Iso-stress architecture from mineral foliation patterns.

The mechanical behavior of polycrystalline materials is significantly influenced by their evolving microstructural features. While numerous experimental techniques have sought to optimize material performance, understanding the role of microstructural morphology in dictating mechanical responses has remained challenging. Here, we demonstrate that mimicking microstructural features found in metamorphic rocks, specifically the sigmoid foliation patterns characteristic of syntectonic porphyroblasts, enables control over the mechanical response of polycrystalline aggregates under deformation. This is achieved via controlled abnormal grain growth (AGG), which induces localized stress relaxation within abnormal grains while enhancing strain-hardening in the surrounding matrix. Driven by grain boundary diffusion and locally accelerated by grain curvature in the initial stages of secondary recrystallization, this AGG process forms shape-mediated iso-stress microstructures that mitigate stress concentrations and homogenize the stress field. Our theoretically informed Monte Carlo simulations, based on an oligocrystalline elastic modified Potts model, elucidate the intricate relationship between grain size distribution, grain shape, and crystallographic orientation in shaping mechanical response. Our model provides a foundational understanding of material design principles that support key experimental observations, revealing how AGG can be strategically harnessed to engineer high-performance metallic alloys. By replicating nature's approach to microstructural optimization, this work presents a transformative pathway for developing advanced materials with tailored mechanical properties, enhancing performance and durability.