bluuebunny/crossref_metadata_2025 huggingface dataset:
Derivation of Rarefaction-Modified Reynolds Equation Considering Porosity of Thin Lubricant Film
Authors: Mitsuya Yasunaga , Deng Zhisheng , Ohka Masahiro
Published: February 2008

A new lubrication model is derived for solving ultra-thin gas lubrication problems encountered in the analysis of a magnetic head slider flying over a magnetic disk coated with giant-molecule lubricant film. In this model, the liquid lubricant film is replaced with a permeable material, and the boundary between the gas and liquid is subject to two kinds of velocity slippage: one due to the rarefaction effect and the other to the porous effect. Using this model, a rarefaction-modified Reynolds equation is derived considering the permeability of the running surface. This equation is then applied to the lubrication of head sliders flying over a magnetic medium. An interesting condition is found to arise wherein total apparent slippage seems to disappear due to the cancellation of the two slippages and the permeability effects are larger for a slider having a steeper pressure gradient.
Characterization of Adhesive Strength of Phosphate Coatings in Cold Metal Forming
Authors: Saiki H. , Ngaile G. , Ruan L.
Published: February 2008

A test method is proposed to characterize adhesive strength of phosphate coatings based on the various deformation patterns at the tool-workpiece interface. The deformation patterns were induced by tools of different surface geometrical profiles, i.e., flat surface, sinusoidal surface, saw-tooth surface and multi-surface profiles, in a localized rod drawing technique. With change in the tool geometry, three deformation regimes were observed, i.e., full film lubrication regime, mixed regime, and seizure regimes, which were categorized by the level of friction coefficient attained, and the degree of galling observed on the surface of the drawn specimens. The full film lubrication regimes were noticed when flat dies were used. In this case, the friction coefficient was maintained at nearly μ = 0.065, irrespective of the change in the surface roughness of the tools and reduction. With sinusoidal surface and other non-flat dies, mixed regime and seizure regimes were observed, and the friction coefficient varied from μ = 0.1 to 0.3. To complement the friction data, surface analysis of the tool-workpiece interface was also conducted. The frictional range of μ = 0.065 to 0.3 obtained in this study, therefore, provides for a manageable characterization of phosphate coatings for cold metal forming of objects with intricate shapes.
Experimental Evaluation of a Steady-State Model for the Wear of Particle-Filled Polymer Composite Materials
Authors: Han Sung Won , Blanchet Thierry A.
Published: February 2008

A model for the steady-state wear behavior of polymer composite materials, including the effects of preferential load support by and surface accumulation of wear-resistant filler particles, is further developed. It is shown that the resultant inverse rule-of-mixtures description of steady-state composite wear rate behavior is independent of the assumed form of filler contact pressure, though preferential load support does affect the degree of surface accumulation of filler particles that occurs. The validity of these descriptions of steady-state wear behavior and surface accumulation as functions of bulk filler volume fraction are investigated by experiments with copper particle-filled PTFE composites for bulk filler volume fractions from 0 to 40 percent. The applicability of the description of surface accumulation for this composite system was limited to bulk filler volume fractions less than 20 percent, a hypothesized result of transition in load-sharing between filler and matrix. The inverse rule-of-mixtures description of steady-state wear rate, however, was maintained over the full range of volume fractions investigated.
Apparatus for Extensional Viscosity Measurements
Authors: Merriman T. L. , Kannel J. W.
Published: February 2008

Although most analyses in tribology deal with the behavior of fluids in shear, many fluids, such as greases or printing inks, can develop significant forces when subjected to pure extension. These forces can impact performance, especially in the exit region of tribological interfaces. The resistance of a fluid to an imposed shear rate is a measure of the fluid’s shear viscosity (usually just referred to as its viscosity). The resistance of a fluid to an imposed extensional strain rate is a measure of the fluid’s extensional viscosity. In this paper, two techniques for the measurement of extensional forces are discussed. A subsequent companion paper will discuss interpretation of the force data in terms of extensional viscosity. Both techniques described have the advantage of a dimensionally small measurement element. The first technique involves the use of a vapor deposited surface pressure transducer. This transducer is a thin strip of ytterbium. The electrical resistance of ytterbium is pressure sensitive. Small changes in resistance can be related to extensional stress. The extensional viscometer apparatus consists of two counter-rotating cylinders. As the fluid exits the nip between the cylinders, the extensional stress is detected by a transducer attached to one of the cylinders. The second technique discussed herein involves the use of a small-beam transducer in conjunction with the counter-rotating cylinder apparatus. The deflection of the beam due to the fluid’s extensional force is detected and interpreted in terms of extensional stress as a function of strain rate at the exit of the nip. Extensional stresses of several hundred thousand Pa have been measured.
Three-Dimensional Flow and Pressure Patterns in a Hydrostatic Journal Bearing Pocket
Authors: Braun M. J. , Dzodzo M. B.
Published: February 2008

