Friction Force, Contact Resistance, and Lubricant Shear Behavior at the Magnetic Head-Disk Interface During Starting

During the starting operation of magnetic rigid disks, a stiction phenomenon characterized by a high friction force may be encountered due to the smoothness of the contacting surfaces and the small thickness of the lubricant film. Since friction measurement using a force transducer yields a signal proportional to the slider displacement, the real friction force at the head-disk interface cannot be measured directly. In the present study, a dynamic data analysis scheme is developed to obtain the real friction force as a function of time based on the measured apparent friction force. Electric contact resistance measurements demonstrate that the transition from static to kinetic friction occurs before the apparent friction force reaches a maximum value. Assuming a constant acceleration of the disk, the relative slip velocity at the contact interface is obtained as a function of time. The relationship between the shear stress and shear strain rate for a relatively thick lubricant film is found to be approximately linear up to a critical value of the shear stress. Due to the extremely high shear strain rates, the maximum real friction force can be significantly greater than the maximum static friction force.