Improvement And Application Of Split Hopkinson Pressure Bar Experimental Techniques

The properties of materials under high strain-rate impact loading are the most important. SHPB is usually utilized to obtain the constitutive relation of materials under high strain-rate from 102s-1 to 104 s-1.According to the theory of stress wave, the transmission of one-dimensional stress wave in the elastic bar and the impact of two elastic bars are discussed firstly, then the principal theory of conventional SHPB technique is illustrated, and our SHPB setting are introduced in brief.Because it is hard to obtain dynamic stress equilibrium and constant strain rate in soft materials specimen during the conventional SHPB experiments, a pulse shaping technique is developed. We stick a copper disk at the front face of the incident bar, the deformation of the copper damps the incident waveform to ensure dynamic stress equilibrium and homogeneous deformation in the specimen. According to the method of pulse shaper designing, the specimens are loaded under constant strain rate easily. Furthermore, we build a theoretical model to forecast the incident stress wave according to the stress wave theory.Instead of a surface strain gage mounted on the transmission bar, a piezoelectric quartz crystal force transducer is embedded in the middle of the transmission bar to directly measure the weak signal in the experiments of silicon rubber. This new technique can improve the signal magnitude by three orders, and enhance the signal-noise ratio. What's more, we mount two piezoelectric quartz crystal force transducers close to the specimen end faces to monitor the dynamic stress equilibrium in the specimen directly. Experimental results show that silicon rubber is strain-rate sensitive.At last, we utilize the modified SHPB technique to test three kinds of nylon matrix composites under dynamic compression, dynamic compressive stress-strain curves of the three materials are obtained during the experiments for different strain rates of 500 s-1, 1000 s-1 and 1500 s-1 respectively. We analyze the strain rate effect of the tested materials, and compare the properties of these three materials under high strain-rate.