Torsional vibrations of functionally graded restrained nanotubes Ömer Civalek, Busra Uzun and Mustafa Özgür Yayli Eur. Phys. J. Plus, 137 1 (2022) 113 Published online: 13 January 2022 DOI: 10.1140/epjp/s13360-021-02309-8