Investigation of damage behavior in composite materials under mode I and mode II loads using peridynamic theory

Composite materials are mostly used in aerospace, defense and automotive industries in order to take advantage of their specific stiffness and strength. Internal failure of composites occurs due to breaking of fibers, development of micro cracks in matrix, debonding between fibers and matrix and delamination. One of the most common failure type is delamination based failure. It is very important to be able to accurately model the damage behavior of composite structures. In most of the studies, Classical Continuum Mechanics formulations are used to model the delamination behavior of the structures. Since these formulations are based on local partial derivatives, structural tests should be made in order to determine the direction and severity of the damage. Therefore, it is difficult to predict the occurrence and the branching of the damage using Classical Continuum Mechanics formulations. Within the scope of the thesis, studies on estimation of damage to composite materials have been carried out with Peridynamic theory. Since Peridynamic theory is nonlocal and it is based on integral equations, it is an appropriate theory for modelling damage initiation and propagation for isotropic and composite materials. In this study, Peridynamic theory is implemented in ABAQUS finite element program and the input files generated using the MATLAB code. In Peridynamic modelling truss elements represent Peridynamic bonds. In this study, a new Peridynamic formulation was developed for modelling the damage behavior of the structure by establishing a relationship between the Peridynamic theory and Cohesive Zone Method. The proposed Peridynamic formulation was applied to composite test specimens under Mode I (Double Cantilevered Beam Test), Mode II (End Notched Flexure Test) and Mixed Mode Bending loading conditions. In these studies, Peridynamic results compared with the obtained results using the Cohesive Zone Method, analytical solutions and the available results in the literature. The obtained results show that, the results of Peridynamic theory have good agreement with the results of other methods. Based on the obtained results it has been found that the Peridynamic theory is an appropriate theory to model crack behavior of the structure.