Misalignment effect in the split Hopkinson pressure bar technique

It is well known that alignment of the bar in a split Hopkinson pressure bar (SHPB) experiment plays a significant role in producing a good clean signal. In this paper, numerical simulations using ANSYS-LSDYNA are employed to comprehensively study the effects of bar misalignment in producing a distorted signal. There are six major types of bar misalignment that are commonly experienced: offset of neutral axis, uneven support height, non-parallel impact face, bar straightness, dome and cone impact face shapes. The numerical simulations are divided into two main sections, i.e. bar calibration and conventional SHPB testing. The distorted signal generated by misalignment produces unreliable data analysis and is mainly due to the presence of a flexural mode of vibration. Recommendations on selecting bar specifications to minimize the deviation of results are presented.

► Recommendation on the bar production tolerances is discussed.
► Distorted signal of SHPB testing is mainly due to the non-parallelism of the interfaces.
► The results of SHPB analysis are very sensitive to the presence of the flexural mode of vibration.
► The authors recommend using one strain gage only (instead of a pair of strain gages) for the strain measurement.