Yeau-Ren Jeng

Theoretical Analysis of Piston-Ring Lubrication Part I—Fully Flooded Lubrication

A one-dimensional analysis for lubrication between the piston ring and cylinder wall has been developed. A fully flooded inlet condition and axisymmetric geometry are considered. The piston ring is treated as a reciprocating, dynamically-loaded bearing with combined sliding and squeeze motion. A system of two nonlinear differential equations is used to model the lubrication including the Reynolds cavitation boundary condition. A numerical procedure is then developed to obtain the cyclic variations of film thickness, frictional force, power loss, and oil flow across the ring. Results are presented for a typical automotive engine. The effects of ring profile, ring tension, and engine speed are examined. It is shown that this analysis can be used to study the influence of ring design parameters in order to improve the design of the ring pack in reciprocating engines.

Theoretical Analysis of Piston-Ring Lubrication Part II—Starved Lubrication and Its Application to a Complete Ring Pack

Most studies of piston-ring lubrication assume fully flooded lubrication in the cylinder-bore and piston-ring conjunction. However, the lubricant supply is not always adequate for fully flooded lubrication. This study incorporates the effects of lubricant starvation into the one-dimensional piston-ring analysis developed earlier and applies it to a complete ring pack. A system of three nonlinear equations is derived to solve the starved lubrication problem. A postulate for lubricant transport in a complete ring pack is also proposed. A computer code is developed to apply the starved lubrication model to a complete ring pack. The findings reveal that lubricant starvation has an important effect on the minimum film thickness of a ring pack, especially at mid-stroke for compression rings. The role of oil-control rings and the evaluation of ring performance as a complete ring pack are also discussed.

A Material Removal Rate Model Considering Interfacial Micro-Contact Wear Behavior for Chemical Mechanical Polishing

Chemical Mechanical Polishing (CMP) is a highly effective technique for planarizing wafer surfaces. Consequently, considerable research has been conducted into its associated material removal mechanisms. The present study proposes a CMP material removal rate model based upon a micro-contact model which considers the effects of the abrasive particles located between the polishing interfaces, thereby the down force applied on the wafer is carried both by the deformation of the polishing pad asperities and by the penetration of the abrasive particles.. It is shown that the current theoretical results are in good agreement with the experimental data published previously. In addition to such operational parameters as the applied down force, the present study also considers consumable parameters rarely investigated by previous models based on the Preston equation, including wafer surface hardness, slurry particle size, and slurry concentration. This study also provides physical insights into the interfacial phenomena not discussed by previous models, which ignored the effects of abrasive particles between the polishing interfaces during force balancing.

An Elliptical Microcontact Model Considering Elastic, Elastoplastic, and Plastic Deformation

This study developed an elastic-plastic microcontact model that considers the elliptical contact of surface asperities. In the elastoplastic regime, the relations of the mean contact pressure and contact area of asperity to its contact interference are modeled considering the continuity and smoothness of variables across different modes of deformation. Results obtained from this model are compared with other existing models such as that calculated by the GW, CEB, Zhao and Horng models. The elliptic contact model and circular contact model can deviate considerably in regard to the separation and real area of contact.

A Microcontact Approach for Ultrasonic Wire Bonding in Microelectronics

Wire bonding is a popular joining technique in microelectronic interconnect. In this study, the effects of applied load, surface roughness, welding power and welding time on bonding strength were investigated using an ultrasonic bonding machine and a pull tester. In order to relate bonding strength to contact phenomena, the asperity model was used to compute real contact area and flash temperature between the wire and the pad. The experimental results show that a decrease in load or ultrasonic power produces a larger weldable range in which the combination of operation parameters allow the wire and pad to be welded. Regardless of roughness and applied loads, the bond strength increases to a maximum with increases in the welding time, and then decreases to fracture between wire and pad. The theoretical results and experimental observations indicate that bond strength curves can he divided into three periods. The contact temperature plays an important role in bonding strength in the initial period, and surface roughness is the dominant factor in the final period. The maximum bonding strength point occurs in the initial period for different loads and surface roughness values. Our results show that bond strength of ultrasonic wire bonding can be explained based on the input energy per real contact area.

