• Title/Summary/Keyword: Material behavior

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Effect of Temperature and Thickness on Fracture Toughness of Solid Propellant (고체추진제의 파괴인성에 대한 온도 및 두께의 영향)

  • Seo, Bo Hwi;Kim, Jae Hoon
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.37 no.11
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    • pp.1355-1360
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    • 2013
  • A cracked solid propellant would have failure or fracture of rocket because of excessive combustion according to increase of burning area, therefore it is important to evaluate the fracture toughness of solid propellant. A procedure is used to investigate the material under a range of test temperatures between -60 and $60^{\circ}C$, three kind of specimen thickness, 4, 12.5 and 24.5 mm to determine the effect of two parameters on the fracture toughness. A center cracked tension (CCT) specimen is used in these tests, which were conducted using INSTRON 5567 testing machine and environmental chamber to evaluate the fracture toughness. The experimental results show that the fracture toughness tends to decreases with an increase in the temperature, and the effect of thickness indicates that the fracture toughness is highest at 12.5 mm under various temperatures except $-60^{\circ}C$. It is found that the fracture toughness of solid propellant is changed due to glass transition behavior around $-60^{\circ}C$.

Dental Caries of Factors the Oral Health Behaviors and Dental Health Services Utilization in the Middle-School Student's - focusing on middle school student's in Daegu - (중학생들의 구강건강행위 및 치과 의료서비스 이용행태가 치아우식증에 미치는 요인 - 대구시 중학교 학생을 중심으로 -)

  • Choi, Sung-Suk;So, Myung-Suk
    • The Journal of Korean Society for School & Community Health Education
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    • v.12 no.1
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    • pp.35-44
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    • 2011
  • Objectives: The purpose of this study were to measure the effect of factors analyse the associated by the oral health behaviors and dental health services utilization factors of dental caries in the middle-school student's and then to provide basic material of preventive oral health and oral health education program. Methods: This subject of study consists of 342 middle schools each 1,2,3 grade Daegu city. The data were collected from July 2 to 30, 2009. by way of the self-reported questionnaire. The data materials are analyzed by demographic characteristics, oral health behaviors and dental health services utilization of frequency analysis, demographic characteristics of dental caries and oral health behaviors and dental health services utilization of one-way ANOVA analysis. Results: Brushing twice a day, which was the higher 69.3%, Students were trained received oral health education. Girls than boys dental caries teeth(DT) index (p<0.05), dental filling teeth(FT) index(p<0.00), dental experience caries teeth(DMFT) index(p<0.00) was higher than all three variables was a statistically significant. Oral health behavior of brushing twice a day 'once' dental caries teeth(DT) index was the highest, there was statistically significant difference (p<0.01), oral health education students experience a higher dental caries teeth(DT) index(p=0.36). dental health services utilization of preventive dental visits last one year when they did not have dental caries teeth(DT) index was higher (p=0.076) Conclusions: Oral health promotion is considered to adolescent as part of the oral health clinics school for elementary school students in the focus to middle school students and enhance.

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Atomic layer deposition of In-Sb-Te Thin Films for PRAM Application

  • Lee, Eui-Bok;Ju, Byeong-Kwon;Kim, Yong-Tae
    • Proceedings of the Korean Vacuum Society Conference
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    • 2011.02a
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    • pp.132-132
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    • 2011
  • For the programming volume of PRAM, Ge2Sb2Te5(GST) thin films have been dominantly used and prepared by physical vapor deposition (PVD), chemical vapor deposition (CVD), atomic layer deposition (ALD). Among these methods, ALD is particularly considered as the most promising technique for the integration of PRAM because the ALD offers a superior conformality to PVD and CVD methods and a digital thickness control precisely to the atomic level since the film is deposited one atomic layer at a time. Meanwhile, although the IST has been already known as an optical data storage material, recently, it is known that the IST benefits multistate switching behavior, meaning that the IST-PRAM can be used for mutli-level coding, which is quite different and unique performance compared with the GST-PRAM. Therefore, it is necessary to investigate a possibility of the IST materials for the application of PRAM. So far there are many attempts to deposit the IST with MOCVD and PVD. However, it has not been reported that the IST can be deposited with the ALD method since the ALD reaction mechanism of metal organic precursors and the deposition parameters related with the ALD window are rarely known. Therefore, the main aim of this work is to demonstrate the ALD process for IST films with various precursors and the conformal filling of a nano size programming volume structure with the ALD?IST film for the integration. InSbTe (IST) thin films were deposited by ALD method with different precursors and deposition parameters and demonstrated conformal filling of the nano size programmable volume of cell structure for the integration of phase change random access memory (PRAM). The deposition rate and incubation time are 1.98 A/cycle and 25 cycle, respectively. The complete filling of nano size volume will be useful to fabricate the bottom contact type PRAM.

