Drag Tests Research Articles

캔버스 카이트의 유체역학적 특성에 관한 연구 - 2. 삼각형 캔버스 카이트의 특성 -

종횡비, 다각형 모양에 따른 평판과 범포의 유체역학적 특성을 규명하고자 직사각형, 사다리꼴 모양으로 모형 평판과 범포를 제작하고 회류수조에서 양 <TEX>${\cdot}$</TEX> 항력 실험을 수행하였다. 그 결과를 요약하면 다음과 같다. 1. 삼각형 평판의 경우, 종횡비가 1 이하인 모형에서는 38<TEX>${\sim}$</TEX>42<TEX>$^{\circ}$</TEX>에서 최대 <TEX>$C_L$</TEX>이 1.23<TEX>${\sim}$</TEX>1.32, 1.5 이상인 모형에서는 20<TEX>${\sim}$</TEX>50<TEX>$^{\circ}$</TEX>에서 <TEX>$C_L$</TEX>이 약 0.85 전후였다. 역삼각형 평판의 경우, 종횡비가 1 이하인 모형에서는 영가가 36<TEX>${\sim}$</TEX>38<TEX>$^{\circ}$</TEX>에서 최대 <TEX>$C_L$</TEX>이 1.46<TEX>${\sim}$</TEX>1.56, 1.5 이상인 모형에서는 22<TEX>${\sim}$</TEX>26<TEX>$^{\circ}$</TEX>에서 1.05<TEX>${\sim}$</TEX>1.21 정도였다. 같은 삼각형 평판 모형에서는 전자의 모형이 후자보다 <TEX>$C_L$</TEX>이 작게, 양항비도 작게 나타났다. 2. 삼각형 범포의 경우, 종횡비가 1 이하인 모형에서는 영각 46<TEX>${\sim}$</TEX>48<TEX>$^{\circ}$</TEX>에서 최대 <TEX>$C_L$</TEX>이 1.67<TEX>${\sim}$</TEX>1.77, 1.5 이상인 모형에서는 20<TEX>${\sim}$</TEX>50<TEX>$^{\circ}$</TEX>에서 <TEX>$C_L$</TEX>이 약 1.1 전후였다. 역삼각형 범포의 경우, 종횡비가 1 이하인 모형에서는 영각 28<TEX>${\sim}$</TEX>32<TEX>$^{\circ}$</TEX>에서 최대 <TEX>$C_L$</TEX>이 1.44<TEX>${\sim}$</TEX>1.68, 1.5 이상인 모형에서는 18<TEX>${\sim}$</TEX>24<TEX>$^{\circ}$</TEX>에서 10.3<TEX>${\sim}$</TEX>1.18 정도였다. 같은 삼각형 범포 모형에서는 전자의 모형이 후자보다 <TEX>$C_L$</TEX>은 크게, 양항비는 작게 나타났다. 3. 모형에서 물의 유체력을 많이 받을 수 있는 곳에서 만곡꼭지점이 만들어지며, 삼각형 모형에서는 종횡비가 클수록, 역삼각형 모형에서는 작을수록 만곡꼭지점의 위치도 컸다. 4. 만곡도는 전 모형에서 종횡비가 클수록 컸으며, 삼각형 모형에서는 영각이 클수록 컸고 역삼각형 모형에서는 작을수록 컸다. As far as an opening device of fishing gears is concerned, applications of a kite are under development around the world. The typical examples are found in the opening device of the stow net on anchor and the buoyancy material of the trawl. While the stow net on anchor has proved its capability for the past 20 years, the trawl has not been wildly used since it has been first introduced for the commercial use only without sufficient studies and thus has revealed many drawbacks. Therefore, the fundamental hydrodynamics of the kite itself need to ne studied further. Models of plate and canvas kite were deployed in the circulating water tank for the mechanical test. For this situation lift and drag tests were performed considering a change in the shape of objects, which resulted in a different aspect ratio of rectangle and trapezoid. The results obtained from the above approaches are summarized as follows, where aspect ratio, attack angle, lift coefficient and maximum lift coefficient are denoted as A, B, <TEX>$C_L$</TEX> and <TEX>$C_{Lmax}$</TEX> respectively : 1. Given the triangular plate, <TEX>$C_{Lmax}$</TEX> was produced as 1.26<TEX>${\sim}$</TEX>1.32 with A<TEX>${\leq}$</TEX>1 and 38<TEX>$^{\circ}$</TEX>B<TEX>${\leq}$</TEX>42<TEX>$^{\circ}$</TEX>. And when A<TEX>${\geq}$</TEX>1.5 and 20<TEX>$^{\circ}$</TEX><TEX>${\leq}$</TEX>B<TEX>${\leq}$</TEX>50<TEX>$^{\circ}$</TEX>, <TEX>$C_L$</TEX> was around 0.85. Given