Dynamic recrystallization in adiabatic shear banding: Effective-temperature model and comparison to experiments in ultrafine-grained titanium

Abstract

Dynamic recrystallization (DRX) is often observed in conjunction with adiabatic shear banding (ASB) in polycrystalline materials. The recrystallized nanograins in the shear band have few dislocations compared to the material outside of the shear band. In this paper, we reformulate the recentlydeveloped Langer-Bouchbinder-Lookman (LBL) continuum theory of polycrystalline plasticity and include the creation of grain boundaries. While the shear-banding instability emerges because thermal heating is faster than heat dissipation, recrystallization is interpreted as an entropic effect arising from the competition between dislocation creation and grain boundary formation. We show that our theory closely matches recent results in sheared ultrafine-grained titanium. The theory thus provides a thermodynamically consistent way to systematically describe the formation of shear bands and recrystallized grains therein.

Thermodynamic theory of crystal plasticity: Formulation and application to polycrystal fcc copper

“…The entropy density S D can be computed by directly counting the microstates across slip systems (e.g., Lieou and Bronkhorst (2018)); the result is…”

“…In the context of high deformation rate loading, we have proposed a novel thermodynamic description of structural evolution taking place during deformation (Lieou and Bronkhorst, 2018;Lieou et al, 2019). This approach is based upon recent work to partition energy and entropy elements to both atomic vibrational and atomic disorder states of matter (Langer et al, 2010;Langer, 2015).…”

“…This general theory based upon atomic scale principles then provides a disciplined thermodynamic framework to describe structural features such as dislocations, dislocation subcells, grain boundaries, and so on. In our prior work (Lieou and Bronkhorst, 2018;Lieou et al, 2019) and other recent applications of this theory (Langer, 2016(Langer, , 2017aLe et al, 2018;Le, 2018Le, , 2019 the atomic disorder component or dislocation, subcell, grain boundary representation was done only through isotropic and scalar representations of these states. There was but one dislocation density and grain boundary density measure used in the theory and subsequent simulations of experimental results.…”

Strain localization and dynamic recrystallization in polycrystalline metals: Thermodynamic theory and simulation framework

“…We recently proposed a minimal, thermodynamic description of DRX in polycrystalline solids during adiabatic shear localization (Lieou and Bronkhorst, 2018), based on the Langer-Bouchbinder-Lookman (LBL) theory of dislocation plasticity (Langer et al, 2010;Langer, 2015). The LBL theory directly addresses the issues with conventional dislocation theories, through the notion of a thermodynamically-defined effective temperature that describes the configurational state of the material in question, and the use of well-posed evolution equations for internal state variables.…”

Some Facts We Can Learn from Analytical Modeling of DDRX in Pure Metals and Solid Solutions

“…Such numerical computations provide the most detailed description of microstructural evolutions, but their ability to reach DDRX steady states, i.e., large to very large strains, is still questionable considering the current computing speeds. Finally, a new microscopic (and more ambitious) approach based on a thermodynamic theory of dislocation plasticity has been proposed [11,12] and applied to the interaction between DRX and adiabatic shear banding under high strain rate loading conditions. A review of DRX including modeling has been published recently by Huang and Logé [13].…”