Experimental and numerical study on the effects of friction and specimen dimension in split Hopkinson pressure bar

Split Hopkinson pressure bar apparatus (SHPB) is used commonly for determining high strain rate material properties. The validity of the SHPB test results depend on many parameters. In this paper, the effect of specimen dimension (aspect ratio) as well as friction on test results is studied both numerically and experimentally. ABAQUS/Explicit is used for numerical study. To this end, the signals at strain gage positions (on input and out bars) are extracted and stress-strain curve of the specimen is determined using wave propagation analysis. By comparing these stress-strain curves for different states of friction and specimen dimensions, the validity of the experimental and numerical results are checked. By increasing friction, the stress increase and strain decrease in the output stress-strain curve and the best result is for no friction condition. Its is observed that by increasing the aspect ratio, the discrepancy of the results for different friction conditions decreases. Specifically, in simulation results, the difference between maximum stresses of with and without lubrication for aspect ratios 0.25, 0.5, 1.0 and 1.5 are 58%, 18%, 9% and 5%, respectively which is in agreement with experimental trends. In other words, different stress-strain curves are obtained for different aspect ratios in the presence of friction which is mainly due to the friction effect rather than strain rate effect. As the friction increases, the error will reduce the overall strain of the sample and increase the yield stress.