the inverted triangular plate, <TEX>$C_{Lmax}$</TEX> was 1.46<TEX>${\sim}$</TEX>1.56 with A<TEX>${\leq}$</TEX>1 and 36<TEX>$^{\circ}$</TEX>B<TEX>${\leq}$</TEX>38<TEX>$^{\circ}$</TEX>. And When A<TEX>${\geq}$</TEX>1.5 and 22<TEX>$^{\circ}$</TEX>B<TEX>${\leq}$</TEX>26<TEX>$^{\circ}$</TEX>, <TEX>$C_{Lmax}$</TEX> was 1.05<TEX>${\sim}$</TEX>1.21. Given the triangular kite, <TEX>$C_{Lmax}$</TEX> was produced as 1.67<TEX>${\sim}$</TEX>1.77 with A<TEX>${\leq}$</TEX>1 and 46<TEX>$^{\circ}$</TEX>B<TEX>${\leq}$</TEX>48<TEX>$^{\circ}$</TEX>. And when A<TEX>${\geq}$</TEX>1.5 and 20<TEX>$^{\circ}$</TEX>B<TEX>${\leq}$</TEX>50<TEX>$^{\circ}$</TEX>, <TEX>$C_L$</TEX> was around 1.10. Given the inverted triangular kite, <TEX>$C_{Lmax}$</TEX> was 1.44<TEX>${\sim}$</TEX>1.68 with A<TEX>${\leq}$</TEX>1 and 28<TEX>$^{\circ}$</TEX>B<TEX>${\leq}$</TEX>32<TEX>$^{\circ}$</TEX>. And when A<TEX>${\geq}$</TEX>1.5 and 18<TEX>$^{\circ}$</TEX>B<TEX>${\leq}$</TEX>24<TEX>$^{\circ}$</TEX>, <TEX>$C_{Lmax}$</TEX> was 1.03<TEX>${\sim}$</TEX>1.18. 2. For a model with A=1/2, an increase in B caused an increase in <TEX>$C_L$</TEX> until <TEX>$C_L$</TEX> has reached the maximum. Then there was a tendency of a very gradual decrease or no change in the value of <TEX>$C_L$</TEX>. For a model with A=2/3, the tendency of <TEX>$C_L$</TEX> was similar to the case of a model with A=1/2. For a model with A=1, an increase in B caused an increase in <TEX>$C_L$</TEX> until <TEX>$C_L$</TEX> has reached the maximum. And the tendency of <TEX>$C_L$</TEX> didn't change dramatically. For a model with A=1.5, the tendency of <TEX>$C_L$</TEX> as a function of B was changed very small as 0.75<TEX>${\sim}$</TEX>1.22 with 20<TEX>$^{\circ}$</TEX>B<TEX>${\leq}$</TEX>50<TEX>$^{\circ}$</TEX>. For a model with A=2, the tendency of <TEX>$C_L$</TEX> as a function of B was almost the same in the triangular model. There was no considerable change in the models with 20<TEX>$^{\circ}$</TEX>B<TEX>${\leq}$</TEX>50<TEX>$^{\circ}$</TEX>. 3. The inverted model's <TEX>$C_L$</TEX> as a function of increase of B reached the maximum rapidly, then decreased gradually compared to the non-inverted models. Others were decreased dramatically. 4. The action point of dynamic pressure in accordance with the attack angle was close to the rear area of the model with small attack angle, and with large attack angle, the action point was close to the front part of the model. 5. There was camber vertex in the position in which the fluid pressure was generated, and the triangular canvas had large value of camber vertex when the aspect ratio was high, while the inverted triangular canvas was versa. 6. All canvas kite had larger camber ratio when the aspect ratio was high, and the triangular canvas had larger one when the attack angle was high, while the inverted triangluar canvas was versa.

