Modeling of progressive damage for composites under ballistic impact

A constitutive model based on the concept of continuum damage mechanics has been proposed to study the progressive damage behavior of composite laminates under ballistic impact. The proposed model is investigated in five steps: First, the quadratic form of damage initiation criteria are presented to predict the initiation of failure in different modes. Second, an exponential form damage evolution law combined with characteristic length based fracture energy approach has been presented. Stiffness degradation is characterized by a variable determined by the equivalent displacement for each failure mode. Third, an experimentally verified strain rate model that considers the rate dependency of the strength and modulus of the composite laminate is considered. Fourth, cohesive elements are inserted at every inter-layer for modeling the delamination evolution. Fifth, the constitutive model has been combined with an element erosion algorithm for the removal of highly distorted elements. Simulations have been performed using reduced integration hexahedra elements (RIHE) and full integration hexahedra elements (FIHE). Implementation of cohesive elements exhibited better delamination progression. Experimentally verified strain rate model enhanced the efficiency of the model showing good correlation between the present simulations and experimental observations, in terms of damage patterns, residual velocity, kinetic energy and ballistic limit.