Testing techniques based on the split Hopkinson bar

To ascertain the effects of a nuclear reactor accident, three testing techniques were developed for determining the mechanical state equations of metallic materials in tension: (1) A system based on the explosion of a detonating explosive. The explosive, placed in two symmetric fire chambers, is ignited by an electric detonator. The pressure wave (of about 200 x 10-6 s duration) impinges, by a buffer, on the end of the bar. The tension wave transmitted along the bar provokes deformation and fracture of the specimen with a strain rate of about 103 s-1. This system has been adopted because it was possible to synchronize the experiment with a fast camera, especially developed for explosives. Unfortunately, the method shows at the moment a rise time not shorter than 40 x 10-6 s. Because of lack of time, the testing method has not been further developed. (2) The second system is based on a prestressed loading bar. By the rupture of a brittle intermediate piece, a tension wave is transmitted along the bar. This method, easy to operate, allows a rise time shorter than 25 x 10-6 s and a pulse duration proportional to the bar length. It has been used up to now in a field of strain rates between 102 and 103 s-1. (3) The third method is based on a shock tube used as a loading device. By this method: a long duration pulse may be generated. The system has been used between 1 and 102 s-1. Results obtained in the strain rate range between 10-2 and 103 s-1 on AISI 304, 304L, 347 steels are presented and discussed. (U.S.)