Continuum crystal plasticity analyses of the plastic flow features underneath single-crystal indentations

Abstract

Continuum crystal plasticity finite element simulations are performed for archetypal pure and alloyed fcc crystals to investigate the role of the crystalline orientation, hardening response and dislocation interactions on the plastic flow patterns developing underneath spherical and pyramidal\ud indenter tips. Following our prior analyses, the orientation of plastic features such as subsurface lobes and surface rosettes goes along that of specific in-plane and out-of-plane slip systems. Interestingly, however, we currently show that the activity of the closely oriented slip systems in such lobes and rosettes is, in general, unaccountable to their development. In highly symmetric (001), (011) and (111) indentations, it is found that the slip systems with a net out-of-plane slip direction may contribute to rosette formation at the surface, whereas in-plane slip directions lead to lobe formation in the subsurface. The present results also show that while the isocontours of maximum shear stress max from anisotropic elasticity\ud analyses indeed provide an indication of the indentation-induced elastic field, it is the projection of the stress tensor in all slip systems that drives lobe formation. The isocontours of max may not therefore dictate the plastic zone shape, even though they are useful in explaining some of its\ud features. Finally, a conical shear band shape is found to develop immediately underneath the imprint, dictating accumulation of shear strains and their spreading towards the thickness of the crystal. This feature varies depending on crystal orientation, hardening response and on whether or not the cross-section under analysis contains normal slip directions.Peer ReviewedPostprint (published version

Reassessing spherical indentation: Contact regimes and mechanical property extractions

“…A reduction of sinking-in or an enhancement of pileup effects with increasing penetration is thus found to occur concurrently with an intensification in the outwards spreading of the plastic zone at the indented surface. Consequently, the plastic zone shape only remains constant in the strict limiting cases of rigid-perfectly-plastic and rigid-power-law hardening material responses, so that geometrical-similarity is again violated in solids with a marked r ys (Mata et al, 2006;Alcalá et al, 2010).…”

Depth Dependence of Nanoindentation Pile-Up Patterns in Copper Single Crystals

“…In this work the stresses, shear strains, and crystal lattice rotation map within the material were obtained and the numerical predictions were validated with the experimental results (nanoindentation tests and EBSD investigation of the indented area). Moreover, both spherical and pyramidal indentation tests in fcc single crystals were simulated by Alcala et al [10] and Narayanan et al [11] Zahedi et al [12] developed their own crystal plasticity models to investigate spherical indentation in copper single crystals. Not only Cu but also single crystals made of other materials have been investigated recently.…”

Deformation mechanisms of metastable stainless steels accessed locally by monotonic and cyclic nanoindentation

“…This is due to the asymmetry of the Berkovich indenter, as discussed before, and differences between the size of plastic zones at both flanks were observed also by other authors 300 . Apart from this asymmetry, Alcalá et al 340,341 found that plastic zones for Berkovich indentations do not differ much from those produced by spherical indenters. Thus, the growth direction of martensite under the nanoindenter can be considered as the result of shear stresses on multiple slip systems activated by nanoindentation.…”

“…Alcalá et al 340,341 performed analyses of the plastic behavior below nanoindentations in Cu. Their results are represented in Figure 95, where the simulation shows that for fcc materials plastic flow is favored parallel to the indentation axis for <111> oriented grains, while for <001> grains it is flattened in vertical direction, but prolonged parallel to the surface plane.…”

“…Plasticity analysis by Alcalá et al 340,341 was carried out for a stable material, i.e. no susceptible to phasetransformation, so care must be taken when comparing the results, especially when evaluating cyclic deformation behavior, due to the hardening involved with phase transformation.…”