Characterisation of slip and twin activity using digital image correlation and crystal plasticity finite element simulation: Application to orthorhombic α-uranium

Grilli, Nicolò; Earp, Philip; Cocks, A.C.F.; Marrow, James

doi:10.1016/j.jmps.2019.103800

Cited by 26 publications

(19 citation statements)

References 70 publications

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“…The first term is stress driven and becomes relevant when the RSS τ β on the twin system is higher than a CRSS τ c β (ϕ) [33], τ c β (ϕ) represents the stress necessary to move the atoms towards the maximum of the energy barrier.γ 0 and n are constants. The value of n = 20 ensures the strain rate independence of the twinning process as observed experimentally [32]. The second term in Eq.…”

Section: Methodsmentioning

confidence: 79%

“…[30]. This model, which uses eight slip systems, has been calibrated using neutron diffraction [30,31] and digital image correlation experiments [32].…”

Section: Methodsmentioning

confidence: 99%

“…The final term in Eq. (6) τ dis represents the interaction between a twin and the mobile dislocations and scales linearly with the total dislocation density ρ as previously determined using digital image correlation experiments [32],…”

Section: Methodsmentioning

confidence: 99%

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In situ measurement and modelling of the growth and length scale of twins in α -uranium

Grilli

Tarleton

Edmondson

et al. 2020

Phys. Rev. Materials

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Twinning is an important deformation mechanism in crystalline materials. Twins nucleate, then grow, forming a discrete pattern of deformation bands with a certain thickness. The mechanism for twin growth is not completely understood. We present a simple phase field model which captures the physics of twin growth and reproduces the details observed during in situ electron backscatter diffraction experiments on α-uranium. The interaction between residual dislocations at twin interfaces and mobile dislocations in untwinned regions increases the stress needed for twin growth. This is described by a nonlocal term in the proposed constitutive equations: the nucleation stress of a twin increases proportionally to the twin phase field in a neighborhood. Competition between slip and twinning favors the nucleation of a new twin rather than the growth of a preexisting twin. The phase field model is coupled with a crystal plasticity finite element solver that includes the plastic deformation due to twinning. Simulations are able to reproduce the number of twins and their thicknesses as a function of the strain observed during in situ electron backscatter diffraction experiments. The stress-strain curve is also reproduced. This comparison allows the values of the nucleation stress and the interaction strength between residual and mobile dislocations to be found. It also gives an estimation of the density of residual dislocations that is consistent with the observed twin thickness. This model can be applied to understand microstructural effects in materials using twinning as a strengthening mechanism.

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Section: Methodsmentioning

confidence: 79%

“…[30]. This model, which uses eight slip systems, has been calibrated using neutron diffraction [30,31] and digital image correlation experiments [32].…”

Section: Methodsmentioning

confidence: 99%

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In situ measurement and modelling of the growth and length scale of twins in α -uranium

Grilli

Tarleton

Edmondson

et al. 2020

Phys. Rev. Materials

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“…The evolution of the dislocation densities is based on multiplicationannihilation rate equations (Kocks and Mecking 2003;Grilli et al 2018b). This hardening model has been able to reproduce the elastic lattice strain in polycrystals measured using neutron diffraction (Grilli et al 2020a) and the strain field inside individual grains measured using digital image correlation (Grilli et al 2020c).…”

Section: Crystal Plasticity Modelmentioning

confidence: 98%

Coupling a discrete twin model with cohesive elements to understand twin-induced fracture

2021

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The interplay between twinning and fracture in metals under deformation is an open question. The plastic strain concentration created by twin bands can induce large stresses on the grain boundaries. We present simulations in which a continuum model describing discrete twins is coupled with a crystal plasticity finite element model and a cohesive zone model for intergranular fracture. The discrete twin model can predict twin nucleation, propagation, growth and the correct twin thickness. Therefore, the plastic strain concentration in the twin band can be modelled. The cohesive zone model is based on a bilinear traction-separation law in which the damage is caused by the normal stress on the grain boundary. An algorithm is developed to generate interface elements at the grain boundaries that satisfy the traction-separation law. The model is calibrated by comparing polycrystal simulations with the experimentally observed strain to failure and maximum stress. The dynamics of twin and crack nucleation have been investigated. First, twins nucleate and propagate in a grain, then, microcracks form near the intersection between twin tips and grain boundaries. Microcracks appear at multiple locations before merging. A propagating crack can nucleate additional twins starting from the grain boundary, a few micrometres away from the original crack nucleation site. This model can be used to understand which type of texture is more resistant against crack nucleation and propagation in cast metals in which twinning is a deformation mechanism. The code is available online at https://github.com/TarletonGroup/CrystalPlasticity. Graphic Abstract

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“…The symmetry plane was fixed from translation in the normal direction, x 2 = 0, the nodes on the top surface were traction free, while the remaining four surfaces of the cube were fixed. Elastic anisotropy was used with the following elastic constants for copper: Further details on the UMAT can be found in [60,63,64,65,62,66]. Simulations provide direct comparison with the EF scratch test.…”

Section: Crystal Plasticity Finite Element Modellingmentioning

confidence: 99%

Scratching the Surface: Elastic Rotations Beneath Nanoscratch and Nanoindentation Tests

et al. 2020

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Characterisation of slip and twin activity using digital image correlation and crystal plasticity finite element simulation: Application to orthorhombic α-uranium

Cited by 26 publications

References 70 publications

In situ measurement and modelling of the growth and length scale of twins in α -uranium

In situ measurement and modelling of the growth and length scale of twins in α -uranium

Coupling a discrete twin model with cohesive elements to understand twin-induced fracture

Scratching the Surface: Elastic Rotations Beneath Nanoscratch and Nanoindentation Tests

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