• 대한기계학회논문집A
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• 제28권5호
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• pp.578-585
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• 2004

Hardness test is performed for determination of the other properties, such as strength, wear resistance and deformation resistance, as well as hardness itself. And it is performed for prediction of residual lifetime by analysis of hardness reduction or hardness ratio. However, hardness test has limitation that observation of residual indent is needed for determination of hardness value, and that is the reason for not to be widely used in industrial field. Therefore, in this study, we performed researches to obtain Brinell hardness value from quantitative numerical formula by analysing relationship between indentation depths from indentation load-depth curve and mechanical properties such as work hardening exponent, yield strength and elastic modulus.

• 한국산업융합학회 논문집
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• 제24권3호
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• pp.283-288
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• 2021

A tungsten material using a pressure sintering process and a titanium sintering additive was prepared to evaluate the microstructure, and mechanical properties of flexural strength and hardness. In addition, the reliability on each hardness data was evaluated by analyzing the distribution of the hardness of the tungsten material using the Weibull probability distribution. In particular, the optimal manufacturing conditions were analyzed by analyzing the correlation between the sintering temperature and the mechanical properties of the tungsten sintered body. Although the sintering density of the tungsten material was hardly changed up to 1700 ℃, but it was increased at 1800 ℃. The hardness of the tungsten sintered material increased as the sintering temperature increased, and in particular, the tungsten material sintered at 1800 ℃ showed a high hardness value of about 1790 Hv. It showed relatively excellent flexural strength at a sintering temperature of 1800 ℃.

• 소성∙가공
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• 제12권6호
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• pp.582-587
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• 2003

This paper is concerned with the mechanical property changes of the milli-size products manufactured by forward extrusion processes with square dies. Experiments are carried out with pure aluminum and pure copper billets. Extrusion ratio and knock-out pad are chosen as the important process parameters affecting the changes of mechanical properties such as shear strength and hardness. Shear strength tests with the extruded milli-size pin have shown the strong relation between victors hardness and shear strength in the neck of a stepped pin. As the extrusion ratio increases, the hardness on both the surface and the center line of a pin also increase. It is also noted that the hardness on the surface is a little higher than that on the center. The existence of knock-out pad in extrusion die causes the hardness in the neck of a extruded pin to increase. Finally, the approximated linear relations between shear strength and hardness of a pin are suggested.

• 한국생산제조학회지
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• 제23권1호
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• pp.48-55
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• 2014

Many techniques are available for destructive and nondestructive measurement of mechanical hardness. The ultrasonic method could be widely applicable as a nondestructive technique. Many studies have examined how changes in the mechanical hardness affect the longitudinal velocity of ultrasonic waves. This approach aims to estimate the overall velocity variations in specimens. However, proper nondestructive examination techniques are needed as effective tools for analyzing the effects of heat treatment on the surface of the specimens. Therefore, in this study, the effect on the hardness of piston rods was nondestructively measured using surface ultrasonic waves. The hardness after heat treatment was investigated at various depths in the specimens, and the velocity of the surface ultrasonic waves was measured with respect to the hardness of the piston rods. In addition, finite element method simulations were performed to confirm the behavior of the waves.

• Tribology and Lubricants
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• 제36권6호
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• pp.320-323
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• 2020

Thin film coatings are commonly exploited to minimize wear and optimize the frictional behavior of various precision mechanical systems. The enhancement of thin film durability is directly related to the performance maximization of the system. Therefore, a fine approach to analyze the thin film wear behavior is required. Archard's equation is a representative and well-developed law that defines the wear coefficient, which is the probability of creating wear particles. A ploughing model is a commonly used model to determine the friction force during the abrasive contact. The equations demonstrate that the friction force and wear coefficient are inversely proportional to the hardness of the material. In this study, Archard's equation and ploughing models are modified with an effective hardness to minimize the gap between the experimental and numerical results. It is noted that the effective hardness is the hardness variation with respect to the penetration depth owing to the substrate effect. The nanoindentation method is utilized to characterize the effective hardness of Cu film. The wear coefficient value considering the effective hardness is more than three times higher than that without considering the effective hardness. The friction force predicted with the effective hardness agreed better with the results obtained directly from the friction force detecting sensor. This outcome is expected to improve the accuracy of friction and wear amount predictions.

