On the Role of Microstructural Heterogeneities on Ductile Damage Evolution

Ductile damage typically proceeds in three stages, respectively associated with nucleation, growth and coalescence of voids. Each of these processes is driven by local micromechanical fields. Deciphering the relative contributions of void evolutionary modes requires the development of microstructure-informed models accounting for the 2-way coupling between void evolution and plastic flow. Given the above, this study introduces a generalized, microstructure-sensitive framework for modeling ductile damage in polycrystalline materials. The model relies on an associated plasticity formalism in which the contribution of voids to plastic flow, as well as their growth are homogenized through the use of a gauge stress, including both deviatoric and dilational components; thereby leading to a non-isochoric plastic flow. The developed formulation is compatible with rate-sensitive and crystal plasticity formalisms whilst maintaining thermodynamic and kinematic consistency. Further, the approach allows for coarse-graining the effects of porosity on plasticity and their evolution without necessitating an explicit representation of the voids. The formulation is implemented in an FFT-based full-field solver. The model is then applied to assess the roles of both elastic and plastic flow heterogeneity on the evolution of ductile damage and on the mechanical response of polycrystalline aggregates. To this end, the model is contrasted with reference elastically and plastically isotropic simulations, revealing that plastic anisotropy, rather than elastic heterogeneity, is the primary driver of porosity growth.Crystal plasticity simulations reveal that, even without any special interfacial treatment, microstructural heterogeneity alone leads to the emergence of preferred sites for damage localization. Specifically, grain boundaries—particularly those with normals aligned with the loading direction—frequently emerge as preferred sites for void growth due to the local stress states generated by heterogeneous deformation. More broadly, the results demonstrate that failure is dictated by extreme local events and the development of percolating damage paths, rather than by the evolution of spatially averaged porosity.In addition, the study clarifies the distinct roles of heterogeneity and constitutive hardening. While microstructural inhomogeneity controls the spatial localization of damage, strain hardening primarily influences the temporal evolution of porosity by delaying void growth and suppressing the amplification of local damage. The consistent delay of failure across both strain-controlled and stress-controlled loading conditions underscores the non-trivial interplay between boundary conditions, hardening behavior, and micromechanical fields. These findings highlight the necessity of microstructure-aware formulations for obtaining physically meaningful predictions of ductile failure.