Theoretical analysis on the pullout behavior of carbon nanotube at cryogenic environment with the consideration of thermal residual stress

A numerical fiber pullout model tailored for carbon nanotube (CNT) reinforced polymer composites is developed based on some classical models, to evaluate the effect of low temperature environment and other parameters to the stress distribution and stress transfer efficiency in CNT/polymer composites. It is assumed that there are no bonding between CNTs and polymer so only frictional slip occurs in the interface. Results show that the required axial stress to pull out a straight CNT at cryogenic temperature is more than 6 times greater than that required at room temperature. Some other parameters, such as the length of CNT and the modulus of polymer, also influence the stresses in the CNT/polymer model. The model is also applied to coiled carbon nanotubes (CCNTs) which are newly-developed carbon nanotubes with a helical configuration. At cryogenic temperature, a greater stress is required to pull out a CCNT than a straight CNT, especially in the case when the pitch angle of CCNT is less than 60°. Hence, the stress transfer in CCNT/polymer composites is better than that in straight CNT/polymer composites.