Dynamic flow stress of shock loaded low carbon steel

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This study identifies the role of twin volume fraction in the dynamic stress-strain relationship of shock loaded low carbon steel. This relationship is modeled using thermal activation concepts based on dislocations interactions with thermal and athermal stress barriers. Model parameters are determined by first subjecting a set of as-received and 3% pre-strained steel specimens to shock loads of 6 GPa, and 11 GPa using a gas gun. These specimens, as well as ones with no prior shock loading, were subjected to dynamic compression tests at temperatures in the range 293–923 K and at strain rates between 1E+ 3 s −1 and 5E+ 3 s −1 using a split Hopkinson pressure bar. The resulting stress-strain curves were partitioned into thermal and athermal stress components in which the role of twin boundaries is discussed in terms of their relation with the interaction of dislocation motion and grain subdivision. Results of this work show that the thermal stress component of both the as-received and pre-strained materials is insensitive to the impact history. The athermal stress component for as-received specimens which have been previously shock loaded is shown to be proportional to the shock loading pressure. For specimens, however, which have been pre-strained before shock loading, the athermal stress did not vary for the two shock load levels. This difference in athermal stress between as received and pre-strained materials is explained in terms of the twin volume fraction generated as a function of the impact load. Model results are presented and discussed in relation to the proposed stress-strain formulations.

Publication Title

Materials Science and Engineering A