The laminar flow in a hydrostatic pocket is described by a mathematical model that uses the three-dimensional Navier-Stokes equations written in terms of the primary variables, u, v, w, and p. Using a conservative formulation, a finite volume multiblock method is applied through a collocated, body fitted grid. The flow is simulated in a shallow pocket with a depth/length ratio of 0.02. The flow structures obtained and described by the authors in their previous two dimensional models are made visible in their three dimensional aspect for both the Couette, and the jet dominated flows. It has been found that both flow regimes formed central and secondary vortical cells with three dimensional corkscrew-like structures that lead the fluid on an outward bound path in the axial direction of the pocket. In the Couette dominated flow the position of the central vortical cell center is at the exit region of the capillary restrictor feedline, while in the jet dominated flow a flattened central vortical cell is formed in the downstream part of the pocket. It has also been determined that a fluid turn around zone occupies all the upstream space between the floor of the pocket and the runner, thus preventing any flow exit through the upstream exit of the pocket. The corresponding pressure distribution under the shaft for both flow regimes is presented as well. It was clearly established that both for the Couette, and the jet dominated cases the pressure varies significantly in the pocket in the circumferential direction, while its variation is less pronounced axially.
A Random Model for Micro-Slip Between Nominally Flat Surfaces
Authors: Bjo¨rklund S.
Published: February 2008

A random surface model has been developed for the deformations of contacting surfaces subjected to both normal and tangential load. The model is restricted to nominally flat (rough) elastic surfaces in contact with perfectly flat (smooth) elastic surfaces. The deformations of the asperities are assumed to be independent of each other and the heights of the asperities are assumed to be randomly distributed. Depending on the height of an asperity, it will either slip or stick. The relation between tangential deformation and load will consequently be non-linear and this effect is often named micro-slip. Results are presented for two types of deformation laws for the individual asperities, with three different asperity height distributions. The results show typical micro-slip behaviour, independent of both the individual asperity deformation and the type of asperity height distribution. The influence of the standard deviation of asperity heights is strong and is an important factor when determining the micro-slip of nominally flat surfaces in contact.
Experimental and Fracture Mechanics Study of the Pit Formation Mechanism Under Repeated Lubricated Rolling-Sliding Contact: Effects of Reversal of Rotation and Change of the Driving Roller
Authors: Murakami Y. , Sakae C. , Ichimaru K. , Morita T.
Published: February 2008

Five rolling contact fatigue tests, Tests {1}–{5} have been conducted. In Tests {1}–{3}, when a fatigue crack was initiated on the surface of a follower, the test was halted. Then, in Test {1} the rotating direction was reversed. In Test {2} the follower and driver were interchanged, and in Test {3} the test was continued unchanged. In Test {3} the original crack grew to a pit. In Tests {1} and {2} the original crack immediately stopped propagating. In Tests {4} and {5}, mating with a harder roller, a softer roller was used as the follower in Test {4} and as the driver in Test {5}. A typical pit occurred in Test {4}. In Test {5}, surface damage substantially different from a typical pit was generated. Based on these experimental results, a 3-D crack analysis including the effect of frictional force on the contact surface and oil hydraulic pressure on crack surfaces, was conducted to elucidate the mechanisms of pit formation and surface damage in contact fatigue.
Finite Element Analysis of Fretting Stresses
Authors: McVeigh P. A. , Farris T. N.
Published: February 2008

Clamped contacts subjected to vibratory loading undergo cyclic relative tangential motion or micro-slip near the edges of contact. This cyclic micro-slip, known as fretting, leads to removal of material through a mechanism known as fretting wear and formation and growth of cracks through a mechanism known as fretting fatigue. In aircraft, fretting fatigue occurs at the rivet/hole interface leading to multisite damage which is a potential failure mechanism for aging aircraft. A finite element model of a current fretting fatigue experiment aimed at characterizing fretting in riveted joints is detailed. A non-symmetric bulk tension is applied to the specimen in addition to the loads transferred from the fretting pad. The model is verified through comparison to the Mindlin solution for a reduced loading configuration, in which the bulk tension is not applied. Results from the model with the bulk tension show that the distribution of micro-slip in the contact is not symmetric and that for some loads reversed micro-slip occurs. Finite element results are given for the effects that four different sets of loading parameters have on the maximum tensile stress induced by fretting at the trailing edge of contact. It can be shown using multiaxial fatigue theory that this stress controls fretting fatigue crack formation. This maximum tensile stress is compared to that of the Mindlin solution for a symmetric distribution of micro-slip. This stress is also compared to that of a variation based on the Mindlin solution for the cases with a non-symmetric distribution of micro-slip. It is concluded that the solution based on the Mindlin variation and the full finite element solution lead to similar predictions of the maximum tensile stress, even when the shear traction solutions differ significantly.
A New Approach to Determine Lubrication Regimes of Piston-Ring Assemblies
Authors: Henein Naeim A. , Huang Shengqiang , Bryzik Walter
Published: February 2008

