• 한국농업기계학회:학술대회논문집
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• 한국농업기계학회 1993년도 Proceedings of International Conference for Agricultural Machinery and Process Engineering
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• pp.1196-1201
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• 1993

Test of Caterpillar Challenger 65 tractor which has rubber tracks, and articulated four wheel drive tractor with dual wheels and a mechanical front wheel drive tractor were conducted on an unplowed and plouwed wheat stubble field. The following parameters were analyzed : tractive efficiency (ηv), net tractive coefficient ($\phi$n), slip ($\sigma$) , drawbar pull(Fv), drawbar power (Pv) and forward velocity(v). The maximum net tractive coefficient was established at the tractive efficiency of 0.60 on the unplowed wheat stubble field : for the Challenger 65 tractor 0.855 ; 4WD 0.624 and MFWD 0.534 and on the plowed wheat stubble field with the tractive efficiency of 0.40 for the Challenger 65 tractor 0.82 : 4WD 0.57 and for tractor MFWD 0.48.

• 한국자동차공학회논문집
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• 제5권2호
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• pp.1-12
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• 1997

A computer program was developed to simulate effect of the initial track tension on the tractive performance of tracked vehicles. The performance was evaluated in terms of drawbar pull, motion resistance, tractive coefficient and tractive efficiency. Results of the simulation showed that increase in track tension decreases the sinkage and mean maximum pressure in clay, making the ground pressure distribution more uniform. This tendency became more evident when the number of roadwheels increased. However, such change in MMPs was negligible in firm soils. Motion resistance was also decreased with increase in track tension and the number of roadwheels. Under weak soil conditions, tractive coefficient and efficiency increased generally as the track tension increased for a slip range of 10∼30%. For slippage less than 3∼4%, however, the tractive coefficient decreased with increase in track tension. In general, it was known that increasing track tension improves tractive performance in weak soil conditions. However, high track tension can reduce efficiency due to the increment of internal motion resistance caused by increased track tension.

• Journal of Mechanical Science and Technology
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• 제20권9호
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• pp.1399-1409
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• 2006

An improved friction model was proposed with consideration of the effect of the sliding speed, the contact pressure and the temperature, and it was implemented into a user subroutine of a commercial FEM code, ABAQUS/Explicit. Then, a smooth tire was simulated for free rolling, driving, braking and cornering situations using the improved friction model and the Coulomb friction model, and the effect of the friction models on the slip, the frictional energy distribution and the cornering force and moment was analyzed. For the free rolling, the driving and the braking situations, the improved friction model and the Coulomb friction model resulted in similar profiles of the slip and the frictional energy distributions although the magnitudes were different. The slips obtained from the simulations were in a good correlation with experimental data. For the cornering situation, the Coulomb friction model with the coefficient of friction of 1 or 2 resulted in lower or higher cornering forces and moments than experimental data. In addition, in contrast to experimental data it did not result in a maximum cornering force and a decrease of the cornering moment for the increase of the speed. However, the improved friction model resulted in similar cornering forces and moments to experimental data, and it resulted in a maximum cornering force and a decrease of the cornering moment for the increase of the speed, showing a good correlation with experimental data.

• Tribology and Lubricants
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• 제23권6호
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• pp.278-282
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• 2007

Friction characteristics of a low-steel friction material were examined to investigate creep groan phenomena. The amount of three ingredients (steel fiber, $ZrSiO_4$, cashew) were changed to produce test specimens using a constrained mixture design. Tribological properties of the friction material specimens were obtained by using a 1/5 scale dynamometer. Results showed that the amount of three different ingredients strongly affected the level of friction coefficient and the difference between the static friction coefficient and the kinetic friction coefficient $({\Delta}{\mu}).\;ZrSiO_4$ and steel fiber tended to increase the average friction coefficient and aggravated the stick-slip phenomena suggesting high creep groan propensity. On the other hand, cashew tended to decrease average friction coefficient and ${\Delta}{\mu}$.

• 대한의용생체공학회:의공학회지
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• 제21권3호
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• pp.295-301
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• 2000

뼈의 성장에 미치는 많은 요소들 중에서 implant의 상대적인 미세운동(relative micromotion)은 뼈의 implant와의 접합을 방해하는 것으로 알려져 왔다. 그런데 이러한 상대적인 운동 및 spinal stability에 직접적으로 영향을 주는 하중조건, spinal material의 물성치, spinal geometry 및 뼈와 implant의 접촉면에서의 마찰계수를 고려하기 위하여, 하나의 titanium interbody cage 가 삽입된 human lumbar segments (L4-L5)의 유한요소 모델이 개발되었다. 이러한 유한요소 모델의 해석을 통하여 상대적인 미세운동, Posterior의 수직적인 변위, von Mises 응력 및 마찰력이 예측되었다. Cancellous bone. annulus fibers 및 ligaments의 기계적인 물성치의 감소 또는 접촉면에서의 마찰계수의 감소는 상대적인 미세운동 (relative micromotion or slip distance)을 증가 시켰다. 접촉면에서의 normal force는 뼈의 밀도 (cancellous bone density) 가 감소하거나 접촉마찰계수가 증가하면 감소했다. 특히 하중조건에 있어서, compressive preload에 대한 torsion의 추가는 접촉면의 anterior부위에서 상대적인 미세운동을 증가 시켰다. 하지만 디스크면적이 증가할수록 상대적인 미세운동은 감소했다. 결론적으로, 접촉면의 기계공학적 거동 (Relative micromotion, stress response, posterior axial displacement and contact normal force)은 접촉면의 마찰계수 뼈의 밀도, 하중조건 및 노화에 따른 형상/물성의 변화에 매우 민감함을 보이고있다.

