Stress wave separation based on standard Hopkinson pressure bar set-up and unlimited duration of experiment data processing

Based on the classical one-dimensional stress wave theory and the assumption of force equilibrium of the specimen, a new method for separating left-going and right-going stress waves on the standard Hopkinson pressure bar set-up is proposed. It can solve the problem of left-going and right-going stress wave signal overlapping in a standard Hopkinson pressure bar used for a long-duration experiment effectively and with simplicity. By introducing virtual strain measuring points at the specimen end of the incident bar and the free end of the transmission bar, the separation problem of stress waves in each bar which using only one strain gage is transformed into the two-point wave separation problem and then the separation of the left and right traveling stress waves is conveniently accomplished. In principle, this new method allows unlimited duration of test data analysis thus the overall experimental process can be analyzed. It thereby significantly enhances the test ability of the standard Hopkinson pressure bar. New experimental data processing formulas based on the left-going and right-going stress wave signals are presented. They are actually the generalizations of the classical data processing formulas. These new formula are equivalent to the classical formulas when the wave separation processing is unnecessary. Full model simulations of the split Hopkinson pressure bar experiment were carried out on the ABAQUS/Explicit finite element simulation platform. The simulated strain signals at the test positions then are processed in the way of virtual experiment under various experimental conditions. Based on this, the effectiveness and errors are verified or evaluated. The simulation result shows that this new stress wave separation method can give a good data processing result. Some experiments were carried out on a standard Hopkinson pressure bar apparatus with a 1-m-length incident bar and a 1-m-length transmission bar. The new wave separation technique and data process formulas were used. For the 2014 aluminum alloy test, the specimen stress and deformation progresses was clearly captured for the first and second loading process. For the aluminum foam test, a quasi-direct impact technique was used to achieve long-time continuous loading on the specimen and the experiment result was complete, clean and satisfactory.