A new approach is developed to determine piston-ring assembly lubrication regimes from the instantaneous frictional torque measured for the whole engine. This is based on the variation of the friction coefficient with the duty parameter in the Stribeck diagram over the mixed and hydrodynamic lubrication regimes. The derived equation determines the lubrication regimes from the slope of the line in the Stribeck diagram. A single cylinder spark ignition engine was instrumented to determine the total instantaneous frictional torque of the engine. Experiments were conducted under different loads at a constant speed. Results show that the regime is mixed lubrication near the top dead center (TDC) and shifts to the hydrodynamic lubrication regime as the piston moves away from TDC. The extent of the mixed lubrication regime depends on engine load and speed.
Raman Measurements of Localized Pressure Variations in Lubricants Above the Glass Transition Pressure
Authors: LaPlant F. , Hutchinson E. J. , Ben-Amotz D.
Published: February 2008

Spatial pressure variations in synthetic lubricants contained in a static high-pressure diamond anvil cell (DAC), as well as in a loaded model bearing contact device, have been measured using the frequency shift of the lubricant’s Raman vibrational modes. Long-lived pressure fluctuations of ±0.5 GPa, with a relaxation time of several days, are observed m the static high pressure systems at an average pressure of 2.5 GPa. Evidence for rapidly varying pressure fluctuations in a concentrated contact is inferred from the increase in lubricant Raman linewidths. These results raise questions about key assumptions made in modeling EHD contacts. It is suggested that the present results are closely linked to recent observations of shear localization made by Winer and Bair.
Friction and Wear Micromechanisms of Amorphous Carbon Thin Films
Authors: Wei B. , Komvopoulos K.
Published: February 2008

The friction and wear micromechanisms of amorphous hydrogenated carbon films were investigated experimentally using commercially available thin-film rigid disks with sputtered carbon overcoats and Al2O3TiC magnetic recording heads. Continuous sliding tests demonstrated the existence of two distinct friction and wear regimes characterized by different dominant micromechanisms. Scanning electron microscopy and Raman spectroscopy revealed that the evolution of friction in the first regime is due to changes of the surface microtopography and the film structure from amorphous carbon to polycrystalline graphite. Atomic force microscopy showed that the topography changes result from asperity nanofracture leading to the gradual removal of carbon material and the generation of ultrafine wear debris. The friction behavior in the second regime is due to various wear processes arising on the carbon film surface. High friction promotes surface micropitting and the formation of significantly deeper and wider texture marks. The erratic fluctuations of the friction force and microplowing of the carbon film at steady state are attributed to the relatively large wear particles generated by micropitting.
An Application of Self-Tuning Fuzzy Controller to Dynamic Positioning
System of Floating Production System
Authors: Inoue Y. , Du J.
Published: February 2008

Position-keeping of a floating body is a very important matter in a production system in the deep sea. How a floating body can be kept stationary is a key problem in this study. Conventionally, the mooring system is adopted to position a floating body under disturbance of wind, wave, and current; but, in general, it is difficult to survive storm disturbance in the deep sea. The dynamic positioning system can solve this problem, but thrusters must be operated at all times against random drift force of wave, wind, and current, and a great deal of energy is required. So a composite system of single-point mooring system and fuzzy control dynamic positioning (FDP) system was studied in a previous paper (Inoue, 1994). However, up to now in almost all kinds of dynamic positioning systems, control strategy must be decided in advance. This is unreasonable under a random condition. In this paper, a self-tuning fuzzy control system is put forward. By this approach, the control precision of the previous fuzzy dynamic positioning is fairly improved. The main concept of this approach is that at first a feasible control strategy is decided in advance, then during the motion of the system, the control strategy is improved automatically according to the sea conditions of operation. This system is more reasonable than the previous system because, in fact, the disturbance of wave, current, and wind cannot be predicted.
Wave Diffraction Around Three-Dimensional Bodies in a
Current
Authors: Cheung K. F. , Isaacson M. , Lee J. W.
Published: February 2008

The effects of a collinear current on the diffraction of regular waves around three-dimensional surface-piercing bodies are examined. With the current speed assumed to be small, the boundary-value problem is separated into a steady current problem with a rigid wall condition applied at the still water level and a linear wave propagation problem in the resulting current field. The boundary conditions of the wave propagation problem are satisfied by a time-stepping procedure and the field solution is obtained by an integral equation method. Free surface profiles, runup, and wave forces are described for a vertical circular cylinder in combined waves and a current. The current is shown to affect significantly the steady drift force and runup predictions. Comparisons of the computed wave forces are made with a previous numerical solution involving a semi-immersed sphere in deep water, and indicate good agreement.
Second-Order Vertical Diffraction Forces on Truncated
Cylinders
Authors: Weggel D. C. , Roesset J. M. , Kim M.-H.
Published: February 2008