Human enamel rod presents anisotropic nanotribological properties.

The AFM combined nanoindentation was performed to observe the ultrastructure of enamel rod from various section plans and positions while probing their mechanical and tribological properties of the area. The nanohardness and the elastic modulus of the head region of the enamel rods are significantly higher than that of the tail region and the axial-sectional plane. Both nanohardness and elastic modulus gradually decrease from enamel surface toward dentino-enamel junction. Such a variation correlates well with the decreasing trend of calcium composition from our element analysis. The friction coefficient and nanowear of the enamel showed an inversed trend to the hardness with respect to their relative topological position in the long axis of enamel rod toward DEJ. The relationship between the nanowear depth and the distance from the outer enamel surface to DEJ presented exponential function. The results presented clarify the basic nanomechanical and nanotribological properties of human enamel rods and provide a useful reference for the future development of dental restorative materials.

Changes of surface topography during running-in process

This study investigated the surface topographical changes during running-in. A theoretical model, which is composed of Johnson translatory system and a microscopic wear model, was used to describe the changes of surface roughness during running-in for general surfaces. Running-in tests were conducted for engine bores with different surface height distributions in order to understand surface topographical changes and validate the theory. Experimental results show that the theoretical model provides a good indication of changes of surface topography for surfaces with different types of initial height distributions.

In situ de-agglomeration and surface functionalization of detonation nanodiamond, with the polymer used as an additive in lubricant oil

This paper presents a novel approach for de-agglomeration and surface functionalization of detonation nanodiamond at the same time in one pot. Various kinds of polymer chains (e.g., polystyrene, polymethyl methacrylate and polyglycidyl methacrylate) can be chemically grafted onto the de-agglomerated nanodiamond by the wet-stirred-media-milling process. The surface grafted polymers were identified by FTIR, TGA and TEM. The polymer grafted onto surface of de-agglomerated nanodiamond was used as an additive in lubricant oil. We investigated the tribological properties of the two-phase lubricant oil and nanodiamond–polymer composite. The results show that this kind of nanodiamond–polymer composite possesses better anti-wear, friction-reduction and load-carrying capacity than the nanodiamond additive. Impressively, the addition of 3000 ppm nanodiamond–polymer composite to lubricating oil can reduce friction coefficient by 75% and wear rate by ∼99%. The polymer grafted onto the nanodiamond significantly improves durability and lubricant performance of the nanodiamond additive. This is because nanodiamond–polymer can be more compatible with lubricant oil than nanodiamond. The surface functionalization of nanodiamond can significantly affect lubricant performance and the durability of nanodiamond additive, which has not been discussed in previous papers.

Experimental Study of the Effects of Surface Roughness on Friction

Experimental verification of lubrication theories for surface roughness effects is lacking. We have conducted an experimental study using riblet tapes to generate repeatable surfaces on the test samples. A computer-assisted pin-on-disk tribometer was developed to measure the friction of the test samples. To study the effects of roughness height and lay orientation on friction, machined samples and. samples with different riblet tapes mounted longitudinally and transversely were tested. Our results show that lower roughness height yields lower friction, and that transverse roughness has lower friction than longitudinal roughness. The surface roughness effects become increasingly significant as the film thickness decreases. These findings substantiate earlier theoretical studies. A flow visualization system for the tribometer was also developed to observe flow characteristics of different surface roughnesses. Presented at the 35th STLE/ASME Tribology Conference In Fort Lauderdale, Florida October 16–19, 1989

Tribological Analysis of CMP with Partial Asperity Contact

Chemical mechanical polishing (CMP) is the most effective technology for global planarization in submicrometer device fabrication. Therefore, much research has been conducted to understand the basic mechanisms of the CMP process. In this study, a model that considers the microcontact mechanism and the grain flow is proposed. The down force acting on the wafer is supported by both the slurry pressure in the noncontact area and the surface asperity contact force in the contact area. The operation parameter effects on the force distribution, separation distance, and real contact area were investigated. The results show that larger down force and lower relative speed between the wafer and the polishing pad lead to increased contact ratio between the polishing interfaces. Larger slurry particle size can decrease the contact ratio.