of a nonhydrostatic stress field, which would entail an interaction between the individual components of the applied stress tensor and the compositional strain tensor, would then conceivably have a much larger effect on the equilibrium distribution of the interstitial atoms than would be anticipated on the basis of a dilatational distortion or isotropic compositional strain, which would interact only with the trace of the stress tensor.Chou et al. [11] and Zhang et al. [12,13,14] have recognized the importance of the interaction between an applied nonhydrostatic stress field and the inherent tetragonal nature of the compositional strain in bcc metals. They derived equations for hydrogen redistribution around crack tips in bcc iron with various loading conditions and predicted hydrogen enhancement ratios of 30 or more above the far-field hydrogen composition and significantly in excess of predictions made assuming an isotropic compositional strain for the interstitial. [9] Zhang and Hack also predict that a correct accounting of the tetragonal distortion can lead to qualitative differences in the hydrogen redistribution. For example, they calculate hydrogen enhancement in the vicinity of a crack tip with pure mode III loading, even though there is no hydrostatic component of the crack stress field.Although such predictions of interstitial solute redistribution based entirely on the interaction of the external field and the compositional strain tensor are insightful, they suffer from an inconsistency in that the interstitial composition field itself generates a nonlocal stress field that interacts with the applied stress field. This interaction generates a compositional self-stress, which tends to inhibit further solute redistribution. Calculation of equilibrium solute profiles that neglect the compositional self-stress, therefore, tend to overestimate solute redistribution.Larché and Cahn recognized that neglecting the compositional self-stress in the determination of the elastic field yielded estimates of solute redistribution in the presence of a material defect that were not correct to even first order in the change in the composition. [15] Assuming a large, binary substitutional crystal with isotropic elastic constants, they linearized the mechanical and chemical equilibrium conditions to obtain a prediction for solute enhancement that is correctA set of open-system elastic constants used to approximate the redistribution of interstitial atoms among the three different interstitial sublattices in a body-centered cubic (bcc) metal is derived accounting for the tetragonal nature of the compositional strain in the presence of a nonhydrostatic stress. Predictions of the stress-induced composition change are calculated and compared to the actual solution and to two other approximation schemes, one based on a hydrostatic compositional strain and one based on ignoring the compositional self-stress. The open-system elastic constants give a qualitatively and quantitatively accurate representation of the composition cha...