Micro-texture regions (MTR), defined as a cluster of grains with similar crystallographic orientations, have a significant detrimental effect on the fatigue life of Ti alloys. This paper proposes a novel multiscale approach, coupling the Parametrically Upscaled Constitutive Model (PUCM) for predicting component-scale deformation with the Parametrically Upscaled Crack Nucleation Model (PUCNM) for fatigue crack nucleation in polycrystalline microstructures of \(\alpha /\beta \) Ti6Al4V alloy containing MTRs. The PUCMs represent higher-scale constitutive models whose coefficients are explicit functions of Representative Aggregated Microstructural Parameters (RAMPs), representing statistical functions of key morphological and crystallographic descriptors of the underlying microstructure. A novel RAMP is proposed for the quantification of the MTR intensity that incorporates a measure of the relation between the MTR crystallographic orientation and the local principal stress direction, in addition to morphological and crystallographic characteristics like MTR size, crystallographic orientation, average misorientation, and misorientation distribution within the MTR. The MTR intensity parameter is incorporated in the physics-informed PUCNM for macro-scale analysis of fatigue crack nucleation. The PUCNM is validated using experimental dwell fatigue tests with different microstructures. A WATMUS-accelerated PUCM-based FE model of a double-edged notched specimen is simulated under dwell fatigue loading to investigate the effect of notch geometry and microstructural features on dwell fatigue crack nucleation. Studies examine the interplay between the specimen geometry, macroscopic stresses, and the underlying microstructure with MTRs on the nucleation life.