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Low Temperature Synthesis and Characterization of Sol-gel TiO2 Layers

  • Jin, Sook-Young;Reddy, A.S.;Park, Jong-Hyurk;Park, Jeong-Young
    • Proceedings of the Korean Vacuum Society Conference
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    • 2011.08a
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    • pp.353-353
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    • 2011
  • Titanium dioxide is a suitable material for industrial use at present and in the future because titanium dioxide has efficient photoactivity, good stability and low cost [1]. Among the three phases (anatase, rutile, brookite) of titanium dioxide, the anatase form is particularly photocatalytically active under ultraviolet (UV) light. In fabrication of photocatalytic devices based on catalytic nanodiodes [2], it is challenging to obtain a photocatalytically active TiO2 thin film that can be prepared at low temperature (< 200$^{\circ}C$). Here, we present the synthesis of a titanium dioxide film using TiO2 nanoparticles and sol-gel methods. Titanium tetra-isopropoxide was used as the precursor and alcohol as the solvent. Titanium dioxide thin films were made using spin coating. The change of atomic structure was monitored after heating the thin film at 200$^{\circ}C$ and at 350$^{\circ}C$. The prepared samples have been characterized by X-ray diffraction (XRD), scanning electron microcopy, X-ray photoelectron spectroscopy, transmission electron microscopy, ultraviolet-visible spectroscopy (UV-vis), and ellipsometry. XRD spectra show an anatase phase at low temperature, 200$^{\circ}C$. UV-vis confirms the anatase phase band gap energy (3.2 eV) when using the photocatalyst. TEM images reveal crystallization of the titanium dioxide at 200$^{\circ}C$. We will discuss the switching behavior of the Pt /sol-gel TiO2 /Pt layers that can be a new type of resistive random-access memory.

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Reliability Analysis and Feilure Mechanisms of Coolant Rubber Hose Materials for Automotive Radiator (자동차 냉각기 고무호스용 재질에 대한 신뢰성 평가 및 고장메커니즘규명)

  • Kwak Seung-Bum;Choi Nak-Sam;Kang Bong-Sung;Shin Sei-Moon
    • Transactions of the Korean Society of Automotive Engineers
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    • v.13 no.5
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    • pp.152-162
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    • 2005
  • Coolant rubber hoses for automobile radiators can be degraded and thus failed due to the influence of contacting stresses of air and coolant liquid under the thermal and mechanical loadings. In this study, test analysis was carried out for evaluating the degradation and failure mechanisms of coolant hose materials. Two kinds of EPDM rubber materials applicable to the hoses were adopted: commonly-used ethylene-propylene diene monomer(EPDM) rubbers and EPDM rubbers with high resistance against electro-chemical degradation (ECD). An increase of surface hardness and a large reduction of failure strain were shown due to the formation of oxidation layer for the specimens which had been kept in a high temperature air chamber. Coolant ageing effects took place only by an amount of pure thermal degradation. The specimens degraded by ECD test showed a swelling behavior and a considerable increase in weight on account of the penetration of coolant liquid into the skin and interior of the rubber specimens. The ECD induced material softening as well as drastic reduction in strength and failure strain. However EPDM rubbers designed for high resistance against ECD revealed a large improvement in reduction of failure strain and weight. This study finally established a procedure for reliability analysis and evaluation of the degradation and failure mechanisms of EPDM rubbers used in coolant hoses for automobile radiators.

