• Corrosion Science and Technology
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• 제5권1호
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• pp.27-32
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• 2006

One of the critical issues in the coating specification is the allowable limit of surface contaminant(s) - such as soluble salt(s), grit dust, and rust - after grit blasting. Yet, there is no universally accepted data supporting the relationship between the long-term coating performance and the amount of various surface contaminants allowed after grit blasting. In this study, it was attempted to prepare epoxy coatings applied on grit-blasted steel substrate dosed with controlled amount of surface contaminants - such as soluble salt(s), grit dust, and rust. Then, coating samples were subjected to 4,200 hours of cyclic test(NORSOK M-501), which were then evaluated in terms of resistance to rust creepage, blistering, chalking, rusting, cracking and adhesion strength. Additional investigations on the possible damage at the paint/steel interface were carried out using an Electrochemical Impedance Spectroscopy(EIS) and observations of under-film-corrosion. Test results suggested that the current industrial specifications were well matched with the allowable degree of rust, whereas the allowable amount of soluble salt and grit dust after grit blasting showed a certain deviation from the specifications currently employed for fabrication of marine vessels and offshore facilities.

• 한국자동차공학회논문집
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• 제14권3호
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• pp.133-141
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• 2006

The Low cycle fatigue behavior of 11.7Cr-1.1Mo heat-resisting steel has been investigated under strain-controlled conditions with mean stresses at room temperature and $300^{\circ}C$. For the tensile mean stress test, the initial high tensile mean stress generally relaxed to zero at room temperature, however, at $300^{\circ}C$ initial tensile mean stress relaxed to compressive mean stress. Low cycle fatigue lives under mean stress conditions are usually correlated using modifications to the strain-life approach. Based on the fatigue test results from different stain ratio of -1, 0, 0.5, and 0.75 at room temperature and $300^{\circ}C$, the fatigue damage of the steel was represented by using cyclic strain energy density. Total strain energy density considering mean stress indicated well better than not considering mean stress at $300^{\circ}C$. Predicted fatigue life using Smith-Watson-Topper's parameter correlated fairly well with the experimental life at $300^{\circ}C$.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.2434-2439
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• 2008

This paper was studied on the cavitation instability of a Solution Pump Inducer in an absorption chiller-heater. Inlet pressure of LiBr and rotational speed at nominal mode are 2,800 Pa and 3,500 rpm respectively. Due to the marginal operation of available NPSH, the cavitation performance of the inducer is critical for the stable operation without the deterioration of head performance. In the study, cavitation performance and its mode of instability was investigated experimentally. Water was used as the working fluid and the test inducer was scaled up as 1.75 times for detail measurements and flow visualization. Inlet pressure was controlled by a vacuum pump. This research focused on types of cavitation instability and phenomena to investigate the possibility of harmful damage due to cavitation instability. Casing wall pressure and instantaneous inlet pressure was measured to observe the unsteady flow characteristics. Through the visualization and spectrum analysis of pressure, the occurrence region and intensity of asymmetric cavitation and cavitation surge are analyzed in the test inducer.

• 한국근적외분광분석학회:학술대회논문집
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• 한국근적외분광분석학회 2001년도 NIR-2001
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• pp.3103-3103
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• 2001

NIR has been extensively used to predict directly measurable properties of materials that are important to the appropriate industries. Commonly, NIR is used to perform fast, routine tests to improve control response as against the response time for the (normally chemical) base test. This paper discusses the use of NIR to measure indirect properties of materials. In these cases, the pure chemical or physical tests are either unable measure the appropriate parameters (eg GMO modification) or there are mitigating effects that are not properly addressed by the base tests. In particular, we looked at the digestible portion of amino acids within meat and bone meal. This is the desired response measurement by end-users of the product (intensive livestock producers) but is currently unable to be offered as a measurement by producers. The base test method is by controlled feeding trials. These are somewhat cumbersome, taking 2-3 months, involving several sets of animals, and considerable expense. A shortened test (feed trial based) would be of little use, as the precision blows out over short period feeding trials. For example, a rat ileal digestibility test requires around 2 months, and costs some $USD1000. This is clearly impractical test for a producer involved in continuous production, with a 1-2 day turn around. While the amino acid abundance is accessible chemically, the uptake of amino acids into usable material by mammalian species is not simply related to the measured abundance within the material. There are many co-related material properties that might help or hinder uptake, some chemical based (eg protein damage), some indirect (eg palatability), some physiological (intestinal tract response vs speed of throughput). We discuss the approaches taken to provide a suitable reference data set, and present the derived prediction and validation relationships.

