Morphology-dependent load transfer governs the strength and failure mechanism of carbon nanotube yarns. (December 2016)

• Record Type: Journal Article
• Authors: Rao, Abhinav; Tawfick, Sameh; Bedewy, Mostafa; Hart, A. John
• Is Part Of: Extreme mechanics letters. Volume 9(2016)Part 1
• Page Start: 55
• Page End: 65
• Publication Date: 2016-12
• Subjects: Carbon nanotube -- Yarn -- Fiber -- Mechanics -- Strength; Mechanics -- Periodicals; Mechanics, Applied -- Periodicals; Mechanics; Electronic journals; Periodicals; 531.05
• DOI: 10.1016/j.eml.2016.05.003
• Languages: English
• ISSNs: 2352-4316

Abstract

Abstract: The outstanding properties of individual carbon nanotubes (CNTs) have motivated interest in CNT fibers and yarns for composite materials, high-strength conductors and multifunctional textiles. However, despite advances in manufacturing, the strength of CNT yarns remains 10–100 fold less than individual CNTs. In light of the complex, multi-scale load transfer in CNT yarns, a hierarchical model taking into consideration the morphology-dependent mechanics is necessary to understand this limitation. We present a coupled analytical and finite element model of three-dimensional morphology and the full tensile behavior of CNT yarns. By incorporating load-induced changes in morphology, simulations of yarns in tension show different load paths such as fracture-type or stick–slip failure depending on the waviness and number density of CNTs. The strength of untwisted pristine CNT yarns is shown to be limited to <10% of the intrinsic CNT strength, even at practical limits to CNT packing density and alignment. Load-induced changes in CNT morphology are verified by tensile testing of CNT yarns along with in-situ X-ray scattering. In addition, the nominal structure of the yarn is shown to strongly influence the improvement in strength achieved by densified and/or cross-linking, and a sublinear relationship between CNT contact enhancement and yarn strength is predicted. Thus, this work provides a means to investigate the complex load transfer mechanisms in CNT yarns and other assemblies, to further study their process–structure–property relationships, and to understand potential property limits.