On the dynamics of axially functionally graded CNT strengthened deformable beams Hossein Bakhshi Khaniki and Mergen H. Ghayesh Eur. Phys. J. Plus, 135 5 (2020) 415 Published online: 19 May 2020 DOI: 10.1140/epjp/s13360-020-00433-5