Qian Zou

An Improved Hydrodynamic Model for Open Wet Transmission Clutches

A mathematical model describing the hydrodynamics of the flow within a disengaged wet transmission clutch is presented. The primary improvement of this model over the existing ones is the inclusion of the surface tension effect, which is expressed in the pressure equation as an additional term. The drag torque predicted by the model correlates well with the test data for nongrooved clutch packs. The significance of the surface tension in this type of flows is discussed as well.

A study of flank wear in orthogonal cutting with internal cooling

Internal cooling is being paid more and more attention as a means to overcome the limitations of cutting fluids. The purpose of this paper is to investigate the effects of internal cooling on the flank wear of cutting tools in orthogonal cutting. A flank wear model for a cutting tool in orthogonal cutting is presented which is based on previous wear models and includes the normal stress and the effect of thermal softening. The effects of internal heat sink intensity and heat sink area on the flank wear of the cutting tool in orthogonal cutting are demonstrated.

An Experimental Study of Bearing and Thread Friction in Fasteners

An experimental procedure is proposed for studying the underhead and thread friction in fasteners. The effective bearing friction radius, the underhead friction coefficient, and the thread friction coefficient are experimentally determined for fasteners with standard hexagonal heads and for flanged head fasteners. Hence, greater accuracy has been achieved in determining the value of the torque components that are consumed in overcoming friction in threaded fasteners. This would lead to a more reliable torque-tension correlation and would enhance the safety and quality of bolted assemblies. A design of experiment procedure is presented in order to investigate the effect of fastener material class, the thread pitch, and the fastener size on thread friction coefficient. For the underhead bearing friction, an experimental model is presented in order to determine the effect of the radii ratio of the contact area on the bearing friction radius.

Friction and Wear Characteristics of Water-Based ZnO and Al2O3 Nanofluids

In recent years, nanofluids have been an active area of research due to their enhanced thermal conductivity over base fluids. However, the tribological properties of nanofluids have not been thoroughly studied. In this research, friction and wear characteristics of water-based nanofluids was carried out. Commercially available water-based nanofluids with 50% ZnO and 50% Al2O3 nanoparticle concentration were used as the lubricant. The 50% concentration nanofluids were diluted using deionized water and an ultrasonic bath into different volume concentrations. The effects of nanoparticle type, particle concentration, and surface roughness of the specimen on the friction and wear characteristics were investigated. The friction and wear tests were performed using a UMT-2 Micro-Tribometer with a ball-on-disk configuration. The surface roughness and wear volume were measured using a WYKO 3D optical surface profiler, and chemical characterization analysis was done using a PHI 5000 VersaProbe X-ray photoelectron spectroscope (XPS). It was found that nanoparticles have a great effect on the friction and wear characteristics of lubricants.

Friction and Wear Characteristics of Oil-Based ZnO Nanofluids

Nanofluids have been an active area of research for almost two decades due to their enhanced thermal conductivity compared to base fluids, but the study of nanofluids for tribological purposes has been slow, with problems encountered in dispersing and stabilizing nanoparticles in lubricants. In this research, the tribological properties of nanofluids were studied through experimental investigation by dispersing ZnO nanoparticles into paraffinic mineral oil. Nanoparticles were dispersed using an ultrasonic homogenizer. Oleic acid was used as the surfactant for the improved dispersibility and stability of nanofluids. A universal microtribometer with a ball-on-disk configuration was used to evaluate the friction properties between the moving mechanical components in the presence of nanofluids. The wear track was measured using a surface profiler, and the material deposition onto the sliding interface was analyzed using X-ray photoelectron spectroscopy. The effects of the surfactant, ultrasonication time, particle concentration, applied load, sliding velocity, and surface roughness on the friction and wear performance of nanofluids were investigated. The results showed that oil-based nanofluids with ZnO nanoparticles reduced friction and wear under certain conditions, and the application of oleic acid as a dispersant contributed to reducing friction to some extent and also improved the dispersibility and stability of the nanofluids.

