Abstract
Owing to its ability to incorporate Schmid’s law at each integration point, crystal plasticity has proven a powerful tool to simulate and predict the slip behavior at the grain level and the ensuing heterogeneous stress/strain localization and texture evolution at the macroscopic level. Unfortunately, notwithstanding substantial efforts during the last three decades, this remarkable capability has not been replicated for materials where twinning becomes a noticeable deformation mechanism, namely in the case of low-stacking fault energy cubic, orthorhombic, and hexagonal close-packed structures. The culprit lies in the widely adopted unphysical pseudo-slip approach for capturing twin formation. While the slip is diffuse, twinning is a localized event that occurs as a drastic burst of a confined number of partial twinning dislocations establishing an interface that pursues growth through a thread of perfect twinning dislocations in the sense of bicrystallography. Moreover, at earlier stages, twin nucleation may require atomic diffusion (Shuffling) and faceting, generally demanding higher stress levels not necessarily on the twin shear plane, while triaxiality at adequate sites might be needed or preferred such as lower grain boundary misorientations or other twin boundaries. Identifying a mathematical framework in the constitutive equations for capturing these twin formation sensitivities has been a daunting challenge for crystal plasticity modelers, which has stalled ameliorating the design of key hexagonal materials for futuristic climate change-related industries. This paper reviews existing approaches to incorporating twinning in crystal plasticity models, discusses their capabilities, addresses their limitations, and suggests prospective views to fill gaps. The incorporation of a new physics-based twin nucleation criterion in crystal plasticity models holds groundbreaking potential for substantial progress in the field of computational material science.
Highlights
Twinning plays a prominent role in the plastic deformation and recrystallization of low symmetry crystals such as those showing hexagonal close-packed, orthorhombic, body-centered cubic and even face-centered cubic crystal structures holding a very low stacking fault energy, e.g., twinning induced plasticity steels
This paper reviews existing accomplishments with the incorporation of deformation twinning into crystal plasticity models and the challenges they faced to break away from a pseudo-slip approach, which has been consistently discounted by many phenomena related to twin nucleation
In light of recent discoveries achieved by novel in situ experimental techniques and powerful simulations at the atomistic level, we emphasized a few key mechanisms for twin nucleation and suggested methods to reflect those mechanisms in a crystal plasticity model: 1. Just like shear banding, twinning is a localized event, but one which challenges the ability to deterministically pinpoint a favorable nucleation site
Summary
Twinning plays a prominent role in the plastic deformation and recrystallization of low symmetry crystals such as those showing hexagonal close-packed (hcp), orthorhombic, body-centered cubic and even face-centered cubic crystal structures holding a very low stacking fault energy, e.g., twinning induced plasticity steels. In hcp metals such as magnesium (Mg), twinning can be profuse depending on the alloy chemical composition, texture, strain rate, and temperature, while concomitant slip leads to complex interactions with existing twins in the deforming lattice, thereby exacerbating hardening and damage. We emphasize efforts to incorporate twin nucleation in these models, which remains the most challenging event in this entire endeavor
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