Phosphate coating is applied to the surface of the round bar material used in the multi-stage cold forging process for the purpose of lubrication. The film characteristics are determined according to the conditions of the phosphate film treatment process. In this study, the film properties according to the phosphate treatment conditions were defined as the coefficient of repeated friction and quantitative analysis was performed. Different friction behaviors were exhibited depending on the film properties, suggesting that optimization of the phosphate film treatment conditions is possible based on this. Finally, as a practical example, friction behavior according to the film characteristics was applied to the automotive engine bolt forming process. As a final conclusion, the need for linkage analysis with phosphating conditions for optimizing the forging process was raised. In addition, it can be seen that damage to the phosphate film should be considered in the process of predicting the limiting life of the die.

A wire rod, a material for multistage cold forging, is subjected to spheroidization and low annealing heat treatment to secure formability, and a phosphate coating treatment on the material surface to secure lubricity. The film layer produced by the phosphate treatment process is involved in adhesion to the material surface, adhesion to the forging die surface, and lubricity. This results in the increase or decrease of the forming load and the increase or decrease of the die life in the cold forging process. In particular, as the cold forging process progresses, the phosphate film is damaged and the original performance is deteriorated, so there is a high possibility of process defects. In case of excessive damage, the film is completely lost and die soldering occurs. Therefore, in this study, quantitative criteria for phosphate film damage are presented and the effect on the cold forging process is analyzed based on this to improve process analysis prediction accuracy. Therefore, in this study, quantitative criteria for phosphate film damage are presented, and based on this, the friction coefficient in the multi-stage cold forging process is to be derived.

This study attempts to find optimal conditions of the friction coefficient using a discrete element method (DEM) simulation with various friction coefficient conditions and three different grinding media with various ball sizes in a traditional ball mill (TBM). Using ball motion of the DEM simulation are obtained using the optimal friction coefficient compared with actual motion; photographs are taken by the digital camera and the snapshot images are analyzed. In the simulation, the rotation speed of the mill, the materials and velocity of the grinding media, and the friction coefficient between the balls and the wall of the pot are fixed as the actual experimental conditions. We observe the velocity according to the friction coefficient from the DEM simulation. The friction coefficient is found to increase with the velocity. Milling experiments using a traditional ball mill with the same experimental conditions as those of the DEM simulation are conducted to verify the simulated results. In addition, particle morphology change of copper powder is investigated and analyzed using scanning electron microscopy (SEM) for the milling experiment.

본 연구에서는 마찰력에 따른 TMD의 작동-정지조건과 각 조건에 따른 운동방정식을 정리하고, TMD의 마찰계수가 풍진동 제어성능에 미치는 영향을 수치해석을 통하여 확인하였다. 일반적인 하중과 달리 풍하중은 크기와 방향의 변화가 크기 때문에 TMD 는 마찰력에 의하여 작동-정지상태를 반복하게 되므로, TMD의 마찰계수를 주요 변수로 설정하였다. 또한 외부하중의 크기, 구조물의 진동수, TMD의 질량비도 매개변수로 설정하여 TMD의 제진성능에 대한 영향을 파악하고자 하였다. 자유진동, 조화강제진동, 풍진동에 대한 수치해석의 결과, 외부하중의 크기가 작고, 구조물의 진동수가 낮을수록 마찰계수에 의한 TMD의 제진성능의 손실이 커질 수 있음을 확인하였으며, 초고층 건물에 대한 TMD 설계시 마찰계수의 영향을 반드시 고려하여야 할 것으로 판단된다.

The friction pendulum system(FPS) is a kind of seismic isolation devices for isolating structures from an earthquake. To analyze the effect of friction materials used in the friction pendulum system, fragility analysis of LNG tank with seismic isolation system was conducted. In this study, titanium dioxide(TiO2) nanoparticles were incorporated into polyvinylidene fluoride(PVDF) matrix to produce friction materials attached to the FPS. The base moment of the concrete outer tank and the acceleration of the structure were evaluated from different mixing ratios of constituents for the friction materials. The seismic fragility curves were developed based on two types of limit state. It is confirmed that evaluation of combined fragility curves with several limit states can be applied to select the optimum friction material satisfying the required performance of the FPS for various infrastructure.

