• Tribology and Lubricants
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• v.31 no.3
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• pp.125-140
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• 2015

In this paper, we present the results of the wear analysis of journal bearings on a stripped-down single-cylinder engine during start-up and coast-down by motoring. We calculate journal bearing wear by using a modified specific wear rate considering the fractional film defect coefficient and load-sharing ratio for the asperity portion of a mixed elastohydrodynamic lubrication (EHL) regime coupled with previously presented graphical data of experimental lifetime linear wear in radial journal bearings. Based on the calculated wear depth, we obtain a new oil film thickness for every crank angle. By examination of the oil film thickness, we determine whether the oil film thickness at the wear scar region is in a mixed lubrication regime by comparing dimensionless oil film thickness, h/σ, to 3.0 at every crank angle. We present the lift-off speed and the crank angles involved with the wear calculation for bearings #1 and #2. The dimensionless oil film thickness, h/σ, illustrates whether the lubrication region between the two surfaces is still within the bounds of the mixed lubrication regime after scarring of the surface by wear. In addition, we present in tables the asperity contact pressure, the real minimum film thickness at the wear scar region, the modified specific wear rate, and the wear angle, α, for bearings #1 & #2. To show the real shape of the oil film at wear scar region, we depict the actual oil film thickness in graphs. We also tabulated the ranges of bearing angles related with wear scar. We present the wear volume for bearings #1 and #2 after one turn-on and turn-off of the engine ignition switch for five kinds of equivalent surface roughness. We show that the accumulated wear volume after a single turn-on and turn-off of an ignition switch normally increases with increasing surface roughness, with a few exceptions.

• Journal of Korean Society for Quality Management
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• v.24 no.2
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• pp.44-53
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• 1996

This paper deals with the problem of selecting optimal wear limit and initial process mean in a wear-out process. Consider a material removal processing machinery where 1)there are deffective items by linear shift in the mean of the diameter of to be processed with varing process variance and 2)there can be any failure in the machine tools or to be processed. In the previous studies, the one is analyzed by 'Model of Producing Goods' in quality control area and the other, any failure, is analyzed by 'Model of Producing Services' in reliability area. We propose a new integrated maintenance model, considering the percent defective and the failure rate. A numerical example for the model is given.

• Journal of Mechanical Science and Technology
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• v.16 no.9
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• pp.1065-1071
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• 2002

The friction and wear behaviors of magnetron sputtered MoS$_2$ films were investigated through the use of a pin and disk type tester. The experiments were performed for two kinds of specimens (ground (Ra 0.5 $\mu\textrm{m}$) and polished (Ra 0.01 $\mu\textrm{m}$) substrates) under the following operating condifions : linear sliding velocities in the range of 22～66 mm/s (3 types), normal loads varying from 9.8～29.4 N(3 types) and atmospheric conditions of air, medium and high vacuum (3types). Silicon nitride pin was used as the lower specimen and magnetron sputtered MoS$_2$ on bearing steel disk was used as the upper specimen. The results showed that low friction property of the MoS$_2$ films could be identified in high vacuum and the specific wear rate in air was much higher than that in medium and high vacuum due to severe oxidation. It was found that the main wear mechanism in air was oxidation whereas in high vacuum accumulation of plastic flow and adhesion, were the main causes of wear.

• Tribology and Lubricants
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• v.31 no.3
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• pp.109-124
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• 2015

This paper presents a wear analysis procedure for the journal bearings on a stripped-down single-cylinder engine during start-up and coast-down by motoring. A journal bearing is in the mixed elastohydrodynamic (EHL) lubrication region when the shaft speed is less than the corresponding lift-off speed. Below the lift-off speed, a wear scar can form on bearing surfaces. In part 1 of this paper, we develop the appropriate formulations and the calculation procedure for the analysis. Specifically, we formulate an equation for modified film thickness in a journal bearing considering the additional wear volume. In order to obtain the modified specific wear rate induced by the modified Archard’s wear coefficient, we utilized the extended non-dimensional diagram for the specific wear rate, k, the fractional film defect coefficient, Ψ and the asperity load sharing factor, γ₂. This asperity load sharing factor is newly calculated by setting the Zhao-Maietta-Chang (ZMC) asperity contact pressure equation coupled with the central film thickness equation derived by using the ZMC asperity contact model equal to the modified central contact pressure derived by using the central (or maximum) contact pressure at the dry rough line-contact configuration. We can use the procedure introduced in this paper to determine the lifetime (or longterm) linear wear in radial journal bearings that is a result of repeated stop-start cycles.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.19 no.2
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• pp.61-68
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• 2023

The phenomenon of fretting wear due to the flow-induced vibration in steam generator (SG) tube is a significant degradation mechanism in nuclear power plants. Fretting wear in SG tube is primarily attributed to the friction and impact forces between the SG tube and the tube support structures, experienced during nuclear power plants operation. While the Archard model has generally been used for the prediction of fretting wear in SG tube, it is limited by its linear nature. In this study, we introduced an "Impact Shear Work-rate" (ISW) model, which takes into account the combined effects of impact and sliding. The ISW model was evaluated using existing experimental data on fretting wear in SG tube and was compared against the Archard model. The prediction results using the ISW model were more accurate than those using the Archard model, particularly for impact forces.

