Failure analysis of carbon nanotube/epoxy composites having a broken carbon nanotube

In the present work, multi-scale finite element analysis of carbon nanotube/epoxy composites having a broken carbon nanotube has been performed to assess the severity of such a fiber (i.e. carbon nanotube) break. A square representative volume element having nine-carbon nanotubes has been considered for the analysis. Considering a small debonding around the broken fiber as a crack front, stress redistribution around the break is studied. Using the concept of linear elastic fracture mechanics, strain energy release rates around the debonding have been calculated using virtual crack closure integral method. Quadratic stress criterion has been used to assess the delamination initiation at the interface of broken carbon nanotube and the matrix. Virtual crack closure integral along with quadratic stress criterion has been used to determine the critical strain energy release rate. Results from the present analysis show that the fiber volume fraction does not have significant influence on the ineffective length of the broken carbon nanotube. A high magnitude of interfacial shear stress is observed to have developed in the vicinity of the fiber break indicating the chances of debonding. All the three components of strain energy release rate have been determined and the influences of important parameters on the value of strain energy release rate have also been studied.