Toward a more complete mechanistic understanding of the mechanical behavior of anisotropic single-phase polycrystalline materials.

摘要

Two mechanical behaviors are investigated using in situ neutron diffraction and elastoplastic self-consistent (EPSC) modeling: (i) strain accommodation in CsC1 (B2) structured intermetallics not expected to display ductility and (ii) the generalized Bauschinger effect, utilizing stainless steel as a case material. The internal elastic lattice strain evolution predicted by the EPSC model is compared with the evolution experimentally measured by in situ neutron diffraction. By means of this comparison, the initiation stresses and hardening behaviors of slip systems are developed, which provide satisfying explanations for the macroscopically observed strain hardening behavior.;Analysis of the lattice strain evolution of CeAg, CoTi and CoZr confirms that cube slip is the dominant, easy deformation mechanism. However, to account for the transition in strain hardening observed in all three materials and identified by a lowering of slope in the macroscopic flow curve and a change in the evolution of internal elastic strains, activation of a secondary slip mode, such as 111> {110} "bcc slip", is required. The approach permitted quantification of 1) the stress conditions required for activation of the primary and secondary slip modes, 2) the hardening behaviors of the individual slip modes, and 3) the level of strain accommodation attributable to the secondary mode.;The grain-level description of strain hardening was modified to include a kinematic backstress at the slip system level. The resulting modified EPSC model was able to a) capture the Bauschinger effect and b) predict the evolution of internal elastic strain with unprecedented accuracy. The model was further modified with a latent hardening evolution commensurate with observations of metal behavior during strain path changes. This latest model description was shown to qualitatively capture experimental features of yield surface evolution observed after pre-straining including: translation, "expansion" (or "contraction"), and adoption of a triangular shape with a "nose" in the forward direction and a flat in the reverse direction. Importantly, it was revealed that the self-consistent framework causes the development of the "nose" in the yield surface and was shown to be related to the initial slip system activation within the grains and previous development of intergranular backstresses.