Three-Dimensional Contact Mechanics Studies of Zdol Hard Disk Lubricants
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THREE-DIMENSIONAL CONTACT MECHANICS STUDIES OF ZDOL HARD DISK LUBRICANTS Barry N. Lucas & Jack C. Hay Fast Forward Devices, LLC, 11020 Solway School Road, Suite 113, Knoxville, TN ABSTRACT This paper reports the results of a study of the dynamic 3-dimensional response between a diamond point probe and a commercial hard-disk overcoat/lubricant system. The specific overcoat was CNx with a thickness of 50 Å. The lubricant layer was ZDOL with nominal thicknesses of 11 Å and 24 Å in unbonded and bonded conditions. The experiments were conducted with a constant lateral displacement oscillation in the z, x & y direction of 1 nm at a frequency of 125 Hz. Results of this study show that the bonded lubricant layer increases the lateral force required to maintain a constant lateral displacement oscillation compared to both the unlubricated CNx coating and the CNx coating with the unbonded lubricant. INTRODUCTION Mechanical and tribological properties at the nanometer-scale are of vital importance to a number of U. S. industries. In an effort to continue the advancement of techniques available for mechanical characterization of surfaces, a new testing system has been developed that allows independent and dynamic control of the forces on, and the displacements of, a point probe along three orthogonal axes. This capability allows studies of dynamic frictional properties during the initial stages of contact between the probe and a surface. 3-DIMENSIONAL SYSTEM
Fig. 1. Schematic of 3-Dimensional System
The 3-dimensional system is based on three, one-dimensional indentation heads mounted orthogonally along the z, x and y axes. The system is shown schematically in Figure 1. The three one-dimensional systems are coupled via long, slender fibers such that cross talk between the three axes is minimized while the stiffness in the direction of motion of each respective axis is maximized. The axial stiffness is greater than 3x105 N/m, while the resulting stiffness perpendicular to each respective axis (bending) is roughly constant at 200 N/m for all three axes.
An independent coil-in-magnet assembly controls the force along each axis. While the system is inherently load-controlled, displacement control can be achieved using closedQ3.9.1
loop feedback control. The respective displacement of each axis is measured using a three plate capacitive system. The linearity of each axis is maintained by two leaf springs that effectively limit the out of plane motion of each axis to the fibers used in the coupling mechanism. One of the most exciting features of the system is that in addition to independently controlling the quasi-static motion of the probe along each of the axes, an independently configurable harmonic force, at a specified frequency, can be added to the quasi-static force for each respective axis[1]. All of the axes have a dedicated phase-lock amplifier that has the ability to control the harmonic displacement amplitude for each axis at a prescribed value via a closed-loop feedback system running in the respective lock-in amplifi
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