Screening for genotoxicity using the DRAG assay: investigation of halogenated environmental contaminants

The DRAG test is a rapid high-throughput screening assay for detection of repairable adducts by growth inhibition of Chinese hamster ovary cells (CHO) characterized by different defects in DNA repair. A more pronounced growth inhibition caused by a certain DNA-reactive substance in a repair-deficient cell line (EM9, UV4 and UV5) as compared to wild-type cells (AA8) is interpreted as a consequence of their inability to repair induced DNA lesions. Thus, the use of such cell lines in the DRAG test may provide information of the type of DNA lesions induced by a certain genotoxic substance. To select optimal assay conditions, as well as to provide a mechanistic basis for interpreting the results, the model compounds benzo(a)pyrene-7,8-dihydrodiol-9,10-epoxide (BPDE), ethyl methanesulfonate (EMS), mitomycin C (MMC) and hydrogen peroxide (H 2O 2) were used. These agents can induce bulky adducts, alkyl adducts, cross-links and oxidative damage, respectively. The specificity of the DRAG test constitutes an important prerequisite for its practical use in a broader context. To assess this aspect, we have investigated the genotoxic and cytotoxic properties of a selection of metabolites of and isomers from polychlorinated biphenyls (PCB) and polybrominated diphenyl ethers (PBDE), along with a few other halogenated compounds. All these compounds have been detected as pollutants in the external environment, and for most of them there is no convincing evidence of mutagenicity from conventional assays. As could be predicted from their mode of action, BPDE, MMC, and EMS were all found to be more toxic in the repair-deficient cell lines compared with wild-type cells. The results with H 2O 2 were inconclusive, and the PCB metabolite 4,4′-diOH-CB80 only exhibited borderline activity, while all other halogenated compounds, or their metabolites, were found to be inactive. In conclusion, the DRAG assay could provide a robust and useful tool when screening large numbers of potentially genotoxic agents, while in addition providing mechanistic information. However, the usefulness of the selected cell lines to detect oxidative damage may be limited.

NR2B selective NMDA receptor antagonist CP-101,606 prevents levodopa-induced motor response alterations in hemi-parkinsonian rats

Sensitization of NMDA receptors containing the NR2B subunit has been increasingly associated with various forms of synaptic plasticity, including those implicated in the pathogenesis of extrapyramidal motor dysfunction. To determine whether activation of NR2B containing receptors contributes to the development and maintenance of levodopa-induced response changes in parkinsonian animals, we evaluated the effects of the selective NR2B antagonist CP-101,606 on these response alterations in unilateral 6-hydroxydopamine (6-OHDA) lesioned rats. Three weeks of twice-daily levodopa treatment decreased the duration of the rotational response to acute levodopa challenge. The response alteration was associated with an increase in GluR1 (S831) phosphorylation in medium spiny neurons of the dorsolateral striatum. Both the attenuated rotational response and augmented GluR1 phosphorylation were decreased by CP-101,606 treatment. These CP-101,606 effects were observed when the compound was administered either at the end of chronic levodopa treatment (ameliorative effect) or together with the twice-daily levodopa treatment for 3 weeks (preventive effect). Furthermore, concurrent administration of CP-101,606 with levodopa potentiated the ability of levodopa challenge to reverse the 6-OHDA lesion-induced contralateral forelimb movement deficit as measured in a drag test. These results suggest that activation of NR2B subunit containing NMDA receptors contributes to both the development and maintenance of levodopa-induced motor response alterations, through a mechanism that involves an increase in GluR1 phosphorylation in striatal spiny neurons.

