• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1998년도 춘계학술대회논문집
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• pp.224-230
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• 1998

Non-heat-treated type material has been investigated for formability compared to heat-treated material. It is very important in automation of metal forming, since it has difficulties of controlling heat treating system by the computer and has bottle neck problem related with heat treatment. In this paper, we have concerned about mechanical properties of non-heat-treated material after the forging. To compare the characteristics between heat-treated material and non-heat-treated material, tensile, compression and fatigue test has been performed. Considering results of mechanical properites of non-heat-treated material, it can replace heat-treated material. Therefore non-heat-treated material may be applied to cold forging.

• 한국철도학회논문집
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• 제7권3호
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• pp.200-207
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• 2004

Theoretical study has been conducted to clarify pressure characteristics of KTX (Korea Train eXpress) in tunnel. The severe pressure change in tunnel may give rise to the ear-discomfort for passenger and fatigue for car body. Critical tunnel lengths which are induced by x-t diagram analysis can be applied to the experimental results measured by using the running test with atmospheric pressure sensors and portable data acquisition system in previous study. In this study, the tunnels from 200m to 4000m in length have been chosen for the investigation of tunnel length effects. We found that there are similar patterns of external pressure change for each critical tunnel length. The critical tunnel lengths are governed by train speed, train length and sonic velocity. And, the patterns of pressure wave in tunnel are classified into eight groups.

• 한국농공학회지
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• 제31권2호
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• pp.66-81
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• 1989

The characteristics of resilient modulus(Mr) which dominates the life of pavement and the design of pavement were investigated on the test specimens which were cement treated and non-treated of the three different soil types. The results are summarized as follows : 1. The resilient modulus was decreased by increasing the cyclic deviator stress ($\sigma$d) , especially the resilient modulus was gradually decreased or sometimes increased when the value of ad was greater than 0.75- 1. 0kg/cm$^2$. 2. The resilient modulus was increased by increasing the homogeneous confined stress ($\sigma$do) and such phenomena were distinct on the coarse soils. 3. The resilient modulus was increased by increasing the ratio of confined stress(Kc), and this phenomena were eminent on the coarse soils too, and the higher permanent strain was showed by increasing the value of Kc. 4. In the drained cyclic triaxial compression test, the value of ad, Kc, and (Oho) was introduced by the following interrelated equations which were similar to the Mr model of Cole. Kcn/Mr=K1(J$_2$/ $\tau$oct)K2 ............. (coarse soli) Mcn/Mr=K3($\sigma$dp/ $\tau$f)k4 ...............(fine soils) 5. The stress path was not much affected by the value of Mr, however, moisture content, dry desity, and contant of fines affected the value of Mr. 6. In the soil-cement specimens, the resilient compression strain($\varepsilon$d) was decreased by the increment of the $\sigma$ho, and Mr was decreased by increasing the $\sigma$d 7. In the flexible pavement. the cement treated layer should be designed not to fail by the fatigue before the designed traffic load, and actually the pavement could cover the traffic load to a certain extent under the post-crack phase, therefore farther studies on this phenomena' are required in the design analysis. 8. The finite element computer program (ANALYS) was used for displacement analysis of pavement containing the cement-treated layer, The result showed that the program used for this analysis was proved to be usable.

• Composites Research
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• 제31권6호
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• pp.392-397
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• 2018

본 연구에서는 기존의 스틸재 타이로드를 브레이딩 공법을 적용한 탄소복합재로 개발하고자 하였다. 탄소복합재 타이로드는 기존 제품과 동등한 성능을 만족시키기 위하여 브레이딩 직조에 필요한 코어 단면설계, 코어와 탄소섬유의 접합부에 대한 구조형상설계를 진행하였다. 그리고 브레이딩 공법을 적용한 시편을 제작하여 시험평가를 통해 구조해석에 적용하였다. 제작 공정은 브레이딩 직조 후 인퓨전 공정을 거쳐 후경화 공정까지 진행하였으며 최종 제품에 대한 시험평가는 인장 시험, 비틀림 시험, 압축 시험과 피로시험을 순차적으로 진행하여 모두 만족시켰다. 또한 탄소복합재 타이로드의 중량을 기존 제품 대비 약 37% 정도 경량화시킬 수 있었다.

