• Title/Summary/Keyword: pre-damage

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Suppression of Macrostep Formation Using Damage Relaxation Process in Implanted SiC Wafer (SiC 웨이퍼의 이온 주입 손상 회복을 통한 Macrostep 형성 억제)

  • Song, G.H.;Kim, N.K.;Bahng, W.;Kim, S.C.;Seo, K.S.;Kim, E.D.
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2002.07a
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    • pp.346-349
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    • 2002
  • High Power and high dose ion implantation is essentially needed to make power MOSFET devices based on SiC wafers, because the diffusivities of the impurities such as Al, N, p, B in SiC crystal are very low. In addition, it is needed high temperature annealing for electrical activation of the implanted species. Due to the very high annealing temperature, the surface morphology after electrical activation annealing becomes very rough. We have found the different surface morphologies between implanted and unimplanted region. The unimplanted region showed smoother surface morphology It implies that the damage induced by high energy ion implantation affects the roughening mechanism. Some parts of Si-C bonding are broken in the damaged layer, s\ulcorner the surface migration and sublimation become easy. Therefore the macrostep formation will be promoted. N-type 4H-SiC wafers, which were Al ion implanted at acceleration energy ranged from 30kev to 360kev, were activated at 1600$^{\circ}C$ for 30min. The pre-activation annealing for damage relaxation was performed at 1100-1500$^{\circ}C$ for 30min. The surface morphologies of pre-activation annealed and activation annealed were characterized by atomic force microscopy(AFM).

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Repair of Pre-cracked Reinforced Concrete (RC) Beams with Openings Strengthened Using FRP Sheets Under Sustained Load

  • Osman, Bashir H.;Wu, Erjun;Ji, Bohai;Abdulhameed, Suhaib S.
    • International Journal of Concrete Structures and Materials
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    • v.11 no.1
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    • pp.171-183
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    • 2017
  • Strengthening reinforced concrete (RC) beams with openings by using aramid fiber reinforcement polymers (AFRP) on the beams' surfaces offers a useful solution for upgrading concrete structures to carry heavy loads. This paper presents a repairing technique of the AFRP sheets that effectively strengthens RC beams, controls both the failure modes and the stress distribution around the beam chords and enhances the serviceability (deflection produced under working loads be sufficiently small and cracking be controlled) of pre-cracked RC beams with openings. To investigate the possible damage that was caused by the service load and to simulate the structure behavior in the site, a comprehensive experimental study was performed. Two unstrengthened control beams, four beams that were pre-cracked before the application of the AFRP sheets and one beam that was strengthened without pre-cracking were tested. Cracking was first induced, followed by repair using various orientations of AFRP sheets, and then the beams were tested to failure. This load was kept constant during the strengthening process. The results show that both the preexisting damage level and the FRP orientation have a significant effect on strengthening effectiveness and failure mode. All of the strengthened specimens exhibited higher capacities with capacity enhancements ranging from 21.8 to 66.4%, and the crack width reduced by 25.6-82.7% at failure load compared to the control beam. Finally, the authors present a comparison between the experimental results and the predictions using the ACI 440.2R-08 guidelines.

A Study on the Application of Pre-Indentation Technique for Fastener Hole Model (FASTENER HOLE 모델의 대한 예비압입 적용 연구)

  • Hwang,Jeong-Seon;Jo,Hwan-Gi
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.31 no.9
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    • pp.26-31
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    • 2003
  • Aging aircraft accumulates widespread fatigue damage commonly referred to as multiple site damage(MSO). For ductile material such as 2024-T3 aluminum, MSO may lower the service life below that which is predicted by conventional fracture mechanics. The present paper is concerned with the fatigue life extension by pre-indentation technique for thin 2024-T3 aluminum plate to decelerate the crack propagation rate in the panels with MSO. The panel with fastener holes can be simply modelled by Hole/Slot type Middle-Tension specimen. Results of fatigue testing show significantly improving failure cycles from 10 to 40 times. This retardation effect is decreased by increasing the loading level in the constant amplitude loading. In the sense of retardation mechanism, the crack propagation rate is gradually attenuated by entering the indentation mark and maintains at the lowest value for a long period after the edge of crack passes the center of indentation area.

