Magnetic information storage technology has made astounding progress since its invention over a hundred years ago. For the last several years, storage packing densities in hard disk drives have doubled every year! This frantic pace is expected to soon slow because of the some very fundamental limits that are becoming increasingly evident in the technology. Conventional magnetic recording technology is expected to ultimately reach densities of several hundred Gigabits per square inch and data-rates of a few Gigabits/s ( current products are ∼25 Gbit/sq.in. and over 0.5 Gbit/s ). We examine the key limiting factors and then try to develop a consistent geometry and set of material properties that could support a density close to one Terabit per square inch. Finally we speculate about the external characteristics of a small hard disk drive that would store one Terabyte of information [1].

Decreasing track width and tape thickness to increase the volumetric recording density of tape drive systems will result in the failure of tracking. The decrease in the tape thickness causes the vertical displacement of the tape forwarding position, which is controlled by pressing the lower tape edge against the lead of a stationary drum. The position of the upper tape edge is controlled by the height of the flanges of the roller guides beside the drum. The displacement of tape forwarding position causes the failure of tracking, especially with narrow track. The reduction of the static friction coefficient between the tape and the roller guides in a drive was found to be effective to reduce the excessive force with which the tape edges are pressed to the flanges or the lead, which will cause the displacement of the tape forwarding position.

In the present paper, the algorithm proposed by Giacopini et. al. [1], based on a mass-conserving formulation of the Reynolds equation using the concept of complementarity is suitably extended to include the effects of compressibility, piezoviscosity and shear-thinning on the lubricant properties. This improved algorithm is employed to analyse the performance of the lubricated small end and big end bearings of a connecting rod of a high performance motorbike engine. The application of the algorithm proposed to both the small end and the big end of a con-rod is challenging because of the different causes that sustain the hydrodynamic lubrication in the two cases. In the con-rod big end, the fluid film is mainly generated by the relative high speed rotation between the rod and the crankshaft. The relative speed between the two races forms a wedge of fluid that assures appropriate lubrication and avoids undesired direct contacts. On the contrary, at the con-rod small end the relative rotational speed is low and a complete rotation between the mating surfaces does not occurs since the con-rod only oscillates around its vertical axis. Thus, at every revolution of the crankshaft, there are two different moments in which the relative rotational speed between the con-rod and the piston pin is null. Therefore, the dominant effect in the lubrication is the squeeze caused by the high loads transmitted through the piston pin. In particular both combustion forces and inertial forces contribute to the squeeze effect. This work shows how the formulation developed by the authors is capable of predicting the performance of journal bearings in the unsteady regime, where cavitation and reformation occur several times. Moreover, the effects of the pressure and the shear rate on the density and on the viscosity of the lubricant are taken into account.

Thermal flying height (TFC) control technology has been used in the past few years to achieve a lower flying height for higher storage areal density. In this paper, a slider with dual thermal protrusion, one produced by the laser used to heat the disk in HAMR and the other one used for TFC, is programmed with feedback control to reduce the flying height modulation (FHM) due to disk waviness and to attenuate the external disturbances. A numerical simulation is conducted to investigate the feasibility of the system. The results show that FHM of the dual protrusion slider is reduced significantly when the protrusion heights and locations are optimized. External disturbance induced FHM can be suppressed as well. This scheme can benefit HAMR because it will provide a more consistent flying height and more freedom to compensate external disturbances.

Numerous studies have been conducted to evaluate the effects of micro dimple surface texturing on friction reduction in mechanical seals [1–7]. Optimum ratios for a dimple configuration, depth (h) to diameter (D) (Fig. 1), range from 0.02 to 0.5, and area density ratio, ratio of dimple area to seal face area, range from 20 to 55%. Within this range it has been shown that friction can be reduced by as much as 50%. These studies indicate that if the ratio of depth to dimple diameter is reduced below 0.02 a dramatic reduction in performance is seen. Also observed in one investigation [8] is the possibility that micro dimples can become filled with debris. This may degrade performance over time. This report will show that with the use of a unique macro/micro feature it is possible to achieve a reduction in friction of 65%, significantly lower face temperature, exhibit debris resistance, showing low to zero measureable leakage, and low to zero wear when compared to an untextured seal face. The term macro/micro feature is used to describe a feature that has a depth to size ratio, h/L (Fig.2), which is two orders of magnitude smaller than current dimple configurations, well below what may be considered useful from a performance standpoint. This new macro/micro feature, a tapered channel, demonstrates significant cavitation affects as well as hydrodynamic load support. These features are believed to be responsible for its low leakage as well as it low friction/wear characteristics.

