• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 추계학술대회 논문집
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• pp.1012-1015
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• 2005

This paper is designed to estimate friction and powdering characteristic of coating layer on galvannealed sheet steel with different annealing temperature, which is 465, 505, 515 and $540^{\circ}C$. Estimations of powdering and friction were done using a $60^{\circ}$ bending test and one side friction test, respectively. In order to obviously understand the effect of coatings on friction cross-section of coatings before and after friction test was also observed by SEM. The results show that powdering of coatings is increased with increasing of annealing temperature and that friction characteristic greatly depends on powdering which leads to increase of real contact area between tools and coatings.

• 한국정밀공학회지
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• 제23권4호
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• pp.109-115
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• 2006

This paper is designed to estimate friction and powdering characteristic of coating layer on galvannealed sheet steel with different annealing temperature, which is 465, 505, 515 and $540^{\circ}C$, Estimations of powdering and friction were done using a $60^{\circ}$ bending test and one side friction test, respectively. In order to obviously understand the effect of coatings on friction cross-section of coatings before and after friction test was also observed by SEM. The results show that powdering of coatings is increased with increasing of annealing temperature and that friction characteristic greatly depends on powdering which leads to increase of real contact area between tools and coatings.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 1999년도 봄 학술발표회 논문집
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• pp.249-258
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• 1999

Dynamic load and static load tests are performed on steel pipe piles and concrete piles at five construction sites in highway to compare the difference of load bearing mechanisms. At each site, one steel pile is instrumented with electric strain gages and dynamic tests are performed on the pile during installation. Damages of strain gages due to the installation are checked and static test is performed upon the same pile after two or seven days as well. It shows that load transfer from side friction to base resistance behaves somewhat differently according to the results of load-settlement analysis obtained from PDA and static load test. Initial elastic stage of load settlement curves of two load tests is almost similar. But after the yielding point, dynamic resistance of pile behaves more stiffer than static resistance, thus, dynamic load test result might overestimate the real pile capacity compared with static result. Analysis of gage readings shows that unit skin friction increases exponentially with depth. The skin friction is mobilized at the 1∼2m above the pile tip and contributes to the considerable side resistance. Comparison of side and base resistances between the measured value and the calculated value by Meyerhof's bearing capacity equation using SPT N value shows that the calculated base resistance is higher than the measured. Therefore, contribution of side resistance to total capacity shouldn't be ignored or underestimated. Finally, based upon the overall test results, a construction control procedure is suggested.

• 한국자동차공학회논문집
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• 제8권1호
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• pp.101-109
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• 2000

Occupant protection in the side impact of a car became one of the most important issues of car crashworthiness due to high injury level in a side impact crash. An accurate simulation of the side impact crash is an essential tool for the reduction of development time and cost for side impact safety system. This paper describes a new test methodology that can accurately generate the crash pulses of a vehicle and a door in a very cost-effective manner, and then evaluates the injury values of the dummy for the various sled pulses. This test methodology is simple and easy to approach because the door velocity is controlled by the hydraulic actuator and brake and the seat velocity is only adjusted by the friction force of the hydraulic brake. The superiority of the proposed test methodology is proven by the evaluation of dummy's injury values according to the change of the pressure of the hydraulic brake and by the application as a tool for the development of side airbag.

• 자동차안전학회지
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• 제16권1호
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• pp.12-20
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• 2024

Side impact with MDB (moving deformable barrier) is common in side crash test protocols around the globe, most of which are quite similar to that of US NCAP side impact protocol but IIHS side impact protocol is considered to be the most harsh one due to the MDB's weight and impact speed. In this study US NCAP side impact and IIHS side impact test conditions are compared with respect to delta-V (impulse of the test vehicle), roll speed, and yaw speed as well as survival space (the smallest distance between the front driver seat cushion center to B pillar after the test). Error factors (friction between tire and ground, tolerance of vertical and longitudinal position of the MDB with respect to the test vehicle), which are resident in the test protocol is studied with respect to the global vehicle behavior (delta-V, roll, yaw) as well as survival space.

• 한국지반공학회논문집
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• 제23권4호
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• pp.149-160
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• 2007

본 논문에서는 송전철탑 심형기초의 주면마찰력을 평가하고자 충북 음성지역의 편마암에 대해 총 6회(1/8규모 5회, 1/2규모 1회) 현장시험을 실시하였다. 시험결과 파괴형태는 기초체와 암반의 마찰파괴가 아닌 굴착으로 인한 손상된 주변암반 및 기존암반의 절리상태에 지배되는 것으로 나타났으며, 주면마찰력 평가결과 기존의 송전철탑 심형기초에 적용하고 있는 값보다 약 20$\sim$30% 증가되는 것을 확인할 수 있었다. 또한 기초타설시 사용되는 라이너플레이트의 영향을 살펴보고자 기존 철탑 기초에 대해 시추조사를 4회 실시하였다. 라이너플레이트 배면콘크리트의 압축강도는 타설시 설계강도의 63$\sim$72%였으며, 주면마찰력의 설계기준치를 만족하는 것으로 나타났다.

