• 한국표면공학회지
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• 제30권3호
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• pp.191-201
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• 1997

Non-passivated electrolytic tinplates withour conventinal chemical treatment self-oxidize in ambient atmosphere to from yellow stain on the outermost surface during the long-term storage. The degree of yellowness of the stain increased linerly with the oxide thickness due to the interfeefence color of the $SnO_2$ Even though the thickness of the oxide layer was very thin, less than 100$\AA$ , it exerts an undesirable influence on the can-making processes, particularly the stripping behavior after ironing. Investigations were carried out on the morphologies of the coating layer, the changes in oxide thickness during successive can-making processes and the averge friction coefficients with the different oxide thinkness. These oxide layers were broken up and distributed within the bulk tin coating during the ironing process. This redistribution of the oxide layer prvented smooth pressing-aside of the tin coating layer, resulting in an increase in the ironing friction coefficient. As the friction was increased, the residual stress along the can wall thinkness(i.e., the hoop stress) was also increased. Due to both the oxibe layer accumulation, which increased the friction coefficient, and the hoop stress, can stripping efficiency without roll-back is reduced.

• 유공압시스템학회논문집
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• 제5권4호
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• pp.17-25
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• 2008

This study presents an analytical model of the pneumatic circuit of an air suspension system to analyze the characteristics of vehicle height control. The analytical model was developed through the co-simulation of Simulink(air spring) and HyPneu(pneumatic circuit). Variant effective area of air spring and flow coefficients of pneumatic valves were estimated experimentally prior to the system test, and utilized in simulation. One-comer test apparatus was established using the components of commercial air suspension products. The results of simulation and experiment were so close that the proposed analytical model in this study was validated. However the frictional loss of conduit and heat dissipation which were ignored in this study need to be considered in future study. As an application example of proposed analytical model, an alternative pneumatic circuit of air suspension to conventional WABCO circuit was evaluated. The comparison of simulation results of WABCO circuit and alternative circuit show that proposed analytical model of co-simulation in this study is useful for the study of pneumatic system of automotive air suspension.

• Steel and Composite Structures
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• 제11권1호
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• pp.39-58
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• 2011

The subject of the ongoing research work is to analyze the composite action of the structural elements of composite slabs with profiled steel decking by experimental and numerical studies. The mechanical and frictional interlocks result in a complex behaviour and failure under horizontal shear action. This is why the design characteristics can be determined only by standardized experiments. The aim of the current research is to develop a computational method which can predict the behaviour of embossed mechanical bond under shear actions, in order to derive the design characteristics of composite slabs with profiled steel decking. In the first phase of the research a novel experimental analysis is completed on an individual concrete encased embossment of steel strip under shear action. The experimental behaviour modes and failure mechanisms are determined. In parallel with the tests a finite element model is developed to follow the ultimate behaviour of this type of embossment, assuming that the phenomenon is governed by the failure of the steel part. The model is verified and applied to analyse the effect of embossment's parameters on the behaviour. In the extended investigation different friction coefficients, plate thicknesses, heights and the size effects are studied. On the basis of the results the tendencies of the ultimate behaviour and resistance by the studied embossment's characteristics are concluded.

• Tribology and Lubricants
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• 제34권6호
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• pp.300-306
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• 2018

In this study, the performance of foil thrust bearings was investigated by performing bearing take-off and load capacity tests, using an in-house designed and manufactured vertical bearing test rig. The mean take-off rotational speed and maximum load capacity of the bearing specimen were ~18,000 rpm and ~80 kPa, respectively. The vertical bearing test rig was observed to yield higher coefficients of friction and frictional torques than a horizontal bearing test rig under identical test conditions. This was a result of its structural characteristics, in that the bearing specimen is placed atop the thrust runner, which keeps it from being separated from the runner after the bearing take-off. In addition, bearing take-off was observed at a higher runner rotational speed as this structure keeps air from flowing between the top foil and runner surfaces, which requires a higher runner speed. The parallel alignment between the bearing specimen and runner surfaces can be maintained within a certain range more easily in a vertical test rig than in a horizontal test rig. Because of these advantages, Korean Industrial Standard, KS B 2060, recommends a vertical bearing test rig as the standard test device for foil thrust bearings.

• 한국정밀공학회지
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• 제12권9호
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• pp.148-155
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• 1995

The object of this study is to achieve a gteater understanding of meterial removal process and its mechanism. In this study, some applications of finite element techniques are applied to analyze the chip formation and cutting heat generation mechanism of metal cutting. To know the effect of cutting parameters, simulations employed some independent cutting variables change, such as constitutive deformation laws of workpiece and tool material, frictional coefficients and tool-chip contact interfaces, cutting speed, tool rake angles, depth of cut and this simulations also include large elastic-plastic defor- mation, adiabetic thermal analysis. Under a usual plane strain assumption, quasi-static, thermal-mechanical coupling analysis generate detailed informations about chip formation process and cutting heat generation mechanism Some cutting parameters are affected to cutting force, plastic deformation of chip, shear plane angle, chip thickness and tool-chip contact length and reaction force on tool, cutting temperature and thermal behavior. Several aspects of the metal cutting process predicted by the finite element analysis provide information about tool shape design and optimal cutting conditions.

