Progressive tensile damage simulation and strength analysis of three-dimensional braided composites based on three unit-cells models

In order to explore the micro-failure mechanism and predict tensile strength of three-dimensional braided composites, the three unit-cells models, namely interior cell, surface cell and corner cell, are established to simulate progressive damage of these materials. Macro model is firstly created and divided into three kinds of unit cells by their periodical distributions. A criterion is approached to determine damage and its pattern of each element, and stiffness degradation is implemented for the damaged elements with geometric damage theory. Periodical boundary conditions are applied on the models to calculate micro-stress and damage propagation is simulated with the increase of load. Each type of damage and its percentage is obtained by simulation and micro-failure mechanism is analyzed. Furthermore, the tensile strengths are predicted from calculated stress-strain curves. From simulation, composites with large braiding angle have more complicated micro-failure mechanism than composites with small braiding angle. It is also observed that there are more damages in surface cell than in interior cell and the damage types in the surface cell are various. The predicted results on the three unit-cells models agree well with the experimental data and are more accurate than only using an interior-cell model.