• Journal of the Korean Data and Information Science Society
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• 제27권2호
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• pp.409-417
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• 2016

본 연구는 시간 (3분, 4분)에 따른 구령방법이 심폐소생술의 피로도와 정확도에 미치는 영향을 자료로 제시하기 위하여 실험집단과 대조집단의 실험 전 신체적 특성의 동질성을 독립표본 t 검정을 실시하여 동질한 집단으로 나타났다. 집단 별 젖산의 차이를 반복측정 분산분석을 실시한 결과, 시간 (F=7.835, p <.01)과 집단 (F=8.695, p <.01)의 주효과 및 시간과 집단의 상호작용효과 (F=12.582, p <.001) 등에서 모두 통계적으로 유의하게 나타났다. 즉 집단과 시간 (3분, 4분)에 따른 주효과 검정을 Bonferroni방법을 이용하여 실시한 결과에서 실험집단의 젖산 양이 대조집단에 비해 더 많다는 것을 알 수 있었고 (p <.01), 젖산이 실험 전과 3분 후는 차이가 나타나지 않았지만, 실험 전과 4분 후 (p<.05), 3분 후와 4분 후 (p<.05)는 각각 차이를 나타냈다. 다음으로 측정 시간에 따른 정확도를 비교하기 위하여 대응표본 t 검정을 실시한 결과에서 3분 후의 정확도가 4분 후의 정확도에 비해서 더 높게 나타났다 (t=4.584, p <.001). 따라서 응급상황에서 119가 도착하기 전까지 심폐소생술 시 처치자는 심폐소생술을 3분 전에 타인과 교대로 실시해야 한다.

• 대한토목학회논문집
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• 제29권5A호
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• pp.519-529
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• 2009

복합소재는 화학적, 역학적인 면에서 여러 장점을 가지고 있다. 피로 저항성과 화학적 저항성이 높을 뿐 아니라, 비강도, 비강성 등이 높아서 높은 감쇠 특성을 보인다. 항만 구조물에 사용되는 파일은 압축 뿐만 아니라 휨을 받기도 하므로 이에 대한 연구가 필요하다. 본 연구는 대구경을 포함하는 콘크리트 충전 유리섬유 복합소재 파일의 압축 거동 혹은 휨-압축 거동을 분석한다. 지름 및 길이가 서로 다른 25개의 실험 파일을 제작하는데, 시편의 복합소재 튜브 내경은 165 mm에서 600 mm에 이르고, 길이는 1,350 mm에서 8,000 mm에 이른다. 수적층 및 필라멘트 와인딩 성형 공법을 모두 사용하여 튜브를 제작하여 적층의 구조가 미치는 차이를 알아보았다. 충전 콘크리트의 강도로는 27 MPa과 40 MPa를 사용하였다. 축방향 및 원주방향의 섬유의 부피비에 변화를 주어 각각의 영향을 분석하였고, 일부 시편에는 나선형 홈을 튜브 안쪽에 성형하여 충전 콘크리트와 튜브 사이의 전단변형을 줄이는데 기여할 수 있는지 분석하였다. 실험결과를 보면, 직포만을 사용하여 수적층 성형 공법으로 파일을 제작하는 것보다 필라멘트 와인딩 성형 공법을 이용하여 제작하는 것이 휨강성을 높이는데 훨씬 유리하다. 나선형 홈을 성형해서 넣더라고 휨강성은 낮은 하중단계에서 부터 지속적으로 감소하는 경향을 보이는 것으로 보아, 충전 콘크리트와 튜브 사이의 전단변형을 완전히 억제하지는 못하는 것으로 판단된다.

• 한국철도학회논문집
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• 제15권5호
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• pp.436-441
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• 2012

열차가 터널에 고속으로 진입하면, 압력파가 발생한다. 열차 선두부의 진입에 의하여 발생한 압축파는 터널을 따라 진행되어 터널 출구에서 반사되어 팽창파로 되돌아오며, 후미부의 진입에 의하여 발생한 팽창파도 터널을 따라 전파되어 터널 출구에서 압축파로 반사되어 터널 입구로 되돌아 온다. 열차 선두부 및 후미부에 의하여 발생한 이러한 압력파는 터널 입구 및 출구에서 각각 반사되어 터널 내부를 왕복하며, 차량 객실에 탑승한 승객들에게는 이명감을 일으키고, 터널 출구에서는 환경소음의 일종인 미기압파를 발생시킨다. 터널에서의 큰 압력 변동은 터널의 최적 단면적 설계에도 주요 인자로 고려되고 있으며, 차체의 반복 피로 하중으로 작용하므로, 이에 대한 정량적 및 정성적 분석이 필요하다. 본 연구에서는 고정 격자계를 이용한 특성 해법을 개발하였으며, KTX를 이용한 실차 시험 결과와 비교하였으며, 해석 결과는 시험 결과와 잘 일치하였다.

