Experimental Observation of Fractal-Regular Surfaces and a Transformation Scheme for Extracting Fractal Parameters

To account for the effects of asperity contacts at various length scales, it is appropriate to characterize an engineering surface as a fractal-regular surface. In spite of significant theoretical advancement, there is a desperate need for experimental verification of the theory of fractal-regular surfaces and a consistent scheme of obtaining the fractal parameters. In the present study, the existence of a fractal region and a regular-shape region in the power spectral density function for fractal-regular surfaces was confirmed experimentally, for the first time, with data obtained from magnetic hard disk and silicon wafer surfaces. A novel scheme involving a variable transformation was developed to extract fractal parameters. This scheme was validated by accurate recovery of fractal parameters from simulated surfaces. The fractal dimension, the fractal roughness parameter and the fractal domain length were found for magnetic hard disk and silicon wafer surfaces.

Determination of Steady-State Adhesive Wear Rate

Wear rates obtained from different investigators could vary significantly due to lack of a standard test method. A test methodology is therefore proposed in this paper to enable the steady-state wear rate to be determined more accurately, consistently, and efficiently. The wear test will be divided into four stages: (i) to conduct the transient wear test; (ii) to predict the steady-state wear coefficient with the required sliding distance based on the transient wear data by using Yang’s second wear coefficient equation; (iii) to conduct confirmation runs to obtain the measured steady-state wear coefficient value; and (iv) to convert the steady-state wear coefficient value into a steady-state wear rate. The proposed methodology is supported by wear data obtained previously on aluminium based matrix composite materials. It is capable of giving more accurate steady-state wear coefficient and wear rate values, as well as saving a lot of testing time and labour, by reducing the number of trial runs required to achieve the steady-state wear condition.

Tribological Applications of WS2 (MOS2) Inorganic Fullerene-Like Nanoparticles as Solid Lubrication

Fullerene-like WS2 (MoS2) nanoparticles (IF) have been studied in the past [1–3] Their efficacy as additives for lubrication fluids has been demonstrated. [4–5] Recently, IF-WS2 nanoparticles were confined inside a porous and densified bronze-graphite matrix, prepared by powder metallurgy (PM) technique. Substantial reduction in both friction and wear, and an increase in the critical load were observed [6]. New applications of IF nanopartcles as development of polymer nanocomposites, burnishing and friction of ceramic materials under severe contact conditions are presented in this work.

Analogy of the Full Curves of Fatigue Under Cyclic Loading and Friction

The analogy of the full fatigue curves under cyclic loading and friction was determined. It is shown that the equations for any of the regions (I, II, III, IV) of the curves of sliding and mechanical fatigue are similar, with the only difference in the numerical values of the parameters.

Soft EHL Lubrication of Complex Multiphase Fluids

The lubrication properties of a series of multiphase water-based fluids of complex rheology and microstructure, including o/w emulsions, have been studied in a rolling-sliding steel ball-on-elastomer flat contact. The results show that friction curves of Newtonian fluids made over a wide range of entrainment speeds and viscosity can be used to identify the prevailing mechanisms of lubrication for more complex fluids and, for emulsions, to show the predominant film-forming phase.

Tribological Behaviour of GFR Polymer Composites

On a Pin-on-Disc test rig with composite disc and steel pin tribological experiments were done on pultruded glass fiber reinforced polymer matrix composites plates. The wear and frictional behavior strongly depends on the structure. Also the normal load plays an important role in the frictional behavior, which is of greater importance than the speed. The formation of a thin polymer film onto the wear track results in a lowering of the coefficient of friction with 20%.

Synthesis of the Multifunctional Additive N-acyl Glutamic Acid and Application in Water-Based Lubricating Fluids

A series of N-acyl glutamic acid were prepared by reaction of glutamic acid with chlorides (1–3) or anhydrides (4–8) in good yield, within the solution of pH 8–10, keeping the reaction at 10∼15°C for 2–3 hours. The tribological behaviors of the resulting N-acyl glutamic acid salts with triethanolamine as additives in water were examined on a four-ball machine. The rust-inhibiting properties were evaluated. The elemental composition of the boundary lubricating film was analyzed by means of auger electron spectroscopy (AES). It was found that the N-acyl glutamic acid with long acyl chain functioned to considerably increase anti-wear and friction-reducing abilities of water. The rust-inhibiting properties got better with increase of the length of acyl-chain of N-acyl glutamic acid triethanolamine slats. And the additives had relative good antimicrobial properties in water.

Relating Surface Roughness to Subsurface Stress

Understanding and anticipating the effects of surface roughness on subsurface stress in the design phase can help ensure that performance and life requirements are satisfied. The specific approach taken in this work to address the goal of improved surface design is to relate surface characteristics of real, machined surfaces to subsurface stress fields for dry contact. This was done by digitizing machined surfaces, simulating point contact numerically, calculating the corresponding subsurface stress field, and then relating stress results back to the surface. The relationship between surface characteristics and subsurface stress is evaluated using several different approaches including analyses of trends identified through stress field visualization and extraction of statistical data. One such approach revealed a sharp transition between cases in which surface characteristics dominated the stress field and those in which bulk, or global contact effects dominated the stress. This transition point was found to be a function of the contact operating conditions, material properties, and most interestingly, the roughness of the surface.

Heat Transfer Properties of Engine Oils

The thermal properties of engine oil are important traits affecting the ability of the oil to transfer heat from the engine. The larger the thermal conductivity and specific heat, the more efficiently the oil will transfer heat. In this work, we measured the thermal conductivity and specific heat of a conventional mineral oil-based diesel engine lubricant and a Group V-based LHR diesel engine lubricant as a function of temperature. We also measured the specific heat of ethylene glycol. The measured values are compared with manufacturers’ data for typical heat transfer fluids. The Group V-based engine oil had a higher thermal conductivity and slightly lower specific heat than the mineral oil-based engine oil. Both engine oils had values comparable to high-temperature heat transfer fluids.

Sunflower Based Grease for Heavy Duty Applications

There is a great consumption of grease in an excavator (∼200 Kg/year). This big amount of lubricant is poured directly to the environment. A grease based in sunflower oil and polymer thickener has been developed. An extensive tribological characterization has been carried out in order to ensure a good compromise between EP and AW properties so that the grease could be used in two different applications: in the reduction gear (crown) and in the articulations (bushing/pin). The performance of the biogrease has been compared with two reference mineral lubricants.