A novel drag test to evaluate media tribology design on head wear

By changing the head's Z-height, a new accelerated drag test has been developed to characterize head wear under high interference conditions. Compared to contact start stop (CSS) and other drag tests, heads wear faster in our approach, due to the stressed condition at the tilted trailing edge. The optimized Z-height has been chosen so that the head-disk interference and acoustic emission are maximized. The wear volume can be estimated by optical microscopy. The influence of lube bonded ratio and X1P additive amount on head wear has been studied for AM3001 lubricant. Lower bonded ratio and higher X1P additive were found to give rise to less head wear, which is in agreement with the existing results of contact start-stop and other drag tests. In media manufacturing, tape burnish processes were found to significantly affect the bonded ratio in the AM3001/X1P lubricant system, which consequently affects head wear. Short tape burnish times were found to reduce the media's head wear.

Effect of substrate and protective coating on the tribological characteristics of optical recording media

To develop a flying-type optical head mounted on a slider with flying height below 100 nm for Near Field Recording (NFR) application where removability of the media is required, plastic media is preferred because of their manufacturing cost effectiveness. In this work the effects of substrate material, carbon protective coating, and lubricant on the tribological characteristics of the slider/media interface were investigated. For the substrate, glass, engineering plastic (PEEK), and polycarbonate (PC) were used. A thin carbon protective layer and a lubricant layer were deposited on the substrates. The tribological characteristics of carbon and lubricant layers were evaluated using an Atomic Force Microscopy (AFM). Also, the flyability test, drag test, Contact-Start-Stop (CSS) test, and load/unload test were performed for each substrate while monitoring the friction as well as acoustic emission signals. It was found that the flyability was the key factor that affected the durability of the disks. As for the carbon coating, better performance was observed in the order of a-C, a-C:H, and a-C:N. Finally, 5 nm lubricant thickness was better than 2 nm lubricant thickness in terms of durability. The results of this work are expected to serve as the basis for developing an optical media with high durability in NFR application using a flying slider.

Relationship between the molecular structures of lubricants and their performance at the head–disk interface of hard disk drives

This paper reports the results of constant speed drag tests on disks with four different lubricants using an ultra-high vacuum (UHV) tribochamber equipped with a mass spectrometer (MS). An optical surface analyzer (OSA) is also used to observe lubricant migration. Based on the analysis of the experimental results, we propose that, in the case of diamond-like carbon (DLC)-coated sliders, the durability of a lubricant is dominated by its mobility, its ability to bond to the carbon overcoat and its thermal stability. However, in the case of uncoated sliders, the durability of the lubricant, is dominated by the strength of the lubricant layer formed on the carbon overcoat, the interaction between lubricant molecules and the Al 2O 3 of the slider surface, the degradation rate of the lubricants caused by catalysis of Al 2O 3, as well as thermal stability of lubricant. Reaction of Al 2O 3 with the oxygen atoms in the backbones of the molecules is the dominant factor in their catalytic degradation.

Measurement of wheelchair rolling resistance with a handle bar push technique

The purpose of this study was to evaluate a technique of pushing a wheelchair at the level of the handle bars as a method for measuring rolling resistance of wheelchair-user systems under different field conditions. Under standardized conditions on a motor driven treadmill, rolling resistance was determined using a 2D strain gauge-based push technique at the level of the handle bars and a commonly used 1D strain gauge-based wheelchair drag test using an adapted push wheelchair and ISO dummy at several velocities and using different push handle heights. After verification of the method, rolling resistance of six different floor surfaces was measured with the experimental push wheelchair in a centre for rehabilitation. Using an analysis of variance for repeated measures, small but significant differences in rolling resistance were found between the drag and push tests on a motor driven treadmill. Belt velocity and push handle height significantly affected rolling resistance. In the field study in the rehabilitation centre, tiles and tarpaulin had the lowest rolling resistance, while high piled carpet had the highest values. It is concluded that the wheelchair pushing method described in this study is usable for the determination of (relative) differences in rolling resistance of different floor materials if performed under standardized conditions and procedures, such as a stable velocity (within a small range of variation), using an ISO-dummy and a constant pushing handle bar height.

