NbC, HfC, TaC, and their solid solution ceramics have been identified as the best materials for ultrahigh-temperature ceramics. However, their structural stability and elastic properties are mostly unclear. Thus, we investigated structure and elastic properties of (Nb1-xTax)C and (Nb1-xHfx)C solid solutions via ab initio calculations. Our calculated results show that the stability of (Nb1-xTax)C and (Nb1-xHfx)C increases with the increase of Hf and Ta content, and (Nb1-xHfx)C is more stable than (Nb1-xTax)C at the same content of Hf and Ta. The lattice constants decrease with increasing of Hf and Ta content. (Nb1-xTax)C and (Nb1-xHfx)C carbides are mechanically stable and brittle. Bulk modulus of (Nb1-xTax)C increases with increasing Ta content. In contrast, bulk modulus of (Nb1-xHfx)C decreases with increasing Hf content. Hardness of solid solutions shows the highest values at the (Nb0.25Ta0.75)C and (Nb0.75Hf0.25)C. In particular, (Nb0.75Hf0.25)C shows the highest hardness for the current system. The results indicate that the overall mechanical properties of (Nb1-xHfx)C solid solutions are superior to those of (Nb1-xTax)C solid solutions. Therefore, controlling the Hf and Ta element and content of the (Nb1-xTax)C and (Nb1-xHfx)C Solid solution is crucial for optimizing the material properties.

PURPOSES : This study is aimed at developing an asphalt pavement material with high elasticity and watertight through mix design and laboratory tests. METHODS: High elastic (HE) asphalt modifier blended of thermoplastic elastomer, naphthene oil, mineral fiber and organic vulcanization accelerator was developed. Mix design was done to determine the aggregate gradation and optimum asphalt content for making high elastic and watertight asphalt mixture. Performance grade test of HE-modified asphalt binder as well as asphalt mixture tests, which include the tensile strength ratio test, Hamburg wheel tracking test, third-scale model mobile loading simulator(MMLS-3) test, four-point flexural fatigue test, and Texas reflection crack test were conducted to evaluate the characteristics of the HE-modified asphalt mixture. RESULTS: 7.7% optimum binder content was determined through the mix design, which met the quality criteria of Marshall asphalt mixture. The binder test indicated that the grade of the HE-modified asphalt was PG76-28. The results of the mixture tests indicated a tensile strength ratio of 0.92 and a rut depth of 6.2 mm at 20,000 cycles of Hamburg Wheel-Tracking Test. The asphalt mixture test also showed that the rut depth of HE-modified mixture was 39% less than that of Guss asphalt mixture. The crack resistance of the HE-modified mixture was 1.65 times higher than that of the Guss asphalt mixture from the Texas reflection crack test results. CONCLUSIONS: It can therefore be reasonable that HE-modified asphalt mixture is used as an intermediate layer in the asphalt overlay on concrete pavements. Additionally, the HE-modified asphalt mixture can be used for the asphalt pavement materials with high performance and watertight.

PURPOSES: The main purpose of this study is to develop a high elastic modulus and low-shrinkage roller-compacted concrete base (RCCB) in order to prevent fatigue cracking and reflective cracking in the asphalt surface layer of composite pavement. Using a rigid base material with low shrinkage can be a solution to this problem. Moreover, a strong rigid base with high elastic modulus is able to shift the location of critical tensile strain from the bottom of the asphalt layer to the bottom of the rigid base layer, which can prevent fatigue cracking in the asphalt layer. METHODS: Sensitivity analysis of composite pavement via numerical methods is implemented to determine an appropriate range of elastic modulus of the rigid base that would eliminate fatigue cracking. Various asphalt thicknesses and elastic moduli of the rigid base are used in the analysis to study their respective influences on fatigue cracking. Low-shrinkage RCC mixture, as determined via laboratory testing with various amounts of a CSA expansion agent (0%, 7%, and 10%), is found to achieve an appropriate low-shrinkage level. Shrinkage of RCC is measured according to KS F 2424. RESULTS : This study shows that composite pavements comprising asphalt thicknesses of (h1) 2 in. with E2 > 19 GPa, 4 in. with E2 > 15 GPa, and 6 in. with E2 > 11 GPa are able to eliminate tensile strain in the asphalt layer, which is the cause of fatigue cracking in this layer. Shrinkage test results demonstrate that a 10% CSA RCC mixture can reduce shrinkage by 84% and 93% as compared to conventional RCC and PCC, respectively. CONCLUSIONS: According to the results of numerical analyses using various design inputs, composite pavements are shown to be able to eliminate fatigue cracking in composite pavement. Additionally, an RCC mixture with 10% CSA admixture is able to reduce or eliminate reflective cracking in asphalt surfaces as a result of the significant shrinkage reduction in the RCC base. Thus, this low-shrinkage base material can be used as an alternative solution to distresses in composite pavement.

본 연구에서는 풍하중을 받는 고층 구조물의 진동저감을 위하여 사용되어온 전단형 점탄성 감쇠기의 2D, 3D FEM 모델을 이용하여 정밀하게 해석하여 점탄성재료와 이들을 결합하는데 사용하는 재료의 특성이 에너지 소산에 미치는 영향을 평가하였다. 특히 점탄성재료와 강재의 접합방식 및 크기, 형상등이 에너지 소산능력에 미치는 영향을 분석하였다. 이러한 정밀해석과정을 통하여 점탄성 감쇠기의 이력거동을 고찰 분석하고 이를 댐퍼설계에 활용하기위한 설계식을 제안하는 기초자료로 사용할 수 있게 하였다.

