Numerical study on microcompression tests of anisotropic single crystals

Micropillar compression of LiF [111] single crystals: Effect of size, ion irradiation and misorientation

“…The numerical simulations demonstrate that a small misalignment in the micropillar orientation leads to a dramatic effect in the shape of the stress-strain curve, which reproduces very accurately the experimental results reported above. This large effect of the initial tilt contrasts with previous simulations (Choi et al, 2007;Raabe et al, 2007) that predicted a very small effect of the initial misorientation on the flow stress. However, these analyses were carried out in fee single crystals with very limited plastic anisotropy as opposed to LiF which presents a large difference in the critical resolved shear stress between the soft and the hard slip systems.…”

“…8, because slip systems with very low Schmid factors might begin to dominate the compression behavior due to the large discrepancies in critical resolved shear stresses between the "soft" and the "hard" orientations. This contrasts with previous studies based on crystal plasticity simulations of fee metals pointing out that misalignment has strong effects on the apparent elastic modulus but that the flow stress is only affected by a few percent (Choi et al, 2007). Other experimental parameters can also have strong effects on the stress-strain curve, such as the lateral constrain imposed by the indenter.…”

“…The experimental procedure was carefully revised to ensure that this behavior reflected the actual response of the micropiUars, which could be attributed to small misalignments in the crystal orientation resulting from instabilities during directional solidification (Llorca and Orera, 2006). It should be noted, however, that previous studies (Choi et al, 2007) did not report such a large influence of micropillar misalignment on the compressive response but these results were obtained in crystals whose plastic anisotropy was much lower than that of LiF. The hypothesis that the plastic anisotropy of LiF was responsible for the variability in the mechanical response will be analyzed in detail in Section 4 with the aid of crystal plasticity simulations.…”

Athermal mechanisms of size-dependent crystal flow gleaned from three-dimensional discrete dislocation simulations

“…This may be attributed to the assumption of a uniform stress distribution over the volume of the simulation cell in the calculations as well as other factors. Also, in real compression testing, end effects from misalignment of loading platen and the specimen and the effects from a compliant base, are expected to lead to a much shallower increase of the stress-strain curve in the preyielding region [56]. Finally, cross-slip, being a stochastic recovery and multiplication mechanism, may extend the strain range needed to achieve a given stress and raise the lower bound flow stress by enhancing obstacle formation.…”

Microcompression Behaviors of Single Crystals Simulated by Crystal Plasticity Finite Element Method

“…[1][2][3][4][5][6][7] Since the microcompression test of single-crystal micro-pillars is different from the standardized compression test, which uses 'bulk' specimens, the crystal plasticity finite element method (CP-FEM) was frequently used for the parametric study of compressive deformation behavior of single-crystal micro-pillars. [4,[8][9][10][11][12][13] Here, the bottom end of the single-crystal micro-pillar is intrinsically constrained in its lateral deformation. Thus, CP-FEM simulations aimed mostly at understanding the effect of bottom-end constraints, applied boundary conditions, and the sensitivity of the choice of constitutive models.…”