Compressive Damage Simulation Of 3-dimensional Braided Composites

The strength analysis of 3-D braided composites is still in the initial stage, and the compressive property research results of this material mainly come from experiments. This thesis adopts the microscopic finite element method to conduct progressive damage simulation for carbon/epoxy 3-D four-directional rectangular braided composites on the basis of linear elastic mechanics. Based on the interior unit cell model provided in literature, the finite element analysis model is firstly constructed. Then different damage initiation criteria and corresponding material degradation models are set for matrix and yarn to model different type of damage in comprising materials, and the non-linear material constitutive caused by damage is compiled by the user material subroutine UMAT in finite element software ABAQUS. Progressive damage analysis is conducted for typical large and small braiding angle specimens individually using five different failure criteria for yarns; strength results are compared with experimental data to verify that the analysis model is correct and to determine the applicability of the criteria. Damage initiation and evolution are analyzed and different failure modes are concluded for both large and small braiding angle specimens. The influence of braiding angle and fiber volume fraction on the material compressive property is then investigated. In the last part, the surface cell model is built on hypothesizes in accordance with the interior cell model, and the progressive damage analysis under compression is conducted for the cell model with surface part, then the damage feature of the surface cell as well as its effect on the material property are analyzed for further study on failure and strength of 3-D braided composites.