• 상하수도학회지
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• 제23권4호
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• pp.447-458
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• 2009

Energy loss at manholes, often exceeding friction loss of pipes under surcharged flow, is considered as one of the major causes of inundation in urban areas. Therefore, it is necessary to analyze head loss at manholes, especially in case of surcharged flow. Hydraulic experiments were conducted with three cases. Case A is to test whether the shapes of the manholes influence head loss coefficients. Case B and C were proposed to further reduce head losses by improving the manhole hydraulic efficiency. In case B, the joining part of the pipe at both shapes of manholes is shifted from central part to side part. The test in case C is to check the average head loss coefficient by installing the side benching in square manhole, based on shifted joining part model. The average head loss coefficient for circular and square manhole on case A was 1.6. This did not show much difference of the head loss coefficients in spite of the discharge variation in this case. However, case B and C show large difference between head loss coefficients due to the strong oscillation of water surface and the horizontal swirl motion. The circular and square manholes in case B reduced the head loss by 30% and 6% than ones in case A, respectively. The average head loss coefficient for circular manhole in case B was 1.1. Case C reduced average loss coefficients of the square manhole in case A from 1.6 to 1.1. Accordingly, the circular manhole in case B and the square manhole in case C showed the effective way to reduce the head loss. These head loss coefficients could be available to apply to the urban sewer system with surcharged flow.

• 한국지반공학회논문집
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• 제28권6호
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• pp.19-29
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• 2012

일반마이크로파일의 저항성능을 개선시키기 위해 최근에 토목섬유을 활용한 팩마이크로파일이 개발되었다. 팩마이크로파일은 일반마이크로파일의 강봉이나 강관을 토목섬유팩으로 감싸고 주입재와 주입압을 토목섬유팩 내부에 가하여 제작한다. 이 주입압에 의하여 천공 직경이 크게 확대된다. 동일한 한 지반 속에 설치된 세 개의 마이크로파일을 대상으로 일련의 말뚝인발시험을 실시하였다. 세 말뚝 중 두 개는 팩마이크로파일였고 나머지 하나는 강봉을 사용한 일반마이크로파일이였다. 토목섬유팩에 적용된 주입압에 의하여 팩마이크로파일의 경우 천공직경이 152mm에서 220mm으로 확대되었다. 마이크로파일의 주면에서 발달하는 단위주면마찰력은 말뚝두부의 인발변위량의 증가와 함께 서서히 증가하여 한계상태에 도달한 한계변위량에서 수렴치에 도달한다. 팩마이크로파일의 인발저항력은 일반마이크로파일의 인발저항력보다 크게 나타난다. 이와 같은 팩마이크로파일의 인발저항력을 증대시킬 수 있는 원인으로는 크게 두 가지를 생각할 수 있다; 첫째는 마이크로파일에 설치한 토목섬유팩내 주입압으로 마이크로파일의 단면적을 증대시키므로 말뚝주면의 마찰저항면적을 증대시킬 수 있기 때문이고, 둘째는 마이크로파일의 단면이 확대될 때 확대되는 부분의 체적만큼의 토사가 주변지반을 압축시켜 말뚝과 지반 사이의 마찰저항력을 증대시킬 수 있기 때문이다. 이 압축효과는 지표면 부근 보다 깊은 지층에서 크게 나타났다. 말뚝 주면에서 발휘되는 단위주면마찰력은 말뚝의 직경이 작은 경우가 더 크게 발휘된다. 즉 마이크로파일의 주면에서 발달되는 단위주면마찰력은 대구경 현장타설말뚝의 주면에서 발달되는 단위주면마찰력보다 크게 나타난다.

• 한국지반공학회논문집
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• 제16권1호
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• pp.211-220
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• 2000

과압밀 점토층에 설치된 4개의 직경 305 mm 현장타설 말뚝(1개의 일반 현장타설 말뚝과 불포화 점토층에서 발생하는 주면 마찰력을 경감시키기 위해 분리형 튜브를 사용한 3개의 분리형 현장타설 말뚝)의 거동을 분석 비교하기 위한 실험적 연구를 수행하였다. 흡수력 측정을 하기 위해 말뚝 주변에 지반흡수력 측정 장치를 설치하였고 지표면 표고 변화도 측정하였다. 지표면 표고는 최고 40 mm까지 팽창하였고, 일반 말뚝은 5 mm, 분리형 말뚝은 1.5 mm 미만의 말뚝 두부 수직인발변위가 관측되었다. 분리형 말뚝에서 관측된 주면마찰력은 일반형 말뚝에 비해 미소하여 분리형 튜브를 사용한 분리형 현장타설 말뚝이 주위 지반의 팽창 수축에 의해 말뚝에 발생하는 주면 마찰력을 경감시키는데 매우 효과적이었다.

• 동력기계공학회지
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• 제21권5호
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• pp.35-40
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• 2017

The effects of the different rib geometries such as V-shaped continuous (case A), parallel broken (case B), and V-shaped broken (case C) ribs on the heat transfer and pressure drops in a divergent channel with $45^{\circ}$ inclined ribs on one wall or two walls are checked out. The top and bottom walls are adiabatic; two side walls are uniformly heated in the divergent rectangular channel. The tested Reynolds numbers are ranged from 22,000 to 75,000. The channel with two opposite walls inclined only has the length of test section of 1 m and the channel divergence ratio of $D_{ho}/D_{hi}=1.49$, corresponding to $1.43^{\circ}$ inclined walls. The results show in the identical pumping power that the V-shaped continuous rib (case A) with two ribbed walls is the greatest, but the parallel broken rib (case B) with one ribbed wall is the worst in the thermal performance.