Homogenization Finite Element Simulation On Mechanical Properties Of Bi-directional Fiber Reinforced Composites

As an important composite, fiber-reinforced composites(FRC) have been widely used in a broad range of applications because of their outstanding physical, mechanical and thermal properties. But most of the studies were based on unidirectional fiber reinforced composites(UFRCs). Unlike UFRCs, bidirectional-fiber-reinforced composites(BFRCs) can have specified in-plane mechanical properties along two distinct in-plane directions. However, the mechanical performance of comoposites consisting of two or more different materials not only depends on the composition and structure, but also is affected by the interface. Therefore, the mechanical properties and the influence of interfacial properties of BFRC are investigated by combing the finite element method and the gradual homogenization method. The following conclusions can be drawn from the present study:Firstly, a simplified micromechanical model is proposed for estimating the influence of the ratios of fiber/matrix modulus and the fiber volume ratio on the effective macroscopic mechanical properties of BFRCs. The model is validated by results from a three-dimensional(3D) representative volume element(RVE) through the homogenized finite element approach, in which the corresponding user subroutine codes are written. The proposed analytical method can give a reliable estimation of effective elastic moduli of the BFRCs and reasonable variation trends of effective tensile strengths via a comparison with the results from the finite element method.Secondly, the influences of interfacial properties of BFRC on the effective modulus and the tensile strength are investigated by the homogenization finite element method, in which the imperfect interface is taken into account by introducing some cohesive contact surfaces. It can be seen from the results that the coefficient viscosity has little influence on tensile strength of BFRCs. An imperfect interface with a different interfacial stiffness may induce different damage onsets in the matrix of BFRCs, and with the decrease of the interface stiffness, macro equivalent parameters are diminishing. Compared with the interfacial fracture energy, both the interfacial stiffness and strength play a more important role in determining the out-of-plane tensile strength of the CBFRCs, while have slight effect on the in-plane tensile strength. The tensile strength of the CBFRCs will be reduced because of the existence of interface. With an increase in the fiber volume fraction, the in-plane tensile strengths increase sharply while the out-of-plane tensile strength decreases slightly. Compared with the case without considering the interface effect, the existence of interface will reduce the tensile strength of BFRC.Finally, an interface with a certain thickness is replaced by the cohesion model with finite element method for analyzing the effects of interphase thickness, modulus and strength on effective mechanical behavior of BFRCs. The results show that with the decrease of the interphase thickness, the macroscopic effective elastic modulus and poisson’s ratio increase gradually. With the increase of interphase modulus, the macroscopic effective elastic modulus increases, but the tensile strength is decreased. As the interphase strength increases, the in-plane tensile strength of BFRC is increased gradually, the out-of-plane strength is increased firsty and then reach a constant value with a further increasing interphase strength. Our numerical results also show that the out-of-plane strength of BFRC is always less than tensile strength of the matrix.