Corrosion Behavior of Super Duplex Stainless Steel (STS 329J4L) Tubes and Fin-Tubes Used in Thermal Power Plant Applications (화력발전소용 슈퍼 듀플렉스 스테인리스 강(STS 329J4L) 조관 튜브 및 핀-튜브재의 부식거동)

  • Jin Sung Park;Yong Hyeon Kim;Seung Gab Hong;Sung Jin Kim
    • Corrosion Science and Technology
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    • v.22 no.6
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    • pp.435-446
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    • 2023
  • Corrosion behaviors of laser-welded super duplex stainless steel (SDSS) tubes after exposure to an actual power plant environment for one year and those of fin-tube welded SDSS were evaluated. Results showed that corrosion damage on the back side of the SDSS tube in the direction of hot air was higher than that on the front side regardless of weldment location. However, corrosion damage showed no difference between weldment and base metal due to recovery of phase fraction in the weldment through post weld heat treatment (PWHT). Nevertheless, the SDSS tube showed severe corrosion damage along grain boundary due to surface phase transformation (δ → γ) and Cr2N precipitation caused by PWHT with a high N2 atmosphere. Corrosion resistance of the SDSS tube was recovered when degraded surface was removed. Corrosion sensitivity of a fin-tube increased significantly due to pre-existing crevice, unbalanced phase fraction, and σ phase precipitation adjacent to the fusion line. Although corrosion resistance was improved by recovered phase fraction and sufficient dissolution of σ phase during PWHT, corrosion reaction was concentrated at the pre-existing crevice. These results suggest that welding conditions for fin-tube steel should be optimized to improve corrosion resistance by removing pre-existing crevice in the weldment.

Protective Effect of Flavonoids on Lymphocyte DNA Damage Using Comet Assay (Comet Assay를 이용한 Flavonoids와 항산화 비타민의 인체임파구 세포 DNA 손상 보호 효과)

  • 박유경;전은재;강명희
    • Journal of Nutrition and Health
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    • v.36 no.2
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    • pp.125-132
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    • 2003
  • The present study was attempted to investigate and compare the antioxidant potency of several well-know flavonoids, antioxidant vitamin and commercially available popular beverages. The antioxidant potency was assessed by the effect on reducing oxidative DNA damage of human lymphocytes. Cellular oxidative DNA damage was measured by SCGE (single-cell gel electrophoresis), also known as comet assay. Lymphocytes were pre-treated for 30 minutes with wide ranges of doses of apigenin, kaempferol, luteolin, myricetin, rutin, quercetin, $\alpha$-tocopherol (10,25,50,100,200,500,1000 $\mu$M) ,green tea extract or grape juice (10,50,100,250,500,1000 $\mu$g/mL) followed by a $H_2O$$_2$(100 $\mu$M) treatment for 5 min as an oxidative stimulus. The physiological function of each antioxidant substance on oxidative DNA damage was analyzed as tail moment (tail length $\times$ percentage migrated DNA in tail) and expressed as relative DNA damage score after adjusting by the level of control treatment. Cells treated with $H_2O$$_2$alone (positive control) had an extensive DNA damage compared with cells treated with phosphate buffered saline (PBS, negative control) or pre-treated with all the tested samples. Of all the six flavonoids, quercetin was the most potent antioxidant showing the lowest $ED_{50}$/ of 8.5 $\mu$g/mL (concentration to produce 50% protection of relative DNA damage). The antoxidant potency of individual flavonoids were ranked as follows in a decreasing order; luteolin (18.4 $\mu$g/mL), myricetin (19.0 $\mu$g/mL) , rutin (22.2 $\mu$g/mL) , apigenin (24,3 $\mu$g/mL) , kaempferol (25.5 $\mu$g/mL). The protective effect of $\alpha$-tocopherol was substantially lower (highest $ED_{50}$value of 55.0 $\mu$g/mL) than all the other flavonoids, while the protective effect was highest in green tea and grape juice with low ED5O value of 7.6 and 5.3, respectively. These results suggest that flavonoids, especially quercetin, and natural compounds from food product, green tea and grape juice, produced powerful anti-oxidative activities, even stronger than $\alpha$-tocopherol. Taken together, supplementation of antioxidants to lymphocytes followed by oxidative stimulus inhibited damage to cellular DNA, supporting a protective effect against oxidative damage induced by reactive oxygen species.

A Prediction Model for Low Cycle and High Cycle Fatigue Lives of Pre-strained Fe-18Mn TWIP Steel (Fe-18Mn TWIP강의 Pre-strain에 따른 저주기 및 고주기 피로 수명 예측 모델)

  • Kim, Y.W.;Lee, C.S.
    • Transactions of Materials Processing
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    • v.19 no.1
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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.