A number of parametric studies were performed on a series of single, truncated cylinders in deep water using second-order potential theory. The cylinders were subjected to a monochromatic incident wave field. Second-order vertical diffraction force components were computed and plotted to illustrate their variation with cylinder aspect ratio and incident wave frequency. These plots make it possible to obtain rough estimates of vertical second-order diffraction force quantities on cylindrical components without having to perform second-order diffraction theory computations. The double-frequency heave response amplitude operator RAO(2) for a freely floating truncated cylinder is presented as a function of cylinder aspect ratio and incident wave frequency. Calculations of the RAO(2) were made using the total double-frequency diffraction force and the first-order radiation coefficients evaluated at the double-frequency.
Peak Response Statistics of Vertical Cylinders in Two-Dimensional
Irregular Waves
Authors: Haritos N.
Published: February 2008

When dealing with the probabilistic estimation of the peak response of an offshore structure dynamically responding under excitation by unidirectional irregular waves, it becomes apparent that nonlinearities introduced by the wave-structure interaction, and principally associated with the drag contribution of the Morison force model that has been traditionally used to describe this forcing, leads to non-Gaussian statistical properties of not only the forcing, but also the response. However, it is also apparent that for lightly damped structures, the response under certain circumstances can be very “narrow-banded,” and hence its statistical description would then approach the Gaussian form irrespective of whether the forcing associated with the response is itself highly non-Gaussian or otherwise. This paper treats both a numerical and experimental investigation of the peak response characteristics of compliant bottom-pivoted surface-piercing cylinders subjected to hydrodynamic excitation by unidirectional Pierson-Moskowitz (P-M) irregular waves and modeled as single-degree-of-freedom (SDOF) oscillators with a fixed “straight line” mode shape (the result of the bottom-pivoted support condition). Conditions under which the response can reasonably be approximated as Gaussian are identified via an upcrossing investigation for the likely peak response in a storm of a nominated period of duration.
Statistical Uncertainty in Long-Term Distributions of Significant
Wave Height
Authors: Guedes Soares C. , Henriques A. C.
Published: February 2008

This work examines some aspects involved in the estimation of the parameters of the probability distribution of significant wave height, in particular the homogeneity of the data sets and the statistical methods of fitting a distribution to data. More homogeneous data sets are organized by collecting the data on a monthly basis and by separating the simple sea states from the combined ones. A three-parameter Weibull distribution is fitted to the data. The parameters of the fitted distribution are estimated by the methods of maximum likelihood, of regression, and of the moments. The uncertainty involved in estimating the probability distribution with the three methods is compared with the one that results from using more homogeneous data sets, and it is concluded that the uncertainty involved in the fitting procedure can be more significant unless the method of moments is not considered.
Crack Arrest Toughness of a Heat-Affected Zone Containing Local
Brittle Zones
Authors: Malik L. , Pussegoda L. N. , Graville B. A. , Tyson W. R.
Published: February 2008

The awareness of the presence of local brittle zones (LBZs) in the heat-affected zone (HAZ) of welds has led to the requirements for minimum initiation (CTOD) toughness for the HAZ for critical applications (API RP 2Z, CSA S473). Such an approach, however, is expensive to implement and limits the number of potential steel suppliers. A fracture control philosophy that is proposed to be an attractive alternative for heat-affected zones containing LBZs is the prevention of crack propagation rather than of crack initiation. Such an approach would be viable if it could be demonstrated that cracks initiated in the LBZs will be arrested without causing catastrophic failure, notwithstanding the low initiation (CTOD) toughness resulting from the presence of LBZs. Unstable propagation of a crack initiating from an LBZ requires the rupture of tougher microstructural regions surrounding the LBZ in HAZ, and therefore the CTOD value reflecting the presence of LBZ is unlikely to provide a true indication of the potential for fast fracture along the heat-affected zone. Base metal specifications (CSA S473) usually ensure that small unstable cracks propagating from the weld zone into the base metal would be arrested. Past work has also shown that unstable crack initiation resulting from interaction of surface semi-elliptical cracks parallel to the fusion boundary with the local brittle zones can get arrested once the crack has popped through the depth of the LBZ. However, the potential for arrest when a through-thickness HAZ crack runs parallel to the fusion boundary, and thus parallel to the LBZs, has not been examined previously. To investigate the likelihood of fast fracture within the HAZ, a test program has been carried out that involved performing compact plane strain (ASTM E1221) and plane stress crack arrest tests on a heataffected zone that contained LBZs, and thus exhibited unacceptable low CTOD toughness for resistance to brittle fracture initiation. The results indicated that in contrast to the initiation toughness (CTOD toughness), the crack arrest toughness was little influenced by the presence of local brittle zones. Instead, the superior toughness of the larger proportion of finer-grain HAZ surrounding the LBZ present along the crack path has a greater influence on the crack arrest toughness. It further seems that there may be potential to estimate the HAZ crack arrest toughness from more conventional smaller-scale laboratory tests, such as conventional or precracked instrumented Charpy impact tests.
Thermoelastic Distortion of EHD Line Contacts During the Passage of Soft Debris Particles
Authors: Nikas G. K. , Sayles R. S. , Ioannides E.
Published: February 2008

