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Research Papers: Magnetic Storage

Analytical and Experimental Elastic-Plastic Impact Analysis of a Magnetic Storage Head-Disk Interface

[+] Author and Article Information
Raja R. Katta

Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801

Andreas A. Polycarpou1

Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801polycarp@illinois.edu

Jorge V. Hanchi, Mallika Roy

 Seagate Technology LLC, Minneapolis, MN 55416

1

Corresponding author.

J. Tribol 131(1), 011902 (Dec 02, 2008) (10 pages) doi:10.1115/1.2991169 History: Received October 08, 2007; Revised August 22, 2008; Published December 02, 2008

As the use of hard disk drives in mobile applications increases, the susceptibility of disk damage due to high velocity slider-disk impact presents a serious challenge. The impact could result in extremely high contact stresses, leading to the failure of the head-disk interface. An elastic-plastic contact-mechanics-based impact model was developed and implemented to study the impact between a slider corner and a disk. The impact model is based on the contact of a rigid sphere on a deformable half-space. The effect of slider corner radii and impact velocities on the contact parameters was initially investigated for a homogeneous disk substrate. To examine the effects of thin-film layers on the disk, the model was extended to a realistic layered disk, where the actual layered mechanical properties were directly measured. At high impact velocities and/or small slider corner radii, the impact was found to be dominated by the substrate and the effect of layers was negligible. At low impact velocities and/or large slider corner radii, the effect of nanometer thick layers could be clearly seen, as these layers are stiffer than the substrate protecting the disk from potential damage at lighter loads. Realistic dynamic impact experiments involving a slider and a spinning thin-film disk were performed using an operational shock tester. The impact damage was characterized in terms of residual penetration depth caused by the impact force of the shock and the impact velocity of the slider. However, the results were inconclusive in correlating with the impact model. To better control the experimental parameters, quasistatic nanoindentation experiments were performed on actual thin-film media and were successfully compared with the model predictions.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Comparison between elastic and elastic-plastic models. Penetration of the slider corner into the glass disk during impact (Vz=0.1 m/s) (Table 1 material properties). The elastic model clearly underestimates the impact damage.

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Figure 2

Impact contact parameters at various impact velocities and slider corner radii (Table 1): (a) maximum penetration and (b) maximum mean contact pressure. At higher velocities, contact parameters are greatly influenced by corner radii.

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Figure 3

Measured mechanical properties of thin-film media as a function of contact depth from nanoindentation experiments: (a) reduced elastic modulus and (b) hardness. Error bars designate a ±1 standard deviation.

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Figure 4

Schematic cross-section of a typical thin-film magnetic disk

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Figure 5

Comparison of the penetration depths of homogeneous and thin-film disks, R=10 μm: (a) high impact velocity, Vz=0.1 m/s; (b) low impact velocity, Vz=0.01 m/s

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Figure 6

Comparison of impact contact parameters for homogeneous and thin-film media: (a) maximum δ, glass; (b) maximum δ, thin-film; (c) maximum pm, glass; and (d) maximum pm, thin film

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Figure 7

Schematic of the operational shock (op-shock) tester used for performing impact experiments

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Figure 8

Typical impact damage measurement using AFM: (a) 3D AFM scan and (b) line scan of the damage shown in (a) to obtain residual penetration

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Figure 9

Residual penetration depths from operational shock experiments obtained by AFM measurements

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Figure 10

Imprint of the slider (shown with white contrast marks) on the magnetic disk for a very high velocity impact (the dark band is the region where the magnetic orientation was changed to easily identify the region of impact damage)

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Figure 11

Impact acceleration designated as “g-force” and residual penetration depth δr versus impact velocity measurements from op-shock experiments

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Figure 12

Typical nanoindentation load-displacement data and related critical parameters

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Figure 13

Impact contact parameters for the thin-film disk at a low velocity range for comparison with experiments: (a) maximum penetration and (b) maximum contact force. Pmax is 5 mN for R=1 μm at Vz=0.027 and the corresponding maximum δ=0.202 μm.

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