• Tribology and Lubricants
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• 제35권6호
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• pp.396-402
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• 2019

Materials made from plastics are increasingly utilized in constructing greenhouses and setting up shield structures. Polyester fabrics have a wide range of use in horticulture and other fields of agriculture. They are utilized as a greenhouse cover and also help in combating intense climate variation in the field. Over time, these fabrics may experience friction against other surfaces. Owing to this, the surface framework of the material degenerates. This study examines the frictional characteristics of aluminized polyester fabric in both dry- and water-lubricated environments under changing applied loads and sliding speeds. Friction experiments are performed at room temperature by employing a pin on a disk. The experiments reveal that the friction coefficient decreases with increase in applied load in both dry sliding and water-lubricated environment. However, the friction coefficient decreases more under the water-lubricated setting than in the dry state. At the maximum applied load, the highest friction coefficient is discovered in the dry state with a range of 0.282 to 0.237, whereas a friction coefficient of 0.229 to 0.189 is observed in the water-lubricated state. Additionally, it is observed that the friction coefficient increases with an increase in sliding speed under both experimental environments. The examination of specimen surfaces reveals that the abrasion is minor in the water-lubricated setting compared with that in the dry state.

• Tribology and Lubricants
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• 제19권4호
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• pp.230-236
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• 2003

In applications such as MEMS and NEMS devices, the adhesion force and contact load may be of the same order of magnitude and the static friction coefficient can be very large. Such large coefficient may result in unacceptable and possibly catastrophic adhesion, stiction, friction and wear. To obtain the static friction coefficient of contacting real surfaces without the assumption of an empirical coefficient value, numerical simulations of the contact load, tangential force, and adhesion force are preformed. The surfaces in dry contact are statistically modeled by a collection of spherical asperities with Gaussian height distribution. The asperity micro-contact model utilized in calculation (the ZMC model), considers the transition from elastic deformation to fully plastic flow of the contacting asperity. The force approach of the modified DMT model using the Lennard-Jones attractive potential is applied to characterize the intermolecular forces. The effect of the surface topography on the static friction coefficient is investigated for cases rough, intermediate, smooth, and very smooth, respectively. Results of the static friction coefficient versus the external force are presented for a wide range of plasticity index and surface energy, respectively. Compared with those obtained by the GW and CEB models, the ZMC model is more complete in calculating the static friction coefficient of rough surfaces.

• Tribology and Lubricants
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• 제34권4호
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• pp.132-137
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• 2018

Ultrasonic waves are used in various applications in multiple devices, sensors, and high-power machinery, such as processing machines, welders, and cleaners, because the acoustic vibration frequencies are above the human audible frequency range. In ultrasonic machining, electrical energy at a high frequency of 20 kHz or more is converted into mechanical vibration by a vibrator and an amplifier. This technique allows instantaneous separation between a tool and a workpiece during machining, machining by pulse impulse force at the time of re-contact and minimizes the minute elastic deformations of the workpiece and machine tools due to the cutting effect. The Al7075 alloy used in this study is a typical aluminum alloy with superior strength that is mainly used in aircrafts, automobiles, and sporting goods. To investigate the optimal conditions for machining aluminum alloy using ultrasonic vibration, the present experiment utilized the Taguchi orthogonal array method, and the coefficient of friction was analyzed using the characteristics of the Taguchi technique. In ultrasonic friction and abrasion tests, the changes in the friction coefficient were measured in the absence of ultrasonic vibrations and at 28 kHz and 40 kHz. As a result, the most considerable influence on the friction coefficient was found to be the normal load, and the frequency of ultrasonic vibrations increases, the coefficient of friction increases. It was thus confirmed that the amount of wear increases when ultrasonic vibration is applied.

• 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.

• 한국자동차공학회논문집
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• 제16권3호
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• pp.52-59
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• 2008

Most accident reconstruction or analysis depend on the coefficient of friction to estimate the vehicle speeds. Skid mark and coefficient of friction are usually utilized to calculate the velocity and behavior of vehicles. For a critical case such as traffic accident reconstruction, however, the initial velocity of the car should be calculated precisely. In this paper, emergency brake tests on ABS and Non-ABS brake system are conducted on the dry pavement asphalt road on speed 40, 60, 80 and 100 km/h respectively. The SWIFT sensor was established in the front wheel and rear wheel at driver side to measure the forces, moments and speeds of revolution of the tires. These tests results can be available to brake tests and accident reconstruction.

• 융합정보논문지
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• 제8권6호
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• pp.59-66
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• 2018

보행 시 지면에 대한 수직력에 대한 전단력의 비율, 즉 보행자가 사용한 마찰계수(UCOF)는 미끄러짐 발생 가능성 있는 시점을 식별하는데 사용된다. 신발보행은 신발창 두께와 경도, 뒤꿈치 모양, 밑창 문양 등의 신발 디자인이 사용마찰계수를 변화시킬 것이다. 본 연구에서는 보행 시 신발 착용 유무에 따른 사용마찰계수(UCOF) 차이를 분석하기 위해 성인남녀 21명(여자 10명, 남자 11명, 나이: $25.2{\pm}2.3yrs$, 키: $165.6{\pm}7.2cm$, 몸무게: $62.2{\pm}7.8kg$)을 대상으로 보행속도, 지면반력, 사용마찰계수(UCOF) 최대 시점, CoP-CoM-수직선 각도의 차이를 알아보고, 사용마찰계수(UCOF)와의 상관관계를 분석하였다. 그 결과, 첫째, 보행 시 신발 착용으로 인해 체중수용기(제동기)의 더 이른 시점에 사용마찰계수가 최대치에 도달하고, 또 그 크기도 증가한다. 둘째, CoP-CoM의 Tangent 값과 사용마찰계수(UCOF1)와의 상관관계는 오른발 제동 초기시점(UCOF1_h)보다 추진 후기에 발생하는 왼발(다음발) 착지시점(UCOF2_h)에서 더 높은 상관관계를 보여, 제동기 보다는 추진기(다음 발 제동기)와의 연관성을 시사한다.