During the passage of a debris particle through an EHD contact, mechanical stresses due to particle compression and thermal stresses due to particle frictional heating produce a thermoelastic/plastic stress field, which governs the way a possible damage is generated. In the present paper, the complete three-dimensional solution of the thermoelastic distortion of surfaces due to the compression of a soft, ductile debris particle in an EHD line contact is presented both theoretically and through a realistic example. It is found that thermal stresses increase the likelihood of yielding and produce a characteristic “omega” shaped thermoelastic displacement. The important outcome of this work is the construction of a map which shows the critical particle size to cause damage (plastic deformations) in combination with operational parameters as the lubricant film thickness and relative sliding velocity of the contact.
Estimation of Traction Properties Based on a Nonlinear Viscoelastic Model
Authors: Makino Tomoaki , Kawase Tatsuo
Published: February 2008

Traction measurements for two kinds of synthetic naphthenic traction oils were carried out, using a two-roller machine. The Eyring stress and shear modulus of test oils were estimated simultaneously by a curve-fitting procedure based on the nonlinear viscoelastic model introduced by Johnson and Tevaarwerk. As a consequence, it has been found that the Eyring stress decreases with an increase in contact pressure, and it increases with oil temperature. It has been also clarified that the effective shear modulus, including the effect of the roller compliance, decreases with an increase in contact pressure. At higher pressure it decreases as the oil temperature increases, whereas at lower pressure it increases with the oil temperature. In addition, the influences of operating conditions such as the kind of oil, pressure, and oil temperature upon the Eyring stress, shear modulus, and traction coefficient were also investigated. It has been shown that under the operating conditions where the effect of oil viscosity is predominant, the accuracy of the shear modulus calculation deteriorates when the shear modulus is estimated by assuming that the oil is perfectly elastic.
An Averaging Technique for the Analysis of Rough Surface High Bearing Number Gas Flows
Authors: White James W.
Published: February 2008

Earlier analytical solutions by White (1980, 1983, 1992, 1993) included Couette effects, transverse diffusion, and mass storage in a model lubrication equation for narrow width wavy surface high bearing number gas films. The model lubrication equation did not include longitudinal diffusion effects due to the high bearing number restriction. Crone et al. (1991), however, reported numerical solutions of the full Reynolds equation for a gimbal mounted slider subject to wavy surface roughness. The first objective of this work is to reconcile the differences observed between the reported results of White and those of Crone et al. for moving and stationary roughness. The second objective is to describe how to best apply what appears to be a universal property of a high bearing number gas film subjected to a rough surface. Each solution of the model lubrication equation by White (1980, 1983, 1992, 1993) produced a product term based on local gas pressure and clearance (Z = Ph) that is independent of roughness details but which is dependent on the statistical properties of the roughness. In the present work, this characteristic is treated as a universal property of all high bearing number rough surface gas films. The product variable Z = Ph is introduced into the generalized full lubrication equation, and the resulting lubrication equation is ensemble averaged before a solution is attempted. This removes the short length and time scale effects due to the surface roughness. Solution of the ensemble averaged equation for Z(x, y, t) then follows by standard analytical or numerical methods. The unaveraged pressure is then given by P(x, y, t) = Z(x, y, t)/h(x, y, t) and the ensemble averaged or mean pressure at a point is computed from Pm(x, y, t) = Z(x, y, t)E(1/h(x, y, t)), where E(1/h) represents the ensemble average of 1/h. Using this technique, numerical solutions of the full generalized lubrication equation based on kinetic theory were obtained for a low flying gimbal mounted slider. Results indicate that the nominal flying height increases and the minimum flying height decreases as surface roughness increases.
Degradation of Perfluoropolyether Fluids With Metal Ions
Authors: Fukuchi Takashi
Published: February 2008

Chemical degradation of lubricant fluids of perfluoropolyether (PFPE), such as Fomblin Z-DOL, Fomblin AM-2001, Fomblin Z-25, Demnum SP-3, and Demnum SA, with bivalent metal ions was examined. The respective reaction mechanisms involve an ether cleavage process which is caused by the coordination of metal ions with oxygen atoms in the main chains of the PFPE. Metal ions were evaluated for their ability to degrade the PFPE, and the results demonstrate that the ions ranking in terms of this ability is as follows: Cu2+ > Ni2+ > Co2+ > Fe2+ > Mn2+ > Mg2+. This trend can be explained by the ionization potentials of the metal atoms. For an identical metal ion, the Demnum lubricants showed a greater stability than the Fomblin lubricants.
Meniscus Shape and Splashing of Magnetic Fluid in a Magnetic Fluid Seal
Authors: Mitsuya Yasunaga , Tomita Kenji , Takeuchi Kaoru , Matsunaga Shigeki
Published: February 2008

