• 한국지반공학회논문집
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• 제18권4호
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• pp.167-177
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• 2002

표준관입시험 시 항타로 인해 시추봉 두부에서 발생하는 응력파가 시추봉 선단과 접해 있는 지반에서 반사되어 돌아오는 동적신호를 분석함으로써, 시추봉 선단부에 인접한 지반의 임피던스(강성)에 관해 보다 상세한 정보를 얻고자 하는 시험방법이 시도되고 있다. 이 시험법의 실규모 시험에 선행하여 본 논문에서는 시추봉-지반시스템에 대한 동적유한요소해석을 통해 동적신호를 얻고, 이들 신호를 분석하여 추정한 지반의 임피던스와 탄성계수의 신뢰도를 평가함으로써 시험법의 적용성을 검토하고자 하였다. 또한 반사파의 특성에 영향을 미칠 수 있는 인자들에 대한 평가를 통해서 실규모 시험을 위한 참고자료를 제공하고자 하였다. 이러한 연구 결과, 시추봉과 지반의 접촉면에서 입사, 반사되는 파동의 진폭비($F_반F_입$)에 가장 심각하게 영향을 미치는 인자는 시추봉 선단과 접촉한 지반강성의 변화임을 알았으며, 이들 파동의 진폭비의 변화는 시추봉과 지반 간의 임피던스 비($\alpha$)의 변화와 밀접한 관련이 있는 것으로 나타났다. 이러한 결과로부터 SPT 동적신호를 분석하여 시추봉 선단과 직접 닿아 있는 지반에 대한 임피던스와 변형 계수를 추정하는 시험법의 적용 가능성이 있다는 결론을 얻었다.

• 한국지반공학회논문집
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• 제19권1호
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• pp.111-120
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• 2003

본 연구에서는 점성토지반의 침하량 평가에 보다 적합한 새로운 응력경로시험을 소개하였다. 새로운 시험기법에서는 배압평형과정을 채택함으로써 특정 응력경로상의 모든 점에 대응하는 변형특성을 하나의 시험을 통해 파악할 수 있다. 따라서, 제안된 시험기법을 적용하는 경우, 응력경로법의 실용적인 적용을 위해 필요한 지반의 전반적인 변형거동을 몇 개의 시험만으로 예측할 수 있으며 나아가 기존의 시험기법으로는 수행이 불가능했던 이방적 압밀응력 경로에 대한 변형거동의 평가 역시 실험적으로 가능해진다. 이와 함께 본 연구에서는 성형 카올리나이트 시료에 대해 다양한 응력경로시험을 수행하여 제안된 시험기법의 실험적 적용성을 확인하였으며, 그 결과를 활용하여 전반적인 변형거동과 침하량을 평가하는 실제 과정을 제시하였다.

• Corrosion Science and Technology
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• 제13권3호
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• pp.102-106
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• 2014

Nickel electrodeposition from sulfamate bath has several benefits such as low internal stress, high current density and good ductility. In nickel deposited layers, sulfur induces high temperature embrittlement, as Ni-S compound has a low melting temperature. To overcome high temperature embrittlement problem, adding manganese is one of the good methods. Manganese makes Mn-S compound having a high melting temperature above $1500^{\circ}C$. In this work, the mechanical properties of Ni-Mn deposited layers were investigated by using various process variables such as concentration of Mn$(NH_2SO_3)_2$, current density, and bath temperature. As the Mn content of electrodeposited layers was increased, internal stress and hardness were increased. By increasing current density, internal stress increased, but hardness decreased. With increasing the bath temperature from 55 to $70^{\circ}C$, internal stress of Ni deposit layers decreased, but hardness didn't change by bath temperature. It was likely that eutectoid manganese led to lattice deformation, and the lattice deformation increased hardness and internal stress in Ni-Mn layers. Increasing current density and decreasing bath temperature would increase a mount of $H_2$ absorption, which was a cause for the rise of internal stress.

• Journal of Welding and Joining
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• 제5권3호
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• pp.53-61
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• 1987

Post weld heat treatment(PWHT) is usually carried out to remove the residual stress and to improve the microstructure and mechanical properties of welded joints. By the way, welding structure transformed owing to PWHT and reheating for repair loads the random cycles fatigue as offshore welding structure of constant low cycle fatigue as pressure vessel, and then, pre-existing flaws or cracks exist in a structural component and those cracks grow under cyclic loading. Therefore, the effects of PWHT and stress ratio on fatigue crack growth behaviors were studied on the three regions such as HAZ, sub-critical HAZ and deposit metal of welded joints in SM53 steel. Fatigue crack growth behavior of as-weld depended on microstructure and fatigue crack growth rate of HAZ was the lowest at eac region, but after PWHT it was somewhat higher than that of as-wel. In case of applying the stress($10kg/mm^2$) during PWHT, fatigue crack growth resistance tended to increase in the overall range of .DELTA.K.

