Numerical Simulations of the Head-disk Interface in Hard Disk Drives PDF Download
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Author: Puneet Bhargava
Publisher:
ISBN:
Category :
Languages : en
Pages : 490
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Author: Puneet Bhargava
Publisher:
ISBN:
Category :
Languages : en
Pages : 490
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Author: Youyi Fu
Publisher:
ISBN:
Category :
Languages : en
Pages : 228
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To achieve an areal density of 1 terabits per square inch (1.55 gigabits/mm2) in hard disk drives, the size of magnetic grains in hard disks has been reduced to approximately 7 nm and the spacing between the magnetic head and the disk has been minimized to 1 to 2 nm. At a spacing on the order of 1 to 2 nm between the head and the disk, it is likely that contacts between the magnetic head and the disk occur during reading and writing, causing erasure of data or even failure of the head/disk interface. Wear particles can be generated as a consequence of contacts between slider and disk, and if particles enter the head/disk interface, catastrophic failure of the head/disk interface can occur. To reduce the generation of wear particles and avoid failure of the head/disk interface, it is important to investigate how the tribological performance of all contact interfaces in hard disk drives can be improved. In this dissertation, the tribological performance of the most important contact interfaces in a hard disk drive are investigated with a focus on the generation of wear particles and lubricant migration. First, fretting wear is investigated to study the effect of a diamond-like carbon (DLC) overcoat on wear of the dimple/gimbal interface. A numerical simulation model based on finite element analysis was developed to explain the experimental results. Then, lubricant migration on the air bearing surface and its effect on the head medium spacing (HMS) was investigated as a function of temperature, slider position, and "parking time" of the slider on the ramp. Thereafter, the thermal response of a thermal sensor during contact with asperities on the disk surface was analyzed. The effects of experimental and environmental conditions on the resistance change of the sensor were studied. Finally, experimental and numerical investigations were performed to analyze contact between the suspension lift tab and the ramp in hard disk drives. The voice coil motor current was used to characterize the change of the friction force and the generation of wear debris at the lift tab/ramp interface during load/unload testing. Numerical simulations were performed to analyze how to reduce contact stress between the lift-tab and the ramp. The results of this dissertation will be helpful in improving the tribological performance of hard disk drives.
Author: Jianfeng Xu
Publisher:
ISBN:
Category :
Languages : en
Pages : 215
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This thesis presents experimental and theoretical studies of the characteristics of the head/disk interface at very low flying height. The study starts with a discussion of the tribological background of the head/disk interface and presents a review of the literature related to studies of the head/disk interface. Then, mechanical scaling laws for hard disk drives are discussed. Numerical results for failure inception of brittle and ductile hard disks due to high shock levels are presented. An experimental setup for measuring slider dynamics in five degrees-of-freedom (DOF) is presented. This is followed by experimental studies of slider vibrations due to slider/disk contacts. Thereafter, a study of slider vibrations due to write-head induced "thermal" pole-tip-protrusion is presented. Numerical simulations of slider vibrations are compared with experimental results. A method for measuring the magnetic spacing based on the read-back signal is presented. Finally, the results of this thesis are summarized and directions for future research are given.
