Electron Affinity Calculations For Thioethers

Previous work indicated that polyphenyl thioethers possessed chemical properties, related to their electron affinities, which could allow them to function as vapor phase lubricants (VPL). Indeed, preliminary tribological tests revealed that the thioethers could function as vapor phase lubricants but not over a wide temperature and Hertzian pressure range. Increasing the electron affinity of the thioethers may improve their VPL properties over this range. Adding a substituent group to the thioether will alter its electron affinity in many cases. Molecular orbital calculations were undertaken to determine the effect of five different substituent groups on the electron affinity of polyphenyl thioethers. It was found that the NO₂, F, and I groups increased the thioethers electron affinity by the greatest amount. Future work will involve the addition of these groups to the thioethers followed by tribological testing to assess their VPL properties.     

A Surface Effect Associated with the Use of Oils Containing Zinc Dialkyl Dithiophosphate

It is shown that the operation of engines on crankcase oils containing appreciable amounts of zinc dialkyl dithiophosphate can increase the small-scale roughness of the lifter-foot surfaces. In addition, the small-scale roughness can be reduced by subsequent operation of the same engine parts on oils containing no zinc dialkyl dithiophosphate. This change in roughness coincides with a change in reflectivity that can be detected visually.

A similar effect of the additive has been demonstrated in a bench test machine. The increase in roughness which accompanies the operation on the additive-treated oil occurs rapidly and is maintained to high contact loads although some smoothing may occur at high loads.

The evidence suggests that the change in roughness results from a reaction of additive decomposition products with the metal surface. The mechanism responsible, however, is not completely understood.     

Effects of Fluid Inertia on Finite-Length Squeeze-Film Dampers

The influence of fluid inertia on the SFD force response to circular-centered motions of arbitrary amplitude is analyzed in detail, For finite length, locally sealed SFDs, integro-differential equations are derived in terms of the mean flow components. Numerical predictions, using the finite-element method, show that the damping and added mass coefficients remain invariant as the Reynolds number increases from small values to a moderate Reynolds number equal to 10. An approximate, finite-length, solution for the fluid-film forces has been analytically obtained which accounts for the fluid-inertia effect as well as local end seal effects in symmetric SFD configurations. The approximate solution, strictly valid for small Reynold numbers (Re < 1), agrees well with the results from the numerical solution for most SFD configurations and orbit radii considered.     

Modeling Wear Traces of Automotive Friction Materials by Cantor Set

Grooves parallel to the disc rotation direction were observed on the surface of non-metallic organic (NMO) friction materials after Friction Assessment Screening Test (FAST). Grooves are traces of wear and formed by abrasive mechanism. Grooves have fractal nature and they can be described by Cantor set. Two equations, one is time coordinate (x-axis) “matheqn” and the other one is wear ordinate (y-axis) “matheqn”, were proposed based on Cantor set to model the linear relationships among wear, time and sliding speed.     

Development of an Apparatus to Investigate Friction Characteristics of Constant-Velocity Joints

Constant-velocity (CV) joints have become standard design and an integral part of modern vehicles, primarily due to their superiority in terms of CV torque transfer. Despite widespread usage of constant velocity joints there are certain aspects of their friction, wear, and contact characteristics that are not well understood. In this article, the need to directly measure CV joint internal contact and friction forces is addressed by designing and constructing an instrumented advanced CV joint friction apparatus using actual tripod-type joint assemblies. The apparatus is capable of measuring key performance parameters such as friction and wear under different realistic operating conditions of oscillatory speeds and CV joint articulation angles. The apparatus incorporates a custom-installed triaxial force sensor inside of the CV joint to measure in situ internal CV joint forces (including friction). The CV joint apparatus is under full computer control and is communicating with all measurement components via a master Labview control program. Experiments under different articulation angles and lubrication conditions were performed and the measurements were correlated with published data.     

