“…Actually, the free dynamics behaviour of two-layer beams has been largely studied in the literature [12][13][14][15][16][17][18][19][20], where numerical [21,22], analytical/theoretical [8,23] as well as experimental [8,11,24,25] studies can be found. Also some specific issues have been investigated, such as, the effect of interface damage [8,26,27], the viscoelastic behaviour of the core [28][29][30], the effect of the temperature [31,32], the lateraltorsional vibration coupling [33], curved beams [34], and boundary conditions effects [35].…”