BCC single crystal plasticity modeling and its experimental identification

Abstract

A crystal plasticity model for body-centered-cubic (BCC) single crystals, taking into account the plastic anisotropy due to non-planar spreading of screw dislocation cores is presented. In view of the longstanding contradictory statements on the deformation of BCC single crystals and their macroscopic slip planes, recent insights and developments are reported and included in this model. The flow stress of BCC single crystals shows a pronounced dependence on the crystal orientation and the temperature, mostly due to non-planar spreading of a/2⟨1 1 1⟩ type screw dislocation cores. The main consequence here is the well-known violation of Schmid's law in these materials, resulting in an intrinsic anisotropic effect which is not observed in, for example, FCC materials. Experimental confrontations at the level of a single crystal are generally missing in the literature. To remedy this, uniaxial tension simulations are done at material point level for α-Fe, Mo and Nb single crystals and compared with reported experiments. Material parameters, including non-Schmid parameters, are calibrated from experimental results using a proper identification method. The model is validated for different crystal orientations and temperatures, which was not attempted before in the open literature.

Subgrain lath martensite mechanics: A numerical–experimental analysis

“…Therefore, non-Schmid effects in the BCC phase are included (e.g. Dao and Asaro, 1993;Yalçinkaya et al, 2008) by redefining the resolved shear stress as…”

“…Next, the initial slip resistance τ 0 for the slip systems in the two phases has been determined while adopting a strain rate sensitivity m ¼0.10 and a reference slip rate of _ γ 0 ¼ 0:01 s À 1 . The non-Schmid parameters for the BCC phase have been taken from the literature (Yalçinkaya et al, 2008). The initial slip resistance τ 0 of the FCC phase was first identified on the stress-strain response of MP2 configuration, which is much more Fig.…”

Sub-surface structures of ITER-grade W (Japan) and re-crystallized W after ITER-similar low-energy and high-flux D plasma loadings

“…Many irregularly shaped structures with strong deformations, intra-granular cracks and lattice bending appear at about 400-500 K (see a similar sample in Fig 5a). However, at 600 K the grains remain apparently undamaged, but material is moved out along a {100}<111> slip system [17,18] forming large extrusions with an associated pore at the grain boundary next to the surface (Fig. 3a,b).…”

Elastic-Plastic Transition under Uniaxial Stress BCC Tantalum

“…At the atomic level, the plasticity is described by the rearrangement of atoms from its current configuration. The plastic anisotropy is caused by preferred planes where dislocations move (slip planes) [3]. In 1926, Frenkel [4] stated that a critical value of shear is necessary to move the atoms in a layer over another.…”