E.T. Thostenson et al. Composites Science and Technology 61(2001)1899-1912 Thermal CVD MPECVD (b) Fig. 9. Micrographs showing(a)nanotubes aligned normal to the surface of a glass fiber and(b) the influence of MPECVD on the structure of the Single-walled nanotubes tend to assemble in'ropes'of nanotubes. Salvetat and co-workers [35 measured the properties of these nanotube bundles with the AFM. As he diameter of the tube bundles increases the axial and shear moduli decrease significantly. This suggests slip- ping of the nanotubes within the bundle. Walters et al [37 further investigated the elastic strain of nanotube bundles with the AFM. On the basis of their experi- mental strain measurements and an assumed elastic modulus of 1.25 TPa, they calculated a yield strength of 45+7 GPa for the nanotube ropes. Indeed, their calcu lated value for strength would be much lower if the elastic modulus of the nanotube bundle is decreased as a Fig 10 Micrograph showing tangled, spaghetti-like carbon nano- consequence of slipping within the bundle, suggested by tubes grown with conventional CVD techniques. Salvetat et al. [ 36] Yu and co-workers [38, 39] have investigated the ten sile loading of multi-walled nanotubes and single-walled transmission electron microscope, the amplitude of their nanotube ropes. In their work, the nanotubes were intrinsic thermal vibration. The average value obtained attached between two opposing AFM tips and loaded over 1l samples was 1.8 TPa. Direct measurement of under tension. Their experimental set-up is shown in the stiffness and strength of individual, structurally iso- Fig. 11. For multi-walled carbon nanotubes [38] the lated multi-wall carbon nanotubes has been made with failure of the outermost tube occurred followed by pull- an atomic-force microscope(AFM). Wong and co- ut of the inner nanotubes This 'sword and sheath' workers [35] were the first to perform direct measure- telescoping failure mechanism of multi-walled carbon ment of the stiffness and strength of individual structu- nanotubes in tension is also shown in Fig. 11. The rally isolated multi-wall carbon nanotubes using atomic experimentally calculated tensile strengths of the outer force microscopy. The nanotube was pinned at one end most layer ranged from 11 to 63 GPa and the elastic to molybdenum disulfide surfaces and load was applied modulus ranged from 270 to 950 GPa. In their sub to the tube by means of the AFM tip. The bending force sequent investigation of single-walled nanotube ropes was measured as a function of displacement along the [39], they assumed that only the outermost tubes assem- unpinned length, and a value of 1. 26 TPa was obtained bled in the rope carried the load during the experiment, for the elastic modulus. The average bending strength and they calculated tensile strengths of 13 to 52 GPa measured was 14.2+8 GPa and average elastic moduli of 320 to 1470 GPa. Xie ettransmission electron microscope, the amplitude of their intrinsic thermal vibration. The average value obtained over 11 samples was 1.8 TPa. Direct measurement of the stiffness and strength of individual, structurally iso￾lated multi-wall carbon nanotubes has been made with an atomic-force microscope (AFM). Wong and co￾workers [35] were the first to perform direct measure￾ment of the stiffness and strength of individual, structu￾rally isolated multi-wall carbon nanotubes using atomic force microscopy. The nanotube was pinned at one end to molybdenum disulfide surfaces and load was applied to the tube by means of the AFM tip. The bending force was measured as a function of displacement along the unpinned length, and a value of 1.26 TPa was obtained for the elastic modulus. The average bending strength measured was 14.28 GPa. Single-walled nanotubes tend to assemble in ‘ropes’ of nanotubes. Salvetat and co-workers [35] measured the properties of these nanotube bundles with the AFM. As the diameter of the tube bundles increases, the axial and shear moduli decrease significantly. This suggests slip￾ping of the nanotubes within the bundle. Walters et al. [37] further investigated the elastic strain of nanotube bundles with the AFM. On the basis of their experi￾mental strain measurements and an assumed elastic modulus of 1.25 TPa, they calculated a yield strength of 457 GPa for the nanotube ropes. Indeed, their calcu￾lated value for strength would be much lower if the elastic modulus of the nanotube bundle is decreased as a consequence of slipping within the bundle, suggested by Salvetat et al. [36]. Yu and co-workers [38,39] have investigated the ten￾sile loading of multi-walled nanotubes and single-walled nanotube ropes. In their work, the nanotubes were attached between two opposing AFM tips and loaded under tension. Their experimental set-up is shown in Fig. 11. For multi-walled carbon nanotubes [38] the failure of the outermost tube occurred followed by pull￾out of the inner nanotubes. This ‘sword and sheath’ telescoping failure mechanism of multi-walled carbon nanotubes in tension is also shown in Fig. 11. The experimentally calculated tensile strengths of the outer￾most layer ranged from 11 to 63 GPa and the elastic modulus ranged from 270 to 950 GPa. In their sub￾sequent investigation of single-walled nanotube ropes [39], they assumed that only the outermost tubes assem￾bled in the rope carried the load during the experiment, and they calculated tensile strengths of 13 to 52 GPa and average elastic moduli of 320 to 1470 GPa. Xie et Fig. 9. Micrographs showing (a) nanotubes aligned normal to the surface of a glass fiber and (b) the influence of MPECVD on the structure of the nanotubes [29]. Fig. 10. Micrograph showing tangled, spaghetti-like carbon nano￾tubes grown with conventional CVD techniques. 1904 E.T. Thostenson et al. / Composites Science and Technology 61 (2001) 1899–1912