Abstract: Mechanical properties of a composite are the key to the simulation of a composite structure. A micromechanical model can predict the mechanical response of a composite from the properties of the fiber and matrix. However, it is frequently encountered that only a part of the mechanical properties of the fiber and the matrix are available in engineering applications, which directly affects the design accuracy of a composite structure. Thus, a reverse calculation process is presented in this work,with which the lacking mechanical parameters can be calculated from limit experimental data of the composite and the fiber and matrix. Firstly, all the available data of the unidirectional composite and the fiber and matrix are collected. Then the undetermined parameters into linear or nonlinear parts are clarified. Finally, the undetermined parameters by the micromechanical bridging model are calculated. The elastic parameters of a composite and the fiber and matrix are enough for the calculation of linear undetermined parameters, while stress-strain curves of a composite must be given for the calculation of nonlinear parameters. In order to validate the reverse calculation process, a series of off-axis tension tests of a T700/Epoxy UD composite are conducted. Only the elastic modulus of the composite, the longitudinal parameters of the fiber and the Young′s modulus of the matrix are available from the material provider. The other elastic parameters of the fiber and the matrix are obtained by the reverse calculation process. Then, the off-axis tensile strengths of the UD composite are predicted based on the bridging model with the reverse calculated parameters. For the cases of 10°, 15°, 60°, 75°, 90° off-axis tension, the predicted errors are less than 10%, which is accurate enough in engineering application. Thus, the reverse calculation process is validated. The presented reverse calculation process can increase the design efficiency and reduce the experimental cost in design.

Key words: bridging model, micromechanics, reverse calculation, mechanical properties, composites