A nonlinear pullout model for unidirectional carbon nanotube-reinforced composites

The effective stiffness of multi-walled carbon nanotubes (CNTs) in the radial direction is derived. A nonlinear pullout model for CNT-reinforced composites is presented in which thermal residual stress, Poisson's contract effect, as well as nonlinear elastic behavior of nanotubes are considered. In the model, the CNT in the matrix is envisaged as an anisotropic cylinder shell submitted to axial tensile load and radial pressure, considering nonlinear in-plane stiffness in the axial direction and the effective stiffness in the circumferential direction. Based on the model, analytical solutions of axial membrane force of the nanotube and the nanotube-matrix interfacial shear stress are obtained. Results of sample calculations suggest that the distribution of interfacial shear stress along the nanotube length is sensitive to its elastic nonlinearity.