• Tribology and Lubricants
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• 제36권6호
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• pp.378-384
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• 2020

The friction surfaces of mechanical parts are heat-treated or coated with hard materials to minimize wear. Increasing the hardness is a very useful way to reduce abrasive wear. The general Brinell hardness test, which is widely used for metallic materials, is not suitable because it hardly shows any change in hardness when coated with thin films. In this study, we propose a basis for the application of the new Brinell hardness test method to the coated friction surface. An indentation analysis of the rigid sphere and elastic-perfectly plastic materials is performed using a commercial finite element analysis software. The results indicate that their loadto-diameter ratio is the same; the Brinell hardness test method can be applied even when the indenter diameter is on the micrometer scale. In the case of hard coating, it is difficult to calculate Brinell hardness using the diameter of the indentation, but the study revealed, for the first time, that it can be calculated using the depth of the indentation regardless of coating. The change in hardness owing to thin film coating over a wide load range implies that the hardness evaluation method is appropriate. Additional studies on various properties related to the substrate and coating material are required to apply the proposed method.

• Biomaterials and Biomechanics in Bioengineering
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• 제1권3호
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• pp.117-130
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• 2014

This paper presents a study on the influence of different thermo-mechanical processing (TMP) parameters on some required properties such as micro-hardness and Young's modulus of a novel near ${\beta}$ alloy Ti-20.6Nb-13.6Zr-0.5V (TNZV). The TMP scheme comprises of hot working above and below ${\beta}$ phase, solutionizing treatment above and below ${\beta}$ phase coupled with different cooling rates. Factorial design of experiment is used to systematically collect data for micro-hardness and Young's modulus. Validity of assumptions related to the collected data is checked through several diagnostic tests. The analysis of variance (ANOVA) is used to determine the significance of the main and interaction effects. Finally, optimization of the TMP process parameters is also done to achieve optimum values of the micro-hardness and Young's modulus.

• KSTLE International Journal
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• 제9권1_2호
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• pp.31-35
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• 2008

DLC (Diamond Like Carbon) films have predominant tribological properties like a high hardness, low friction and high chemical resistance; therefore, DLC films are applied in a wide range of industrial fields. This paper evaluated the characteristics of DLC films deposited on bearing steel with different hardness by RF-PECVD (Radio Frequency - Plasma Enhanced Chemical Vapor Deposition) method. Si-interlayer was deposited on bearing steel to improve adhesion strength by RF-Sputtering method. The DLC film structures were analyzed with Raman spectra and Gaussian function. Adhesion strength of DLC films was measured with a scratch tester. Friction and wear test were carried out with a ball-on -disc type to investigate the tribological characteristics. Experimental results showed that DLC films deposited on bearing steel under same deposition condition have typical structure DLC films regardless of hardness of bearing steel. Adhesion strength of DLC film is increased with a hardness of bearing steel. Friction coefficient of DLC film showed lower at the high hardness of bearing steel.

• Design & Manufacturing
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• 제13권1호
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• pp.13-18
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• 2019

The size and prospects of the domestic semiconductor equipment market are increasing every year. In the case of various parts used inside semiconductor equipments, high durability such as high strength and abrasion resistance is demanded. Particularly, the gases used in semiconductor production processes are toxic. In order to prevent such toxic gas leakage, a precision processing technique and a surface treatment technique for preventing corrosion are required. Electro-polishing is an electro-chemical method of polishing a metal surface to make it smooth and polished. Electro-polishing is mainly used in the finishing process of metal surface. Unlike mechanical polishing, electro-polishing is used in many fields, such as fine chemical etching equipment, since no damaged layer or burr, fine polishing groove and particles are generated. However, in order to withstand the gas used in the semiconductor equipment, the parts must have high corrosion resistance. However, the surface hardness generally become lowered through electro-polishing. Therefore, in this study, surface hardness were experimentally observed before and after electro-polishing. Then, a method of improving hardness by preparing a nitrided layer by plasma ion nitriding treatment.

• KSTLE International Journal
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• 제2권1호
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• pp.17-21
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• 2001

Surface treatment technologies are frequently used to improve mechanical properties of surface layers of machinery components in many practical situations. Surface hardness of piston in the oil hydraulic piston pumps is very important about wear resistance. To improve hardness, wear resistance of the oil hydraulic axial piston pump, it is needed to know the surface layer characteristics in the sliding contact parts. This paper reports an experimental study on surface treatment characteristics in the piston of the oil hydraulic axial piston pump. We investigated the surface wear of a piston between untreated and nitriding-treated surfaces. We obviously observed that the surface hardness of piston in the oil hydraulic axial piston pump plays an important role to have wear resistance and remain a longer life.