• 한국광물학회지
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• 제32권3호
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• pp.201-211
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• 2019

단층 비지는 단층의 미끌림에 의해 입도와 결정도가 낮아지는 특성을 가지는 것으로 알려져 있다. 활석을 비롯한 층상규산염 광물은 단층 비지에 존재하며 단층 약화에서 중요한 역할을 할 수 있는데, 특히 광물 표면에 흡착된 물분자의 존재 여부에 따라 마찰계수가 달라진다. 본 연구에서는 고에너지 볼 밀을 이용해 입도와 결정도를 체계적으로 변화시킨, 분쇄 전후 활석의 함수율과 탈수반응 거동의 변화를 통해 활석이 단층 약화에 미치는 영향에 대해 알아보고자 하였다. 적외선 분광분석 및 열분석 결과, 분쇄 전 활석은 소수성을 띠며 물분자가 거의 존재하지 않는다. 이후 최대 720분까지 진행된 분쇄를 통해 입도가 약 100~300 nm 내외까지 감소하고 비정질화가 진행된 활석에서는 물분자에 의한 함수량이 분쇄 전에 비하여 약 8 wt.% 증가하였다. 또한 분쇄된 시료를 가열할 경우, 분쇄 전에 비하여 기화되는 수증기의 양이 증가한다. 입도 및 결정도 감소에 따라 탈수산기 반응 온도도 분쇄 전 약 $900^{\circ}C$에서 720분 분쇄 후 약 $800^{\circ}C$로 감소하였다. 이와 같이 분쇄된 활석의 입도 및 결정도 감소에 의해 소수성이 친수성으로 바뀌며 층상 규산염 광물의 마찰계수를 낮출 것으로 생각된다. 지진 사이클을 통해 반복되는 단층의 미끌림은 지속적으로 단층 비지에 존재하는 활석의 마찰 계수를 낮출 것으로 생각되며, 오래된 단층이 점점 약화되는 원인에 대한 실마리를 제공할 수 있을 것으로 기대된다.

• 한국구조물진단유지관리공학회 논문집
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• 제15권2호
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• pp.136-143
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• 2011

고력볼트의 현장 조립시 볼트 구멍 간의 불일치로 인하여 볼트 구멍을 확장하는 경우가 빈번하게 발생하고 있으며, 이를 위해서 외국 기준에서는 볼트 구멍 크기, 형태, 하중 방향에 따라 미끄럼하중에 대한 규정을 따로 두고 있다. 그러나 우리나라의 경우 과대구멍에 대한 시방규정이나 이에 대한 접합부 특성에 관한 연구는 미흡한 실정이다. 따라서, 접합부재 표면처리와 볼트구멍 크기의 변화가 접합부 내력에 어떠한 영향을 미치는 지를 실험을 통해 정량적으로 평가할 필요가 있다. 본 연구에서는 볼트 구멍 크기 및 형태에 따른 접합부의 미끄럼하중의 변화와 체결 후, 장기축력이완의 경향을 분석하기 위하여 160시간 및 800시간 동안 고력볼트의 축력의 변화를 측정하였다. 본 실험대상 고력볼트로 KS B 2819에 규정된 TS(Torque Shear)형 고력볼트를 사용하였다. 표준 볼트구멍 대비 그 외 볼트구멍의 미끄럼하중의 변화는 10% 미만으로 나타났으며, 장기축력이완은 직경 2.5배의 슬롯구멍에서, 2.66%로 가장 높게 나타났다.

• Geomechanics and Engineering
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• 제11권4호
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• pp.515-530
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• 2016

In this paper, five different quantitative parameters were proposed for the characterization of the primary roughness which is the component of surface morphology that prevails during large strike-slip faults of more than 50 m. These parameters are mostly the anisotropic properties of rock surface morphology at various scales: (i) coefficient ($k_a$) and degree (${\delta}_a$) of apparent structural anisotropy of surface; (ii) coefficient ($k_r$) and degree (${\delta}_r$) of real structural anisotropy of surface; (iii) surface anisotropy function P(${\varphi}$); and (iv) degree of surface waviness ($W_s$). The coefficient and degree of apparent structural anisotropy allow qualifying the anisotropy/isotropy of a discontinuity according to a classification into four classes: anisotropic, moderately anisotropic/isotropic and isotropic. The coefficient and degree of real structural anisotropy of surface captures directly the actual surface anisotropy using geostatistical method. The anisotropy function predicts directional geometric properties of a surface of discontinuity from measurements in two orthogonal directions. These predicted data may subsequently be used to highlight the anisotropy/isotropy of the surface (radar plot). The degree of surface waviness allows qualifying the undulation of anisotropic surfaces. The proposed quantitative parameters allows their application at both lab and field scales.

• 한국산업융합학회 논문집
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• 제17권1호
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• pp.7-14
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• 2014

In this study, characteristic of elastic paving materials in bicycle road using polyurethane were studied experimentally. As a results, following their good result was obtained. Bicycle road packaging materials are flexural strength g test, ratio of mass change after freezing and thawing, repulsion elasticity test, water Permeation coefficient test and slip resistance test results showed good performance.

• Tribology and Lubricants
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• 제13권2호
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• pp.68-73
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• 1997

The adhesion between wheel and rail plays an important role in the braking performance of trains. Though there have been numerous studies on the characteristics of adhesion phenomenon, a general understanding from the physical point of view is still lacking. In this work, the adhesion mechanism between wheel and rail was investigated by studying the mechanisms of pure rolling and sliding experiments. Tests were performed under various conditions to determine the physical phenomenon responsible for adhesion between wheel and rail. The results of this study is expected to aid in improving the braking performance of trains.