Shear-lag analysis of capped carbon nanotube reinforced composites with interface damage

Abstract A shear-lag model is proposed for stress analysis of carbon nanotube-reinforced composites with interface damage. A cylindrical representative volume element (RVE) is used as a simplified unit cell to study the composite. We first demonstrate using detailed cohesive zone modeling that describing the interface with the bilinear cohesive damage evolution law and replacing the capped nanotube with an effective solid fiber is a reliable strategy for the stress analysis of the RVE. Depending on the fiber-matrix interface damage conditions, the fiber debonding process is divided into three phases in the monotonic stretch of the composites. Governing equations for the fiber stresses are derived and the associated closed-form solutions are obtained in different phases. In particular, our priority lies in dealing with the situation that the fiber ends are adhesive to the matrix. Extensive parametric studies demonstrate that the present model achieves high accuracy in predicting fiber responses in the pre-debonding and debonding phases and qualitatively captures the evolution trend of the fiber stresses in the post-debonding phase. The aspect ratio greatly influences the reinforcing efficiency of the nanotube. However, the presence of the damaged interfaces limits the development of the maximum axial force in the fiber. The present model takes into account the effects of the damaged interfaces and of the adhesive fiber ends, providing a valuable analytical tool for the stress transfer analyses in fiber-matrix composites.