A variable-speed drag test for characterizing wear of ultra-thin carbon films

A drag test with a speed alternating between two levels was developed to create wear tracks on disk surfaces. This approach reduces the uncertainty involved in the contact start/stop (CSS) test of thin carbon overcoats. The wear tracks were identified with an optical surface analyzer as regions with higher values of the absorption ratio calculated from reflectivity data of both P- and S-polarized lights. Calibrated with scanning micro-ellipsometry, the absorption ratio was converted to a wear depth. The amount of wear in a drag test increased with time, and a low-flying head resulted in more wear than a high-flying head. The 45-angstrom nitrogenated carbon film sputtered at a lower temperature exhibited a smaller wear depth. The higher wear resistance of the low-temperature sputtered film is supported by less wear in a nanowear test, a lower Raman G-peak position, and less frequent crashes in CSS tests.

The DRAG test: an assay for detection of genotoxic damage.

A high throughput assay (the DRAG test) is described, which could be a useful tool for the detection of repairable DNA adducts, and which is based on the inhibition of the growth of DNA repair-deficient Chinese hamster ovary (CHO) cells. The cytotoxicity of a test substance towards DNA repair-deficient CHO cell lines is compared with the corresponding cytotoxicity in the parental wild-type CHO cell line (AA8). A more pronounced toxicity toward a DNA repair-deficient cell line is interpreted as being the consequence of its inability to repair the DNA adduct induced by the compound. (+)-7beta,8alpha-Dihydroxy-9alpha,10alpha-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene, camptothecin, ethyl methanesulphonate and mitomycin C were used as reference substances, and the overall results indicate that the DRAG test could be useful in the screening of compounds for the production of repairable DNA adducts. The main advantages with the DRAG test are that it provides a relevant endpoint, it is rapid, it requires small amounts of the test item, and it permits a large number of compounds to be tested.

Aerodynamic drag of mountain bike tyres

This paper proposes the concept of a front wheel air deflector for downhill mountain bikes. Downhill mountain bike tyres are becoming larger with more aggressive tread patterns in order to cope with the increasingly severe conditions of modern downhill courses, which in turn leads to increased aerodynamic drag forces caused by air flow, and consequently a reduction in speed over a downhill course. A front wheel air deflector was designed and constructed from fibreglass that, when fitted to the bike, could be adjusted to give different clearance settings between the tyre and deflector inner surface to cope with varying mud conditions. Various designs of downhill bike tyres, a cross-country tyre and a slick racing tyre were selected and tested in a wind tunnel in the range 0–72 km h–1 to determine their benchmark aerodynamic drag characteristics with no deflector fitted. Further wind tunnel tests were then conducted for one of the tyres with the deflector in various clearance positions. The trend of increasing aerodynamic drag with current downhill tyre development was verified, while the drag tests indicated that the power input to the wheel can be reduced by up to 50% with the deflector fitted in its smallest first clearance setting. This represents a drag reduction of up to 10%, and a reduced drag coefficient of almost 40%.

Effect of lubricant bonding fraction at the head–disk interface

Tribochemical studies of the effect of lubricant bonding on the tribology of the head–disk interface (HDI) were conducted using hydrogenated (CHx) carbon disk samples coated with perfluoropolyether ZDOL lubricant. The studies involved drag tests with uncoated and carbon-coated Al2O3–TiC sliders and also thermal desorption experiments in an ultrahigh vacuum (UHV) tribochamber. The friction and catalytic decomposition mechanisms as well as the thermal behavior of ZDOL are described. We observed that a larger mobile lubricant portion significantly enhances the wear durability of the HDI by providing a reservoir to constantly replenish the lubricant displaced in the wear track during drag tests. In the thermal desorption tests we observed two distinct temperatures of desorption. The mobile ZDOL layer is desorbed at the lower thermal desorption temperature and the residual bonded ZDOL layer is desorbed at the higher thermal desorption temperature.

