions. (slower loading rate)
Government mandates for fuel-efficient vehicles lends impetus for vehicle manufacturers to study weight reduction strategies, without sacrificing safety. Engineers are developing and/or evaluating lighter materials that maintain required strength and energy adsorption during an impact event. The Split Hopkinson Pressure Bar can be utilized to understand material properties at high strain rates because it provides a controlled impulse of energy that simulates what the material will experience in a dynamic event.
- High strain rate testing
- Material characterization
- Material response
- Johnson-Cook parameters
New methods are being developed to test in both tension and shear. Likewise, new applications for this test include:
- Prediction of volcanic eruptions
- Viscoelastic response
- Earthquake waves
- Soil (aggregates) in shear
- Development of explosives
- Blunt trauma
Split Hopkinson Pressure Bar has proven to be successful in the evaluation of energy absorbing materials including metals, glasses, ceramics, polymers, and foams. See the reference material for examples in various applications.
The Split Hopkinson Pressure Bar runs by a gas gun being pressurized and released. This causes the striker bar to impact the incidence bar. The incident pulse wave triggers the oscilloscope which then begins to record the pulse signals. These pulse signals are produced by the change in resistance in the strain gages on the incidence and transmission bars. Raw data is collected and stored in a graph of voltage vs. time and is then converted to a stress-strain plot.
REL has a Split Hopkinson Pressure Bar Laboratory (pictured above) complete with test material preparation, X-Ray, SEM, and for testing and evaluation of new methods. REL tailors to the needs of customers to determine the best test method for their individual material needs. REL provides machined test samples and striker bars.
REL provides custom-built Split Hopkinson Pressure Bars specific to customer’s laboratories and built to their needs.