Effect of Surface Forces on Ultrathin Film Lubrication

Lubricated contact with nanoscale oil film is modeled for friction. Effect of the van der Waals pressure and the solvation pressure forces on such ultrathin lubricating oil film is considered while finding the friction and other parameters. Hydrodynamic action is represented using transient thermoelastohydrodynamics. Net pressure due to hydrodynamic, solvation, and van der Waals’ action is integrated over the contact area to find contact load. Conjunctional friction due to thermal activation of such ultrathin film is derived using the Eyring model. Effect of molecular dimension on friction is studied.

Effect of Surface Roughness on the Squeeze Film Lubrication of Finite Poroelastic Partial Journal Bearings with Couple Stress Fluids: A Special Reference to Hip Joint Lubrication

A simplified mathematical model has been developed for understanding the combined effects of surface roughness and couple stresses on the squeeze film behavior of poroelastic bearings in general and that of hip joints in particular. The cartilage is modeled as biphasic poroelastic matrix and synovial fluid is modeled as couple stress fluid. The modified form of averaged Reynolds equation which incorporates the randomized roughness structure as well as elastic nature of articular cartilage with couple stress fluid as lubricant is derived. For the study of rough surfaces, Christensen's stochastic theory is used to study the effect of two types of one-dimensional random roughness, namely, longitudinal roughness pattern and the transverse roughness pattern. The averaged film pressure distribution equations are solved numerically by using the conjugate gradient method. It is observed that the surface roughness effect is dominant and pattern dependent and the influence of couple stresses is to improve the joint performance.

Effect of Fiber Content on Abrasive Wear Behavior of Date Palm Leaf Reinforced Polyvinyl Pyrrolidone Composite

The effect of fiber contents on wear behavior of date palm leaf reinforced polyvinyl pyrrolidone (PVP/DPL) composites has been experimentally investigated. The test samples with fillers in 10, 20, 30, and 40% based on weight of fibers were prepared using injection molding. The optimum fiber content (i.e., 26 wt%) for maximum mechanical strength of the composites was determined by regression analysis. The dry sliding wear tests were conducted for each composition at different sliding velocities (0.392, 0.471, and 0.549 m/s) and sliding distances (188, 254, and 376 m) by applying normal loads of 5, 10, 15, and 20 N using pin-on-disc wear testing machine. The specific wear rate, wear loss, and coefficient of friction were plotted against the normal load and sliding distance at all sliding velocities. The results reveal that incorporation of date palm leaf fibers leads to significant improvement in the wear resistance of composites up to optimum fiber content and then decreases as fiber content increases. Further, it is found that surface modification has significant effect on wear performance. Worn surfaces of some selected samples were studied by scanning electron microscopy to analyze the wear mechanism.

Development of Machining Processes for the Use of Multilayer High-Performance Coatings

The development of corrosion- and wear-resistant high-performance coatings is important to improve components of mobile and stationary turbines, aerospace undercarriages, combustion engines, and hydraulic modules. New micro- and nanostructured coating materials and processes to machine these coatings are developed in order to increase the performance of workpieces and components, to enhance durability, and to reduce maintenance and manufacturing costs. At the Institute of Machining Technology (ISF), milling and grinding procedures have been developed for the preparation of the workpiece surface for the subsequent coating process. In contrast to conventional applications, the workpieces are not manufactured with the aim of achieving a minimized resulting surface roughness. Instead of this, a defined and adequate structure has to be generated, providing a good adhesion of the thermal sprayed coating on the workpiece surface. After first coating of the prepared substrates by a High-Velocity-Oxygen-Fuel (HVOF) coating process, the resulting surface topography does not have the required surface quality for a subsequent (Diamond Like Carbon) DLC coating process. In order to generate a more uniform surface structure, the deteriorated surface resulting from the HVOF coating process also has to be processed. Therefore, the application of an adapted grinding process with diamond wheels is used.

Friction Behavior of a Wet Clutch Subjected to Accelerated Degradation

This study aims at experimentally investigating the sliding friction characteristics of a wet clutch during its lifetime. More precisely, the objective is to understand how the Stribeck and the frictional lag (i.e, sliding hysteresis) parameters evolve as the clutch degradation progresses. For this purpose, a novel test procedure has been proposed and a set of experiments has been carried out on a fully assembled (commercial) clutch using a modified SAE#2 test setup. Furthermore, a systematic methodology for the Stribeck and the frictional lag parameters identification is developed. Regardless of the applied pressure, it appears that the first three identified Stribeck parameters tend to decrease with the progression of the degradation, while the last parameter tends to increase. In regard to the frictional lag parameter, the trend shows pressure dependency.

