Multi Scale And Fatigue Properties Research On Mechanical Behaviors Of Three Dimensional Woven Composites

This paper is divided into two parts. In the first part ,A multi-scale coupled numerical model was developed to investigate the mechanical behaviors of 3D woven composite pipe first. In the second part, researching fatigue damage on 3D woven composite with the finite element simulation and experimental methods.In the first part:1. Micro- and meso-scale unit cells were built to represent the inhomogeneity of fiber tow and weave structure of 3D woven composite pipe, respectively. The periodic boundary condition of the camber shape meso-scale unit cell was specified. Then, the micro, meso unit cell of the periodic boundary conditions were implemented on the commercial software by Multi-point constraint method(MPC), and multi-axial loads either in terms of average stresses or average strains can be easily applied through master-slave node technology.2. Multi-scale coupled numerical approaches for 3D woven composite pipe structure were pursued. The macro-scale stiffness of 3D woven pipe was obtained by averaging stiffness of unit cells from micro-scale to meso-scale. Using the multi-scale unit cells, the converse stress analysis process under multi-axial loads was carried out, i.e. to transfer stresses from macro-scale to meso-scale and finally micro-scale. A model of embedding meso-unit cell into a homogenous ring was suggested for meso stress analysis in case of meso-scale stress without periodicity in annular direction.In the second part:1. static tensile and tensile - tensile fatigue tests on 3D woven composite were performed to work out the material's initial stiffness, staticstrength and residual strength degradation. The fracture surfaces were observed using a scanning electron microscope(SEM), and the material fatigue damage mechanism was summed up.2. a finite element model was estalished to research fatigue damage on 3D woven composite. A degraded mode of the material properties on fatigue damage was developed by stress analysis under fatigue loading. The fatigue failure criteria and the sudden material property degradation rules of unidirectional fiber-reinforced composite laminates have been developed. The fatigue damage accumulation was simulated with the user-defined material (UMAT) subroutine of ABAQUS.