Comparison of the Protective Effect of Antioxidant Vitamins and Fruits or Vegetable Juices on DNA Damage in Human Lymphocyte Cells Using the Comet Assay (Comet Assay를 이용한 항산화 비타민과 과일.야채즙의 인체 임파구 세포 DNA 손상 감소 효과 비교)

  • 전은재;박유경;김정신;강명희
    • Journal of Nutrition and Health
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    • v.37 no.6
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    • pp.440-447
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    • 2004
  • In this study the in vitro protective effects of several antioxidant vitamins (vitamin C, $\alpha$-tocopherol, $\beta$-carotene), fruits and vegetables (strawberry, tangerine, orange and 100% orange juice, carrot juice), on the levels of isolated human lymphocyte DNA damage was measured using Comet assay. Comet assay has been used widely to assess the level of the DNA damage in the individual cells. Lymphocytes were pre-treated for 30 minutes with antioxidant vitamins (10, 50, 100, 500 $\mu$M) or fruits$.$vegetables (10, 100, 500, 1000 $\mu$g/ml), an4 then oxidatively challenged with 100 $\mu$M $H_2O$$_2$ for 5 min at 4$^{\circ}C$. The protective effect of antioxidant vitamins against DNA damage at a concentration of 50 $\mu$M were 50% in vitamin C, 32% in $\alpha$-tocopherol, whereas, fJ-carotene showed a 55% protection at a dose as low as 10 $\mu$M. The inhibitory effects of DNA damage by strawberry, tangerine, orange, orange juices, carrot juices were 50 - 60% with wide ranges of doses. The results of the present study indicate that most the antioxidant vitamins and fruits$.$vegetables juices produced a significant reduction in oxidative DNA damage.

Developing a Standardized Patient Program using Internal Damage Fever Cases in Korean Medical Education (한의학 교육에서 내상발열(內傷發熱) 증례를 이용한 표준화환자 프로그램 개발 연구)

  • Jo, Hak-jun;Jo, Na-young
    • Journal of Korean Medical classics
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    • v.33 no.4
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    • pp.33-56
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    • 2020
  • Objectives : The objective of this paper is to develop a standardized patient program with a focus on diagnosis and treatment of internal damage fever in Korean Medical education. Methods : First, cases of diagnosis and treatment of internal damage fever were collected from various classical texts, then a module was developed according to pre-existing standardized patient program's protocols based on selected cases. Careful consideration was given to developing evaluation criteria on history taking and physical examination that are necessary to accurately differentiating the 9 types. Results : Nine types of differentiation models on internal damage fever were selected, which are qi deficiency from overexertion/fatigue and famish; blood deficiency from overexertion/fatigue, famish and fullness; fire stagnation from excessive eating and cold foods; food damage; yang deficiency; yin deficiency; phlegm; stagnated blood; liver qi stagnation. For each type, evaluation criteria in regards to history taking, physical examination, communication with patient, and patient education were developed. Conclusions : When developing a standardized patient program using internal damage fever cases, it would better reflect the characteristics of Korean Medicine in clinical education of Korean Medicine if the program is based on classical texts. It would also be useful in evaluating students' graduation competence in exams such as CPX.

The tap-scan method for damage detection of bridge structures

  • Xiang, Zhihai;Dai, Xiaowei;Zhang, Yao;Lu, Qiuhai
    • Interaction and multiscale mechanics
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    • v.3 no.2
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    • pp.173-191
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    • 2010
  • Damage detection plays a very important role to the maintenance of bridge structures. Traditional damage detection methods are usually based on structural dynamic properties, which are acquired from pre-installed sensors on the bridge. This is not only time-consuming and costly, but also suffers from poor sensitivity to damage if only natural frequencies and mode shapes are concerned in a noisy environment. Recently, the idea of using the dynamic responses of a passing vehicle shows a convenient and economical way for damage detection of bridge structures. Inspired by this new idea and the well-established tap test in the field of non-destructive testing, this paper proposes a new method for obtaining the damage information through the acceleration of a passing vehicle enhanced by a tapping device. Since no finger-print is required of the intact structure, this method can be easily implemented in practice. The logistics of this method is illustrated by a vehicle-bridge interaction model, along with the sensitivity analysis presented in detail. The validity of the method is proved by some numerical examples, and remarks are given concerning the potential implementation of the method as well as the directions for future research.

CNN-based damage identification method of tied-arch bridge using spatial-spectral information

  • Duan, Yuanfeng;Chen, Qianyi;Zhang, Hongmei;Yun, Chung Bang;Wu, Sikai;Zhu, Qi
    • Smart Structures and Systems
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    • v.23 no.5
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    • pp.507-520
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    • 2019
  • In the structural health monitoring field, damage detection has been commonly carried out based on the structural model and the engineering features related to the model. However, the extracted features are often subjected to various errors, which makes the pattern recognition for damage detection still challenging. In this study, an automated damage identification method is presented for hanger cables in a tied-arch bridge using a convolutional neural network (CNN). Raw measurement data for Fourier amplitude spectra (FAS) of acceleration responses are used without a complex data pre-processing for modal identification. A CNN is a kind of deep neural network that typically consists of convolution, pooling, and fully-connected layers. A numerical simulation study was performed for multiple damage detection in the hangers using ambient wind vibration data on the bridge deck. The results show that the current CNN using FAS data performs better under various damage states than the CNN using time-history data and the traditional neural network using FAS. Robustness of the present CNN has been proven under various observational noise levels and wind speeds.