• 대한기계학회논문집B
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• 제41권3호
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• pp.171-181
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• 2017

2상 횡 유동은 응축기, 증발기와 원자력의 증기 발생기와 같은 열교환기의 튜브와 셀 사이에 존재한다. 공기/물의 2상 유동에 놓인 관군에 작용하는 항력을 실험적으로 평가하였다. 2상 유동에 놓인 관군은 정사각형 배열이다. 피치 직경 비는 1.35이었고, 실린더의 직경은 18 mm이다. 관군에 유동방향으로 작용하는 항력을 측정하여 항력계수와 2상 유동 감쇠비를 계산하였다. 2상 유동 감쇠비는 균질 2상 유동의 이론식을 사용하여 구하여 실험의 결과와 비교하였다. 압력과 항력의 상관계수를 실험결과를 고려하여 평가하였다. 상관계수는 이론적으로 항력을 계산할 때에 사용된다. 질량유량을 증가할수록 측정된 항력으로부터 구한 항력계수와 감쇠비가 균질 유동의 이론적 결과와 잘 일치함을 보이고 있다. 결과적으로 충분히 큰 질량 유량의 기포 유동인 경우에는 감쇠비를 균질 유동에 근거한 이론식으로 계산할 수 있다.

• 한국산학기술학회논문지
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• 제14권8호
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• pp.3631-3637
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• 2013

갱웨이 벨로우즈는 관절형 고속철도차량 객차 끝단부 사이에 다양한 변위차를 고려하여 갱웨이 프레임에 장착된 이중 주름구조 네오프렌 고무부품이다. 실제 운행중의 벨로우즈의 파손은 터널 통과시 기밀 파손으로 인한 이명현상 발생과 함께 소음 증가로 승객의 승차감에 심각한 영향을 미친다. 본 연구에서는 고속철도차량 갱웨이 벨로우즈의 안전성 연구일환으로서, 차량주행시 차량 끝단부의 3축 회전변위(롤링, 요잉, 피칭변위차)를 고려한 갱웨이 벨로우즈의 비선형 해석을 수행하였다. 본 고무의 비선형 재료 특성은 단축인장 및 등2축 인장시험을 수행하여 구하였다. 또한, 비선형 해석결과로부터 회전변위 및 마찰계수의 영향을 평가하였다.

• 대한치과교정학회지
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• 제45권1호
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• pp.29-37
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• 2015

Objective: The coefficients of friction (COFs) of aesthetic ceramic and stainless steel brackets used in conjunction with stainless steel archwires were investigated using a modified linear tribometer and special computer software, and the effects of the bracket slot size (0.018 inches [in] or 0.022 in) and materials (ceramic or metal) on the COF were determined. Methods: Four types of ceramic (one with a stainless steel slot) and one conventional stainless steel bracket were tested with two types of archwire sizes: a $0.017{\times}0.025$-in wire in the 0.018-in slots and a $0.019{\times}0.025$-in wire in the 0.022-in slot brackets. For pairwise comparisons between the 0.018-in and 0.022-in slot sizes in the same bracket, an independent sample t-test was used. One-way and two-way analysis of variance (ANOVA) and Tukey's post-hoc test at the 95% confidence level (${\alpha}$ = 0.05) were also used for statistical analyses. Results: There were significant differences between the 0.022-in and 0.018-in slot sizes for the same brand of bracket. ANOVA also showed that both slot size and bracket slot material had significant effects on COF values (p < 0.001). The ceramic bracket with a 0.022-in stainless steel slot showed the lowest mean COF (${\mu}$ = 0.18), followed by the conventional stainless steel bracket with a 0.022-in slot (${\mu}$ = 0.21). The monocrystalline alumina ceramic bracket with a 0.018-in slot had the highest COF (${\mu}$ = 0.85). Conclusions: Brackets with stainless steel slots exhibit lower COFs than ceramic slot brackets. All brackets show lower COFs as the slot size increases.

• 대한조선학회논문집
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• 제57권3호
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• pp.133-139
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• 2020

In order to study the resistance test technique for the submerged body in Large Cavitation Tunnel (LCT), DARPA Suboff, submarine model publicly available was manufactured. DTRC released the resistance test data of DARPA Suboff conducted at ship speeds up to 18.0 knots in high-speed towing tank in 1990. As LCT is considered restricted waterways with walls, the resistance test results must be corrected with three wall blockage effects called buoyancy effect, solid blockage effect and wake blockage effect. Before correction, the resistance of LCT was 16~20 % higher than that of DTRC. After correction, the resistance and the resistance coefficients were compared with those of DTRC. The corrected resistance of LCT shows good agreement with that of DTRC. The residual resistance coefficient shows the difference according to the calculation method of buoyancy and frictional resistance coefficient. This paper suggests the best way for the calculation of residual resistance coefficient, On the basis of the present study, it is thought that the operating conditions for the propeller cavitation and noise tests can be drawn through LCT tests.

• International Journal of Air-Conditioning and Refrigeration
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• 제12권3호
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• pp.158-167
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• 2004

Condensation heat transfer experiments were conducted with a oblong shell and plate heat exchanger without oil in a refrigerant loop using R-134a. An experimental refrigerant loop has been developed to measure the condensation heat transfer coefficient $h_r$ and frictional pressure drop ${\Delta}p_f$ of R-134a in a vertical oblong shell and plate heat exchanger. Four vertical counter flow channels were formed in the oblong shell and plate heat exchanger by four plates having a corrugated sinusoid shape of a $45^{\circ}$ chevron angle. The effects of the refrigerant mass flux, average heat flux, refrigerant saturation temperature and vapor quality were explored in detail. Similar to the case of a plate heat exchanger, even at a very low Reynolds number, the flow in the oblong shell and plate heat exchanger remains turbulent. The results indicate that the condensation heat transfer coefficients and pressure drops increase with the vapor quality. A rise in the refrigerant mass flux causes an increase in the $h_r\;and\;{\Delta}p_f$. Also, a rise in the average heat flux causes an increase in the $h_r$. But the effect of the average heat flux does not show significant effect on the ${\Delta}p_f$. On the other hand, at a higher saturation temperature, both the $h_r\;and\;{\Delta}p_f$. found to be lower. Based on the present data, the empirical correlations are provided in terms of the Nusselt number and friction factor.