Shear transfer in fractured carbon nanotubes under torsion

The experimental evidence revealed that torsional fracture of a carbon nanotube (CNT) is triggered from the outermost graphene layer, and then the crack grows toward the inner layers. This work studies load transfer among the graphene layers when a crack grows into the inner CNT. Both shear-lag modeling and finite element analysis (FEA) have been employed for analyzing the stress distribution in the graphene layers. Numerical computations are given to the cases in which the layer numbers are two, five, and ten, respectively. The effects of the layer number and the aspect ratio on the shear transfer efficiency have been examined. The strain energy release and the effective shear modulus of a fractured CNT with respect to the number of broken layers are calculated. The results show that the layered structure can increase the shear stress concentration. Under a stroke-controlled condition, the growth of crack becomes stable, and the crack can grow only when the twisting angle is increased. In comparison, under a load-controlled condition, the crack will grow unstably once the crack is triggered.