• 한국세라믹학회지
• /
• 제47권2호
• /
• pp.117-121
• /
• 2010

$SnO_2-(1-x)P_2O_5-xB_2O_3$ glass system were prepared by melt-quenching technique in the compositional series containing 50, 55 and 60 mol% of $SnO_2$. Local structure of the glasses was investigated by Raman and FT-IR measurements. A large glass-forming region was found at the phosphate side of the ternary system with homogeneous glasses containing up to 5~25 mol% of $B_2O_3$. According as content of $B_2O_3$ increases, theraml expansion coefficient of glass decreased but transition temperature and softening temperature increased. Because these phenomenon changed local structure of glass. According as content of $B_2O_3$ increases, quantity of bridging oxygen increased. Also, according as content of $SnO_2$ increases, confirmed that quantity of non-bridging oxygen increases.

• Transactions on Electrical and Electronic Materials
• /
• 제8권1호
• /
• pp.5-10
• /
• 2007

Using a reference slurry, ammonium dodecyl sulfate (ADS), an anionic and environmentally friendly surfactant, was investigated as an alternative to BTA for its inhibition and lubrication characteristics. Results demonstrated that the inhibition efficiency of ADS was superior to that of BTA. Coefficient of friction (COF) was the lowest when the slurry contained ADS. This suggested that adsorbed ADS on the surface provided lubricating action thereby reducing the wear between the contacting surfaces. Temperature results were consistent with the COF and removal rate data. ADS showed the lowest temperature rise again confirming the softening effect of the adsorbed surfactant layer and less energy dissipation due to friction. Spectral analysis of shear force showed that increasing the pad-wafer sliding velocity at constant wafer pressure shifted the high frequency spectral peaks to lower frequencies while increasing the variance of the frictional force. Addition of ADS reduced the fluctuating component of the shear force and the extent of the pre-existing stick-slip phenomena caused by the kinematics of the process and collision event between pad asperities with the wafer. By contrast, in the case of BTA, there were no such observed benefits but instead undesirable effects were seen at some polishing conditions. This work underscored the importance of real-time force spectroscopy in elucidating the adsorption, lubrication and inhibition of additives in slurries in CMP.

• 대한토목학회논문집
• /
• 제4권2호
• /
• pp.55-64
• /
• 1984

본(本) 논문(論文)에서는 콘크리트의 점진적(漸進的) 인장파괴현상(引張破壞現象)을 해석(解析)할 수 있는 증분형(增分形)이며, 진로종속적(進路從屬的)이고, 텐서적으로 불변성(不變性)인 비선형구성(非線型構成)모델이 제안(提案)되었다. 전(全) 변형도(變形度)는 탄성성분(彈性成分)과 비탄성성분(非彈性成分)의 합(合)으로 표시(表示)된다. 콘크리트내부(內部)에는 미세균열(微細龜裂)의 근원(根源)이 되는 약(弱)한 면(面)들이 모든 방향(方向)으로 좌우(左右)하며, 이 약(弱)한 면(面)에서의 법선응력(法線應力)은 법선변형도(法線變形度)의 함수라고 가정된다. 이와 같은 근본개념(根本槪念)아래 가상(假想)일의 원리(原理)로부터 콘크리트의 접선강도(接線剛度)가 유도된다. 본(本) 이론(理論)은 비비례하중(非比例荷重)이나 주응력(主應力)의 방향(方向)이 변(變)하는 경우 등의 일반적(一般的)인 하중상태(荷重狀態)에 적용할 수 있으며, 이것이 본(本) 모델의 주요(主要)한 목적이 될 수 있다. 본(本) 이론(理論)을 변형연화현상(變形軟化現象)을 보이는 직접인장실험자료(直接引張實驗資料)와 비교한 결과 좋은 일치를 얻었다.

• 대한기계학회논문집A
• /
• 제24권3호
• /
• pp.777-785
• /
• 2000

The low-cycle fatigue behaviors of cast AI-Si alloy and composite with reinforcement of SIC particles were compared with those of extruded unreinforced matrix alloy and composite in order to investigate the influence of cast and extrusion processes on the cyclic deformation and fatigue life. Generally, both cast and extruded composites including the unreinforced alloy exhibited cyclic hardening behaviour, with more pronounced strain-hardening for the composites with a higher volume fraction of the SiC particles. However, cast composite under a low applied cyclic strain showing no observable plastic strain exhibited cyclic softening behavior due to the cast porosities. The elastic modulus and yield strength of the cast composite were found to be quite comparable to those of the extruded composite, however, the extrusion process considerably improved the ductility and fracture strength of the composite by effectively eliminating the cast porosities. Low-cycle fatigue lives of the cast alloy and composite were shorter than those of the extruded counterparts. Large difference in life between cast and extruded composites was attributed to the higher influence of the cast porosities on the fatigue life of the composite than that of the unreinforced alloy material. A fatigue damage parameter using strain energy density effectively represented the inferior life in the low-cycle regime and superior life in the high-cycle regime for the composite, compared to the unreinforced alloy.

