Crystal plasticity finite element simulation of lattice rotation and x-ray diffraction during laser shock-compression of Tantalum

Abstract

Wehrenberg et al [Nature 550 496 (2017)] used ultrafast in situ x-ray diffraction at the LCLS xray free-electron laser facility to measure large lattice rotations resulting from slip and deformation twinning in shock-compressed laser-driven [110] fibre textured tantalum polycrystal. We employ a crystal plasticity finite element method model, with slip kinetics based closely on the isotropic dislocation-based Livermore Multiscale Model [Barton et al., J. Appl. Phys. 109 (2011)], to analyse this experiment. We elucidate the link between the degree of lattice rotation and the kinetics of plasticity, demonstrating that a transition occurs at shock pressures of ∼27 GPa, between a regime of relatively slow kinetics, resulting in a balanced pattern of slip system activation and therefore relatively small net lattice rotation, and a regime of fast kinetics, due to the onset of nucleation, resulting in a lop-sided pattern of deformation-system activation and therefore large net lattice rotations. We demonstrate a good fit between this model and experimental x-ray diffraction data of lattice rotation, and show that this data is constraining of deformation kinetics.

Slip competition and rotation suppression in tantalum and copper during dynamic uniaxial compression

“…This account is supported by our simulations: we find that the direction of the (10 1) planes, which are initially parallel to the proposed rotation axis, is almost invariant, while the (101) planes originally aligned with the compression axis, whose orientation is controlled exclusively by these primary systems, are deflected by several degrees. That the primaries are largely responsible for the observed rotation is already well-established [14,16,19]; what our analysis suggests is that the crystal rotates about [10 1] not because there are no other active plasticity mechanisms, but because the rotations caused by any additional mechanisms (i.e., the secondaries) mutually cancel. Hence, these single-crystal simulations suggest it is the asymmetric activation of the primaries combined with the symmetric activation of the secondaries that leads to the texture evolution observed by Wehrenberg et.…”

“…al. [19]: the inherently larger length-scale at which the finite-element-method framework operates means polycrystals can be simulated at just a fraction of the cost required in MD, which, when combined with its having the most faithful constitutive model of high-pressure tantalum to date, makes the Avraam model uniquely placed to explore the interplay of plasticity and intergranular interactions during dynamic compression. A study of grain-grain effects could form the basis of future work.…”

“…al. [19], there are additional active slip systems with which the two dominant systems are competing. In this section, we address this question by studying the defects nucleated under shock in [001] Cu as predicted by large-scale MD simulations, and by interpreting these results and those of the above-mentioned experiment with a simple rotation model.…”

“…al. [19], it was found that the contrast between the activities of the two primary plasticity mechanisms -which controlled the net rotation -was a highly non-linear function of the applied FIG. 16.…”

“…al. [19]. In this computational study, the authors conducted finite-element simulations of the above-mentioned experiment, using a dislocationbased crystal plasticity (CP) model to treat the tantalum crystal's constitutive response.…”