Testing and response of large diameter brittle materials subjected to high strain rate

Tests on large diameter specimens using a split Hopkinson pressure bar (SHPB) facility are essential to obtain representative dynamic characteristics of engineering materials such as rocks, concrete, and steel fiber-reinforced concrete (SFRC). However, direct application of the conventional SHPB technique to measure the dynamic behavior of these materials has serious limitations, especially if the size of the specimen is relatively large. The background to material testing using the SHPB facility is explored in this paper. The experimental technique and analytical waveform analysis, together with their attendant problems, are presented. Waveform oscillations and nonhomogeneous deformation of brittle specimens are major problems in test data originating from the conventional SHPB technique. These problems are identified and addressed; techniques for circumventing such problems are described. The design and commissioning of a short-length 75 mm diameter SHPB is presented. To overcome a number of problems associated with such a large diameter short length facility, a novel loading method for eliminating oscillation and maintaining uniform deformation of specimens is proposed. Experimental waveforms are presented for brittle engineering materials to underscore the validity of the technique.