• 대한전자공학회논문지SP
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• 제47권4호
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• pp.28-34
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• 2010

본 논문에서는 마찰계수의 비접촉 추정을 위한 영상정보 활용방법을 제안한다. 마찰계수는 이동체의 도로주행 또는 장애물 극복에 있어 매우 중요한 요소이다. 이동체가 이동경로의 마찰계수를 미리 알 수 있다면 이동성향상을 기대할 수 있다. 본 논문의 마찰계수 추정방법은 영상정보를 활용하기 때문에 이동체가 지면과 접촉하기 전에 마찰계수를 추정 할 수 있다는 장점이 있다. 마찰계수의 비접촉 추정을 위한 영상정보 활용방법은 마찰계수측정실험과 물질그룹생성을 포함한 학습단계와 물질그룹 분류과정과 마찰계수 함수 활용을 포함한 마찰계수 추정단계로 구성되어 있으며 물질 조성비를 생성하는 영상처리는 두 단계에 모두 포함된다. 이 과정을 통해 얻은 마찰계수는 무인이동로봇이 이동경로 진입 전에 미끄러움을 판단하여 미끄럼지역을 회피 할 수 있도록 하며, 저속으로 이동이 가능한 경우 미끄럼이 발생하지 않는 적정속도를 계산하는데 확용 가능하다. 본 논문에서 사용한 지형의 마찰계수와 영상정보는 마찰계수 측정실험을 통해 취득하였다. 마찰계수 추정방법을 평가하기 위해 실험지형의 실제 마찰계수와 추정 마찰계수의 차이를 비교하였다.

• Tribology and Lubricants
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• 제24권2호
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• pp.96-103
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• 2008

PTFE is generally utilized as the form of composites with adding various fillers. The purpose of this paper lies on clarifying the friction and wear properties of the PTFE coating layer on steel. Especially, the effects of PTFE powder size for coating and surface roughness of the counter material on the properties are investigated. Sliding friction and wear tests are conducted at several sliding speeds by employing two types of PTFE coating layer using different powder sizes. One type of coating layer is composed of uniform fine powder, whereas the other type is made up of mixture powder of different sizes. As results, it is found that PTFE coating layer are effective to improve the wear resistance and to reduce the friction coefficient. It is clear that PTFE coating layers are abrasively removed by asperities of the counter material during sliding contact. However, PTFE coating layer with uniform fine powder shows somewhat better wear resistance than that with mixture powder of different sizes in low sliding speed region. It can be seen that the wear of the coating layer are drastically reduced because wear fragment from counter material are transferred to the coating layer. On the other hand, friction coefficient is shown not to be directly related with PTFE powder size in coating layer.

• 한국인터넷방송통신학회논문지
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• 제12권5호
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• pp.115-122
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• 2012

자동차 충돌해석은 다양한 형태로 구성되어 충돌중 차량에 대한 속도변화는 차량간의 충돌정도 또는 승객의 안전도를 평가하는 데 중요한 요소로 활용된다. 이로 인해 충돌해석 프로그램을 활용한 속도변화에 따른 결과치를 해석하는 방법이 필요하다. 본 연구에서는 PC-Crash 프로그램을 이용하여 노면의 마찰계수에 따라 차량속도에 따른 제동거리를 실제값과 해석값을 비교하여 마찰계수가 작을 때 오차가 큼을 알 수 있었고, 서로 다른 주 차량(MATIZ, SONATA 및 버스 적용)이 교차로에서 충돌하는 속도의 오차범위는 차량무게의 차이에 따라 최대오차는 1.2%, 1.8%, 3.1%으로 나타났다. 또한 인천대교 버스추락 사고를 재현하기 위하여 시뮬레이션을 한 결과로 다소 오차는 있었으나 사고 재구성을 검증할 수 있었다.

• 대한기계학회논문집A
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• 제28권9호
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• pp.1344-1351
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• 2004

This study develops a haptic display model which is an indispensable for the force generation in the virtual environment. In developing the haptic display model, a Proxy concept and a Karnopp friction model are utilized to generate the reaction force and the friction force. Also this study develops a 2 D.O.F. remote wiping system. This system is composed of a 2 D.O.F. master manipulator, a force sensor equipped 2 D.O.F. slave manipulator and a real time controller. With the developed remote wiping system, this study identifies the friction characteristic of the aluminum, acryl and rubber plate. The results are used as the dynamic friction coefficient of the haptic display model. This study shows the efficiency of the developed haptic display model by the comparison between the friction characteristic of the haptic display with the developed haptic display model and the friction characteristic of the real aluminum, acryl and rubber plate.