Coarse-to-Fine vs. Fine-to-Coarse Graded Media Through a Micro-Mechanics–Based Strain-Gradient Approach to Brittle Fracture

De Santis C.; Rapisarda A.C.; Barchiesi E.; León Trujillo F.J. · Fatigue and Fracture of Engineering Materials and Structures (2026) · DOI: 10.1111/ffe.70428

Resumen

This paper investigates how grain-size gradients affect dynamic fracture nucleation and propagation in brittle materials through a second-gradient hemivariational continuum framework employing strain-gradient regularization. The constitutive parameters, including the Mindlin coefficients and a spatially varying characteristic length (Formula presented.) representing the mean intergranular distance, are analytically derived from a granular micromechanics upscaling, so that (Formula presented.) carries a definite physical meaning rather than a purely numerical one. Damage evolution is governed by Karush–Kuhn–Tucker conditions enforcing irreversibility. A systematic campaign is conducted on compact tension specimens with Coarse-to-Fine and Fine-to-Coarse gradings, across velocities from quasi-static to highly dynamic, complemented by mesh-convergence and reference-case analyses. By monitoring kink and branching angles, dynamic increase factors, reaction forces, and strain invariants, the study reveals that the grain-size gradient direction is a primary driver of fracture stability, rate sensitivity, and crack-path selection, governed by the microstructural transition traversed by the crack rather than the local grain size alone.

Instituciones: Universidad Continental