Jeng Haur Horng

An Elliptic Elastic-Plastic Asperity Microcontact Model for Rough Surfaces

An elastic-plastic microcontact model, that takes into account the directional nature of surface roughness, is proposed for elliptic contact spots between anisotropic rough surfaces. In addition, the plasticity index was modified to suit more general geometric contact shapes. This contact model, which expands the usefulness of the CEB model, is also utilized to determine the effect of effective radius ratio (γ) on microcontact behavior and to compare the results of this model and other models under different surface topographies. The results show that the elliptic contact model and circular contact model deviate considerably in regard to the separation (h), total real contact area (At ), plastic area (Ap ) and plasticity index (Ψ). The present model can be simplified to become other stochastic models.

True Friction Power Intensity and Scuffing in Sliding Contacts

Scuffing failure phenomenon in sliding lubricated contacts is studied experimentally in this work. Factors influencing the scuffing resistance of rough surfaces, including contact temperature, surface pitting, specific film thickness, and frictional heating, are investigated. A new criterion (the TFPI criterion) that takes into account the effect of oil in surface roughness valleys, microcontact characteristics, and the protective filin formation mechanism is proposed to predict onset of scuffing failure. Good agreement is found between experimental scuffing data and predicted failure criterion. The results show that the modified TFPI value can be considered as a performance parameter that represents the scuffing failure resistance capacity and the effectiveness of the running-in process. A low modified TFPI value has a high scuffing resistance in lubricated system.

Studies of tribological behavior and separation between surfaces at initial boundary lubrication

Abstract The tribological behavior and separation of steel surfaces during sliding at initial boundary lubrication were investigated over a wide range of roughness values. Tests were performed on a disk-on-block machine in an oil bath. The friction coefficient and electrical contact resistance of the interface during step load tests were monitored in situ. The experimental results show that wear increases suddenly at the transition from mixed to boundary lubrication. After this period in the wear process, an increase in the contact load does not induce an increase in the wear volume. The friction coefficient at initial boundary lubrications increases to reach a stable value as the roughness value of the block specimen increases. A rather wide range in friction coefficients at the initial boundary lubrication indicates that the surface roughness and sliding speed notably affect the variation of the transition friction coefficient from mixed to boundary lubrication. Using the microcontact model for rough surfaces as a base, a modified formula h /(2.0 σ 1.39 ) ⩽1.0 is developed to analyze the relationship between separation and composite r.m.s. roughness at initial boundary lubrication and to distinguish the onset of boundary lubrication.

Scuffing as evaluated from the viewpoint of surface roughness and friction energy

The surface scuffing occurring in line-contact lubrication is related to the rollers roughness pattern and asperity height. For surfaces with same contact asperity height, the magnitudes offriction power (P f = fW V s ) relevant to various roughness patterns are found to have the same sequence as the critical local temperatures. Instead of using the nominal contact area, the real contact area (A t ) is used to obtain the true friction power intensity (P t fi=P f /A t ). A new scuffing failure model (P tfi .σ -0.317 = C, where σ denote rms roughness) shows that the scuffing resistance of surfaces with transverse roughness pattern is higher than that of surfaces with longitudinal and oblique patterns. For certain roughness patterns, a high root mean square roughness height σ is always associated with the high P tfi value just before scuffing.

Three-Body Microcontact Model of Rough Surfaces and Its Application on Polishing of Wafer

In this study, a three-body microcontact model for rough surfaces is proposed in order to understand the effects of particles between surfaces on contact characteristics and its application on polishing of wafer. Both transitional surface-to-surface and particle-to-surface two-body microcontact simulations can be obtained according to the simplification of this model. In the three-body contact situation, the curves of contact area ratio versus dimensionless load are located in the range between two straight lines. The surface-to-surface two-body contact situation is the upper bound and the particle-to-surface two-body contact situation is the lower bound. As the value of D/σ increases, the contact situation will approach the pure particle-to- surface 2-body contact situation. The model also is used to study the wear mechanisms of the silicon wafer.

