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With the increased use of hard disk drives (HDDs) in mobile and consumer applications combined with the requirement of higher areal density, there is enhanced focus on reducing head disk spacing, and consequently there is higher susceptibility of slider/disk impact damage during HDD operation. To investigate this impact process, a dynamic elastic-plastic finite element model of a sphere (representing a slider corner) obliquely impacting a thin-film disk was created to study the effect of the slider comer radius and the impact velocity on critical contact parameters. To characterize the energy losses due to the operational shock impact damage, the coefficient of restitution for oblique elastic-plastic impact was studied using the finite element model. A modification to an existing physics-based elastic-plastic oblique impact coefficient of restitution model was proposed to accurately predict the energy losses for a rigid sphere impacting a half-space. The analytical model results compared favorably to the finite element results for the range from low impact angles (primarily normal impacts) to high impact angles (primarily tangential impacts). [DOI: 10.1115/1.3078770] Keywords: magnetic storage tribology, oblique impact, shock, elastic-plastic impact, coefficient of restitution

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. Keywords: magnetic storage tribology, impact, elastic-plastic contact, shock, thin-film media