Abstract
Molecular dynamics (MD) simulations of nanoindentation of multiwalled carbon nanotubes(MWCNTs) are carried out to study the deformation mechanism and the mechanicalproperties of MWCNTs in the radial direction. The MWCNT is found to be soft in itsradial direction, with nanohardness rising slowly from about 6 to 15 GPa. The soft phasepersists until all spaces between adjacent layers of the MWCNT are compressedbeyond a critical value of about 1.9 Å. Beyond the critical stage the formation ofnew bonds between different layers starts to increase, producing a super-hardamorphous phase with a hardness of up to 94 GPa. Though locally compressedto a large radial strain of about 63%, the amorphous phase with a mixture ofsp3 andsp2 bondsis completely reversible upon unloading, showing super-elasticity. Further indentation afterwards leads topermanent sp3 and even sp rehybridization, the MWCNT is badly damaged and the hardness fluctuateswith a maximum of about 124 GPa which is comparable to the microhardness of diamond.
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