Magnetic fluid splashing from a magnetic fluid seal due to high-speed rotation of the seal ring was experimentally investigated in relation to clearance and magnetic field strength around a gap to be sealed. Meniscus deformation, owing to fluid rotation, was accurately observed by a silhouette formed when the meniscus was illuminated with a bold laser beam from behind. Deformation was found to occur in three stages. In the first stage, the meniscus static width shrank while the meniscus rotation height remained essentially unchanged. In the second stage, rotational height increased slightly and then returned to equilibrium. In the third stage, there was an abrupt entire shrinkage accompanied by splashing at the back side of the gap. With a further increase in rotation speed, splashing at the front side of the gap occurred, which resulted in irreversible loss of fluid. Relationships between the splashing initiation speed at the front gap and meniscus size just before the occurrence of splashing were clarified with the clearance and magnetic field strength as parameters. A useful simple indicator of splashing initiation was established based on these results.
Boundary Additive Effect on Abrasive Wear During Single Asperity Plowing of a 3004 Aluminum Alloy
Authors: Opalka Susanne M. , Hector Louis G. , Schmid Steven R. , Reich Ronald A. , Epp June M.
Published: February 2008

Aluminum forming processes such as rolling, extrusion, and ironing involve the transfer of large loads through a tooling/workpiece interface to plastically deform the workpiece to a desired shape. Sharp tool surface asperities can plow the workpiece and lead to elevated friction and temperatures in the interface with a subsequent increase in abrasive wear debris which in turn degrades the surface aesthetics of the final product. To minimize associated friction and wear levels in aluminum forming processes, a base oil with one or more boundary additives is used as a lubricant. At the present time, however, little is known about the mechanisms by which a given additive influences abrasive wear in an aluminum metal forming interface. In the present work, a series of single asperity plowing experiments on a 3004-O aluminum alloy with selected lubricant components was conducted. Three additives were separately investigated, viz., stearic acid, butyl stearate, and lauryl alcohol. The plowing motion of a pyramidal diamond indentor with a cutting edge oriented in the plowing direction (i.e., a sharp indentor) was controlled with the piezo-electric transducers of an atomic force microscope. The experiments help to provide insight about the interplay between additive reaction with the surface and plowing mechanics. Further insight into this interplay and abrasive wear debris generation was sought, albeit qualitatively, through additional experiments involving a diamond indentor for which no one cutting edge was oriented in the plowing direction (i.e., a blunt indentor). The tests allowed evaluation of the boundary lubricant mechanism and propensity for generating wear debris.
Tribological Properties and Microstructure Evolution of Ultra-High Molecular Weight Polyethylene
Authors: Klapperich C. , Komvopoulos K. , Pruitt L.
Published: February 2008

The friction and wear properties of unmodified ultra-high molecular weight polyethylene (UHMWPE) were investigated experimentally. Dinks of semicrystalline UHMWPE were slid against polished CoCrWNi pins in bovine serum at ranges of contact pressure and sliding speed typical of those encountered in total joint replacements. The coefficient of friction was monitored continuously during testing, and the wear rate was determined from surface profilometry measurements of worn disk surfaces accounting for strain relaxation. Scanning electron microscopy (SEM) results demonstrated that surface deterioration comprises adhesion, third-body abrasion by polyethylene wear debris, and delamination wear. The contribution of these mechanisms to the overall wear rate and the formation of wear debris depends predominantly on the contact pressure and secondarily on the sliding speed. Transmission electron microscopy (TEM) yielded new insight into the evolution of the microstructure morphology of UHMWPE during sliding. Cross sections parallel to the wear tracks obtained from various depths were analyzed with the TEM to develop a spatial mapping of the subsurface microstructure as a function of contact pressure. Alignment of crystalline regions (lamellae) in the polyethylene microstructure parallel to the sliding surface was found to occur during sliding even at relatively low contact pressures. SEM observations suggested that the highly oriented microstructure is the precursor to delamination wear, leading to the formation of wear particles larger than those produced by adhesion and third-body abrasion at the contact interface.
Third Body Effects on Graphite/XC48 Steel Magnetized Sliding Contact
Authors: El Mansori Mohamed , Schmitt Marjorie , Paulmier Daniel
Published: February 2008

This paper completes previous studies concerning the mechanisms governing friction and wear of a steel/graphite couple under an external applied magnetic field. Friction tests were performed in a controlled chamber with a magnetised steel pin sliding against a graphite disk exposed to oxygen, argon, and vacuum environments. Wear debris and friction tracks generated by reactions with the gases after sliding, with and without magnetic field, were identified ex situ by scanning electron microscopy and energy-dispersive X-ray analysis. It shows that the magnetic field modifies the third body behavior which depends on the gases surrounding the contact; this governs the friction state, the type of graphite wear (fatigue or abrasive wear), and the surface reactivity.
Wear Mechanisms at the Metal Evaporated Magnetic Tape-Head Interface
Authors: Berar Pascal , Kato Koji , Osaki Hiroyuki , Terazono Toshiyuki , Kapsa Philippe
Published: February 2008

The wear mechanisms of Metal-Evaporated magnetic tape-head interfaces have been investigated. A new apparatus was designed for the continuous observation of the tape surface when run in the still frame mode. The mild wear mechanism of the bumps on the ME tapes was proven using SEM and AFM. Four different types of wear debris were observed. Depending on wear debris formation, two types of spalling were emphasized. The effect of humidity in the range of 30–70 percent was also investigated. The wear mechanisms are discussed in terms of contact mechanics theory, coating failure modes, and humidity induced stiction theory.
A Simple Numerical Method for Contact Analysis of Rough Surfaces
Authors: Chang L. , Gao Y.
Published: February 2008