Tribological Properties of Paraffinic Oil with Nanodiamond Particles

Friction accounts for a large amount of energy lost in mechanical systems and applications. Nanofluids, with particles less than 100 nm, added to a base fluid have been proven to be effective in reducing friction and wear. Diamond has superior mechanical, thermal, optical, electrical, and chemical properties. Therefore, nanodiamond holds a lot of promise for use in nanofluids. The tribological properties of oil-based nanofluids with spherical nanodiamond particles with the size of 3–10 nm in diameter were investigated using a ball-on-disk friction test by varying nanodiamond concentration, sliding velocity, normal load, and disk roughness. The friction testing was performed using a UMT-2 Micro Tribometer. Wear analysis was performed and chemical composition of the disk surface was examined using a WYKO 3D surface profiler and X-ray photoelectron spectroscopy. In general, the addition of nanodiamonds to oil leads to a reduction in the coefficient of friction but an increase in wear of the disk.

Abrasive wear model for lubricated sliding contacts

A lubricated wear model for stochastic rough surface in sliding contacts is presented. In this model, the visco-elastic characteristic of the solid, the effects of surface roughness profiles, hardness of materials and operating conditions are included. The reasonableness of the model is proved by comparing calculated values with the test results on a ring-on-block test machine. They coincide well. From the model, the relationship between wear rate and film thickness ratio can be deduced. It provides a theoretic basis for wear prediction and prevention.

Evaluation of the convective heat transfer coefficient for minimum quantity lubrication (MQL)

Purpose – The purpose of this paper is to evaluate the cooling ability of minimum quantity lubrication (MQL) cutting fluid.Design/methodology/approach – An experimental system is devised to find the heat transfer coefficient of MQL under simulated reaming conditions. Cooling rate of the specimen is measured with an infrared camera. The effect of air pressure and oil volume on cooling rate is tested. Metal cutting tests are performed to evaluate the effect of heat transfer coefficient on workpiece temperature.Findings – Convective heat transfer coefficient for MQL increases with increasing air pressure. Oil volume has an indeterminate effect on the heat transfer coefficient; however, it is a dominant factor for controlling temperature during reaming.Practical implications – The results of the study can provide guidance to optimize the temperature controlling ability of MQL for production.Originality/value – There is limited information available in literature regarding the heat transfer coefficient of meta...

Friction and Wear of Low-Phosphorus Engine Oils with Additional Molybdenum and Boron Compounds, Measured on a Reciprocating Lubricant Tester

Previous research has already extensively characterized the effects of a variety of engine oils on engine performance. However, low-phosphorus engine oils, which are of growing importance due to the reduction of automotive emissions, have not been studied much. This paper sets forth the results of an initial investigation involving the effects of low-phosphorus engine oils on the friction and wear characteristics of typical engine cylinder kit components from a 3.8-liter, four-cylinder engine. For these tests, sections of molybdenum-coated piston rings were oscillated against segments of production cast iron cylinder bores. The oils were evaluated under two sets of conditions; i.e., the frequency of 20 Hz and a load of 60 N and a frequency of 40 Hz and a load of 120 N. The friction coefficients were continuously recorded, and the wear depths on the cylinder bore segments were measured at the conclusion of each experiment. The oils consisted of low-phosphorus prototype oil (LPPO) containing 0.05 wt% phosphorus, which is half the amount of ZDDP in GF–3 oils, and the LPPO treated with six different supplemental antiwear, anti-friction additives. The remaining additives in the LPPO were present in the amount required for full GF–3 formulation. The supplemental additives were selected to lower friction and replace and/or enhance antioxidant and antiwear properties lost due to lower zinc dithiophosphate (ZDDP) content. The results of low phosphorus concentration oils were compared to the results obtained with formulated ILSAC GF-3 engine oil. The oils that contained organomolybdenum ester showed the greatest benefit in friction reduction in the two different operating conditions. SEM/EDS/XPS surface analyses on the surfaces run with oils containing organomolybdenum ester showed evidence of molybdenum compound formation on the cylinder bore surface. In addition, antiwear film formation mechanisms due to surface interaction among the ZnDTP, organomolybdenum compounds, and metal oxides are discussed.

Contact Mechanics Approach to Determine Effective Radius in Bolted Joints

The effective radius is a very important factor in determining frictional torque under the bolt head and nut in bolted joints. Since the effective radius is hard to be precisely determined in practice, the mean radius, which is the mean value of the inner and outer radii of the contact area under the bolt head and nut, is used. In this paper, contact mechanics analysis is used to determine the real contact pressure distribution between the bolt head and nut and the joint surface. Based on the pressure distribution, the effective radius can be precisely calculated. The effect of the surface roughness, underhead load distribution, underhead load value, and the ratio of the maximum to minimum contact radii are investigated. The results are compared with the result from theoretical formulas and the value of mean radius. These data will be very useful in enhancing the reliability and safety of bolted joints.