Finite element analyses on bending fatigue of three-dimesional five-directional braided composite T-beam with mixed unit-cell model

Abstract

This paper reports the bending fatigue behavior of three-dimensional five-directional braided T-shaped composite from finite element analyses and experimental characterizations. The braided composite microstructure was divided into five types of unit cell models, that is, interior cell, surface cell, corner cell, interior cell in joint region, and corner cell in joint region. A user-defined material subroutine was developed to characterize the unit cells properties, damage accumulation, and failure criterion of the T-beam under different stress levels. The stiffness degradation curves and bending displacement curves were obtained from the finite element analysis to show the three stages of fatigue developments, that is, matrix cracks, interface debonding, and fiber breaking. The stress and strain concentration areas were found in the middle of the flange and the web of the T-beam composites. The high strength reinforced fibers are recommended to add in the middle of the flange and the web for improving the bending fatigue resistance. And also, we hope the mixed unit-cell model could be extended to the other braided composite structures under quasi-static or cyclic loadings.