This paper presents a simple method that may be used to calculate the pressures and surface displacements in contacts of rough surfaces. A main feature of the method is that the pressure is calculated (updated) individually at each surface location rather than simultaneously at all locations by solving a system of equations. The pressure update at a given location is computed solely based on the surface interpenetration at that location; consequently, both 2-D and 3-D contact problems are solved in exactly the same way. Furthermore, this scheme of calculation does not produce negative pressures in the solution process, which is a main source of numerical instability in other types of methods of solution. The method is conceptually simple and easy for computer implementation. It is numerically stable and can solve various types of problems of high contact severity. Measured roughness data can be used directly without any mathematical treatment such as filtering or frequency decomposition. The method is also computationally efficient and requires minimum computer storage, making it suitable for integration into computer programs for design-analysis calculations of practical contact/lubrication problems.
Investigations Into Asperity Persistence in Heavily Loaded Contacts
Authors: Lee-Prudhoe I. , Sayles R. S. , Kaderic A.
Published: February 2008

Experimental results are presented along the lines of the early work of Moore (1948) where a hard smooth roller is pressed into a softer rough surface to study the resulting real to apparent areas of contact and their associated local contact pressures. Results are presented for a hard steel roller deforming mild-steel and aluminum-alloy rough surface specimens. An analysis of the local contact mechanics is performed before and after indentation using a recently developed numerical elastic contact simulation method which allows local asperity contact pressures and areas to be studied in detail. The method is shown to reveal the level and distribution of pressures and asperity contact areas prevalent during the indentation process, and therefore allows the contribution of elastic and plastic load support to be quantified. The persistence of asperities during such indentation tests is discussed in terms of the pressures the asperities can support in relation to reported mechanisms of persistence. Results of subsequent sub-surface stresses are also presented and discussed in terms of how the method might be used to create an elastic-plasticdeformation model that can account for asperity persistence in future numerical contact simulation models.
Dynamic Motion of Two Elastic Half-Spaces in Relative Sliding Without Slipping
Authors: Adams George G.
Published: February 2008

Two isotropic linear elastic half-spaces of different material properties are pressed together by a uniform pressure and subjected to a constant shearing stress, both of which are applied far away from the interface. The shear stress is arbitrarily less than is required to produce slipping according to Coulomb’s friction law. Nonetheless, it is found here that the two bodies can slide with respect to each other due to the presence off a separation wave pulse in which all of the interface sticks, except for the finite-width separation-pulse region. In this type of pulse, the separation zone has a vanishing slope at its leading edge and an infinite slope at its trailing edge. Nonetheless, the order of the singularity at the trailing edge is small enough so as not to produce an energy sink. The problem is reduced to the solution of a pair of singular integral equations of the second kind which are solved numerically using a variation of the well-known method of Erdogan et al. (1973). Results are given for various material combinations and for a range of the remote shear-to-normal-stress ratio.
Diagnosis of Rolling Bearing by Measuring Time Interval of AE Generation
Authors: Yoshioka Takeo , Korenaga Atsushi , Mano Hiroki , Yamamoto Takashi
Published: February 2008

We have developed a new method for measuring time intervals of Acoustic Emission (AE) generation for diagnosis of a radial rolling bearing. The method makes the AE signal itself a trigger of the oscillation of the clock pulse and measures the time interval of AE generation by integration of the clock pulses. The measurement device consists of the threshold, clock, time interval measurement and memory circuit, and was applied to rolling contact fatigue experiments. It was confirmed by the experiments that the measured time intervals of AE generation on the inner raceway or the ball agreed with the value calculated based on the kinetics of the rolling bearing. Moreover, we could identify the elements in which a fatigue crack was propagating by the method before the spalling appeared. The identified elements agreed with the failed elements.
Air Bearing Dynamics of Sub-Ambient Pressure Sliders During Dynamic Unload
Authors: Hu Yong , Jones Paul M. , Li Kangjie
Published: February 2008

The increasing effort to use sub-ambient pressure air bearing sliders for dynamic load/unload applications in magnetic hard disk drives requires desirable air bearing characteristics during the dynamic unload event. This paper establishes air bearing design criteria for achieving a smooth head unload performance, through a correlation study between the modeled unloading air bearing dynamics of two 30 percent proximity recording sub-ambient pressure sliders and motion sequence of the same sliders by a high-speed video camera. It is shown that the air bearing lifting force quickly responds to changes in fly height and pitch, while the suction force is relatively resistant to changes in fly height, but somewhat more sensitive to changes in pitch. This unique distinction results in different decreasing rates between the air bearing lifting and suction forces during the unload process, creating a strong dependence of the unloading characteristics on the location of the suction cavities. Both the modeled unloading air bearing dynamics and experimentally recorded motion sequence illustrate that a toward-trailing-edge located suction force acts to pitch the slider up, while the moment produced by a toward-leading-edge located suction force induces a negative pitch motion, resulting in an excessive flexure deformation and dimple separation. Therefore, placing the suction cavities towards the trailing edge offers a reliable unloading performance for the sub-ambient pressure air bearing sliders.
Theoretical Prediction of Ramp Loading/Unloading Process in Hard Disk Drives
Authors: Peng J. P.
Published: February 2008