Smoothed Particle Hydrodynamics in cosmology: a comparative study of implementations

We analyse the performance of 12 different implementations of Smoothed Particle Hydrodynamics (SPH) using seven tests designed to isolate key hydrodynamic elements of cosmological simulations which are known to cause the SPH algorithm problems. In order, we consider a shock tube, spherical adiabatic collapse, cooling flow model, drag, a cosmological simulation, rotating cloud-collapse and angular momentum transport. In the implementations special attention is given to the way in which force symmetry is enforced in the equations of motion. We study in detail how the hydrodynamics are affected by different implementations of the artificial viscosity including those with a shear-correction modification. We present an improved first-order smoothing-length update algorithm that is designed to remove instabilities that are present in simple forward prediction algorithms. Gravity is calculated using the adaptive particle–particle, particle–mesh algorithm. For all tests we find that the artificial viscosity is the single most important factor distinguishing the results from the various implementations. The shock tube and adiabatic collapse problems show that the artificial viscosity used in the hydra code prior to version 4.0 performs relatively poorly for simulations involving strong shocks when compared to a more standard artificial viscosity. The shear-correction term is shown to reduce the shock-capturing ability of the algorithm and to lead to a spurious increase in angular momentum in the rotating cloud-collapse problem. For the disc stability test, the shear-corrected and previous hydra artificial viscosities are shown to reduce outward angular momentum transport. The cosmological simulations produce comparatively similar results, with the fraction of gas in the hot and cold phases varying by less than 10 per cent amongst the versions. Similarly, the drag test shows little systematic variation amongst versions. The cooling flow tests show that implementations using the force symmetrization of Thomas & Couchman are more prone to accelerate the overcooling instability of SPH, although the problem is generic to SPH. The second most important factor in code performance is the way force symmetry is achieved in the equation of motion. Most results favour a kernel symmetrization approach. The exact method by which SPH pressure forces are included in the equation of motion appears to have comparatively little effect on the results. Combining the equation of motion presented by Thomas & Couchman with a modification of the Monaghan & Gingold artificial viscosity leads to an SPH scheme that is both fast and reliable.

Smoothed Particle Hydrodynamics in cosmology: a comparative study of implementations

We analyse the performance of 12 different implementations of Smoothed Particle Hydrodynamics (SPH) using seven tests designed to isolate key hydrodynamic elements of cosmological simulations which are known to cause the SPH algorithm problems. In order, we consider a shock tube, spherical adiabatic collapse, cooling flow model, drag, a cosmological simulation, rotating cloud-collapse and angular momentum transport. In the implementations special attention is given to the way in which force symmetry is enforced in the equations of motion. We study in detail how the hydrodynamics are affected by different implementations of the artificial viscosity including those with a shear-correction modification. We present an improved first-order smoothing-length update algorithm that is designed to remove instabilities that are present in simple forward prediction algorithms. Gravity is calculated using the adaptive particle–particle, particle–mesh algorithm. For all tests we find that the artificial viscosity is the single most important factor distinguishing the results from the various implementations. The shock tube and adiabatic collapse problems show that the artificial viscosity used in the hydra code prior to version 4.0 performs relatively poorly for simulations involving strong shocks when compared to a more standard artificial viscosity. The shear-correction term is shown to reduce the shock-capturing ability of the algorithm and to lead to a spurious increase in angular momentum in the rotating cloud-collapse problem. For the disc stability test, the shear-corrected and previous hydra artificial viscosities are shown to reduce outward angular momentum transport. The cosmological simulations produce comparatively similar results, with the fraction of gas in the hot and cold phases varying by less than 10 per cent amongst the versions. Similarly, the drag test shows little systematic variation amongst versions. The cooling flow tests show that implementations using the force symmetrization of Thomas & Couchman are more prone to accelerate the overcooling instability of SPH, although the problem is generic to SPH. The second most important factor in code performance is the way force symmetry is achieved in the equation of motion. Most results favour a kernel symmetrization approach. The exact method by which SPH pressure forces are included in the equation of motion appears to have comparatively little effect on the results. Combining the equation of motion presented by Thomas & Couchman with a modification of the Monaghan & Gingold artificial viscosity leads to an SPH scheme that is both fast and reliable.

