ELIMINATION OF LOADING REVERBERATION IN THE SPLIT HOPKINSON TORSIONALBAR

The loading reverberation is a multiple wave effect on the specimen in the split Hopkinson torsional bar (SHTB). Its existence intensively d estroys the microstructure pattern in the tested material and therefor e, interferes with the study correlating the deformed microstructure t o the macroscopic stress-strain response. This paper discusses the pro blem of the loading reverberation and its effects on the post-mortem o bservations in the SHTB experiment. The cause of the loading reverbera tion is illustrated by a stress wave analysis. The modification of the standard SHTB is introduced, which involves attaching two unloading b ars at the two ends of the original main bar system and adopting a new loading head and a couple of specially designed clutches. The clutche s are placed between the main bar system and the unloading bars in ord er to lead the secondary loading wave out of the main bar system and t o cut off the connection in a timely manner. The loading head of the s tandard torsional bar was redesigned by using a tube-type loading devi ce associated with a ratchet system to ensure the exclusion of the ref lected wave. Thus, the secondary loading waves were wholly trapped in the two unloading bars. The wave recording results and the contrasting experiments for examining the post-mortem microstructure during shear banding both before and after the modification highly support the eff ectiveness of the modified version. The modified SHTB realizes a singl e wave pulse loading process and will become a useful tool for investi gating the relation between the deformed microstructure and the macros copic stress-strain response. It will play an important role especiall y in the study of the evolution of the microstructure during the shear banding process. (C) 1995 American Institute of Physics.