Current Issue : October - December Volume : 2013 Issue Number : 4 Articles : 5 Articles
The challenges in designing future head disk interface (HDI) demand efficient theoretical modeling tools with flexibility in\r\ninvestigating various combinations of perfluoropolyether (PFPE) and carbon overcoat (COC) materials. For broad range of time\r\nand length scales, we developedmultiscale/multiphysical modeling approach, which can bring paradigm-shifting improvements in\r\nadvanced HDI design. In this paper, we introduce our multiscale modeling methodology with an effective strategic framework for\r\nthe HDI system. Our multiscale methodology in this paper adopts a bottom to top approach beginning with the high-resolution\r\nmodeling, which describes the intramolecular/intermolecular PFPE-COC degrees of freedomgoverning the functional oligomeric\r\nmolecular conformations on the carbon surfaces. By introducing methodology for integrating atomistic/molecular/mesoscale levels\r\nvia coarse-graining procedures, we investigated static and dynamic properties of PFPE-COC combinations with variousmolecular\r\narchitectures. By bridging the atomistic and molecular scales, we are able to systematically incorporate first-principle physics into\r\nmolecular models, thereby demonstrating a pathway for designing materials based on molecular architecture. We also discussed\r\nfuture materials (e.g., graphene for COC, star-like PFPEs) and systems (e.g., heat-assisted magnetic recording (HAMR)) with\r\nhigher scale modeling methodology, which enables the incorporation of molecular/mesoscale information into the continuum\r\nscale models....
The present paper describes an experimental test and a coupled contact-thermal-wear analysis of a railway wheel/brake block\r\nsystem through the braking process. During the test, the friction, the generated heat, and the wear were evaluated. It was found\r\nthat the contact between the brake block and the wheel occurs in relatively small and slowly moving hot spots, caused by the wear\r\nand the thermal effects. A coupled simulation method was developed including numerical frictional contact, transient thermal\r\nand incremental wear calculations. In the 3D simulation, the effects of the friction, the thermal expansion, the wear, and the\r\ntemperature-dependent material properties were also considered. A good agreement was found between the results of the test\r\nand the calculations, both for the thermal and wear results. The proposed method is suitable for modelling the slowly oscillating\r\nwear caused by the thermal expansions in the contact area....
The aim of this work is related to an analysis of journal bearings lubrication using non-Newtonian fluids which are described by a\r\npower-lawmodel.The performance characteristics of the journal bearings are determined for various values of the non-Newtonian\r\npower-law index ââ?¬Å?nââ?¬Â which is equal to: 0.9, 1, and 1.1. Obtained numerical results show that for the dilatant fluids (n > 1), the\r\nload-carrying capacity, the pressure, the temperature, and the frictional force increased while for the pseudo-plastic fluids (n < 1)\r\nthey decreased. The influence of the thermal effects on these characteristics is important at higher values of the flow behavior index\r\nââ?¬Å?n.ââ?¬Â Obtained results are compared to those obtained by others. Good agreement is observed between the different results....
We analyse in terms of efficiency and traction capabilities a recently patented traction drive, referred to as the double roller fulltoroidal\r\nvariator (DFTV). We compare its performance with the single roller full-toroidal variator (SFTV) and the single roller\r\nhalf-toroidal variator (SHTV). Modeling of these variators involves challenging tribological issues; the traction and efficiency\r\nperformances depend on tribological phenomena occurring at the interface between rollers and disks, where the lubricant\r\nundergoes very severe elastohydrodynamic lubrication regimes. Interestingly, the DFTV shows an improvement of the mechanical\r\nefficiency over a wide range of transmission ratios and in particular at the unit speed ratio as in such conditions in which the DFTV\r\nallows for zero-spin, thus strongly enhancing its traction capabilities.Thevery highmechanical efficiency and traction performances\r\nof the DFTV are exploited to investigate the performance of a flywheel-based Kinetic Energy Recovery System (KERS), where\r\nthe efficiency of the variator plays an important role in determining the overall energy recovery performance. The energy boost\r\ncapabilities and the round-trip efficiency are calculated for the three different variators considered in this study. The results suggest\r\nthat the energy recovery potential of the mechanical KERS can be improved with a proper choice of the variator....
This paper reviews the state of the head-disk interface (HDI) technology, and more particularly the head-medium spacing (HMS),\r\nfor todayââ?¬â?¢s and future hard-disk drives. Current storage areal density on a disk surface is fast approaching the one terabit per square\r\ninch mark, although the compound annual growth rate has reduced considerably from ~100%/annum in the late 1990s to 20ââ?¬â??30%\r\ntoday. This rate is now lower than the historical,Mooreââ?¬â?¢s law equivalent of ~40%/annum. A necessary enabler to a high areal density\r\nis theHMS, or the distance fromthe bottomof the read sensor on the flying head to the top of themagneticmediumon the rotating\r\ndisk. This paper describes the various components of the HMS and various scenarios and challenges on how to achieve a goal of\r\n4.0ââ?¬â??4.5nm for the 4 Tbit/in2 density point. Special considerations will also be given to the implication of disruptive technologies\r\nsuch as sealing the drive in an inert atmosphere and novel recording schemes such as bit patternedmedia and heat assisted magnetic\r\nrecording....
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