Author: Eric Michael Jayson
Publisher:
ISBN:
Category :
Languages : en
Pages : 372
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Author: Alejandro Rodriguez Mendez
Publisher:
ISBN:
Category :
Languages : en
Pages : 85
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In this dissertation we investigate the lubricant behavior at the head-disk interface of a hard disk drive (HDD) by numerically simulating the formation of lubricant moguls on the disk and the accumulation of lubricant on the slider's air bearing surface (ABS). We use classical lubrication theory from continuum mechanics to model both the air bearing and the lubricant motion. The numerical simulations were compared to experimental tests of lubricant reflow on the disk after laser heating. A good agreement was found between experiments and numerical simulations. We investigate the effects of the slider's flying height, skew angle and ABS design on the lubricant flow and reflow. We describe the lubricant thickness profile and volume evolution on the slider's ABS and lateral walls. It was found that a smaller flying height contributes to a faster lubricant removal from the ABS due to the induced increase in the air shear stress. When the HDD is at rest, the lubricant accumulated on the deposit end flows back into the ABS driven by the action of disjoining pressure. It is found, for a particular slider design, that increasing the slider's radial position and thus changing its skew angle has the effect of enhancing the lubricant flow process due to a decrease in the slider's flying height. The lubricant migration process is significantly dependent on the ABS design. It is found that slider designs that accumulate most lubricant on a broader area on the deposit end and have larger values of air shear stress remove lubricant from the ABS at higher volume rates than those designs where accumulation is concentrated near the center of the deposit end and have smaller values of average shear stress. We simulate the flow and reflow processes of unstable lubricant films. We study the spreading of droplets with thickness larger than the critical de-wetting thickness. It is observed that, if surface tension is neglected from the governing equations, the disjoining pressure acts as a destabilizing force inducing an unrestrained growth of the film. The disjoining pressure breaks up the initial droplet into smaller ones which narrow down in width and increase in height. As the growth continues, the curvature of each droplet becomes sufficiently large to balance the disjoining pressure. The final state consists of a few isolated droplets connected by a uniform film. When we include the effect of air shear stress and air pressure gradient the initial droplet breaks up into smaller ones, which are then sheared downstream in the direction of the air shear stress. It was not possible to simulate the de-wetting behavior of the lubricant film on the entire slider domain, since it was found that surface tension is significant only at length scales several orders of magnitude smaller than the size of the slider. Finally we investigate the changes in magnetic spacing due to lubricant migration on the ABS and study the formation of lubricant clots on the disk surface known as "moguls". It is observed that the minimum magnetic spacing of a lubricant contaminated slider is significantly larger than that of a clean slider even after a relatively long time of flying the slider over the disk. This increase in spacing is detrimental for the read/write performance of the HDD. It is also observed that the air shear stress can generate lubricant moguls on the disk surface due to oscillations of the slider along the vertical, downtrack and offtrack directions.
Author: Rohit Pradeep Ambekar
Publisher:
ISBN:
Category :
Languages : en
Pages : 64
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Author: Du Chen
Publisher:
ISBN:
Category :
Languages : en
Pages : 342
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Author: Mike Suk
Publisher:
ISBN:
Category : Dissertations, Academic
Languages : en
Pages : 320
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Author: Lin Wu
Publisher:
ISBN:
Category :
Languages : en
Pages : 380
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Author: Yuan Ma
Publisher:
ISBN:
Category :
Languages : en
Pages : 104
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Since its introduction in 1956, hard disk drives have become one of the dominant products in the industry of data storage. The capacity of the hard disk drives must keep evolving to store the exploding data generated in the era of big data. This demand pushes the development of technologies including heat assisted magnetic recording (HAMR), microwave assisted magnetic recording (MAMR) and bit-patterned media (BPM) to increase the areal density beyond 1Tb/in2. In the development of these technologies, it is essential to have a clear understanding of the dynamics and nanoscale heat transfer behavior across the head-disk interface. In this dissertation, dynamics and nano-scale heat transfer in the head disk interface are discussed. Experimental study of nano-scale heat transfer is conducted with the specifically designed static touchdown experiment. Simulation strategy that incorporates the wave-based phonon conduction theory was also developed. In the flying condition, correlation between the temperature and head disk spacing was found at both passive flying stage and modulation stage. When the flying height increases due to either disk surface microwaviness or contact induced modulation, head temperature will increase, with a slight time delay, indicating the existence of a cooling effect as the head approaches the disk. The static touchdown experiment, which decouples the complicated air bearing from the nano-scale interface was further designed and performed. The heat transfer behavior across a closing nano-scale gap between head and disk was observed and measured. Experimental and simulation results showed general agreement with the theoretical predictions of the wave based theory for radiation and phonon conduction. The effect of different factors including humidity, air pressure, lubricant layer and disk substrate in the static touchdown experiment were also studied separately. Furthermore, the dynamics of HAMR condition was studied with waveguide heads. The laser induced protrusion was found to be around 1~2 nm in height. The findings of this dissertation could be applied to future HAMR head/media design, and the static touchdown experiment could be potentially improved to be a new approach to measure material conduction coefficient and emissivity with high special resolution.