• Structural Engineering and Mechanics
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• v.84 no.1
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• pp.17-33
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• 2022

An experimental study is carried out to investigate the performance of the cutting tool regarding the insert wear, surface roughness, cutting forces, cutting power and material removal rate of three coated carbides GC2015 (TiCN-Al₂O₃-TiN), GC4215 (Al₂O₃-Ti(C,N)) and GC1015 (TiN) during the dry turning of AISI4140 steel. For this purpose, a Taguchi design (L₉) was adopted for the planning of the experiments, the effects of cutting parameters on the surface roughness (R_a), tangential cutting force (F_z), the cutting power (P_c) and the material removal rate (MRR) were studied using analysis of variance (ANOVA), the response surface methodology (RSM) was used for mathematical modeling, with which linear mathematical models were developed for forecasting of R_a, F_z, P_c and MRR as a function of cutting parameters (V_c, f, and a_p). Then, Multi-Objective Ant Lion Optimizer (MOALO) has been implemented for multi-objective optimization which allows manufacturers to enhance the production performances of the machined parts. Furthermore, in order to characterize and quantify the flank wear of the tested tools, some machining experiments were performed for 5 minutes of turning under a depth of 0.5 mm, a feed rate of 0.08 mm/rev, and a cutting speed of 350 m/min. The wear results led to a ratio (V_B-GC4215/V_B-GC2015) of 2.03 and (V_B-GC1015/V_B-GC2015) of 4.43, thus demonstrating the efficiency of the cutting insert GC2015. Moreover, SEM analysis shows the main wear mechanisms represented by abrasion, adhesion and chipping.

• Journal of the Korean Ceramic Society
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• v.33 no.5
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• pp.479-484
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• 1996

The tribological properties of ceramics are very important in the application to engineering ceramic parts such as mechanical seal slurry valve disc and so on. In this study the effect of graphite addition on the mechanical and tribological properties of RBSC/graphite composites were investigated. The composites were prepared by adding graphite powder to the mixture of SiC powder metallic siliconcarbon black and alumina. Bending strength water absorption friction coefficient the amount of worn out material at a certain time and maximum surface roughness(Rmax) of the prepared composites were measured and crystalline phases were examined with XRD. The composite containing 5 vol% graphite powder showed improved bending strength due to high green density and decreased friction coefficient and wear resistance. The friction coefficient and the wear resistance of the composite were increased by adding graphite powder up to 10 vol% They decreased however as increasing the amount of graphite powder more that 10vol% There was no linear relationship between the tribological properties and bending strength of the composites.

• Journal of Korean Society for Quality Management
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• v.26 no.4
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• pp.51-64
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• 1998

Mean shifts may be found in tool wear in machining, drawing, stamping and moulding operations, which make the process quality level deteriorate over time. In such situations, it is necessary to reset or readjust the manufacturing process at regular time basis or by inspection to prevent defective items produced. Although the deterioration rate may be assumed to be linear in a production cycle, there are many cases where the rate varies after resetting due to the variation of tool characteristics or by using the resharpened tools. In such cases, the deterioration rate should not be assumed to be a deterministic constant but a random variable. This paper is to find an optimal resetting period and quality level for such production processes.

• Journal of the Korean Ceramic Society
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• v.34 no.5
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• pp.519-527
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• 1997

The effect of Al content and heating rate on the sintering behavior, microstructure, and mechanical properties of reaction bonded alumina (RBAO) was investigated. As the heating rate became slower a critical Al content which could be added to RBAO increased. The weight gain and linear shrinkage of RBAO containing of 55 vol% Al were 28% and 6.5%, respectively. The relative density of RBAO decreased from 96 to 94%, as the amount of Al increased from 15 to 55 vol%. The hardness of RBAO increased from 17.8 to 19.9 GPa and the bending strength enhanced from 370 to 570 MPa, as the amount of Al increased from 15 to 55 vol%. On the other hand, the wear rate of RBAO degraded from 6.7 to 3.39$\times$10-5 $\textrm{mm}^2$/kg and the fracture toughness decreased from 4.1 to 3.6 MPa.m1/2, as the amount of Al increased from 15 to 55 vol%. Fracture modes were shown to the mixed mode of inter/transgranular. However, transgranular fracture was dominant with increasing the content of Al.

• Applied Science and Convergence Technology
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• v.26 no.2
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• pp.34-41
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• 2017

A 2.45 GHz microwave plasma with linear antenna has been prepared for hydrophobic and wear-resistible surface coating of carbon steel. Wear-resistible properties are required for the surface protection of cutting tools and achieved by depositing a hydrogenated amorphous carbon film on steel surface through linear microwave plasma source that has $TE_{10}-TEM$ waveguide. Compared to the existing RF plasma source driven by 13.56 MHz, linear microwave plasma source can easily generate high density plasma and provide faster deposition rate and wider process windows. In this study, $Ar/CH_4$ gas mixtures are used for hydrogenated amorphous carbon film deposition. When microwave power of 1000 W is applied, 40 cm long uniform $Ar/CH_4$ plasma could be obtained in gas pressure of 200~400 mTorr. The Vickers hardness measurement of hydrogenated amorphous carbon film on steel surface was evaluated. It was found the optimized deposition condition at $Ar:CH_4=25:25$ sccm, 300 mTorr with microwave power of 1000W and RF bias power of 100W. By deposition of hydrogenated amorphous carbon film, contact angle on steel surfaces increases from $43.9^{\circ}$ to $93.2^{\circ}$.