Experimental Characterization and Modeling of the Anisotropy and Tension–Compression Asymmetry of Polycrystalline Molybdenum for Strain Rates Ranging from Quasi-static to Impact

Abstract

A systematic experimental investigation of the room-temperature quasi-static behavior and dynamic mechanical response of polycrystalline commercially pure molybdenum is presented. It was established that the material has ductility in tension at 10−5/s and that the failure strain is strongly dependent on the orientation. A specimen taken along the rolling direction (RD) sustains large axial strains (20%), while a specimen taken at an angle of 45° to the RD could only sustain 5% strain. It was observed that irrespective of the loading orientation the yield stress in uniaxial compression is larger than in uniaxial tension. While in tension, the material has a strong anisotropy in Lankford coefficients, while in uniaxial compression, it displays weak strain-anisotropy. Due to the material’s limited tensile ductility, successfully acquiring data for impact conditions is very challenging. For the first time, Taylor impact tests were successfully conducted on this material for impact velocities in the range 140–165 m/s. For impact velocities beyond this range, the very high tensile pressures generated in the specimen immediately after impact lead to failure. An elastic–plastic anisotropic model that accounts for all the specificities of the plastic deformation of the material was developed. Validation of the model was done through comparison with data on quasi-static notched specimens and Taylor impact specimens. Quantitative agreement with both global and local strain fields was obtained. In particular, the effect of loading orientation on the response was very well described for all strain rates.