In the present study, the vibrational properties of straight and non-straight hetero-junction carbon nanotubes (HJCNTs) are investigated. The molecular mechanics technique in combination with the finite element method is applied to obtain the first four natural frequencies as well as the corresponding mode shapes. The effects of connecting region length on the frequencies of straight and non-straight structures with clamp-clamp and clamp-free boundary conditions (BCs) are discussed in details. The results show that for the clamp-free BCs, the first and second frequencies increase with increasing the connecting length whereas the third and fourth ones decrease. Also, for the clamp-clamp BCs, increasing the connecting length leads to decrement in the first two frequencies while the changes of the second two frequencies depend on the total length of the structure. Moreover, for the clamp-clamp BCs, the mode shapes are affected by the total length of the structures. Finally, to avoid resonance and its damage in dynamic applications, for some modes of excitation appropriate structures are proposed.

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