Study On Split Hopkinson Pressure Shear Bar Technique And Its Applications

In the engineering and scientific fields relating with blast and dynamic loading, the dynamic constitutive research is one of major issues. However, traditional one dimension wave experiments is not compatible for furnishing all the constitutive parameters. The combined pressure and shear waves can disclose both the dynamic compression and shear properties of materials directly, which offers more integrated parameters. Besides, materials'yield, damage evolution, failure, phase transition etc, have great correlation to shear process. Study on the dynamic compression and shear load on materials not only enriches materials'dynamic phenomenon and extends the research field, but also makes a great sense to understand the dynamic response evolution and its mechanism of materials. In weapon system application, the study on the compression and shear response of explosives is the key part correlated to the security of the weapon system. So, to investigate and develop the experiment technique of compression and shear load is not only important for academic research, but also the imperious requirement of practical application.This dissertation focuses on developing a SHPSB (Split Hopkinson Pressure Shear Bar) technique, validating the experimental results, extending the application of the SHPSB and finally makes the technique well serving researches of materials constitutive, especially energetic materials. This work was supported by the Natural Science Foundation of China (NSFC) through Grant No. 10672177 and 10872215.The main contents are divided into three parts:The first partial work includes basic theory and the propagation of stress waves in the SHPSB bars. The combined propagation of the bending wave and longitudinal wave are discussed. The analysis indicates that two kinds of waves are coupled in general; but in the case of small elastic deformation, they can be uncoupled approximately, which is validated by the numerical results. Detailed simulation of the SHPSB experimental process has been taken. The numerical results indicate that the reflected wave in the incident bar is the longitudinal wave without bending motion; the compression and shear forces are balanced in the specimen.The second partial work is measuring techniques of the SHPSB, the corresponding error analysis and the optimization of specimen outline. The measurements of the compression stress and strain are based on the strain gauges on the bars. The shear stress is measured by two piezoelectric transducers of quartz (Y-cut with rotation angle-17.7°, yzw/17.705°) embedded at the close-to-specimen end of transmission bars; the shear strain is measured with a novel optical technique which is based on the luminous flux method. The numerical and experimental results validate the measuring techniques of the SHPSB. It indicates that the error of the compression stress measuring is mainly introduced at early stage of testing, due to the force un-equilibrium in the sample. The error of the compression strain is mainly introduced during data processing. The measuring error of shear stress is aroused by the difference of the shear stress in the specimen and that in the transmission bar, the scatter of the calibration and the system noise of the charge amplifier. The error of shear strain measuring is resulted by the scatter of the calibration and the system noise of the photodiode light detector. The errors of the shear stress and strain measurement are respectively 0.24 MPa and 0.00038 in the examples provided in this paper.Two kinds of specimen outline (plane stress and plane strain specimen) are proposed, and validated by the numerical simulations and experimental results. The results indicate that the plane stress specimen is better than the plane strain model. When the strain is less than 5%, the simulation and the validated experiment yield good agreement with the analytic results of the plane stress specimen.The third partial work is application of the split Hopkinson pressure and shear bar technique.We performed SHPSB experimental method on a PBX. The plane stress specimens are used. The results indicate that the dynamic compression and shear forces equilibrium are reached in specimens; the compression failure stress enhances, but the shear failure stress decreases with the strain rate increasing; the compression and shear failure time run earlier with the strain rate increasing; the shift of compression failure time is larger than that of shear failure time. Based on the maximum shear failure criterion, we analyze the experimental results. The analysis results show that the above mentioned experimental phenomena are related with experimental loading path. A damage constitutive model including rate-effect is built up. The parameters of the model are calibrated by confinement-SHPB tests, flattened Brazilian disc tests and SHPSB experiments. The proposed damage model is implemented in LS-DYNA as a user defined subroutine. SHPB tests, flattened Brazilian disc tests and SHPSB tests are simulated. The numerical results yield good agreement with experimental results. It indicates that the proposed damage model can rationally predict the PBX mechanical behaviors at different dynamic loadings.The SHPSB technique is extended to investigate dynamic friction of a steel-PBX friction pair. The results indicate that rough steel-PBX pair takes on a larger friction coefficient (0.09-0.14) than that of the flat one (0.09-0.19). Based on the SHPSB, the response of the PBX at the process of the compression and shear failure-friction loading is investigated. The results indicate that process of the compression and shear failure includes three stages; micro cracks developing, macro cracks appearing and macro cracks developing-macro cracks sliding. In the early process of dynamic friction, the friction coefficient is less than the ratio of the shear stress to the compression stress in the failure process. The friction coefficient increases finally. It may be related with the roughness change in the cracks.