Investigation of rock material under combined compression and shear dynamic loading: An experimental technique

Based on the Split Hopkinson Pressure Bar (SHPB) device, a new combined compression and shear loading technique is developed by adding cushions with designed oblique surfaces. Employing steel as standard material, the technique is calibrated by a series of quasi-static and dynamic experiments. A reliable data processing method of the technique is proposed to decompose the normal stress (sigma) and the shear stress (tau) on the oblique surface. The results show that the coupled compression and shear responses of steel exhibit obvious strain rate effect. Validation of the technique is confirmed by using Von Mises criterion in sigma-tau plane to describe the coupled strength of steel. Thus, series of experiments are conducted to investigate the compression and shear behaviors of a granite under quasi-static loading (strain rates similar to 3 x 10(-5) s(-1)) and impact loading with strain rates 50 s(-1) and 100 s(-1). Five oblique angles, e.g. zero, 15,30,45, and 60 degrees, are involved in the experiments. Slopes of the decoupled normal and shear stress-strain curves exhibit obvious load-path dependency, which is known as the coupled compression and shear effect, and strain rate effect. These two effects become more important with oblique angle increasing. Failure criterion of granite specimen at different strain rates can be preliminarily described by the Drucker-Prager (D-P) model, and the strengths of granite exhibit obvious strain rate sensitivity and load-path dependency. The technique is helpful for the investigation of the dynamic properties of rock materials under complex stress states. (C) 2015 Elsevier Ltd. All rights reserved.