Contact analysis of rough surfaces under transition conditions in sliding line lubrication

Abstract This experiment investigated the transitional lubrication mechanism of fully submerged sliding line contacts under continuous operating conditions. Transition curves with three average roughness values were established. This experiment illustrates the effects of sliding speed, specific load, and roughness value on transition behavior by means of a microcontact model. Except for the inflection point on the first transition curve, the results show that ( A t ) lt >( A t ) t ≥( A t ) m ·( A p ) n >( A p )>( A p ) m and A p A t m >( A p A t ) t >( A p A t ) n . The deviation of the first transition and second transition points is most notable due to the low sliding speed and the low roughness value. However, in this experiment, the greater part of the total contact area exhibits plastic deformation at transition points whether the general plasticity index is low or high (0.79–3.79) as the average roughness value is from 0.2 μm to 1.1 μm. Three contact areas ( A t , A p , A e ) at three transition points decrease when the sliding speed or roughness value increases, while the general plasticity index (ψ) has the opposite tendency. The A p A t decrease with increases in the sliding speed or decreases in the roughness value. The values of the friction coefficient recordings under continuous operating conditions can be summarized as: f RI f RH f t > f RH , f t > f RI , and f RIII > f RII . The general plasticity index decreases gradually from boundary lubrication to scuffing failure ( ψ I > ψ II ) for all roughness values and sliding speeds. As a result, it can not be considered as a single indicator for the second transition.

Effect of surface roughness on steel roller scuffing

Abstract Experiments were carried out utilizing a gear-cam adapter to simulate line-contact lubrication and wear. Roller specimens with various asperity heights and roughness patterns were riding on roller plates and sliding over the two lands of the lower specimen. The scuffing loads for the rollers with various roughness conditions were measured while changing the applied load and spindles rotational speed. The effects of the roughness parameters on scuffing load, particularly roughness pattern and asperity height, were thus investigated. The displacement of the bottom specimens during the lubrication and wear process were measured to establish their correlation with scuffing behaviour. The variations of bottom specimen displacement can offer information regarding the film thickness formation on the rollers with various roughness patterns and asperity heights.

Thermal Analysis of a Ball-Screw System

High speed ball-screw system has serious friction heat to form thermal expansion to each component. An analyzing model considering with contact deformation and thermal expansion is established in realizing positioning error for a high speed ball-screw system. A finite element model of nut is also built in calculating elongation of nut. Surface strain of nut is measured by strain gages in order to confirm with data obtained from finite element model. Temperature of nut and screw were also measured by thermal couples and are used in calculation of elongation by the use of linear elongation equation. The tendency of positioning error is well estimated by the analyzing model. The model can be used in feedback positioning control factor and develop precision high speed ball-screw system.

The Analysis of Three-Body Contact Temperature under the Different Third Particle Size, Density, and Value of Friction

Recently, many studies have investigated the friction, wear, and temperature characteristics of the interface between two relative movements. Such analyses often set the coefficient of friction as a fixed value and are analyzed in cases of two-body contact; however, the interface is often a three-body contact and the coefficient of friction varies depending on the operating conditions. This is a significant error in the analysis of contact characteristics, therefore, in this study, the actual interface and the change of the coefficient of friction were analyzed based on three-body micro-contact theory where the contact temperature was also analyzed and the difference between the generally assumed values were compared. The results showed that under three-body contact, the coefficient of total friction increased with an increase in particle size; and at a different particle size and area density of particles, the surface contact temperature increased with the plasticity index and load increases, and the particle contact temperature increased with the increasing particle size. The surface temperature rise was mainly affected by the ratio of the average temperature between surface 1 and surface 2 to the multiplication between the 100th root of the area density of particles and the square root of the equivalent surface roughness (Ts1s2_ave*/ηa0.01σ0.5) and the ratio of the 10th root of the mean particle diameter to the 100th root of the equivalent surface roughness (xa0.1/σ0.001). Particle temperature was mainly affected by the ratio of the 10th root of the mean particle diameter to the 100th root of the equivalent surface roughness (xa0.1/σ0.001) and the area density of particles ηa. Our study indicated that when the contact of surface with surface and the contact of the particles with the surface, the resulting heat balance was assigned to the particles and the surface in a three-body contact situation. Under this contact behavior, it could avoid a too high a rise in micro-contact temperature to achieve the material failure temperature.

Design of a New Micro Single Flute Drill

A new micro single flute drill was presented in this study. For the convenience of developing a solid model, and doing a geometrical analysis, its geometry including the flute and flank surfaces is presented mathematically. According to the geometrical analysis, the normal clearance angles and normal rake angles along the cutting lip of the new micro dill are always invariant, and positive, respectively. Hence its cutting force in drilling is reduced. Furthermore, with only one main flute, the new micro drill gets stronger, and its cutting torque can be also decreased. Therefore it is expected that the tool life of the new micro drill is much longer than that of the conventional drill. Keyword: New micro drill, micro drill, single cutting edge