Modeling the Effects of Slip, Twinning, and Notch on the Deformation of Single-Crystal Austenitic Manganese Steel

TL;DR

This work addresses how slip, deformation twinning, and notch geometry interact to shape the deformation of single-crystal Hadfield steel. It develops a 3D rate-dependent CPFE model incorporating deformation twinning, with a probabilistic twin-volume–consistent (PTVC) reorientation scheme to allow coexisting parent and twin orientations and to account for twin volume effects, implemented efficiently via AceGen/AceFEM. The model, calibrated against uniaxial tests for $\<001 angle$ and $\<111 angle$ orientations, accurately reproduces orientation-dependent hardening, twin evolution (e.g., twin volume fraction reaching ~0.5 by $\\epsilon\approx 0.09$ and saturating near 0.95), notch strengthening, and notch deformation asymmetry, and reveals how twinning shifts deformation from slip-dominated to twin-dominated modes and influences local stress states near notches. The results provide mechanistic insight into slip–twinning–notch interactions with practical implications for designing Hadfield-steel components to mitigate deformation-induced failure, while delivering a computationally efficient modeling approach that can accommodate local geometry effects.

Abstract

The objective of this work is to deconvolute the interaction of slip, twinning, and notch on the deformation response of an austenitic manganese (Hadfield) steel using detailed finite element simulations. The simulations employ a rate-dependent crystal plasticity constitutive model that incorporates both slip and twinning deformation mechanisms. The model accounts for the spatially non-uniform appearance of new twin-related orientations, hardening due to slip--twin interactions, and modified properties of the twinned crystal. Limited experiments on single-crystal dog-bone and single-edge notch specimens, with two crystal orientations, are also conducted to aid the simulation. Several features of the experimental observations are accurately captured in the simulations. For example, simulations accurately capture distinct stress--strain responses associated with different crystallographic orientations, including variations in initial hardening behavior followed by either decreasing or increasing hardening depending on the dominant deformation mechanisms. The simulation also captures the observed orientation-dependent asymmetric deformation of the notch in single-edge notch specimens. Additionally, by selectively activating deformation mechanisms, the role of twinning is isolated and its influence on both global and local response is clearly demonstrated. These results provide a mechanistic understanding of how deformation mode interactions and local geometry (i.e., notch) influence the response of these materials.

Figures (19)

• Figure 1: Geometry and FE mesh of the specimens: (a)–(b) flat dog-bone and (c) single-edge notch with (d) zoomed-in view of the notch region.
• Figure 2: Pole figure $\{011\}$ showing the orientations listed in Table \ref{['tab:crystal orientations']}.
• Figure 3: (a) Comparison of experimentally obtained and predicted normalized force–displacement ($F_n -\delta_n$) curves for dog-bone specimens with crystal orientations $[001]$ and $[111]$ subjected to uniaxial tension. (b) Predicted evolution of accumulated slip and twin volume fractions, averaged over the gauge region of the specimen for the two orientations.
• Figure 4: Contour plots showing the predicted evolution of accumulated slip and twin volume fraction in dog-bone specimens with crystal orientations $[001]$ and $[111]$ subjected to uniaxial tension. Results are shown at three levels of normalized displacement: $\delta_n = 0.05$, $0.09$, and $0.3$, which are also marked in Fig. \ref{['fig:identification']}.
• Figure 5: (a) Predicted normalized force–displacement ($F_n$–$\delta_n$) curves for single-edge notch specimens with crystal orientations $[001]$ and $[111]$. For the $[111]$ orientation, parametric studies are also conducted to assess the effect of deviations from the exact $[111]$ orientation. All orientation cases analyzed are listed in Table \ref{['tab:crystal orientations']}. (b) Experimentally obtained $F_n$–$\delta_n$ curves for single-edge notch specimens with crystal orientations $[001]$ and $[111]$Exp.