Mesoscale modelling of void growth and fracture initiation in steel

Abstract

Accurate prediction of ductile fracture in steels requires a mechanistic understanding of the evolution of microstructural voids under multiaxial loading. This work presents a mesoscale finite element framework implemented in Abaqus to characterise fracture initiation in structural steel using a representative volume element (RVE) containing a single spherical void. Periodic boundary conditions are applied to ensure compatibility with the surrounding material, enabling the RVE to represent bulk behaviour. Controlled deformation modes, including uniaxial tension, pure shear, and plain strain tension, are imposed to span a wide range of stress states. The proposed approach focuses on extracting the equivalent plastic strain at fracture initiation and mapping it as a function of stress triaxiality and Lode angle parameter, defining the fracture initiation locus in the η–ξ space. A key feature of the methodology is that all material input is identified exclusively from standard uniaxial coupon tensile test data. Based on this information, the mesoscale model predicts fracture initiation under shear‐dominated and biaxial stress states without requiring additional shear or plain strain tension experiments. Void growth, plastic strain localisation, and loss of stability within the RVE are monitored to determine the critical strain associated with each stress state. The resulting framework provides a physically motivated procedure for constructing fracture initiation loci from limited experimental data, offering an alternative to multi‐axial experimental calibration.