• Computers and Concrete
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• 제33권5호
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• pp.605-619
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• 2024

The increase of reclaimed asphalt pavement (RAP) content in recycled asphalt concrete (RAC) is accompanied by the degradation of low-temperature cracking resistance, which has become an obstacle to the development of RAC. This paper aims to reveal the meso-scale mechanisms of the low-temperature fracture behavior of RAC and provide a theoretical basis for the economical recycling of RAP. For this purpose, micromechanical heterogeneous peridynamic model of RAC was established and validated by comparing three-point bending (TPB) test results against corresponding numerical simulation results of RAC with 50% RAP content. Furthermore, the models with different aggregate shapes (i.e., average aggregates circularity (${\bar{C_r}}=1.00$, 0.75, and 0.50) and RAP content (i.e., 0%, 15%, 30%, 50%, 75%, and 100%) were constructed to investigate the effect of aggregate shape and RAP content on the low-temperature cracking resistance. The results show that peridynamic models can accurately simulate the low-temperature fracture behavior of RAC, with only 2.9% and 13.9% differences from the TPB test in flexural strength and failure strain, respectively. On the meso-scale, the damage in the RAC is mainly controlled by horizontal tensile stress and the stress concentration appears in the interface transition zone (ITZ). Aggregate shape has a significant effect on the low-temperature fracture resistance, i.e., higher aggregate circularity leads to better low-temperature performance. The large number of microcracks generated during the damage evolution process for the peridynamic model with circular aggregates contributes to slowing down the fracture, whereas the severe stress concentration at the corners leads to the fracture of the aggregates with low circularity under lower stress levels. The effect of RAP content below 30% or above 50% is not significant, but a substantial reduction (16.9% in flexural strength and 16.4% in failure strain) is observed between the RAP content of 30% and 50%. This reduction is mainly attributed to the fact that the damage in the ITZ region transfers significantly to the aggregates, especially the RAP aggregates, when the RAP content ranges from 30% to 50%.

• 대한화장품학회지
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• 제46권3호
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• pp.295-305
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• 2020

염색과 같이 산화제를 이용한 미용은 모발의 큐티클 구조를 바꾸거나 단백질 변성 및 지질의 소실을 야기하여 모발을 손상시킨다. 본 연구에서는 모발 손상 변화를 기기 평가를 통해 마찰계수를 측정하고 이것이 소비자들의 손상 인지와 상관성이 있는지 알아보고, 더 나아가 손상 원인을 수분 변화에서 찾아 분석 하였다. 염색, 펌, 탈색 과정을 모발에 반복할 때 마찰계수를 측정한 결과 염색의 경우는 3 회 처리에서 마찰계수 0.60을 기록했는데, 일반인들을 대상으로 동일 모발에 대한 촉감에 의한 손상 인지 조사에서 응답자의 58%가 이 모발에서 처음으로 손상을 인지한다고 답하였다. 탈색의 경우 3 회 처리에서 마찰계수가 0.84 로 크게 변하였는데 응답자의 88%가 손상모로 인지하였다. 지질 소실을 통한 손상에 따른 인지를 알아보기 위하여 모발 표면의 18-methyleicosanoic acid (18-MEA)를 제거해가며 마찰계수를 인위적으로 높인 다양한 모발을 제작하였다. 이 경우 마찰계수가 0.60 인 모발부터 전체 응답자의 68%가 최초로 손상을 인식한다고 답하였다. 기기평가로 확인된 마찰계수와 이와 연관되는 손상 인지가 모발에서 가장 많은 양을 차지하는 수분으로부터 기여되는지 확인하기 위하여 손상모의 수분함량을 측정하였다. 염색 처리 횟수가 증가할수록 모발의 접촉각이 감소하며 모발이 친수성으로 변함을 확인하였는데, 실제로 염색 손상모가 건강한 모발보다 0.42% 더 많은 수분량을 가짐을 유의차 있게 확인하였다. 최종적으로는 손상 모발의 수분량 증가가 마찰계수와 비례하는 점착력 증가를 유도하며 마찰계수가 0.60 이상으로 증가할 때 손상 인지가 됨을 알아보았다.

