STUDY OF WAVE SHAPING TECHNIQUES OF SPLIT HOPKINSON PRESSURE BAR USING FINITE ELEMENT ANALYSIS

Graham, R.A., mentioned in his book “Solids under High-Pressure Shock Compression”, that for testing materials at high rates of strain, the split Hopkinson pressure bar (SHPB) is used. During very high impacts and extreme applications higher rates of strain are obtained. These high strains are used to induce the strain hardening and phase a transition phenomenon which affects the strength of materials [1]. For the strain rates of 10 in/in-s (s) SHPB is widely used to study the mechanical properties of most materials as it is very simple and robust to operate. At the National Institute for Aviation Research (NIAR), research has been conducted to study the wave shaping techniques of SHPB using finite element analysis. In split Hopkinson pressure bar (SHPB) experiment, specimen is pressed in between two long cylindrical input and output bars. There is also a third cylindrical bar known as striker bar which is used to hit the input bar using a high pressure gas gun. With the high impact of striker bar on the input bar, a compressive stress wave is generated which travels from the input bar to the test specimen. At the interface of the specimen and input bar, partial stress wave propagates from specimen as a compressive wave and partial reflects into the input bar as a tensile stress wave. The stress wave that is transmitted from the specimen to the output bar causes elastic and plastic deformation in the test specimen. Stress generated in the specimen is calculated by the transmitted strain pulse and using this strain pulse, strain and strain rate in the specimen are calculated. The research presented in this thesis, is not to test materials at high strain rates, rather it is to study the wave shaping testing techniques in split Hopkinson bar by using finite element code LS-DYNA and also to study the tensile testing methods of SHPB.

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