• 한국재료학회지
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• 제14권9호
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• pp.642-648
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• 2004

The microstructure and crack tip opening displacement (CTOD) of deposit weld metal were investigated for a 30 mm- thick plate welded with flux cored arc welding (FCAW) and submerged arc welding (SAW) processes. The CTOD test was carried out both as welded condition and as stress-relieved specimen by local compression. The crack growth rates in FCAW were faster than those in a SAW, and the acicular ferrite content by the SAW process was increased relatively more than that by the FCAW process. The fatigue crack growth rate in a welded specimen was faster than that in locally compressed specimen. The CTOD value of locally compressed specimens was lower than that of as welded specimen. Furthermore, the CTOD value tested with the SAW process was higher than that tested with the FCAW process.

• Tribology and Lubricants
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• 제39권5호
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• pp.212-215
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• 2023

Diaphragm compressors play a crucial role in safely compressing large volumes of high-purity hydrogen gas without contamination or leakage, thereby ensuring quality and reliability. Diaphragm compressors use a thin, flat, triple-layered diaphragm plate that is subjected to repetitive piston pressure for compression. They are usually made of metallic materials such as stainless steel or Inconel owing to their high-pressure resistance. However, since they are consumable components, they fail due to fatigue from repetitive pressure and vibration stress. This study aims to evaluate the scratch characteristics of diaphragms in operational environments by conducting tests on three different samples: Inconel 718, AISI 301, and Teflon-coated AISI 301. The Inconel 718 sample underwent a polishing process, the AISI 301 sample used raw material, and the Teflon coating was applied to the AISI 301 substrate at a thickness of 50 ㎛. To assess the scratch resistance, reciprocating motion friction tests were performed using a tribometer, utilizing 220 and 2000 grit sandpapers as the counter materials. The results of the friction tests suggested that the Teflon-coated sample exhibited the lowest initial friction coefficient and consistently maintained the lowest average friction coefficient (0.13 and 0.11 with 220 and 2000 grit, respectively) throughout the test. Moreover, the Teflon-coated diaphragm showed minimal wear patterns, indicating superior scratch resistance than the Inconel 718 and AISI 301 samples. These findings suggest that Teflon coatings may offer an effective solution for enhancing scratch resistance in diaphragms, thereby improving compressor performance in high-pressure hydrogen applications.

• Structural Engineering and Mechanics
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• 제65권6호
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• pp.679-687
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• 2018

In composite materials technology, the fiber-reinforced polymers (FRP) have opened up new horizons in infrastructural engineering field for strengthening existing structures and components of structure. The Carbon fiber reinforced polymer (CFRP) sheets are well suited for RC columns to this application because of their high strength to weight ratio, good fatigue properties and excellent resistance to corrosion. The main focus of present experimental work is to investigate effect of shapes on axial behavior of CFRP wrapped RC columns having same cross-sectional area and slenderness ratio. The CFRP volumetric ratio and percentage of steel are also adopted constant for all the test specimens. A total of 18 RC columns with slenderness ratio four were cast. Nine columns were control and the rest of nine columns were strengthened with one layer of CFRP wrap having 35 mm of corner radius. Columns confined with CFRP wrap were designed using IS: 456:2000 and ACI 440.2R.08 provisions. All the test specimens were loaded for axial compression up to failure and failure pattern for each shaped column was investigated. All the experimental results were compared with analytical values calculated as per the ACI-440.2R-08 code. The test results clearly demonstrated that the axial behavior of CFRP confined RC columns is affected with the change in shapes. The axial deformation is higher in CFRP wrapped RC circular column as compared to square and rectangular columns. Stress-strain behaviour revealed that the yield strength gained from CFRP confinement was significant for circular columns as compare to square and rectangular columns. This behaviour may be credited due to effect of shape on lateral deformation in case of CFRP wrapped circular columns at effective confinement action.