Steering cracks via auxetic zebra-composites

By taking advantage of Eshelby's inclusion problem, the present work combines analytical and numerical strategies for analyzing the mechanical response of two-dimensional composite media that include auxetic components, focusing on how cracks propagate and deviate within the domain. The analytical formulation is used to quantify how stresses induced by spherical and cylindrical inclusions in an infinite elastic matrix vary non-homogeneously as Poisson ratios of both matrix and inclusion change. Then, insights gained from analytical results are exploited to guide numerical finite element analyses of hollow plates under selected boundary conditions, focusing on how auxetic inclusions may alter local stress states to finally delay failure and potentially increase overall plate toughness. Building upon these outcomes, the zebra-composite structural paradigm, namely square plates featuring alternating bands of auxetic and standard (positive Poisson ratio) materials, is introduced to systematically investigate the potential in steering fracture paths. In particular, topological configurations of the material components are chosen to obtain the above-mentioned patches as embedded in a modified single-edge notched specimen to be tested under bending conditions and compared to standard models. Numerical simulations show that orientation, number, and distribution of auxetic regions all significantly influence local direction changes and global path of cracks, driven by qualitatively different strain energy and stress distributions. Specifically, auxetic bands seem to act as crack deflectors or attractors depending on their placement and orientation, leading to glimpse possible new strategies to fine-tune crack propagation and avoid catastrophic fracture for designing next-generation high-performance, self-healing, and smart materials.