Twinning behavior of polycrystalline alpha-uranium under quasi static compression

Zhou, Ping; Xiao, D.H.; Wang, Wenyuan; Ge, Shenguang; Zhao, Yawen; Zou, Dongli; He, Li

doi:10.1016/j.jnucmat.2016.05.041

Cited by 20 publications

(6 citation statements)

References 43 publications

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“…A value τ 0 twin-loc = 200 MPa is sufficient to limit considerably the twin interpenetration and it will be used in all the following simulations. This is because twin intersections are not commonly observed in αuranium (Zhou et al 2016). A simulation with l m = 30 µm and with cohesive elements is carried out to understand the correlation between discrete twins and fracture.…”

Section: Twin-twin Interaction Coefficientmentioning

confidence: 99%

Modelling the nucleation and propagation of cracks at twin boundaries

Grilli

Cocks

2021

Int J Fract

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Fracture arising from cracks nucleating and propagating along twin boundaries is commonly observed in metals that exhibit twinning as a plastic deformation mechanism. This phenomenon affects the failure of macroscopic mechanical components, but it is not fully understood. We present simulations in which a continuum model for discrete twins and a cohesive zone model are coupled to aid the understanding of fracture at twin boundaries. The interaction between different twin systems is modelled using a local term that depends on the continuum twin variables. Simulations reveal that the resolved shear stress necessary for an incident twin to propagate through a barrier twin can be up to eight times the resolved shear stress for twin nucleation. Interface elements are used at the interfaces between all bulk elements to simulate arbitrary intragranular cracks. An algorithm to detect twin interfaces is developed and their strength has been calibrated to give good agreement with the experimentally observed fracture path. The elasto-plastic deformation induced by discrete twins is modelled using the crystal plasticity finite element method and the stress induced by twin tips is captured. The tensile stress caused by the tip of an incident twin on a barrier twin is sufficient to nucleate a crack. A typical staircase fracture path, with cracks propagating along the twin interfaces, is reproduced only if the strength of the twin interfaces is decreased to about one-third of the strength of the bulk material. This model can be used to help understand fracture caused by the activation of multiple twin systems in different materials.

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Section: Twin-twin Interaction Coefficientmentioning

confidence: 99%

Modelling the nucleation and propagation of cracks at twin boundaries

Grilli

Cocks

2021

Int J Fract

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“…Similarly, the twinning slip direction is s β and twin interface normal is n β , which has a maximum shear magnitude γ twin β . A single twin system will be used in the following simulations, but the model can be readily generalized to include additional twin systems by summing over β.γ α is the slip rate on the α slip system, whileφ is the time evolution of the twin phase field, which is positive because detwinning is not allowed in the present model, even though it is observed in some materials [51]. The slip rateγ α in the first term of the right-hand side of Eq.…”

Section: Crystal Plasticity Finite Element Modellingmentioning

confidence: 99%

A phase field model for the growth and characteristic thickness of deformation-induced twins

Grilli

Cocks

Tarleton

2020

Journal of the Mechanics and Physics of Solids

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Deformation-induced twinning is an important mechanism in metals with a limited number of slip deformation modes. The mechanisms for twin nucleation and growth are not completely understood, and modelling these processes is challenging because of the different length and time scales involved. Twins grow at the speed of sound up to a length of several millimetres and thickness of only a few microns. We present a phase field model for twinning, coupled with a dislocation-density based model for slip, implemented within the crystal plasticity finite element method. Softening of the critical resolved shear stress for twinning is used to reproduce the shear localisation that is typical of twin bands. Two interaction terms are introduced. The first one is a non-local term that models the interaction between residual dislocations at the twin interface and mobile dislocations in untwinned regions. The second is a local term that models the hardening of the twin system due to the presence of dislocations. By introducing these interaction terms, it is possible to reproduce a discrete pattern of twin bands after deformation. These interaction terms and interaction strength parameters determine the nucleation and spatial position of twins, twin thickness and number density of twins as a function of strain. The model is validated by comparing the simulated twin phase field with the dynamic formation of twins in tension, as measured by electron backscatter diffraction experiments on α-uranium. This model sheds light on the mechanism that determines twin growth and twin thickness. Specifically, twins stop thickening after a critical density of residual dislocations at the twin interface is reached. The interaction coefficients are interpreted in terms of the stacking fault energy in order to apply the model to different metals. 1

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“…Additionally, ε 33 denotes the contribution of twinning deformation for macro-strain tensor component ε 33 applied along the 3 axis (the ND direction) in Figure 1. Furthermore, L denotes the free path of the twin lamella prior to encountering an obstacle (grain boundary, precipitate or other twins) and is visualized with its longest boundary traces on the sample observation plane by means of stereographic [30] that determines the orientation of twinning variants by using the trace method [46,47] and is illustrated in Figure 3a. Thus, the results indicate that L = 35.7 µm in grain G2-1.…”

Section: Discussionmentioning

confidence: 99%

“…The value of CRSS in nucleation was initially significantly high. It then decreased and subsequently increased when the onset of propagation was minimum [42,47,55]. Thus, the work derived from CRSS in the onset of propagation can be viewed as the threshold, and the value can be approximately viewed as deformation energy.…”

Section: Orientation Of Grainsmentioning

confidence: 99%

Mechanism of {332}<113> Twinning Formation in Cold-Rolled Ti-Nb-Ta-Zr-O Alloy

Sun

Chen

2018

Metals

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In this study, the mechanism of {332}<113> twinning formation in cold-rolled Ti-35Nb-2Ta-3Zr-O (wt %) alloy was investigated based on the Taylor-Bishop-Hill theory. The experimental data of crystal orientation in the rolling bite zone was obtained via electron back-scattered diffraction (EBSD). The deformation energy of {332}<113> twinning in the propagation stage was calculated using data from EBSD in terms of the Hall-Petch-type relation. The calculation results revealed that the mechanism of {332}<113> twinning formation in β-type Ti-35Nb-2Ta-3Zr-O (wt %) alloy contained two valid models, namely the shear-shuffle model and α″-assisted twinning model. This can help to clarify the mechanism of {332}<113> twinning formation further.

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Twinning behavior of polycrystalline alpha-uranium under quasi static compression

Cited by 20 publications

References 43 publications

Modelling the nucleation and propagation of cracks at twin boundaries

Modelling the nucleation and propagation of cracks at twin boundaries

A phase field model for the growth and characteristic thickness of deformation-induced twins

Mechanism of {332}<113> Twinning Formation in Cold-Rolled Ti-Nb-Ta-Zr-O Alloy

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