• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.3
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• pp.313-318
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• 2001

To establish nondestructive test method for aerospace composite materials, various composite specimens were tested and analyzed using acoutic emission. The hit rate of acoustic emission closely was rotated with crack initiation and propagation. This report also presents defection capability of crack initiation pressure, initial crack active location, and crack propagation using acoustic emission.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2011.06a
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• pp.231-232
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• 2011

• Composites Research
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• v.33 no.5
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• pp.315-320
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• 2020

In this study, when strand specimens were manufactured using an automatic winding device to obtain uniform strand specimens, analysis and test were conducted to investigate the effect of thermal expansion of the mandrel on strand specimens. Also, necessity of changing materials and mandrel configuration was checked. According to the results, strand specimen received unintended tension that was created by thermal expansion of the mandrel and this unintended tension depended on the curing temperature and position of specimens. Tensile test was conducted to check that initial tension affected on the performance of carbon fiber tow prepreg. All other conditions were fixed and only the initial tension was controlled at 40 N, 60 N, and 80 N. From the results of analysis and test, neither additional tension and tension deviation due to the thermal expansion of the mandrel and the initial tension difference had a significant effect on tensile test results, because carbon fiber had sufficiently high strength compared with tension. Therefore, it was confirmed that the change of the mandrel material and configuration of the automatic winding device was unnecessary.

• Journal of the Korean Society for Precision Engineering
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• v.11 no.5
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• pp.134-142
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• 1994

An upper bound elemental technique (UBET) is applied to predict variations of neutral plane and optimal position of the initial billet for rib-wep shaped ring forging. In the analysis, the neutral plane position and velocity fields are determined by minimizing the total power consump- tion with respect to chosen parameters. The degree of die-cavity filling by initial billet-position and the variations of neutral plane by friction condition are investigated. Experiments have been carried out with pure plasticine billets at room temperature. The theoretical predictions of the forging load and the flow pattern are in good agrement with the experimental results.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2016.11a
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• pp.106-106
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• 2016

강의 산화 및 부식을 방지할 수 있는 표면처리 강판의 수요가 늘어나고 있다. 그 중 용융아연도금 강판은 뛰어난 경제성 및 도금성, 그리고 희생적 방식 특성으로 각광받고 있다. 자동차용 강판의 경우 도금 공정 이후의 표면 상태가 매우 중요하다. 도금 공정의 주된 표면 결함은 강판이 도금욕 내에서 이동 하면서 수반된 도금욕 내의 Zn-Fe-Al dross 입자에 기인한다. 도금공정 중 강판으로부터 용출된 Fe는 도금욕 내의 Zn 와 Al 과 반응하여 밀도가 높은 Bottom dross 나 밀도가 낮은 Top dross를 형성한다. 이에 본 연구에서는 강판으로부터 Fe의 용출속도에 미치는 도금욕 내 초기Fe 농도의 영향을 속도론적으로 평가하였다. 본 연구에서는 'Finger rotating method (FRM)' 방법론을 적용하였으며. 실험을 위해 수직 관상로 내부에 Zn-Al-Fe 시료를 장입한 알루미나 도가니를 위치시킨 후 온도를 $455^{\circ}C$로 설정하고, 지름 20mm의 Iron rod를 회전모터에 연결하여 Zn-Al-Fe 용탕에 침적한 후 회전시켰다. 실험 결과, 초기 Fe 함량과 용탕의 Fe포화 농도의 차이가 적을수록 Fe의 용출 속도는 감소하였으며 Dross 생성량 또한 적었다. 용탕 및 Iron rod 샘플 관찰 결과를 바탕으로 회전하는 Fe 시편으로부터 도금욕으로의 Fe 용출 메커니즘을 고찰하였다. 용출 모델을 토대로 모델링 한 결과, 용탕 내 Fe 농도 변화양상이 모델링 data와 실험 data가 동일한 양상을 보임을 확인 하였다.