• 대한기계학회논문집A
• /
• 제27권10호
• /
• pp.1793-1799
• /
• 2003

An optimal design of a multi-layered plate structure to endure high-velocity impact has been suggested by using size optimization after numerical simulations. The NET2D, a Lagrangian explicit time-integration finite element code for analyzing high-velocity impact, was used to find the parameters for the optimization. Three different materials such as mild steel, aluminum for a multi-layered plate structure and die steel for the pellet, were assumed. In order to consider the effects of strain rate hardening, strain hardening and thermal softening, Johnson-Cook model and Phenomenological Material Model were used as constitutive models for the simulation. It was carried out with several different gaps and thickness of layers to figure out the trend in terms of those parameters' changes under the constraint, which is against complete penetration. Also, the measuring domain has been shrunk with several elements to reduce the analyzing time. The response surface method based on the design of experiments was used as optimization algorithms. The optimized thickness of each layer in which perforation does not occur has been obtained at a constant velocity and a designated total thickness. The result is quite acceptable satisfying both the minimized deformation energy and the weight criteria. Furthermore, a conceptual idea for topology optimization was suggested for the future work.

• 한국전산구조공학회논문집
• /
• 제18권4호통권70호
• /
• pp.395-404
• /
• 2005

본 논문에서는 동적하중 재하 시 공간 강뼈대 구조물의 비선형 시간이력 해석에 대한 간편하고 효율적인 수치해석 기법을 제시하였다. 뼈대의 강성행렬에 안정함수를 적용함으로서 기하학적 비선형성 즉 P-$\delta$ 및 P-$\Delta$ 효과를 고려하였다. 접선계수 개념 및 New Orbison 완전 소성면에 기초한 연화소성힌지를 적용하여 축방항력에 의한 부재의 점진적 항복 및 휨에 의한 부재의 부분 소성화를 고려하였다. 증분형태로 정식화된 뼈대 구조의 동적평형방정식의 해를 수치적으로 구하기 위하여 적분형태의 평균가속도법을 사용하여 컴퓨터 프로그램을 개발하였다. 검증 예제에 대하여 보요소 모델을 사용한 ABAQUS 및 개발된 프로그램에 의한 해석결과를 비교함으로서 개발된 프로그램의 정밀도와 해석시간에 대한 효율성을 입증하였다.

• Journal of Advanced Marine Engineering and Technology
• /
• 제24권6호
• /
• pp.70-77
• /
• 2000

In this paper, the effect of solution and age heat treatment to the corrosion behavior for the Ti-6Al-4V alloy were studied by cyclic polarization methods. Ti-6Al-4V was solution heat treated at $1,066^{\circ}C$ and $966^{\circ}C$ for 5 hours, and followed by age heat treated at $650^{\circ}C$, $600^{\circ}C$ and $550^{\circ}C$ with 1, 2, 4, 8 and 16 hours under vacuum environment. Test solution was 3.5% NaCl with temperature $25^{\circ}C$. The obtained results were as follows: 1. Base metal was exhibited higher electrical charge than that of solution and aged material. With decrease of solution-treatment temperature from 1066 to $966^{\circ}C$, the electrical charge was increased due to softening of micro structure. 2. The corrosion resistance of specimen that solution treated at $966^{\circ}C$ for 5 hours and age heat treated at 650, 660 and $550^{\circ}C$ were increased with increase of aging time to 4, 8 and 16 hours respectively, and then decreased. 3. In case of 316L stainless steel, measured charge and corrosion potential was 0.0627 coulomb and -614 mV respectively. Corrosion resistance of Ti-6Al-4V was higher than that of 316L.

• 한국터널지하공간학회 논문집
• /
• 제2권2호
• /
• pp.62-71
• /
• 2000

지하채굴작업에 의한 공동 및 폐갱 등은 지반침하 및 지표함몰현상의 주요 원인이 되며, 근접시공 지하구조물 또는 인근 구조물의 안정성 저해요소로 대두되고 있다. 이에 대한 대책방안으로 폐갱을 충진재로 채우는 보강시공을 수행하는 경우가 있으나 설계방법 및 안정성 해석방법이 미흡한 실정이다. 따라서 본 연구에서는 폐갱 등 지하공동에 의한 주변지반의 영향권을 수치적으로 분석하고 실제 수치해석 과정에서 주변 암반의 장기거동을 고려할 수 있는 방안을 제시하였다. 아울러 폐갱 인근의 구조적 안정성을 향상시키기 위하여 지하공동을 뒷채움재로 충진한 경우, 안정성 평가 및 암반의 거동을 수치적으로 분석할 수 있는 기법을 제시하였으며 불완전한 뒷채움재의 영향을 함께 고려하였다.

• 한국도로학회논문집
• /
• 제19권2호
• /
• pp.45-53
• /
• 2017

PURPOSES: The objectives of this study are to develop a new cold-applied crack sealant and to evaluate its properties and field applicability by comparing with other conventionally used crack sealants. METHODS : A new cold-applied crack sealant was developed by using neoprene latex to improve material properties. The fundamental properties such as viscosity, residue %, penetration, and softening point of the developed crack sealant were tested by TxDOT criteria to evaluate crack sealing capability. Moreover, the performance of the developed cold-applied crack sealant was evaluated under both laboratory and field conditions. In the laboratory, the bond property was evaluated using the developed cold-applied crack sealant and conventional hot-applied crack sealant by the bond-properties test standardized under ASTM D 6690. In the field, test sections were constructed on three areas: a trunk road, bus-only lane, and motorway, with the developed crack sealant and three conventional crack sealants. After construction, early field-inspection was performed on the test sections. RESULTS AND CONCLUSIONS : Overall, the developed cold-applied crack sealant demonstrates reasonable storage stability, durability, and bond property compared to conventional hot-applied crack sealants. From the test sections, it was established that the developed cold-applied crack sealant does not pose construction issues. Moreover, the early performance was verified through field inspection. However, as the field inspection was conducted a week after the construction, it is necessary to conduct an inspection of performance from a long-term point of view.

• 한국자동차공학회논문집
• /
• 제13권5호
• /
• pp.152-162
• /
• 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.