| Viscoelasticity is one of the most important properties of3D braided composites; howeverthere is little research on this subject. In this paper, the viscoelasticity of3D braided compositeshas been studied.Firstly, according to the meso-structures of materials, the unit cell models of3D braidedcomposites are constructed, in which the sectional shapes of different kinds of yarns aredistinguished and the adjacent yarns can contact closelySecondly, based on the homogenization theory, the elastic properties of3D braidedcomposites are predicted, and the influence of braided structures and processing parameters(braiding angle, fiber volume fraction) on the elastic properties is also studied. It is shown thatwith the increase of fiber volume fractions, the elastic moduli of3D braided composites in thebraiding direction increase, while with the increase of braiding angles, the elastic moduli of3Dbraided composites in the braiding direction decrease.Then, the viscoelastic properties are studied by expanding the homogenization method in theelastic domain to the viscoelastic domain, and the influence of braided structures and processingparameters on the viscoelastic properties is also studied. It is shown that with the increase ofbraiding angles, the viscoelastic properties of3D braided composites in the braiding directionincrease, while with the increase of fiber volume fractions, the viscoelastic properties of3Dbraided composites in the braiding direction decrease.Furthermore, by using the relationship between the static and dynamic viscoelastic properties,the dynamic viscoelastic properties of3D braided composites are studied.Finally, the relaxation moduli of resin-based3D braided composites were calculated underdifferent temperatures. Then a general method for determining the relaxation moduli undervariable temperatures from those under constant temperatures for resin-based3D braidedcomposites was constructed. |
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