Material Property Evaluation of High Temperature Creep on Pb-free Solder Alloy Joint to Reflow Time by Shear Punch-creep Test (전단펀치-크리프 시험에 의한 리플로우 시간별 Pb-free 솔더 합금 접합부에 대한 고온 크리프 물성 평가)

  • Ham, Young Pil;Heo, Woo Jin;Yu, Hyo Sun;Yang, Sung Mo
    • Transactions of the Korean Society of Automotive Engineers
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    • v.21 no.1
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    • pp.145-153
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    • 2013
  • In this study, shear punch-creep (SP-Creep) at Sn-4Ag/Cu pad the joint was tested by using environment-friendly Pb-free solder alloy Sn-4Ag of electronic components. Pb eutectic alloy (Sn-37Pb) joints limited to environmental issues with reflow time (10sec, 30sec, 100sec, 300sec) according to two types of solder alloy joints are compared and evaluated by creep strain rate, rupture time and IMC (Intermetallic Compound) behavior. As the results, reflow time increases with increasing thickness of IMC can be seen at overall 100sec later in case of two solder joints on the IMC thickness of Sn-4Ag solder joints thicker than Sn-37Pb solder joints. In addition, when considering creep evaluation factors, lead-free solder alloy Sn-4Ag has excellent creep resistance more than Pb eutectic alloy. For this reason, the two solder joints, such as in the IMC (Cu6Sn5) was formed. However, the creep resistance of Sn-4Ag solder joints was largely increased in the precipitation strengthening effect of dispersed Ag3Sn with interface more than Sn-37Pb solder joints.

Finite Element Analysis of Pilgering Process of Multi-Metallic Layer Composite Fuel Cladding (다중금속복합층 핵연료 피복관의 필거링 공정에 관한 유한 요소 해석 연구)

  • Kim, Taeyong;Lee, Jeonghyeon;Kim, Ji Hyun
    • Transactions of the Korean Society of Pressure Vessels and Piping
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    • v.13 no.2
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    • pp.75-83
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    • 2017
  • In severe accident conditions of light water reactors, the loss of coolant may cause problems in integrity of zirconium fuel cladding. Under the condition of the loss of coolant, the zirconium fuel cladding can be exposed to high temperature steam and reacted with them by producing of hydrogen, which is caused by the failure in oxidation resistance of zirconium cladding materials during the loss of coolant accident scenarios. In order to avoid these problems, we develop a multi-metallic layered composite (MMLC) fuel cladding which compromises between the neutronic advantages of zirconium-based alloys and the accident-tolerance of non-zirconium-based metallic materials. Cold pilgering process is a common tube manufacturing process, which is complex material forming operation in highly non-steady state, where the materials undergo a long series of deformation resulting in both diameter and thickness reduction. During the cold pilgering process, MMLC claddings need to reduce the outside diameter and wall thickness. However, multi-layers of the tube are expected to occur different deformation processes because each layer has different mechanical properties. To improve the utilization of the pilgering process, 3-dimensional computational analyses have been made using a finite element modeling technique. We also analyze the dimensional change, strain and stress distribution at MMLC tube by considering the behavior of rolls such as stroke rate and feed rate.