In order to improve seismic safety of nuclear power plant (NPP) structures in high seismicity area, seismic isolation system can be adapted. In this study, friction pendulum system (FPS) is used as the seismic isolation system. According to Coulomb‘s friction theory, friction coefficient is constant regardless of bearing pressure and sliding velocity. However, friction coefficient under actual situation can be changed according to bearing pressure, sliding velocity and temperature. Seismic responses of friction pendulum system with constant friction and various velocity-dependent friction are compared. The velocity-dependent friction coefficients of FPS are varied between lowand fast-velocity friction coefficients according to sliding velocity. From the results of seismic analysis of FPS with various cases of friction coefficient, it can be observed that the yield force of FPS becomes larger as the fast-velocity friction coefficient becomes larger. Also, the displacement response of FPS becomes smaller as the fast-velocity coefficient becomes larger.

In this study, the effect of interface friction coefficient about interfacial crack of bimaterials are discussed. The fracture parameters are analyzed by finite element method using ANSYS. With increasing the interface friction coefficient, normal crack opening displacements and normal stress distributions are analyzed. In this case with surface contact in interface crack, the energy release rates decreases with interface friction coefficient increasing. Increase in the friction coefficient of the crack surface are tend to suppressing for the initiation of interfacial crack. In this case with surface non-contact, the energy release rates are constant with interface friction coefficient increasing, and so the friction coefficient are not related with the fracture parameter.

The characteristics of abrasive wear on sliding speed of glass fiber reinforcement (GF/PUR) composites were investigated at ambient temperature by pin-on-disc friction test. The cumulative wear volume, friction coefficient and surface roughness of these materials on sliding speed were determined experimentally. The major failure mechanisms were lapping layers, deformation of resin, ploughing, delamination, and cracking by scanning electric microscopy (SEM) photograph of the tested surface. As increasing the sliding speed the GF/PUR composites indicated higher friction coefficient. The surface roughness of the GF/PUR composites was increased as the sliding speed was higher in wear test.

본 논문에서는 국내 공항 활주로에 적합한 마찰계수 측정 및 고무 퇴적물 제거에 대한 합리적 기준 개발을 위해 관련 해외 기준 및 연구결과에 관한 문헌을 조사하였다. 그리고 2007년 8월부터 2009년 7월까지ASFT(Airport Surface Friction Tester)장비를 이용하여 인천국제공항 활주로의 마찰계수를 측정하고 항공기 집중 착륙 지점에 대한 분석을 실시하였다. 타이어 고무의 퇴적 및 제거에 따른 마찰계수의 변화를 분석하였고 이에 미치는 계절적 영향을 포장 형식별로 조사하였다. 고무 퇴적물 제거 작업을 주기적으로 수행해도 활주로 표면의 마찰계수는 장기적으로 시간에 따라 점차 감소되는 것으로 확인되었다. 여름철 마찰계수의 변화가 다른 계절에 비해 컸으며 아스팔트 포장이 콘크리트 포장보다 계절적 영향에 민감했다. 매크로한 표면조직을 갖는 아스팔트 포장의 마찰계수가 마이크로한 표면조직을 갖는 재령 초기 콘크리트 포장의 마찰계수보다 큰 것으로 나타났다. 타이어 고무의 퇴적 및 제거에 따른 마찰계수의 변화도 아스팔트 포장에서 더 큰 것으로 확인되었다.

In this paper some physical evidences indicate that reduced friction occurs in an cryogenic machining process, in which LN2 is applied to the selected cutting zone. LN2 also reduced the tool wear rate to a great extent and elongated the tool life up to four times compared to emulsion cooling.

This paper presents some physical evidences indicating that reduced friction occurs in an cryogenic machining process, in which LN2 is applied selectively in well-controlled jets to the selected cutting zone. In machining tests, cryogenic machining reduced the force component in the feed direction, indicating that the chip slides on the tool rake face with lower friction. This study also found that the effectiveness of LN2 lubrication depends on the approach how LN2 is applied regarding cutting forces related.