• Journal of the Korean Society for Nondestructive Testing
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• v.29 no.4
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• pp.323-330
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• 2009

The objective of this research was to develop a practical integrated approach using extracted features from electrical resistance measurements and coupled electromechanical models of damage, for in-situ damage detection and sensing in carbon fiber reinforced plastic(CFRP) composites. To achieve this objective, we introduced specific known damage (in terms of type, size, and location) into CFRP laminates and established quantitative relationships with the electrical resistance measurements. For processing of numerous measurement data, an autonomous data acquisition system was devised. We also established a specimen preparation procedure and a method for electrode setup. Coupon and panel CFRP laminate specimens with several known damage were tested. Coupon specimens with various sizes of artificial delaminations obtained by inserting Teflon film were manufactured and the resistance was measured. The measurement results showed that increase of delamination size led to increase of resistance implying that it is possible to sense the existence and size of delamination. A quasi-isotropic panel was manufactured and electrical resistance was measured. Then three different sizes of holes were drilled at a chosen location. The panel was prepared using the established procedures with six electrode connections on each side making a total of twenty-four electrodes. Vertical, horizontal, and diagonal pairs of electrodes were chosen and the resistance was measured. The measurement results showed the possibility of the established measurement system for an in-situ damage detection method for CFRP composite structures.

• Proceedings of the KSAR Conference
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• 2003.06a
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• pp.70-70
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• 2003

조류의 배자는 포유류의 배자처럼 모체로부터 영양분을 공급받는 것이 아니라 알속에 저장되어 있는 영양물질로 발육한다. 배자의 발육은 대부분 체외에서 진행된다. 난자는 배란된 후 수정되어 난관팽대부에서 1세포기 수정란이 된다. 그 후 난관협부로 이동하여 최초로 분열이 일어나 배자의 발육이 진행되고, 산란시에는 세포수가 약6만여 개에 달한다. 따라서 수정란에 유전조작기법을 사용하기 위해서는 모체의 난관속에서 일어나는 배발생과 난각속에서 일어나는 개체발생을 위한 체외배양법과 대리난각 배양법이 확립되어 있어야 한다. 그와 같은 기술은 닭 수정란의 배 발생 관찰 및 분석과 유용한 물질을 생산하기 위한 형질전환 가금 연구에 중요한 기술로 사용되고 있다. 따라서 본 연구는 1세포기 닭 수정란의 체외배양과 대리난각 배양에 있어서 수정란의 조건과 대리난각의 조건이 배자의 생존율과 부화율에 미치는 영향을 조사하여 체외배양과 대리난각 배양에 의한 병아리 생산 효율을 제고하기 위한 기초자료를 얻고자 실시하였다. 주요 조사 항목은 수정란의 채란위치, 배자의 발생단계, 수정란의 무게, 대리난각용 계란의 보존 기간, 대리난각의 두께, 대리난각 두께의 감소율, 대리난각의 크기 등을 조사하여 배자의 생존율과 부화율에 미치는 영향에 대하여 조사하였다. 본 실험의 결과는 초기 발생이 빠른 배자가 생존율과 부화율이 높았으며, 본 실험에 사용한 대리난각용 계란의 보관기간이 짧을수록 배자의 생존율과 부화율이 높은 것으로 조사되었다(p<0.05). 그러나 대리난각용 계란의 크기와 대리난각의 두께 차이는 배자의 생존율과 부화율에 큰 영향이 없는 것으로 조사되었다.하였을 때 분할율은 68.0%였으며, 이중 12.0%가 상실배 또는 배반포로 발달하였다. 뿐만 아니라 10% FBS가 첨가된 TCM-199 배양액에 난관상피세포와 공배양을 실시하였을 경우는 72.0%가 분할하였으며, 이중 16.7%가 상실배 또는 배반포로 발달하였다. 이상의 결과로 볼 때 활성화 처리는 ionomycin과 6-DMAP 용액처리가 적합하며, 단위발생란의 체외배양은 보다 적합한 배양조건의 확립이 필요한 것으로 생각된다.icalcium lactate 공동배양은 체외배양에 별다른 영향을 미치지 못하는 것으로 나타났다.생산하는 것을 확인할 수 있었다.4시간에 등급별 회수율이 각각 GI(27.4%), GII(14.7%), GIII(43.2%), GIV(14.7%)로 나타났으며, 46~50시간에는 GI(12.0%), GII(12.0%), GIII(28.0%), GIV(48.0%)로 나타났다. 이상의 결과로 볼 때 미성숙 난자의 회수는 hCG 투여 후 29~34시간이 적합한 것으로 생각된다. 가금의 생산에 있어서 매우 효율적이고 주목할 만한 방법으로 사료된다. 것으로 나타났다.적외선.열풍 복합건조방법이 높게 나타나 이것은 곡물 표면에 원적외선 방사에의한 복사열이 전달되어 열장해를 받았기 때문으로 판단되며, 금후 더 연구하여 적정 열풍온도 및 방사체 크기를 구명해야 할 것이다.으로 보여진다 따라서 옻나무 유래 F는 포유동물의 생식기능에 중요하게 작용하는 것으로 사료된다.된다.정량 분석한 결과이다. 시편의 조성은 33.6 at% U, 66.4 at% O의 결과를 얻었다. 산화물 핵연료의 표면 관찰 및 정량 분석 시험시 시편 표면을 전도

