• KSTLE International Journal
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• 제3권1호
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• pp.38-42
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• 2002

Diamond-like Carbon(DLC) films were deposited on Si wafers by an RF-plasma-assisted CVD using CH$_4$gas. Tribological tests were conducted with the use of a rotating type ball on a disk friction tester with dry air. This study made use of four kinds of mating balls that were made with stainless steel but subjected to different annealing conditions in order to achieve different levels of hardness. In all load conditions, testing results demonstrated that the harder the mating materials, the lower the friction coefficient was. The friction coefficients were fecund to be lower with austenite mating balls than with fully annealed martensite balls. Conversely, the high friction coefficient found in soft martensite balls appeared to be caused by the larger contact area between the DLC film and the ball. The wear tracks on DLC films and mating balls could prove that effect. Measuring the wear track of both DLC films and mating balls revealed a similar tendency compared to the results of friction coefficients. The wear rate of austenite balls was also less than that of fully annealed martensite balls. Friction eoefficients decrease when applied leads exceed critical amount. The wear track on mating balls showed that a certain amount of material transfer occurs from the DLC film to the mating ball during a high friction process. Raman Spectra analysis Showed that the transferred materials were a kind of graphite and that the contact surface of the DLC film seemed to undergo a phase transition from carbon to graphite during the high friction process.

• 대한치과기공학회지
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• 제21권1호
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• pp.67-75
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• 1999

The purpose of this study is to evaluate the friction coefficients between abutment materials and clasp materials, and to an estimation formula for retention force. The coefficients of friction between three clasp materials and four abutment materials were measured under various conditions, polished and sandblasted and wet and dry. The measurement was repeated for each combination up to a total measurement of 1200 times. Estimation formula for retention force is measured as sum of two terms, which the one time is proportional to the product of friction coefficient ${\mu}$ and undercut u and the other term is proportional to u-squared. Two proportional coefficient were obtained by least square method. The results are as follows: 1. Friction coefficients were ranged from 0.08 to 0.53 under various conditions. 2. Friction coefficients of non-metal abutment materials are greater in wet conditions than dry conditions. 3. Friction coefficients of sandblasted clasp against abutment are greater than that of polished clasp. 4. Clasp retention force can be estimated with the model as F=$F_d(3.0{\mu}u+1.5u^2/h)$ with minor error.

• Journal of Welding and Joining
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• 제15권2호
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• pp.43-53
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• 1997

The complete joining method for dissimilar press punch materials and its real-time evaluation method is not available at present. Brazing method has been used for joining them, but it is known that the welded joint by the brazing has the lower bonding efficiency and reliability than the diffusion welding. The friction welding with a diffusion mechanism in bonding was applied in this study. This work was carried out to determine the proper friction welding conditions and to analyze mechanical properties of friction welded joints of sintered carbide tool materials (SKNM50 for the blade part of press punch) to alloy steel (SCM440 for the shank part of press punch) using aluminum (A6061 for the interlayer material) as an insert material between the sintered carbide tool materials and the alloy steel. In addition, acoustic emission test was carried out during friction welding to evaluate the weld quality.

• 소성∙가공
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• 제15권6호
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• pp.428-435
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• 2006

IC leadframe needs precision shape for good efficiency. Friction conditions also have a significant impact on blanking deformation. Therefore, studying the friction produced by the tribology between die and materials becomes necessary. In this study, in order to measure mechanical properties and frictions for leadframe materials such as Ni alloys and coppers, tensile test and straight pulling friction test are executed. In particular, the effect of clearance on the blanking characteristics depending on friction coefficient is examined by finite element simulation. From the finite element simulation, the metal flow, side pressure of punch and crack initiation are evaluated according to the leadframe materials.

