Vibration and critical speeds of composite-ring disks for data storage

A new concept for data storage disks is proposed to increase operating speed with minimum changes in the geometry and design of conventional data storage disks. The disk-named a composite-ring disk-is composed of a storage material inside and a thin composite ring outside. Stress distributions are found for the rotating disk composed of two annular disks, of which the inside is made of isotropic material and the outside is made of orthotropic material. The dynamic equation for a composite-ring disk in rotation is formulated to calculate its natural frequencies and critical speeds. For the solution of transverse vibration, a rotational symmetry condition is applied in the circumferential direction and a finite element interpolation with Hermite polynomials is performed in the radial direction. The results show that reinforcing a disk at the rim increases critical speeds drastically, and can cause buckling in mode (0,0) which occurs above the lowest critical speed.