Research On Combined Planar Compression-Shear Techenique By Using Split Hopkinson Bars

In order to investigate the phenomenon of dynamic shear damage exist widely in engineer -ing application, and the dynamic response of material under combined compression-shear load-ing, SHSPB (Split Hopkinson Shear Pressure Bar) system has been built up. The apparatus struc-ture of traditional Hopkinson bars has been modified to meet need of the testing, from the idea of oblique flying plate impact tests.The stress and strain states in SHSPB tests have been analyzed by using stress wave theory. Furthermore, finite element analysis software ANSYS/LS-DYNA has been used to analyze the states in detail. Simulation results of four different models are compared to evaluate the design rationality of the apparatus. Then problems which may be encountered in the testing have been predicted.To deal with the difficulty in high strain-rate shear testing, shear stress gauge has been devel-oped independently to measure the dynamic shear stress. After studying the feasibility compre-hensively, Lithium Niobate, a piezoelectric anisotropic crystal, is chosen as the gauge material. Based on the consideration of stress wave propagation in an anisotropic crystal, specific di-rections of Lithium Niobate have been calculated out. Both specific directions and piezoelectric effects are analyzed synthetically; the most suitable cutting direction of the crystal which would be sensitive to shear stress without wave decomposition has been obtained. Then the calibration of the gauge is conducted, the constants of piezoelectric have been corrected for further experi-ments.After the apparatus being set up, the data processing program is designed. Preliminary tests for a concrete are carried on by the new technique. Comparison between experiments and com-putation results show that the SHSPB system can realize the high strain-rate planar compres-sion-shear loading, and achieve the primary goal for the measurement.