• 한국자동차공학회논문집
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• 제15권4호
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• pp.171-177
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• 2007

In this paper, an evaluation method of fracture toughness on interface cracks was investigated in friction welded dissimilar materials with interfacial edge cracks. To establish a reasonable strength evaluation method and fracture criterion, it is necessary to analyze stress intensity factor under the load and residual stress condition on friction welded interface between dissimilar materials. The friction welded specimens with an edged crack were prepared for analysis of stress intensity by using the boundary element method (BEM) and the fracture toughness. A quantitative fracture criterion for friction welded STS 304/SM 45C with interface crack is suggested by using stress intensity factor, F and the results of fracture toughness experiment.

• 한국세라믹학회지
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• 제34권8호
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• pp.797-802
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• 1997

The use of carbon materials in mechanical components such as bearings, seals, and bushings that do not require lubricants is increasing rapidly. This paper reports on establishing the optimal condition for resin-bonded carbon materials. We fixed the content ratio of materials, which include graphite powder and diatomite as a lubricant modifier and a friction modifier, respectably, with resin used as a bonding material. We then produced bushings using hot-pressing within the temperature range of resin curing. The properties of bushing, the friction coefficient, wear rate and the mechanical strengths are discussed in relation to the content of respective materials, with correlation of friction coefficient and sliding distance. Finally, we examined the friction coefficient changes according to the applied load on bushing and the friction coefficient changes according to contact speed of bushing.

• 한국기계가공학회지
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• 제3권3호
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• pp.5-10
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• 2004

The effect of bronze sintered friction materials on frictional and mechanical properties is studied with the content(8~18 wt,%) and shapes (flake and irregular) of graphite that is used as solid lubricants to meet diverse characteristics such as low coefficient of friction, low wear rate and high bending strength. The content and shapes of graphite are optimized by statistical experiments. Friction test was carried out measure friction coefficient, temperature dependence and wear rate. As a result of experiments, the density, hardness and bending strength with a shape of flake graphite are lower and decrease rapidly than that of Irregular, as the content of graphite increases up to 18 wt% Aftei friction test, coefficient of friction is 0.3~0 4 and wear rate is $0.32{\sim}2.98{\times}10^{-7}cm^3/kg{\cdot}m$. When the content of graphite increases, coefficient of friction increases In a shape of flake graphite and decreases in a shape of irregular graphite.

• Tribology and Lubricants
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• 제18권3호
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• pp.204-210
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• 2002

Automotive brake pads with four different sizes of zircon particles (average sizes of 1㎛, 6㎛, 75㎛, and 140㎛, respectively) were investigated to evaluate the size effect of abrasive particles on friction performance. Results showed that the brake pads with the larger size of zircon particles tend to show better frictional stability and low pad wear. However, the rotor surface was severely abraded in the case of using larger zircon particles. On the other hand, the small zircon particles in the pads showed the fast increase of the coefficient of friction with friction force oscillation and the tendency was pronounced at low sliding speeds. The brake pads with small particle sizes also exhibited strong fade phenomena at elevated temperatures.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 proceedings of the second asia international conference on tribology
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• pp.233-234
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• 2002

Diamond composites hold promise as a tribological material because of low friction and high wear resistance. We studied friction and wear of polyimide-20vol% PTFE-diamond composites in open air at room temperature, focusing on the effects of diamond size, and diamond content, sliding conditions, and mating material. Friction coefficient and wear tend to Increase with increasing diamond size and content. Composites of appropriate diamond size and content showed a friction coefficient below 0.1 and specific wear of $10^{-7}\;mm^3/Nm$. Friction and wear of composites sliding against stainless steel were higher than those of Al_2O_3$ an increase that became increasingly not able with increasing diamond size.

• 소성∙가공
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• 제3권1호
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• pp.51-62
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• 1994

Cup drawing test and U-bending test were performed to evaluate the friction characteristics of sheet materials for the different deformation modes involved in stamping process. The coefficient of friction calculated from the each test was compared to that obtained from the draw bead friction test. It was clarified that the cup drawing test could be simply used for evaluating the friction characteristic of sheet material in deep drawing process with high contacting pressure. However the U-bending test is suitable to evaluate the frictional characteristic of sheet material in bending process with low contacting pressure.