Thermo-viscoelastic analysis of three-dimensionally braided composites

Thermo-viscoelastic properties of 3D braided composites are studied by a numerical method proposed in this paper. A finite element model with periodic boundary conditions is constructed based upon the three-cell division scheme. The Time–Temperature Superposition Principle is applied to characterize the thermal effects on the viscoelastic properties of 3D braided composites. An equivalent thermal expansion coefficient assumption is put forward, in which the equivalent thermal expansion coefficients of 3D braided composites are functions of time, and follow the same time–temperature relationship of the equivalent relaxation modulus. The equivalent thermal expansion strain obtained from the assumption agrees well with the result from the finite element analysis. Based on the assumption, the thermo-viscoelastic constitutive relationship is obtained by the finite element method and Prony series fitting. Furthermore, the thermo-viscoelastic properties of 3D braided composites in different temperature states are investigated.