Physically-based strain hardening rule for HR2 alloy

To describe the plastic deformation behavior of HR2 alloy, a physically-based strain hardening model is developed. A series of uniaxial tensile tests and microstructural evolution analysis are performed at different strain levels by using miniaturized specimens of HR2 alloy. The microstructural analysis indicates that dislocation multiplication, grain elongation and refinement, appearance of strain-induced martensite phase and its content increase are critical in dominating the plastic deformation of HR2 alloy. The evolution equations of dislocation density are then developed based on these physical information, and the flow stress is formulated from the athermal stress and thermally activation stress. This physically-based strain hardening model is realized by finite element method into ABAQUS user material subroutine (UMAT), using an implicit stress update algorithm. The results show the new strain hardening model could give more reasonable and accurate prediction to the plastic behavior of HR2 alloy, comparing to other conventional constitutive models of continuum plasticity.