Under boundary and mixed lubrication surface roughness and topography have significant influence on the tribological behaviour of contact surfaces, where even a small change in surface topography can lead to a considerable change in tribological behaviour. In recent years an effort for better controlling friction and wear has been focused also on the surface topography modification, especially on surface texturing. The aim of the present research work was to investigate the possibility of using roughness parameters kurtosis and skewness as design parameters for optimizing texturing pattern in boundary and mixed lubricated contacts. Results of the investigation performed on groove and dimple textured surfaces under low load low sliding speed conditions confirm correlation between kurtosis and skewness parameters and coefficient of friction. For textured surfaces increase in kurtosis and more negative skewness, obtained by reducing cavity size, increasing cavity depth and decreasing texturing density were found to yield lower friction. Furthermore, kurtosis and skewness were recognized as suitable parameters for textured surfaces optimization. Through virtual texturing effect of different texturing parameters on kurtosis and skewness parameters can be identified and then optimized to result in reduced friction under boundary and mixed lubrication.

A discrete dislocation plasticity analysis of plane-strain indentation of a single-crystal half-space by a smooth or rough (fractal) rigid asperity is presented. The emission, movement, and annihilation of edge dislocations are incorporated in the analysis through a set of constitutive rules [1,2]. It is shown that the initiation of the first dislocation is controlled by the subsurface Hertzian stress field and occurs in the ±45° direction with respect to the normal of the crystal surface, in agreement with the macroscopic yielding behavior of the indented halfspace. For fixed slip-plane direction, the dislocation density increases with the applied normal load and dislocation source density. The dislocation multiplication behavior at a given load is compared with that generated by a rough indenter with a fractal surface profile. The results of the analysis provide insight into yielding and plastic deformation phenomena in indented single-crystal materials.

The thermal elastohydrodynamic analysis of lubrication is applied to investigate the influence of misalignments of the meshing members on lubrication in spiral bevel gears. The calculation is based on the simultaneous solution of the Reynolds, elasticity, energy, and Laplace’s equations. The full thermal EHD lubrication analysis is applied, therefore, the oil viscosity variation with respect to pressure and temperature and the density variation with respect to pressure are included. By using the corresponding computer program, the influence of pinion’s running offset and axial adjustment errors, and angular position error of pinion axis on maximum oil film pressure and temperature, EHD load carrying capacity, and on power losses in the oil film is investigated. On the basis of the obtained results it can be concluded that the EHD load carrying capacity and the friction factor are very sensitive to misalignments of the mating members in the spiral bevel gear pair, the friction factor is reduced by the increase of EHD load carrying capacity and vise versa, and the maximum inlet oil temperature is almost insensitive to the misalignments.

A numerical analysis method for elastic contact mechanics between a sphere and a flat with a sub-nanometer roughness is presented by taking account of Lennard-Jones (LJ) surface forces. In contrast to conventional theories, the elastic deformations and LJ surface forces of both mean surfaces and contacting asperities are taken into account. Convergent solutions obtained by a simple under-relaxation iteration method are discussed for 2-mm radius glass slider and 20-mm radius head slider contacting with a magnetic disk. It is found that the increase in adhesion force with a decrease in surface roughness can be suppressed by deceasing asperity radius and increasing asperity density.

An ultrathin (<4 nm) film of amorphous carbon ( a -C) is used in contemporary disk drives to protect the magnetic medium of the hard disk from corrosion and mechanical wear due to intermittent impact of the low-flying magnetic head. Because of increasing demands for much higher magnetic storage densities (i.e., >10 Tbits/in 2 ), the a -C film thickness must be decreased to <2 nm. However, the tribological and mechanical properties of such thin a -C films are not well understood and, moreover, are extremely difficult to determine experimentally. The objective of this study was to obtain insight into the tribological behavior of ultrathin a -C films by performing molecular dynamics (MD) simulations. MD results of the hardness and friction properties of nanometer-thick a -C films are interpreted in terms of the ratio of tetrahedral-to-trigonal carbon atom hybridization. A critical thickness for the effective protection of the magnetic medium by the a -C film is estimated from MD results. The results of this study elucidate the nanomechanical and nanotribological properties of ultrathin a -C films used as protective overcoats in extremely-high-density magnetic recording.

In most industrial applications, a thin film of lubricant improves the tribological behaviour of the load carrying conjunctions. Modern hard disk drives are no exception, where one of the challenges is the progressive demand for higher data storage capacity, while decreasing the physical size of the device. This paper investigates the load carrying capacity of an ultra thin lubricant film formed between the hard disk drive platter and its flying read-write head slider. Hydrodynamic wedge action is responsible for the entrainment of a film of perfluoropolyether into the conjunction, but does not account for the main share of the load carrying capacity of the very thin discretized film, several molecular diameters of the fluid in thickness. It is shown that the main mechanism of pressure generation is in fact the solvation effect. Additionally, starvation of contact may well occur, further exacerbating the thinness of a lubricant film. There is often a cavitation region at the contact exit, which is followed by film reformation, changing the density distribution of lubricant on the surface and consequently the attainable data storage density. This is caused by the observed clumps of lubricant in the reformation zones (a phenomenon referred to as lubricant mogul) which can also cause transient motions of the read-write head.

