Collaborative multiscale phase-field model for trans-scale fracture propagation of fiber-reinforced composites

Owing to their inherent multiscale characteristics, cracks in fiber-reinforced composites initiate and propagate normally at the microscale level during loading, spanning spatial scales up to the macroscopic fracture failure of the material. Motivated by this phenomenon, this study proposes a collaborative multiscale phase-field (CMPF) approach to model the trans-scale fracture propagation of fiber-reinforced composites. The CMPF model includes a region-based phase-field model for characterizing matrix cracking, fiber breaking, and interface debonding at the microscale; a two-modes phase-field model for characterizing the axial and transverse fracture modes at the macroscale; and a bridging model for exchanging information (fracture modes, nonlinear stress–strain relationship, and strain levels) between the macro- and micro-models. Specifically, the real-time attenuation mechanical properties of the composite caused by crack propagation are first obtained at the microscopic scale and then transferred to the macroscopic two-modes phase-field model to map the trans-scale fracture propagation. The CMPF model is implemented within a finite-element package for numerical calculations and then applied to analyze the tensile-fracture behavior of needled carbon/carbon composites, which is a typical type of fiber-reinforced composite. The calculated results show that the transverse fracture mode nucleates successively within the needled region and then in a 90° nonwoven cloth layer, whereas the axial fracture mode arises within a 0° nonwoven cloth layer. The source of the transverse fracture is matrix cracking and that of the axial fracture is fiber breaking at the microscopic scale. In addition, the fracture properties and overlap of the needled region significantly affect the propagation paths of cracks, thus changing the strength and toughness of the composite. This CMPF model offers a promising approach for modeling and understanding the trans-scale fracture mechanisms of fiber-reinforced composites.