Experimental Investigation of Strain-Rate- and Temperature-Dependent Mechanical Properties of SA516Gr.70 Steel and Development of an Appropriate Material Model

The objective of this work is to develop an appropriate strain-rate- and temperature-dependent material constitutive model to simulate plastic deformation behavior of SA516Gr.70 steel in the sub-zero temperature regime (− 128 to 25 °C). For this purpose, tests have been conducted at three different strain rates covering an order of 6 in the rates, i.e., from 0.001 to 1400/s. Tests at high strain rates have been conducted using a modified split Hopkinson pressure bar test setup. The tensile tests have been designed in such a way that the strain rate remains almost constant during the test. A critical comparison of results of both tension and compression high strain-rate tests has been carried out, and the suitability of tensile experiments has been highlighted. A modified Ramberg–Osgood model, with temperature- and strain-rate-dependent parameters, has been presented. The parameters of the new model have been evaluated from a large set of experimental data. It was observed that the yield stress and ultimate tensile strength of the material increase monotonically with decreasing temperature and increasing strain rates. The ductility at fracture and extent of uniform elongation of the specimen decrease for the intermediate strain rate of 0.925 s−1, when compared to the corresponding values at quasistatic rate of loading. At very high rate of loading, ductility increases due to the increased resistance of the material to growth and coalescence of voids. From the comparison of results of model and experiment, it has been observed that the modified material model is able to predict the true stress–strain curve of the material satisfactorily in the sub-zero temperature regime over a wide range of strain rates. The nature of variation of mechanical properties with temperature and strain rate has been explained from the point of view of dislocation-based micromechanism of the plastic deformation process.