The Etiologic Roles and Carcinogenic Mechanisms of Human Papilloma Virus in Head and Neck Squamous Cell Carcinoma (두경부 편평세포암종의 발암 원인으로 인간유두종 바이러스(Human Papilloma Virus)의 역할 및 이와 관련된 발암 기전에 관한 연구)

  • Shin, Dong-Hyun;Lee, Sei-Young;Koo, Bon-Seok;Kim, Se-Heon
    • Korean Journal of Head & Neck Oncology
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    • v.25 no.1
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    • pp.28-32
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    • 2009
  • Background : The most frequently reported risk factors for head and neck suamous cell carcinoma are smoking and alcohol. But in a recent overview, human papilloma virus(HPV) infection was revealed the important carcinogenic factor in oropharyngeal cancer. We aimed to clarify whether HPV directly effects on the oncogenesis and biologic behavior of hean and neck squamous cell carcinoma by comparison with infection prevalence, and physical status of virus. Material and Method : We used HPV genotyping DNA chip(Biocore, Korea, Seoul) arrayed by multiple oligonucleotide probes of L1 sequence of 26 types of HPV and HPV genotypes are identified by fluorescence scanner. The copy numbers of HPV E2 and E6 open reading frames(ORF) were assessed using a TaqMan-based 5'-exonuclease quantitative real-time PCR assay. The ratio of E2 to E6 copy numbers was calculated to determine the physical status of HPV-16 viral gene. Results : We observed a significant difference in HPV prevalence between tonsillar cancer group and control group(73.1% vs. 11.6%), and most of the HPVs were type 16(87.2%) and integrated(94.1%) state. In terms of oral tongue cancer, we demonstrate that 30.5% has integrated HPV-16 in cancer tissue. But Glottic cancer only 1% is related to HPV-16 integration. Conclusion : This study revealed significant relationship of HPV prevalence with oropharyngeal and oral tongue squamous cell carcinoma. Most of HPV were 16 type and integrated or mixed, HPV-16 integration could be directly related to the carcinogenesis.

Evaluation of Mechanical Properties and Crack Resistant Performance in Concrete with Steel Fiber Reinforcement and CSA Expansive Admixture (CSA 팽창재를 혼입한 강섬유 보강 콘크리트의 역학적 성능 및 균열 저항성능 평가)

  • Choi, Se-Jin;Park, Ki-Tae;Kwon, Seung-Jun
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.18 no.1
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    • pp.75-83
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    • 2014
  • In order to prevent brittle failure of concrete, steel fiber reinforcement is effective composite material. However ductility of steel fiber reinforced concrete may be limited due to shrinkage caused by large content of cement binder. Chemical prestressing for steel fiber reinforcement in cement matrix can be induced through expansive admixture and this can increase reinforcing effect of steel fiber. In this study, mechanical performances in concrete with CSA (Calcium sulfoaluminate) expansive admixture and steel fiber reinforcement are evaluated. For this work, steel fiber reinforcement of 1 and 2% of volume ratio and CSA expansive admixture of 10% weight ratio of cement are added in concrete. Mechanical and fracture properties are evaluated in concrete with steel fiber reinforcement and CSA expansive admixture. CSA concrete with steel fiber reinforcement shows increase in tensile strength, initial cracking load, and ductility performance like enlarged fracture energy after cracking. With appropriate using expansive admixture and optimum ratio of steel fiber reinforcement, their interactive action can effectively improve brittle behavior in concrete.

The Analysis of Creep characteristics for Turbine blade using Theta projection method (θ 투영법을 이용한 터빈 블레이드의 크리프 특성 분석)

  • Lee, Mu-Hyoung;Han, Won-Jae;Jang, Byung-Wook;Lee, Bok-Won;Park, Jung-Sun
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.39 no.4
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    • pp.321-331
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    • 2011
  • The present work is aimed to analyze the creep characteristics of a turbojet engine turbine blade using the theta projection method. The theta projection method has been widely used due to its advantages and flexibility. For the creep characteristic analysis of the turbine blade, tests are performed considering the operating conditions and the non-linear material properties. Results from the creep test are fitted using the four theta model. The predicted proprieties using the four theta model are compared with the prediction model and creep test results. To obtain an optimum value of the four theta parameters in non-linear square method, a number of computing processes in the non-linear least square method were carried out to obtain full creep curves. Results using the theta model has more than 0.95 value of $R^2$. The results between the experimental values and predicted four theta model has about 90.0% accuracy. The theta projection method can be utilized for a design purpose to predict the creep behavior.