• Journal of the Korean Society of Marine Environment & Safety
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• v.29 no.5
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• pp.479-487
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• 2023

Recently, the destructive power of typhoons is continuously increasing owing to global warming. In a situation where the installation of floating wind turbines is increasing worldwide, concerns about the huge loss and collapse of floating offshore wind turbines owing to strong typhoons are deepening. A new type of disconnectable mooring system must be developed for the safe operation of floating offshore wind turbines. A new submersible mooring pulley considered in this study is devised to more easily attach or detach the floating of shore wind turbine with mooring lines compared with other disconnectable mooring apparatuses. To investigate the structural safety of the initial design of submersible mooring pulley that can be applied to an 8MW-class floating type offshore wind turbine, scale-down structural models were developed using a 3-D printer and structural tests were performed on the models. For the structural tests of the scale-down models, tensile specimens of acrylonitrile butadiene styrene material that was used in the 3-D printing were prepared, and the material properties were evaluated by conducting the tensile tests. The finite element analysis (FEA) of submersible mooring pulley was performed by applying the material properties obtained from the tensile tests and the same load and boundary conditions as in the scale-down model structural tests. Through the FEA, the structural weak parts on the submersible mooring pulley were reviewed. The structural model tests were conducted considering the main load conditions of submersible mooring pulley, and the FEA and test results were compared for the locations that exceeded the maximum tensile stress of the material. The results of the FEA and structural model tests indicated that the connection structure of the body and the wheel was weak in operating conditions and that of the body and the chain stopper was weak in mooring conditions. The results of this study enabled to experimentally verify the structural safety of the initial design of submersible mooring pulley. The study results can be usefully used to improve the structural strength of submersible mooring pulley in a detailed design stage.

• Journal of the Korean Wood Science and Technology
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• v.2 no.2
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• pp.5-7
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• 1974