Air bearing slider dynamic performance during the ramp loading and unloading processes was investigated theoretically in this paper. The air bearing was modeled by the modifiedcompressible Reynolds equation, and it was solved by the finite volume method. Slider dynamic equations were derived in this paper to include the ramp loading/unloading mechanism. These two sets of coupled equations were solved iteratively. Both Tripad and negative pressure air bearing (NPAB) were included in the analysis. Effects of loading/unloading velocity, disk rotational speed, as well as suspension flexure stiffness, were investigated. Slider-disk impact will occur during the Tripad loading process, especially at high loading velocity. On the other hand, this impact can be avoided for an NPAB at loading velocity up to 200 mm/s. However, an NPAB requires a longer unloading time due to its suction force. This unloading process is further delayed if a soft flexure is combined with an NPAB.
An Investigation of the Take-Off Behavior of Proximity Recording Sliders Using Acoustic Emission and Phase Demodulated Interferometry
Authors: McMillan T. C. , Talke F. E.
Published: February 2008

The “take-off” behavior of proximity recording sliders is investigated using acoustic emission and phase demodulated laser interferometry. A biquadratic surface fit of the air bearing surface is used to determine the position of the slider with respect to the disk. Acoustic emission data is examined in both the time and frequency domain to analyze the location of slider/disk contacts. Two distinct frequencies are observed in the frequency spectrum of the acoustic emission signal, corresponding to torsional mode and bending mode vibrations of the rigid slider. As the velocity increases, the magnitude of the torsional mode decreases relative to that of the bending mode, indicating that slider/disk contacts change from side rails contacts to trailing edge contacts.
Effects of Design Parameters on Bouncing Vibrations of a Single-DOF Contact Slider and Necessary Design Conditions for Perfect Contact Sliding
Authors: Ono Kyosuke , lida Kohei , Takahashi Kan
Published: February 2008

The general characteristics of the bouncing vibrations of a IDOF contact slider model over the surface of a harmonic wavy disk were studied both by computer simulation and theoretical analysis. The necessary design conditions for a contact slider and the surface of a disk were discussed in terms of perfect contact sliding and wear durability. It was found that the bouncing vibrations change with the amount of waviness amplitude A(fr) at the contact resonant frequency fr(=(1/2π)kc/m) relative to static penetration depth δ, or fr relative to limiting critical frequency fcl, above which the downward acceleration of the surface of a disk is larger than that of a slider due to slider load. When the contact stiffness is large enough so that δ < A(fr) (fcl < fr), the slider bounces with a large amplitude similar to an elastic impact in a wide frequency range. When the contact stiffness is small enough so that δ > A(fr) (fcl > fr), bouncing vibrations occur near the contact resonance, similar to the resonance of a nonlinear soft spring system. Here, the bouncing vibration can be completely eliminatedby increasing the contact damping ratio and decreasing the slider mass and the waviness amplitude.
Predicting Traction in Web Handling
Authors: Ducotey K. S. , Good J. K.
Published: February 2008

A simple algorithm has been developed for predicting traction in web handling applications. Minimal traction exists when the minimum air film height between the roller and web is greater than three times the rms roughness of the two surfaces in contact. Classical foil bearing theory modified for permeable surfaces is used to determine the air film height. A piecewise linear solution using squeeze film theory is also used to account for side leakage. The minimum air film height is a function of web tension, web and roller velocity, air viscosity, web width, web permeability and roller radius. The algorithm is applicable for permeable and nonpermeable webs. Values obtained from the algorithm can be used to predict if sufficient traction is available between the web and roller for a given set of physical and operating parameters. Traction values can also be used as input for winding, wrinkling, and spreading models.
A Simplified Diagram of Seizure Criteria for Lubricated Sliding Rough Surfaces
Authors: Makino T. , Sayles R. S.
Published: February 2008

This paper describes an attempt to include surface roughness effects in the conventional pressure-velocity (PV) map for lubricated sliding surfaces. The criteria proposed involve two different boundaries: a plasticity limit and a temperature limit. The first criterion is given by a certain normal load to the system at which the plastically deformed asperities start interacting with each other. The second is given by an operating condition at which the surface temperature reaches a prescribed value. The effect of fluid film formation is considered in calculating effective normal load for these two criteria. By employing an exponential roughness height distribution and a long bearing approximation in fluid film pressure prediction, the diagram can easily be modified or reproduced for the system having different surfaces and materials. The diagram was adopted to evaluate a steel/steel end-face friction test result. Reasonable agreement was found.