• Journal of Nutrition and Health
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• 제32권6호
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• pp.644-653
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• 1999

Background : Excessive intakes of $\omega$6 polyunsaturated fatty acid (PUFA) can increase oxidative stress, which may increase insulin resistance and could be the cause of metabolic syndrome X such as diabetes mellitus. One of the ways to reduce oxidative stress is the consumption of antioxidants such as vitamin E. It is controversial that vitamin E intakes may alleviate insulin resistance. The purpose of the study was whether high vitamin E intake may influence whole body glucose disposal rate(GDR), glycogen deposites, triglyceride content, lipid peroxide levels and antioxidant enzyme activities in Sprague Dawley rats fed high $\omega$6 PUFA diest. Methods : Sprague Dawley rats were divided into three groups. The control group consumed chow diet. High and low vitamin E groups consumed 40% PUFA of total energy intakes. One kilogram of diet mixture contained 300IU of $\alpha$-tocopherol in high vitamin E group, while it had 30 IU in low vitamin E group. Diets were given for 8 weeks. After 7 were of diet consumption, indwelling catheters were inserted in carotid artery and jugular vein of all rats so that GDR could be measured in awake and unstressed state. Results : Daily PUFA intakes were lower in the control group than others. Daily vitamin E intake of high vitamin E group was about ten times higher than those of low vitamin E group and the control group(p<0.0001). $\alpha$-tocopherol content in lier was highest in the high vitamin E group. GDR of the control group was 24% higher than others, and vitamin E intakes did not affect GDR. Glycogen deposit of liver in the control group was significantly higher than others, and it was not altered by vitamin E supplementation. Muscle glycogne content showed a similar tendency as liver glycogen in different diet groups. Triglyceride deposit in muscle was not different among groups. Lipid peroxide content of liver in the high vitamin E group was lower than the low of glutathione peroxidase were lowered in low vitamin E group than others, however, those of superoxide dismutase and catalase were not different. Conclusions : High vitamin E intakes can decrease oxidative stress in rats fed high (())-6 PUFA diet, but they cannot alleviate insulin resistance. Thus, increased oxidative stress through high (())-6 PUFA diet may be minimal for influencing insulin resistance.

• 한국재료학회지
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• 제14권9호
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• pp.642-648
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• 2004

The microstructure and crack tip opening displacement (CTOD) of deposit weld metal were investigated for a 30 mm- thick plate welded with flux cored arc welding (FCAW) and submerged arc welding (SAW) processes. The CTOD test was carried out both as welded condition and as stress-relieved specimen by local compression. The crack growth rates in FCAW were faster than those in a SAW, and the acicular ferrite content by the SAW process was increased relatively more than that by the FCAW process. The fatigue crack growth rate in a welded specimen was faster than that in locally compressed specimen. The CTOD value of locally compressed specimens was lower than that of as welded specimen. Furthermore, the CTOD value tested with the SAW process was higher than that tested with the FCAW process.

• Geomechanics and Engineering
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• 제7권3호
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• pp.279-295
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• 2014

A series of one-dimensional consolidation tests and triaxial creep tests were performed on Nansha clays, which are interactive marine and terrestrial deposits, to investigate their time-dependent behaviour. Based on experimental observations of oedometer tests, normally consolidated soils exhibit larger secondary compression than overconsolidated soils; the secondary consolidation coefficient ($C_{\alpha}$) generally gets the maximum value as load approaches the preconsolidation pressure. The postsurcharge secondary consolidation coefficient ($C_{\alpha}$') is significantly less than $C_{\alpha}$. The observed secondary compression behaviour is consistent with the $C_{\alpha}/C_c$ concept, regardless of surcharging. The $C_{\alpha}/C_c$ ratio is a constant that is applicable to the recompression and compression ranges. Compared with the stage-loading test, the single-loading oedometer test can evaluate the entire process of secondary compression; $C_{\alpha}$ varies significantly with time and is larger than the $C_{\alpha}$ obtained from the stage-loading test. Based on experimental observations of triaxial creep tests, the creep for the drained state differs from the creep for the undrained state. The behaviour can be predicted by a characteristic relationship among axial strain rate, deviator stress level and time.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2004년도 추계학술발표대회 개요집
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• pp.76-78
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• 2004

The phenomenon of weld shrinkage mainly occurs owing to residual stress by heating, which largely effects on welding quality, Actually as the shrinkage rate depends on the weld deposit amount, so it is desired that the sectional area of weld joint shall be reduced. In this respect the Electron beam welding has more profitable position compare to Narrow-gap TIG welding which is even superior to other arc welding processes. In case of thick austenitic stainless steel the shrinkage rate of Electron beam welding has about $10\%$ of Narrow-gap TIG welding's, which means that residual stress is a lot less than that of Narrow-gap TIG welding. And heat input and welded section area also indicate large difference between two processes.

• 한국전기전자재료학회논문지
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• 제14권10호
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• pp.779-784
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• 2001

In this work, we studied the characteristics of nitride films for the optimization of PMD(pro-metal dielectric) linear process, which can be applied to the recent semiconductor manufacturing process. We split the deposit condition of nitride films into four parts such as PO(protect overcoat) nitride, baseline, low hydrogen and high stress and low hydrogen, respectively. We tried to find out correlation between BPSG deposition and densification. In order to analyze the changes of Si-H and Si-NH-Si bonding density, we used FTIR area method. We also investigated the crack generation on wafer edge after BPSG densification, and the changes of nitride film stress as a function of RF power variation to judge whether the deposited films.

• 한국표면공학회지
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• 제47권6호
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• pp.303-310
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• 2014

In this study, the average in-situ stress in metallic thin film was measured during deposition of the Cu thin films on the Si(111) wafer and then the phenomenon of stress shift by the interruption of deposition was measured using Cu thin films. We have observed the stress shift in accordance with changing amount of atom's movement between the surface and grain boundary through altering the grain size of the Cu thin film with variety of parameters. The grain size is known to be affected on the deposition rate, film thickness and deposition temperature. As a experimental results, the these parameters was not adequate to explain stress shift because these parameters affect directly on the amount of atom's movement between the surface and grain boundary as well as the grain size. Thus, we have observed the stress shift toward tensile side in accordance with the grain size changing through the interlayer deposition. From an experiment with inserting interlayer before deposit Cu, in thin film which has big grain size with high roughness, amount of stress movement is higher along direction of tensile stress after deposition that means, after deposition process, driving force of atoms moving in grain boundary and on the surface of the film is relatively higher than before.