This study is to present a female high school summer blouse with high movement functionality and satisfying appearance. For the experimental research 6 subjects with closest average body shapes and their body surface was measured at beginning and after selecting a representative movement the tested uniform was worn and the appearance and movement functionality was evaluated. The results of this research are as follows. In the research with the aims to improve the sleeve designed the height in 3 types as A.H/4+3, A.H/4+2, A.H/4+1 and their evaluation showed that in the order of best appearance was A.H/4+2, A.H/4+1, A.H/4+3. In the order of best comfort was A.H/4+2, A.H/4+3, A.H/4+1 and the best order for movement functionality was A.H/4+1, A.H/4+2, A.H/4+3. Additional height types designed produced from elastic materials were A.H/4+3, A.H/4+2, A.H/4+1 and the resulting order of appearance was A.H/4+3, A.H/4+2, A.H/4+1, order of comfort was A.H/4+3, A.H/4+2, A.H/4+1 and the order of movement functionality was A.H/4+1, A.H/4+2, A.H/4+3. Integrating these results shows that in using the same concurrent materials, the experiment pattern of setting the sleeve height as A.H/4+2 was the best while in using elastic materials, the experiment pattern of setting the sleeve height as A.H/4+3 was the best.

본 논문은 유한요소법을 이용하여 Edwards MIRA 기계식인공심장판막에 높은 혈압이 작용할 때 발생하는 비선형 탄성 변형률을 계산하였다. 상용 유한요소해석 코드인 MISA의 수치해석기법을 채택하여 Edwards MIRA 기계식인공심장판막에 대하여 판첨의 두께를 조금씩 변화시키면서 구조해석을 수행하여 판첨내에 발생하는 최대응력이 판첨재질(Si-Alloyed PyC)의 항복응력보다 작도록 판첨 표면에 혈압이 작용할 시에 판첨에 발생하는 탄성변형률을 계산하였다. 따라서 높은 혈압 작용 시에 판첨의 재질에 따른 물질비선형변형률 보다는 구조적인 기하학적 형강비선형변형률만이 예상되기 때문에 오직 기하학적 형상비선형성만 가정되었다. 계산된 선형, 비선형 변형률들은 발생한 탄성변형률의 비선형성을 확인하기 위하여 비교검토 되었다 비교검토 결과는 비교적 매우 얇은 판첨에서 혈압이 높게 작용할 때에 높은 탄성변형률이 발생하는 것을 보여주고 있다. 그렇지만 동시에 해석결과는 매우 낮은 혈압이나 매우 두꺼운 두께의 판첨에서는 높은 혈압이 작용하더라도 매우 작은 탄성변형률이 발생함을 보여주고 있다. 따라서 기계식인공심장판막의 구조설계 시 비선형 구조해석은 꼭 필요함을 알 수 있다.

최근 강구조물의 장경간화 및 고층화로 인하여 고강도강재의 사용이 점차 증가하고 있다. 고강도강재(POSTEN60, POSTEN80)가 적용된 강구조물의 정확한 내진설계를 위해서는 반복하중 작용시 발생하는 대변형 및 비선형반복거동을 구현할 수 있는 해석기법이 필요하다. 본 연구에서는 고강도강재의 단조재하실험 및 반복하중실험을 기초하여 반복소성모델을 제안하였다. 제안된 소성모델과 유한변위이론을 적용한 3차원 탄소성 유한변위해석기법을 개발하였으며 이를 실험값과 비교하여 검증하였다. 검증된 3차원 탄소성 유한변위해석을 이용하여 고강도 원형강교각의 내진해석을 수행하였다. 또한, 고강도 원형강교각의 지름-두께비에 따른 내진성능을 명확히 하였다.

In order to analysis creep characteristics and elastic recovery of the high-tech fibers for fishing gear materials, creep and elasticity tests were carried out on netting twines made of nylon, kevlar 29 and techmilon respectively. After creep tests, the rupture surface of raw materials was observed by scanning electron microscope(SEM). The results obtained are as follows: 1. Netting twines were arranged in order of creep rupture time as follow: techmilon, kevlar 29, nylon. The creep progressive pace was the fastest in techmilon. 2. In order of the creep elongating, netting twines were arranged as follows: nylon, techmilon, kevlar 29. 3. The rupture time T sub(r) decreased almost linearly with the increase of applied load L on the log-log scaled graph. The empirical equations computed for kevlar 29 and techmilon are as follows: T sub(r kevlar 29)=1.9512×1037L super(-15.773). T sub(r techmilon)=2.7146×1016L super(-6.831). 4. It was observed by SEM that creep was progressed in all netting twines. The difference of rupture morphology was recognized clearly in tensile and creep tests. 5. In order of the elastic recovery, netting twines were arranged as follows: techmilon, kevlar 29, nylon.

This thesis will provide the baseline data of a suitable road repairing solution by analyzing the freeze-and-thaw resistance of inorganic-organic hybrid mortar. The resilience of polymer mortar and high-elastic mortar to freeze thaw resistance showed that the high-elastic mortar showed excellent resistanc

This research provides the baseline data for choosing the inorganic/organic hybrid material as the repairing solution by analyzing its efficiency in securing high vibration resistance and very low permeability. As a result of analysis of the mechanical properties of hybrid composite mortar, the strength increased with age. Therefore, it is considered that an inorganic binder having a certain amount or more is required for high strength development.

The elastic modulus of high-strength steel fiber reinforced concrete was measured 37 GPa to 41.98 GPa. Comparing the difference value of the measured stress and the stress calculated by the regression analysis results were within ± 1 MPa. Measured data acorrding to applied LPF was more stable than unapplied LPF data. but, it was slightly different.