강도활용을 극대화한 볼트의 소성역체결시 볼트의 항복은 볼트에 발생한 인장응력과 너트 나사산과의 접촉면에서 오는 마찰토오크에 의한 전단응력과의 조합에 의한 영향을 받는다. 볼트는 최소단면적인 나사부중 너트와 물리지 않은 여우나사부에서 먼저 항복을 일으킨다. 볼트재료는 대체로 항복과 더불어 소성경화를 보이며 그 정도는 고강도재료에서 인장강도의 10%정도이다. 본 연구에서는 소성역체결시의 거동해석을 변형도증분이론에 의거 해석하였다. 항복은 최소단명이 원통의 표면에서 시작되며 이를 두께가 얇은 원통으로 취급하였다. 항복의 전파는 이들 얇은 원통이 체결이 진행됨에 따라 순차적으로 항복에 이르는 것으로 보고 이 얇은 원통들을 항복시키는데 필요한 축력과 토오크를 합하여 체결종료시의 볼트축력과 (나사면마찰) 토오크로 하였다. M10미터 가는 나사를 계산과 실험에 사용하였다. 축력과 마찰토오크의 마찰계수에 대한 변화관계를 보여주는 그래프와 더불어 실험에서 사용한 볼트의 설계보조 선도를 제시하였다. 이 설계보조용 선도는 실험실에서 얻어진 토오크계수와 마찰계수와의 관계를 그린 것으로 윤활, 포면처리등 현장조건에 따라 달라진 마찰계수를 적절히 취급하는데 효과적으로 활용이 가능하다.

1. 미소한 단면적 변화율의 관재인발에서는 직접적인 방법에 의한 평균마찰계수(Mean friction coefficient)와 Sachs의 이론치가 매우 근사한 오차를 나타내므로 축방향 응력으로부터 마찰계수를 결정할 수 있다. 2. 비교적 높은 단면적 감소율의 인발에 있어서는 직접적인 방법에 의한 평균마찰계수가 Sachs등의 값 보다 더욱 실험치에 더욱 접근하므로 반경방향분력의 측정이 필요하다. 3. 봉재인발가공에 사용되는 평균마찰계수의 추정치도 관재인발의 경우에 확대 적용이 가능하다.

For a mobile robot that travels along a terrain consisting of various geology, information on tire force and friction coefficient between ground and wheel is an important factor. In order to estimate the lateral force between ground and wheel, a lot of information about the model and the surrounding environment of the vehicle is required in conventional method. Therefore, in this paper, we are going to estimate lateral force through simple model (Minimal Argument Lateral Slip Curve, MALSC) using only minimum data with high estimation accuracy and to improve estimation reliability of the friction coefficient by using the estimated lateral force data. Simulation is carried out to analyze the correlation between the longitudinal and transverse friction coefficients and slip angles to design the simplified lateral force estimation model by analysing simulation data and to apply it to the actual field environment. In order to verify the validity of the equation, estimation results are compared with the conventional method through simulation. Also, the results of the lateral force and friction coefficient estimation are compared from both the conventional method and the proposed model through the actual robot running experiments.

This paper presents a mathematical model derived from the upper-bound theorem of concrete plasticity to rationally evaluate the shear friction strength of concrete interfaces with a construction joint. The upper limit of the shear friction strength was formulated from the limit state of concrete crushing failure on the strut-and-tie action along the construction joints to avoid overestimating the shear transfer capacity of a transverse reinforcement with a high clamping force. The present model approach proposed that the cohesion and coefficient of friction of concrete can be set to be 0.27(fck)0.65 and 0.95, respectively, for rough construction joints and 0.11(fck)0.65 and 0.64, respectively, for smooth ones, where fck is the compressive strength of concrete. From the comparisons with 155 data compiled from the available literature, the proposed model gave lower values of standard deviation and coefficient of variation of the ratios between predictions and experiments than AASHTO and fib 2010 equations, indicating that the proposed model has consistent trends with test results, unlike the significant underestimation results of such code equations in evaluating the shear friction strength.