A moving mesh-based numerical investigation of the failure response of nano-filled ultra-high-performance concrete structures

In recent years, important advances in the field of nanotechnology have demonstrated that using a proper percentage of dispersed nanomaterials inside concrete elements allows their strength and toughness to be significantly improved. This study aims to present a novel methodology for predicting crack propagation phenomena in Ultra-High-Performance Fiber-Reinforced Concrete (UHPFRC) structures enhanced with embedded nanomaterials. The proposed numerical strategy combines a Moving Mesh (MM) technique, based on the well-established Arbitrary Lagrangian-Eulerian formulation, and an Interaction Integral (i.e., the Mintegral) method, both implemented in a finite element framework. The MM is used for tracking the crack advance-related variations in the geometry of the given computation domain, while the M-integral is adopted to extract the Mixed-Mode Stress Intensity Factors (SIFs) at the moving crack front. The mesh is moved according to a maximum principal stress-based fracture criterion. In addition, the proposed strategy incorporates a mesh regularization technique able to ensure the consistency of the mesh points' motion, thus avoiding excessive mesh distortions. By virtue of this feature, the overall number of remeshing events is drastically reduced. Another novelty aspect of this work is the adoption of an R-Curve approach to accurately capture the quasi-brittle fracture behavior of UHPFRC members enhanced with nano-fillers, even though in the setting of Linear Elastic Fracture Mechanics (LEFM). Comparisons with experimental data reported in the literature are developed to assess the reliability and efficacy of the proposed methodology.