13th International Conference on Fracture June 16–21, 2013, Beijing, China interface between the CNT and the matrix, and study mechanical property of the interface of CNT composite with various method, such as the experimental method and the Melecular Dynamics (MD) method [8]. There are still many technical limitations in experimental method, and the calculation cost of the MD method is too huge. The Finite Element Method (FEM) combined with the CZM is the effective and economy method to study mechanical property of the interface of CNT composite, and the CZM was utilitied in this paper to predict local damage initiation and fracture propagation. 2. CZM Model of Interface The key problem of the CZM is the definition of the two important parameters, the cohesive strength Tc and the energy release rate Gc. There is few experimental data providing the interface parameters accurately and directly for the CZM. Gou[9] has calculated the shear strength by the MD simulation of the CNT’s pull out from the matrix. The result 75MPa was adopted to be the shear strength .Tan[6] has deduced the normal strength 470MPa and the energy release rate 0.107Jm-2, from the Lennard-Jones potential from the van der Waals interactions, the results was adopted as the normal cohesive strength and the energy release rate Gc. The interface between the CNT and the matrix was modeled by the 2 dimension, 4 node cohesive element COH2D4 to reproduce the damage of interface between the CNT and polymer. The Young’s modules of the CNT and the epoxy matrix are respectively 1 TPa and 4GPa. The FEM model of the CNT composite was established by the generally used software ABAQUS. It is with three phases: the CNT fiber phase, the cohesive interface phase employing the CZM and the epoxy matrix phase. The unit cell was extracted to represent the effective properties of CNT composite based on the homogenization theory, as is shown in Fig. 2. Figure 2. Unit cell of CNT composite Since composite structures are usually designed for the loading in the reinforcement orientation, the displacement load was exerted at one side of the unit cell, and the other side was fixed, the boundary conditions of the unit cell was demonstrated in Fig. 3. Figure 3. Boundary conditions of unit cell 3. Results and discussion
RkJQdWJsaXNoZXIy MjM0NDE=