Squeeze Film Lubrication between Rough Poroelastic Rectangular Plates with Micropolar Fluid: A Special Reference to the Study of Synovial Joint Lubrication

The effects of surface roughness and poroelasticity on the micropolar squeeze film behavior between rectangular plates in general and that of synovial joints in particular are presented in this paper. The modified Reynolds equation, which incorporates the randomized surface roughness structure as well as elastic nature of articular cartilage with micropolar fluid as lubricant, is derived. The load-carrying capacity and time of approach as functions of film thickness during normal articulation of joints are obtained by using Christensen stochastic theory for rough surfaces with the assumption that the roughness asperity heights are to be small compared to the film thickness. It is observed that the effect of surface roughness has considerable effects on lubrication mechanism of synovial joints.

Finite-Element-Based Multiple Normal Loading-Unloading of an Elastic-Plastic Spherical Stick Contact

The repeated normal elastic plastic contact problem of a deformable sphere against a rigid flat under full stick contact condition is investigated with a commercial finite element software ANSYS. Emphasis is placed on the effect of strain hardening and hardening model with the maximum interference of load ranging from elastic to fully plastic, which has not yet been reported. Different values of tangent modulus coupled with isotropic and kinematic hardening models are considered to study their influence on contact parameters. Up to ten normal loading-unloading cycles are applied with a maximum interference of 200 times the interference required to initiate yielding. Results for the variation of mean contact pressure, contact load, residual interference, and contact area with the increasing number of loading unloading cycles at high hardening parameter as well as for low tangent modulus with two different hardening models are presented. Results are compared with available finite element simulations and in situ results reported in the literature. It is found that small variation of tangent modulus results in same shakedown behavior and similar interfacial parameters in repeated loading-unloading with both the hardening rules. However at high tangent modulus, the strain hardening and hardening rules have strong influence on contact parameters.

Effect of Addition of Fine SiC Particles on the Dry Sliding Wear Behaviour of Extruded 2014 Al-Alloy

Composites of 2014 alloy made by dispersing 10 vol.% of fine (20–50 µm) SiC particles using vortex method ensuring uniform distribution of SiC particles in the matrix have shown uniform distribution of SiC particles. Mechanical properties of the composites have also registered an improvement over the alloy. In an attempt to further improve the properties, the composites were subjected to hot extrusion of cylindrical rods along with the alloys under similar experimental conditions. A temperature range of 300–350°C and an extrusion ratio of 10 : 1 were maintained during the process. The extruded samples were compared for their mechanical properties, and improvement was noted. The mechanism of material failure from fractographic studies showed difference in behaviour between the alloy and composite. Dry sliding wear studies carried out on extruded specimens exhibited improved wear behaviour in composites over alloys as measured by volume loss and wear rate. Wear mechanism was studied from the worn surface and correlated with the wear performance. It was observed that the presence of SiC particles reduces the tendency of delamination and thus material removal from the wear surface.

Pressure Distributions Generated along a Self-Acting Fluid-Lubricated Herringbone-Grooved Journal Bearing with Trapezoidal Groove

Numerical studies are carried out to investigate pressure distributions of a fluid-lubricated herringbone-grooved journal bearing with trapezoidal grooves of various angles. Additionally, the optimal trapezoidal groove geometry is discussed in terms of the radial load capacity and friction torque.

High-Speed Ice Friction Experiments under Lab Conditions: On the Influence of Speed and Normal Force

Using a high-speed tribometer, coefficients of friction for bobsled runners were measured over a wide range of loads and speeds. Between 2.8 m/s and 28 m/s (equal to 10 km/h and 100 km/h), the measured coefficients of friction showed a linear decrease with increasing speed. The experiments revealed ultra-low friction coefficients of less than 0.01 after exceeding a sliding speed of about 20 m/s. At maximum speed of 28 m/s, the average coefficient of friction was 0.007. The experiments help to bridge the gap between numerous low-speed friction tests by other groups and tests performed with bobsleds on real tracks. It was shown that the friction data obtained by other groups and our measurements can be approximated by a single master curve. This curve exhibits the largest decrease in friction up to a sliding speed of about 3 m/s. The further increase in speed generates only a small decrease in friction. In addition, friction decreases with increasing load. The decrease stops when ice wear becomes effective. The load point of constant friction depends on the cross-sectional radius of the runner. The larger the radius is, the higher the load is, before the ice shows signs of fracture. It turned out that besides aerodynamic drag (not considered in this work), ice friction is one of the main speed-limiting factors. In terms of runner geometry, a flat contact of runner and ice ensures the lowest friction. The rocker radius of the runner is of greater importance for a low coefficient of friction than the cross-sectional radius.