Determination of the Strouhal number based on the aerodynamic behavior of rectangular cylinders

The Strouhal number is an important nondimensional number which is explanatory of aerodynamic instability phenomena. It takes on the different characteristic constant value depending upon the cross-sectional shape of the body being enveloped by the flow. A number of investigations into this subject, especially on the drag test, surface pressure test and hot-wire test, have been carried out under the fixed state of the body in the past. However, almost no investigations concerning the determination of the St on wind-induced vibration of the body have been reported in the past even though the aerodynamic behavior of the body is very important because the construction of wind-sensitive structures is recently on the sharp increase. Based on a series of wind tunnel tests, this paper addresses a new method to determine the Strouhal number of rectangular cylinder in the uniform flow. The central idea of the proposed method is that the Strouhal number can be obtained directly by the aerodynamic behaviors of the body through wind-induced vibration test. The validity of proposed method is evaluated by comparing with the results obtained by previous studies in three B/Ds at attack angle <TEX>$0^{\circ}$</TEX> and a square cylinder with various attack angles. The values and trends of the proposed Strouhal numbers are in good agreements with values of previous studies. And also, the Strouhal numbers of B/D=1.5 and 2.0 with various attack angles are obtained by the proposed method and verified by other method. This proposed method is as good as any other previous methods to obtain the Strouhal number.

The effects of texture height and thickness of amorphous carbon nitride coating of a hard disk slider on the friction and wear of the slider against a disk

In order to minimize the stiction force caused by contact of the extremely smooth surfaces of head sliders and disks in hard disk drives, texture is usually applied on the disk surface. For future contact/near-contact recording, the stiction-induced high friction between slider and disk will become a problem. Texture on the slider/disk interface will still be an expected method to reduce friction. Recently, it was suggested to texture the slider surface. A protective coating is usually required on the textured slider surface to reduce wear of the texture. The results showed that texture on the slider surface was effective in reducing the friction between head sliders and disks. On the other hand, the texture and coating on the slider surface increase the spacing between the read/write element and the magnetic layer of the disk. The necessary and effective texture height and coating thickness are still not clear. In the present research, island-type textures with different heights (3–18 mn) were formed on slider surfaces by ion-beam etching. Amorphous carbon nitride (a-CN x ) coatings of different thicknesses (0–50 nm) were coated on the textured slider surfaces as a protective overcoat. The friction and wear properties of these sliders were evaluated by constant-speed drag tests against hard disks coated with diamond-like carbon (DLC). The results show that 2 nm texture on a slider surface is sufficient for low (0.3–0.5) and stable friction of the slider against the disk in a drag test, and coatings thicker than 5 nm show similar wear resistances of the texture on slider surfaces.

Friction and wear properties of hard coating materials on textured hard disk sliders

It has been a common practice to apply a surface texture to disk surface in hard disk drive in order to minimize the stiction force caused by the contact of extremely smooth surfaces of head sliders and disks. The slider surface texture was also suggested recently with the advantage of using smoother disks. The slider surface texture reduced the stiction effect, meanwhile it increased the contact pressure between sliders and disks. The protective coating is required on the textured slider surface to reduce the wear of the texture. In the present research, four kinds of hard coating materials were synthesized by IBAD and evaluated on textured slider surfaces by drag test. The results showed that the a-CN x coating had higher wear resistance than sputtered carbon, TiN x and BN x coatings on textured slider surfaces.

Spreading Mechanism of PFPE Lubricant on the Magnetic Disks

The lubrication mechanism when the magnetic head is sliding on the magnetic disk in the drag test with cyclic interval rest periods, is discussed. A long rest period decreased the wear of disks and friction force. This result indicated that the reflow of lubricant into the contact areas decreased the wear of texture asperities. Next, the molecular spreading behavior of a lubricant film was calculated by Monte Carlo method to estimate the effect of lubricant recovering velocities. The lubricant replenishment into a thinner lubricant area made by an etching technique was measured. The measured profiles of lubricant replenishment were approximately agreed with the calculated profiles using a spreading model. It was clearly estimated that the reflow velocities changed in various cases of the environmental temperature, the radius of removal lubricant area, and the thickness of the lubricant films. Experimentally, the dependencies of temperature, the radius of removal lubricant area, and the lubricant thickness were measured in the drag test. This lubricant-spreading model adequately explained these results.

