Modeling of crack bridging and failure in heterogeneous composite materials: A damage-plastic multiphase model

Abstract

Bridging effects in heterogeneous composite materials are traditionally treated as tractions lumped at the crack surface. This conventional equivalence, however, may fail to reveal the fundamental mechanisms of composite toughening. Hereby, a damage-plastic multiphase model is proposed and developed which is capable of capturing the engaging bridging mechanisms of fiber reinforced cementitious composites without the need for explicit representation of fibers. The key idea is to idealize the composites as the mixture of an activated fiber phase integrating all bridging fibers and an effective Cauchy continuum phase representative of the matrix and bonded fibers which interact through a nonlinear interface. The kinematics of matrix and fiber phases are independently described through the introduction of additional slip fields. This proposed modeling framework has the following novelties: (1) a new nonlocal slip theory is proposed which allows to depict the micro-slippage of arbitrarily distributed activated fibers with a minimum number of auxiliary kinematic descriptors, (2) a unified damage-plastic framework for the fiber–matrix interface is developed, enabling the method to characterize simultaneously the slip-dependent interface, fiber pull-out and fiber rupture, and (3) it is demonstrated that the composite toughening effect originates not only from interfacial friction but also from elasto-plastic stretching of fibers and pulley force actions, among which interfacial friction is the dominating energy absorbing mechanism. The proposed damage-plastic multiphase model is validated against experimental data from the single-fiber level and the structural level.