Carbon nanotubes (CNTs) are one of the strongest known materials. When assembled into fibres, however, their strength becomes impaired by defects, impurities, random orientations and discontinuous lengths. Fabricating CNT fibres with strength reaching that of a single CNT has been an enduring challenge. Here, we demonstrate the fabrication of CNT bundles (CNTBs) that are centimetres long with tensile strength over 80 GPa using ultralong defect-free CNTs. The tensile strength of CNTBs is controlled by the Daniels effect owing to the non-uniformity of the initial strains in the components. We propose a synchronous tightening and relaxing strategy to release these non-uniform initial strains. The fabricated CNTBs, consisting of a large number of components with parallel alignment, defect-free structures, continuous lengths and uniform initial strains, exhibit a tensile strength of 80 GPa (corresponding to an engineering tensile strength of 43 GPa), which is far higher than that of any other strong fibre.

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This study was supported by the National Natural Science Foundation of China (grant no. 21636005), the Foundation for the National Basic Research Program of China (grant no. 2016YFA0200102), the NSFC (grant nos. 11227202, 1147215) and the National Basic Research Program of China (grant no. 2013CB934203). We thank R. H. Baughman for his advice on the manuscript. We also thank P. Shi, H. Wang and H. Xie for discussions.

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Author notes

  1. These authors contributed equally: Yunxiang Bai, Rufan Zhang, Xuan Ye.


  1. Beijing Key Laboratory of Green Chemical Reaction Engineering and Technology, Department of Chemical Engineering, Tsinghua University, Beijing, China

    • Yunxiang Bai
    • , Rufan Zhang
    • , Zhenxing Zhu
    • , Huanhuan Xie
    • , Boyuan Shen
    • , Dali Cai
    • , Chenxi Zhang
    • , Zhao Jia
    • , Shenli Zhang
    •  & Fei Wei
  2. Center for Nano and Micro Mechanics, Tsinghua University, Beijing, China

    • Yunxiang Bai
    • , Xuan Ye
    • , Zhenxing Zhu
    • , Huanhuan Xie
    • , Chenxi Zhang
    • , Xide Li
    •  & Fei Wei
  3. Department of Engineering Mechanics, AML, Tsinghua University, Beijing, China

    • Xuan Ye
    •  & Xide Li
  4. Department of Materials Science and Engineering, Stanford University, Stanford, CA, USA

    • Bofei Liu


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F.W., Y.B. and R.Z. conceived the project. Y.B. designed and performed the experiments, analysed the data and wrote the manuscript. R.Z. participated in the data analysis and figure design, and co-wrote the manuscript. X.Y. participated in the mechanical measurement. X.L. supervised the mechanical measurement and participated in the data analysis and manuscript preparation. Z.Z., H.X. and B.S. participated in the synthesis and characterization of ultralong CNTs/CNTBs. D.C. participated in the establishment of the mathematical model. B.L. participated in the figure processing. C.Z. and Z.J. provided theoretical assistance with hydromechanics. S.Z. participated in the manuscript preparation.

Competing interests

The authors declare no competing interests.

Corresponding authors

Correspondence to Rufan Zhang or Xide Li or Fei Wei.

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