Tribochemistry of monodispersed ZDOL with hydrogenated carbon overcoats

Tribochemical studies of the lubricant molecular weight effect on the tribology of the head/disk interface were conducted using hydrogenated (CHx) carbon disks coated with ZDOL lubricant. The studies involved drag tests with uncoated and carbon-coated Al2O3–TiC sliders and thermal desorption experiments in an ultrahigh vacuum tribochamber. The studies showed that the lubricant interaction with the carbon overcoat varies as a function of lubricant molecular weight. The friction coefficient increases as the molecular weight increases. The higher friction is due to the higher viscosity. The friction and catalytic decomposition mechanisms of ZDOL are described. In general, the perfluoropolyethers polymers are decomposed by chain scission involving the breakage of the backbone bonds to yield free-radical segments. Chain scission can occur by three mechanisms: (1) random degradation, (2) depolymerization, and (3) weak-link degradation. Our studies further support previous observations that catalytic reactions occurred at the endgroups. The lower number of endgroups for ZDOL with higher molecular weight reduces the possibility of the occurrence of catalytic reactions. Moreover, the ZDOL desorbed peak temperatures shifted to higher temperatures with increasing molecular weight in thermal desorption tests. The spreading diffusion coefficient of ZDOL decreases with increasing molecular weight. As the mobility of the lubricant chain decreases, the desorption energy needed to break the lubricants increases, resulting in higher desorption peak temperatures.

Effects of Backbone and Endgroup on the Decomposition Mechanisms of PFPE Lubricants and Their Tribological Performance at the Head-Disk Interface

Tribo-chemical studies of the lubricant endgroup effect on the tribology of the head-disk interface were conducted using carbon disks coated with PFPE lubricant. The studies involved drag tests with uncoated and carbon-coated Al2O3-TiC sliders in an ultrahigh-vacuum (UHV) tribochamber. The UHV drag tests show that a good lubricant should have one active OH endgroup and one nonactive endgroup. The active one insures the lubricant is adsorbed very well onto the disk carbon surface, resulting in a lower removal rate of the lubricants during the contact sliding. The nonactive one prevents the catalytic decomposition of the lubricant in the presence of the Al2O3 surface of the uncoated slider. The studies also demonstrate that the catalytic degradation process of ZDOL in the presence of Lewis acid occurs most readily at the acetal units -O-CF2-O within the internal backbones (CF2O and CF2CF2O) instead of the endgroup functionals. Therefore, demnum, without any acetal units, experiences less catalytic degradation with the uncoated Al2O3/TiC sliders as compared to ZDOL.

Additive Mechanism Investigation of Perfluoropolyether Lubricants with a Phosphazene Additive

The tribological characteristics of magnetic thin film media coated with perfluoropolyether (PFPE) lubricants (ZDOL and AM300J) and a phosphazene additive (X-IP) were investigated in this study. The drag test results show that under ambient and hot/wet conditions the media coated with AM300J lubricant have higher retention on the test track than those coated with ZDOL 2000 PFPE lubricant. The phosphazene additive X-IP was observed to strongly anchored to the surface and was not as easily removed as PFPE lubricants alone. The retention characteristics of X-IP are independent of either AM or ZDOL. Secondary Ion Mass Spectroscopy (SIMS) depth profile data and Angle-Resolved X-Ray Photo-electron Spectroscopy (XPS) reveal that X-IP molecules were distributed near the disk surface in the X-IP and PFPE lubricants mixed layer, indicating a strong bonding/adhesion of X-IP to the disk surface. Together with the drag testing data, the authors conclude that the preferential distribution of X-IP close to the disk surface in the mixed layer helps to improve lubricant retention performance at the head-disk interface. Presented as a Society of Tribologists and Lubrication Engineers Paper at the STLE/ASME Tribology Conference in Orlando, Florida, October 11–13, 1999