Fracture Behavior of Carbon Nanotube-Based Composites with a Broken Fiber Using Multi-Scale Finite Element Modeling

Present study deals with the debonding between the broken carbon nanotube (CNT) and the matrix in CNT-based composites. A three dimensional (3D) square representative volume element (RVE) with one CNT fiber surrounded by matrix has been considered. A full 3D finite element (FE) analysis with multi-scale modeling has been carried out to calculate the stresses at the interface of the broken fiber and matrix near the vicinity of the break. Considering a very small debonding around the fiber break as a crack front, the strain energy release rates (SERRs) are also calculated using virtual crack closure integral (VCCI) method to assess the propensity of such a crack to grow leading to complete fiber debonding. Effects of important parameters like matrix properties and volume fraction on the stress distribution and on SERR have been studied. It is observed that matrix properties and volume fraction decide the magnitude of stresses near the fiber break and SERR thus deciding the chance of debonding. Variations of SERRs with crack length have also been investigated. It has also been observed that the stresses produced due to mode-II are only responsible for fiber debonding.