Modelling flow stress of AISI 316L at high strain rates

• An existing dislocation density material model is enhanced in order to accommodate plastic deformation at high strain rates.
• A rate dependent dislocation cell formation equation is proposed and evaluated.
• Dislocation drag due to electron and phonon drag is evaluated.
• The flow stress is best modelled using the rate dependent dislocation cell formation.
• Dislocation drag did not improve the predictability within the measured strain rate range.

Modelling of the material behaviour is crucial for machining simulations. Strain and strain rates can reach values of 1–10 and 103–106 s−1 during the severe deformations associated with machining. An existing dislocation density model for AISI 316L based on a coupled set of evolution equations for dislocation density, mono vacancy concentration is enhanced in order to accommodate plastic deformation at high strain rates. Two mechanisms are evaluated with respect to their contribution in this respect. One is rate dependent cell formation and the other is dislocation drag due to phonons and electrons. Furthermore a temperature and strain rate dependent recovery and a proportionality interaction factor and short range component that both depends on the dislocation density are also considered. High strain rate compression tests are performed using Split-Hopkinson technique at various initial temperatures. Experimental results are then used to calibrate the models via an optimization procedure. Evaluation of various flow stress models shows that the flow stress behaviour of 316L stainless steel is best modelled by the model with a rate dependent cell formation. Its numerical solution is implemented in a format suitable for large-scale finite element simulations.