1. This study indicates that above the fiber saturation point the drying rate can be increased with increasing the velocity of the air circutation, i.e., the drying rate of sample boards is proportional to the air velocity, but below the fiber saturation point, the effect of the velocity of air circulation is very low as shown in Figs. 1 and 2. 2. Under the controlled temperature and humidity in the kiln, the more the sample boards have moisture, the higher drying rate of it can be obtained. In other words, this means that even though in the case of drying various moisture content of wood, at the final drying stage, approximately the same percentage of moisture content of wood can be secured by employing the higher velocity of air circulation. 3. This study shows that the rate of drying in kiln changes distinctly at the fiber saturation point, i, e., above the fiber saturation point, the drying curve shows concave aginst the X axsis, but below the fiber saturation point, in the range from 30 percent of moisture content to 20 percent of moisture content, the curve shows convex as shown in Fig. 3. As the drying progresses, however, the drying curve shows concave again below 20 percent of moisture content. This means that inflection point of drying curve may be located clearly at the fiber saturation point, i.e., 30 percent of moisture content. As mentioned above, the 30 percent of moisture content of wood at which the inflectional point appears can be recognized as a critical point, i. e., the fiber saturation point at which all free water was removed from wood. The existence of inflectional point indicates that the evaporation of hygroscopic water in a cell wall is more difficult than the evaporation of free water in a cell cavity and the minor space of cell wall. The convex curve in the range of moisture content from 30 percent to 20 percent means that the evaporation of capillary condensed water has a tendency of the same rates of drying approximately, but as approaching to the 20 percent of moisture, the transfusion of moisture from wood becomes difficult because of having less moisture in cell wall. Below 20 percent of moisture content, the drying curve shows concave again, which means that it is difficult to remove the moisture located nearer to the surface of cellulose molecules and the surface bound water. These relations were revealed in Fig. 4. In comparison AC curve which does not have the two inflection points with BD curve which has two inflection points, i.e., Band D, they are mentioned already, by existence of the inflection points, the curve BD shows that the change of drying rate in the interval from 20 percent of moisture content to 30 percent of moisture content is not greater than in the case of the curve AC in the same interval. At the inflection point of 30 percent of moisture content, it can be noticed that the changing of the drying rate is very conspicuous. This phenomenon also can be recognized, as it is noticed by the Fig. 3, the drying rate from green to 30 percent of moisture content is very great. But the inclination of the curve is very slow from 30 percent of moisture content to 20 percent of moisture content, i.e., the inclination of the curve becomes almost horizontal lines. Acknowledgments Gratitude is expressed to Fred E. Dickinson, Professor of 'Wood Technology, School of Natural Resources, University of Michigan, USA for his suggestion to carry out this study.

• The Journal of Korean Academy of Prosthodontics
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• v.48 no.3
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• pp.209-214
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• 2010

Purpose: The purpose of this study was to investigate whether the re-osseointegration of the implants that had mechanical unscrewing possibly occurred or not. Furthermore, if it happened, the degree of re-osseointegration was evaluated by comparing with previous osseointegration. Materials and methods: The smooth implant (commercial pure titanium 99%) specimens, whose diameter and length was 3.75 mm, 4 mm, respectively were produced. Two implants were inserted into each tibia of 7 New Zealand female white rabbits weighing at least 3.0 kg. The torque removal force for each implant after 6 weeks of implants placement was measured and included in group I. The torque removal forces were assessed after the fixtures were re-screwed to original position and the subjects were allowed to have 4 more weeks for healing and included in group II. One rabbit was sacrificed after first measurement and produced 4 slide specimens in group I, and two rabbits were sacrificed after 2nd measurement, 7 slide specimens, in group II for histomorphologic investigations. All slide specimens were assessed based on the proportion of BIC (bone-implant contact) as well as CBa (Bone area in the cortical passage) value produced by counting the screw threads embedded in the compact bones under the optical microscopic analysis (${\times}20$). Statistical analysis was conducted to evaluate the torque removal force, BIC and CBa between group I and II. Results: As for the torque removal force, the result was $10.8{\pm}3.6$ Ncm for group I and $20.2{\pm}9.7$ Ncm for group II. Furthermore, the torque removal force of group II increased by 98.1% in average compared to group I (P<.05). On the other hand, histomorphologic analysis displayed that there was no statistical significance in BIC and CBa values between group I and the group II (P>.05), and RT/BIC and RT/CBa between group I and group II were statistically significant (P<.05). Conclusion: It is possible to obtain more substantial re-osseointegration within shorter periods than the period needed for the initial osseointegration in case of iatrogenically unscrewed implants.