Concrete exhibits brittle behaviour and is weak under tensile and flexural loading. The response of concrete to dynamic loading is of interest in a variety of civilian and military applications. Understanding the response of concrete to impact or explosive loading is important for effective protection of defence and civil structures. The split Hopkinson pressure bar (SHPB) technique has been used widely to measure the dynamic strength enhancement of materials at high strain rates. Although, SHPB technique has been verified for metallic materials, but validity and accuracy of SHPB results for non-metallic, e.g. concrete materials have not been thoroughly studied so far. The present study examines the application of SHPB to determine the dynamic strength of concrete under compressive loading. The aim of this study is to understand the strain rate effect on the ultimate uniaxial compressive strength of concrete in SHPB tests for two different grades of concrete. The behaviour of concrete at strain rates of the order of 200 - 600 per second and pressures up to 0.38 MPa are studied experimentally. The strength of concrete is found to be increased with the increase in strain rates. Further, it is observed that due to the composite microstructure of concrete, deformation and stresses are non-uniform in the concrete specimens.
Split Hopkinson pressure bar (SHPB) is commonly used to characterize materials under high strain rates. However, conventional SHPB tests on brittle materials has encountered several experimental challenges for the high strain rate loading. In relatively brittle materials like concrete, the deformation of the specimen is very small when subjected to the impact loading; hence, it is very difficult to obtain the prerequisites of valid SHPB tests like dynamic equilibrium and constant strain rate in the specimen. To overcome these issues, the current study presents the importance of the pulse shaper approach in SHPB application for dynamic characterization of concrete material. The pulse shaper serves as a function of increasing the loading duration of the incident pulse. An incident pulse with a longer loading duration is a preferred loading pulse for achieving dynamic stress equilibrium in the specimen. Selection of appropriate dimension of pulse shaper assists in facilitating dynamic stress equilibrium and constant strain rate in the specimen. In the present experimental study, copper pulse shapers are used for evaluation of concrete under high strain rate loading using an SHPB setup. Parameters such as the effect of dimensions (diameter and thickness) of pulse shapers on the loading pulses, dynamic equilibrium, constant strain rate, and material responses are studied. Experimental results revealed the prediction of suitable pulse shapers for 50-200 /sec strain rates. In addition, numerical simulation is also performed, and results are validated with the experimental data.
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