Wear Characteristics of Diamond Tools in Machining Ceramics

Wear characteristics of natural diamonds used to machine ceramic materials at a depth of cut of 2 μm and a speed of 1600 m/min were investigated. The diamond tools used for the machining tests were inspected using the Laue back reflection technique and scanning electron microscopy (SEM). Wear characteristics of the diamond tools appeared to be influenced by the material properties of the ceramics being machined, the build-up on the tips of the diamond tools, and the crystallographic orientations of the diamond crystals. Three wear patterns were identified: single-flat wear, double-flat wear, and micro-chipping wear. The single-flat and double-flat wear patterns were primarily observed in machining silicon nitride and alumina; the microchipping wear pattern was observed in machining silicon carbide. The wear rate for the microchipping pattern was found to be one to two orders of magnitude higher than those for other wear patterns. Silicon nitride wore the diamond tools faster than alumina did; however, it often formed built-up lips which reduced the wear of the diamond tools.     

Large Bearing Number Stability Analysis for Tango Class Gas Bearing Sliders

Air bearing sliders in the Tango class use load bearing pads with inlet-throttled leading edges to control the mass flux and lift. The influence of leakage or diffusion effects is always present in real sliders. In some designs such as railed taper flat designs leakage is dominant. The behavior of such sliders must be determined with numerical methods that obscure deeper understanding. Many aspects of the behavior of Tango class sliders can be understood with the vast simplification allowed by inlet throttling. In this paper such a simplified analysis is applied to describe a complete air bearing slider composed of two pads. The conditions for static level flight are determined, as well as the linear stability of heaving and pitching oscillations. Both stable and unstable modes are identified. Either damping or amplification can result from convective effects in the absence of mechanical damping. In real implementations of Tango class sliders instability has not been observed thanks to diffusion. The present analysis can serve as a guide to select initial choices for the operating parameters that correspond to maximum convective damping.     

Accelerated High Speed Water Erosion Test for Concrete Wear Debris Analysis

This paper contains investigations of wear particles generated during the erosive wear of four different concrete, mixtures by high velocity water flow at velocities of about 700 m/s.ⁱ The wear particles were collected, dried and analyzed by sieve experiments. Based on the sieve analysis, specific surface and average grain diameter of the particle samples were estimated. 'Using simple, comminution relations, the specific crack length of every' sample is calculated. It is shown that all estimated parameters exhibit a strong relationship to characteristic material properties, such as compressive strength, Young's modulus, and absorbed fracture energy. It was found by regression analysis that the average debris wear size can be effectively characterized by the absorbed fracture energy of the concrete sample. It is concluded that these relations are the result of different paths of fracture propagation through the materials during the generation of a microcrack network.     

Effects of Gas Composition,Humidity and Temperature on the Tribology of the Head/Disk Interface—Part II: Model and Analysis

A qualitative model for the effect of water condensation on the frictional behavior of unlubricated and lubricated carbon-overcoated disks is presented. The model suggests that for unlubricated disks adsorbed water acts as a lubricant, protecting the unlubricated disk surface from direct solid/solid contact and direct exposure to the environment. For lubricated disks, the interaction between adsorbed water and lubricant molecules seems to be responsible for the effect of humidity on the frictional behavior of lubricated disks. The effect of temperature on the frictional behavior of the head/disk interface is discussed in terms of surface energy, lubricant viscosity and mobility.     

Analytical Solution of the General Linear Viscoelastic Radial Load Equation for Rotary Shaft Seals

The viscoelastic radial load equation for a cylindrical shell representing the seal was derived from the static solution by the correspondence principle and from first principles. The equation decoupled in space and time by a normal mode analysis was solved both by conventional methods with an impact initial condition and rather more efficiently by the Laplace transform method, for a general linear Maxwell body in plane stress. The solution was in the form of a recurrence relation, allowing representation of material properties by any number of Maxwell elements. When subjected to the standard creep test, step radial load, the seal responded with an impact displacement, followed by transient and finally steady creep. The equation was also solved by the finite element method with the semidiscrete approximation. The solution for stress relaxation and oscillatory strain are given in the Appendix.