Molecular-dynamics study of the carbon nanotube mechanical metahelix

Abstract

Hierarchical helical structures extensively exist in both natural and artificial systems and hold remarkable mechanical properties. Here, tensile mechanical properties of metahelix designed by twisting multiply twisted helical carbon nanotube ropes are investigated by coarse-grained molecular dynamic simulations. One-level metahelix are slightly mechanically strengthened with increasing twist angle α. However, two-level ones are more sensitive to the twist operation angles α and β, with maximum reduction in strength and Young's modulus by 64% and 87%, respectively. Three distinct failure modes are identified, although all metahelix show brittle failure under tension. For type I fracture mode, regardless the twist angle in metahelix, stress is uniformly distributed, resulting in simultaneous breakage of bonds at a cross-section. The type II and III failure modes are featured by stepwise localized failures, resulting from non-uniform stress distribution along each filament and identical cross-section of metahelix. This work provides molecular insights into optimal mechanical performance of CNT-based hierarchical helical yarns.