• 항공우주시스템공학회지
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• 제15권5호
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• pp.98-105
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• 2021

본 연구에서는 우주발사체용 복합재 산화제탱크의 구조 강건성을 검증하기 위해 수행된 정하중시험 결과를 제시하였다. 먼저, 복합재 산화제탱크 정하중시험에 사용된 시험장비를 소개하고, 복합재 산화제탱크가 만족해야 하는 시험 요구도를 설명하였다. 그리고, 정하중 시험치구, 유압, 제어장비, 데이터획득장비로 구성되는 시험셋업 구성도를 제시하였고, 전단, 등가압축, 굽힘, 조합시험으로 구성된 복합재 산화제탱크 정하중 시험의 하중 프로파일을 제시하였다. 하중 제어의 결과로 시험하중 증가에 따른 각 하중부과기에서 입력하중과 출력하중 사이의 오차와 각 로드셀 A와 b 채널사이의 오차를 제시하여 본 시험의 신뢰성을 확인하였다. 정하중 시험 결과로, 각 시험에서 하중부과기의 하중은 허용 오차 범위 내에서 적절히 잘 제어되었으며, 시험시편도 요구 하중 내에서 파손이나 심각한 구조적 결함을 유발하는 좌굴은 발생하지 않는 것으로 확인되었다.

• Transactions on Electrical and Electronic Materials
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• 제9권4호
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• pp.143-146
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• 2008

In this study the thermal impact characteristics by forest fire are extensively investigated using temperature controlled ovens. The test conditions for thermal impact damage are simulated according to the characteristics of natural forest fire. The test pieces are suspension porcelain insulators made by KRI in 2005 for transmission lines. In the thermal impact cycle tests with $300\;^{\circ}C$ thermal impact gradient (-70 to $230\;^{\circ}C$), cycling in 10 minute periods, no critical failures occurred in the test samples even with long cycle times. But in tests with thermal impact gradient from room temperature to $200-600\;^{\circ}C$, cycling in 10 to 30 minute periods, there were critical failures of the porcelain insulators according to the thermal impact gradient and quenching method. In the case of thermal impact by forest fire, it was found of that duration time is more important than the cycling time, and the initiation temperature of porcelain insulator failures is about $300\;^{\circ}C$, in the case of water quenching, many cracks and fracture of the porcelain occurred. It was found that the thermal impact failure is closely related to the displacement in the cement by thermal stress as confirmed by simulation. It was estimated that the initiation displacement by the thermal impact of $300\;^{\circ}C$ is about 0.1 %. Above 1% displacement, it is expected that the most porcelain insulators would fail.

• Structural Engineering and Mechanics
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• 제53권2호
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• pp.311-324
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• 2015

The purpose of this study was to investigate experimentally the fatigue performance of reinforced concrete (RC) beams with hot-rolled ribbed fine-grained steel bars of yielding strength 500MPa (HRBF500). Three rectangular and three T-section RC beams with HRBF500 bars were constructed and tested under static and constant-amplitude cyclic loading. Prior to the application of repeated loading, all beams were initially cracked under static loading. The major test variables were the steel ratio, cross-sectional shape and stress range. The stress evolution of HRBF500 bars, the information about crack growth and the deflection developments of test beams were presented and analyzed. Rapid increases in deflections and tension steel stress occured in the early stages of fatigue loading, and were followed by a relatively stable period. Test results indicate that, the concrete beams reinforced with appropriate amount of HRBF500 bars can survive 2.5 million cycles of constant-amplitude cyclic loading with no apparent signs of damage, on condition that the initial extreme tensile stress in HRBF500 steel bars was controlled less than 150 MPa. It was also found that, the initial extreme tension steel stress, stress range, and steel ratio were the main factors that affected the fatigue properties of RC beams with HRBF500 bars, whose effects on fatigue properties were fully discussed in this paper, while the cross-sectional shape had no significant influence in fatigue properties. The results provide important guidance for the fatigue design of concrete beams reinforced with HRBF500 steel bars.

• 소성∙가공
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• 제19권1호
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• pp.11-16
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• 2010

The influence of pre-strain on low cycle fatigue behavior of Fe-18Mn-0.05Al-0.6C TWIP steel was studied by conducting axial strain-controlled tests. As-received plates were deformed by rolling with reduction ratios of 10 and 30%, respectively. A triangular waveform with a constant frequency of 1 Hz was employed for low cycle fatigue test at the total strain amplitudes in the range of ${\pm}0.4\;{\sim}\;{\pm}0.6$ pct. The results showed that low-cycle fatigue life was strongly dependent on the amount of pre-strain as well as the strain amplitude. Increasing the amount of prestrain, the number of reversals to failure was significantly decreased at high strain amplitudes, but the effect was negligible at low strain amplitudes. A new model for predicting fatigue life of pre-strained body has been suggested by adding ${\Delta}E_{pre-strain}$ to the energy-based fatigue damage parameter. Also, high-cycle fatigue lives predicted using the low-cycle fatigue data well agreed with the experimental ones.