We present preliminary results from a study of the friction of surfaces with nanoscopic roughness. Surfaces with asperities of a chosen height and average spacing were formed by self-assembly of nanometer-sized solid particles on a flat substrate. The adsorption density of particles was investigated with Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM), and the suitability of these substrates for friction experiments at different length scales was evaluated. Initial results from friction experiments with a nanoparticle-covered surface in non-adhesive contact with an atomically flat surface in a surface forces apparatus (SFA) are presented.

The average flow model proposed by Patir and Cheng offers a great convenience for the analysis of rough surfaces in lubrication. The contact factor introduced by Wu and Zheng helps to solve a difficulty in local film evaluation using the average flow model. This paper reports a simple method to calculate the contact factor. Method validation is demonstrated by the comparison of the contact factors for Gaussian surfaces obtained with the present method and the fitting formula of Wu and Zheng. The proposed method can not only easily compute the contact factor values for Gaussian surfaces, it can also be used for those of non-Gaussian and measured surfaces, especially those with unknown probability density distribution of the roughness height.

Surface micro dents may act as lubricant reservoirs to reduce friction and wear in sliding and rolling contact applications. Surface patterning has become a valuable technique for fabricating micro dents. Alternative methods such as micromachining present obvious limitations in comparison with laser shock peening (LSP). In this paper, the use of LSP along with an automatic X-Y table proves to be an attractive and reliable method for producing micro dent arrays with enhanced surface integrity and free of cracks. Surface topography, residual stress, and microhardness of the fabricated micro dent arrays on polished Ti-6Al-4V have been characterized. It was found that a 10% density of micro dent array reduces coefficient of friction compared with a smooth surface. However, a higher dent density not necessarily reduces coefficient of friction.

A stochastic analysis was derived for the lapping process of magnetic recording heads. Numerical results of the final surface roughness, material removal rate, and wear coefficient are presented in terms of material properties, applied pressure, topographies of original ceramic surface and lapping plate surface, kinematics, diamond particles density and sizes of lapping plate. The estimated final roughness is in good agreement with experimental results.

Employing friction reduction coatings is one of the most effective methods to palliate the fretting damage. However, facing numerous available coatings, how to compare them and select the optimum one for a specific application is still a challenging task. In this paper, based on the investigation of the fretting behaviors of several bonded solid lubricant coatings, an energy approach in terms of “initial maximal dissipated energy density” was suggested to compare the tribological response of coatings. According to test results, the lifetime of each coating under different test parameters can be fitted by one master curve. The definition of this master curve for a given coating may be used for the prediction of the coating lifetime only by knowing the initial energy dissipated in the contact. The comparison of different master curves for different coatings can be employed to help the coating selection.

A probabilistic model of third-body particle embedment was derived for surfaces separated by a hydrodynamic slurry film. The analysis yields estimates of the density of embedded particles in terms of surface topography parameters, particle size distribution, and mean surface gap determined by the applied load, macroscopic geometry of the moving surfaces, and fluid properties. The model has direct application to chemical-mechanical polishing and fabrication of lapping plates for polishing magnetic recording heads.

Gas foil bearings (GFBs) enable efficient, reliable and maintenance free operation of high-power-density microturbomachinery (< 200 kW). High speed rotors supported on bump-type GFBs, however, are prone to show large-amplitude subsynchronous motions albeit reaching limit cycle performance. Presently, commercial GFBs are simply modified to introduce a mechanical preload that induces a hydrodynamic wedge to generate more load support and direct stiffnesses. Three metal shims inserted under the bump strip layers and in contact with the bearing housing create a multiple lobe clearance profile at a very low cost. Shaft speed coastdown measurements reveal the rotordynamic performance of a rotor supported on original GBFs and (modified) shimmed GFBs. The later GFBs determine a raise in the rotor-bearing system natural frequency, as expected, and also act to delay the onset speed of large-amplitude subsynchronous motions. Predictions of imbalance response implementing linearized bearing force coefficients are in good agreement with measured amplitudes of synchronous response for both GFB configurations, original and modified.

A plasticity index and a plasticity number were proposed to indicate the severity of plastic deformation by considering the multi-scale and hierarchical nature of surface roughness. A distribution density function of the plastic deformation depth was introduced to characterize the evolution of plastic deformation with increasing load. By integrating this function, the fraction of the real contact area where plastic deformation depths are within any given range can be calculated.

The full thermal EHD lubrication analysis is applied, therefore, the oil viscosity variation with respect to pressure and temperature and the density variation with respect to pressure are included. By using the corresponding computer program, the influence of oil viscosity, pressure-viscosity and temperature-viscosity exponents, supplied oil temperature, speed and minimum oil film thickness on maximum oil film pressure and temperature, EHD load carrying capacity, and on power losses in the oil film is investigated. Small part of the obtained results is presented and discussed.