In the pursuit of high areal recording density towards 10 Tb/in2, it is necessary to improve the positioning accuracy of the magnetic head in the hard disk drive head-positioning control system. Ultrasonic motors (USMs) are novel electric motors used for positioning controls. Due to the drive characteristic of USMs, wear and fatigue of friction material at the contact friction interface are inevitable. Contact deformation can cause local damage of USMs. Therefore, obtaining the details of the stress distribution in the friction material due to the inelastic deformation is important. In this work, a contact model of traveling wave ultrasonic motor (TWUSM) is proposed. A three dimensional finite element model with cohesive zone elements embedded between friction material and rotor is then developed. Infinite finite elements are incorporated in this modeling as the boundary condition as the model thickness is typically many orders smaller than the longitudinal dimension. The evolution of deformation in friction material and rotor due to the mechanical surface loading is presented. The possible interfacial delamination process between friction material and rotor is numerically studied. And the friction coefficient effect of the friction material on the delamination propagation is also investigated.

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