• 열처리공학회지
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• 제14권4호
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• pp.212-219
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• 2001

The fatigue test was carried out to evaluate the fatigue characteristics of fire resistance steel for frame structure and heat affected zone (HAZ) by the one side Gas Metal Arc Welding (GMAW). In this paper, the fatigue crack growth behavior was investigated with the compact tension specimen of base metal and the HAZ according to chemical composition and rolling end temperature, respectively. And the acoustic emission signals obtained from the fatigue test were analyzed by the time-frequency analysis method as a nondestructive evaluation. Main results obtained are summarized as follows; The hardness was appeared softening phenomenon that weld metal and HAZ are lower than that of base metal. Fatigue life of welded specimen was longer than that of base metal. m was 3~4.5 in base metal and 3.8~5.8 in HAZ. The main frequency range of acoustic emission signal analyzed from time-frequency method is different with the range by noise and crack. Also, it could be classified that it was also generated by fracture mechanics of dimple, inclusion etc.

• 대한금속재료학회지
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• 제49권12호
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• pp.967-976
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• 2011

Conventional fracture tests of resistance spot welds have been performed without consideration of the paint baking process in the automobile manufacturing line. The aim of this paper is to investigate the effect of the paint baking process on load carrying capacity and fracture mode for resistance spot welded 590 dual phase (DP), 780DP, 980DP, 590 transformation in duced plasticity (TRIP), 780TRIP and 1180 complex phase (CP) steels. With paint baking after resistance spot welding, the l-shape tensile test (LTT) and nano-indentation test were conducted on the as-welded and paint baked samples. Paint baking increased the load-carrying capacity of the resistance spot welded samples and improved the fracture appearance from partial interfacial fracture (PIF) to button fracture (BF). Improvement in fracture appearance after LTT is observed on weldments of 780 MPa grade TRIP steels, especially in the low welding current range with paint baking conditions. The higher carbon contents (or carbon equivalent) are attributed to the low weldability of the resistance spot welding of high strength steels. Improvement of the fracture mode and load carrying ability has been achieved with ferrite hardening and carbide formation during the paint baking process. The average nano-indentation hardness profile for each weld zone shows hardening of the base metal and softening of the heat affected zone (HAZ) and the weld metal, which proves that microstructural changes occur during low temperature heat treatment.

• 한국결정성장학회지
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• 제23권1호
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• pp.44-50
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• 2013

E-glass 섬유는 항공기, 자동차, 레져기구의 복합재료 보강용으로 가장 널리 사용되는 유리섬유이다. 그러나 최근 E-glass 섬유의 원재료비 상승, 환경문제 및 화학적 저항성과 기계적 특성을 향상시키기 위해 산화붕소 함량을 8 %에서 0(제로)까지 감소시키는(소위 'Boron free E-glass'라고 불리는) 연구가 진행되고 있다. 본 연구에서는 'BF(Boron free E-glass)' 조성의 벌크유리와 섬유유리를 제조하고, 열적특성 및 광학적특성을 평가하였다. 5~10 %의 서로 다른 알루미나 함량을 갖는 배치를 $1550^{\circ}C$에서 2시간 용융하여 'BF(Boron free E-glass)'가 얻어졌고, 81~86 %의 높은 가시광투과율, $4.2{\sim}4.9{\times}10^{-6}/^{\circ}C$의 낮은 열팽창계수, $907{\sim}928^{\circ}C$의 연화점을 갖는 투명하고 맑은 유리가 얻어졌다. 'BF' 섬유 시편에 대한 화학적내구성 시험에 있어서는 알루미나 함량이 높아질수록 더 좋은 침식저항성을 나타냄을 확인할 수 있었다.

• Journal of Welding and Joining
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• 제28권4호
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• pp.61-66
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• 2010

Silicon nitride is widely used as an engineering ceramics because it has high strength, abrasion resistance and corrosion resistance even at high temperature. However, machining of silicon nitride is difficult due to its high hardness and brittleness. Laser assisted machining(LAM) allows effective cutting using CBN tool by locally heating the cutting part to the softening temperature of YSiAlON using the laser beam. The effect of preheating depending on process parameters were studied to find out the oxidation mechanism. If silicon nitride is sufficiently preheated, the surface is oxidized and $N_2$ gas is formed and escapes from the material, thereby making the cutting process more advantageous. During laser preheating process before machining, high temperature results in strong oxidation which makes the bloating, silicate layers and micro cracks. Using the results of these experiments, preheating characteristics and oxidation behavior were found out.

• International Journal of Naval Architecture and Ocean Engineering
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• 제11권2호
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• pp.796-808
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• 2019

In this paper, a Smoothed Particle Hydrodynamics (SPH) method is extended to simulate the ice failure process and ice-ship interactions. The softening elastoplastic model integrating Drucker-Prager yield criterion is embedded into the SPH method to simulate the failure progress of ice. To verify the accuracy of the proposed SPH method, two benchmarks are presented, which include the elastic vibration of a cantilever beam and three-point bending failure of the ice beam. The good agreement between the obtained numerical results and experimental data indicates that the presented SPH method can give the reliable and accurate results for simulating the ice failure progress. On this basis, the extended SPH method is employed to simulate level ice interacting with sloping structure and three-dimensional ice-ship interaction in level ice, and the numerical data is validated through comparing with experimental results of a 1:20 scaled Araon icebreaker model. It is shown the proposed SPH model can satisfactorily predict the ice breaking process and ice breaking resistance on ships in ice-ship interaction.

• 한국응용과학기술학회지
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• 제12권1호
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• pp.29-34
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• 1995

Silicone softner(SSN-3) for permanent press(PP) finish was prepared by blending beef tallow hardened oil for Improving softness, water, the emulsion, which was synthesized from pentaerythritol monostearate as a softening component and silicone oil KF-96 as a lubricating component. The prepared SSN-3 and the PP finishing resin were applied to PP finishing cotton broad cloth and P/C gingham samples using one bath method. The properties such as crease recovery, tear strength, bending resistance test were tested. The samples treated with SSN-3 and PP finishing resin have improved properties, compared with nontreated samples, those treated only with PP finishing resin, those treated with commercial PP finishing softners and PP finishing resin. Also from the bending resistance test, the two kinds of fabric samples treated with SSN-3 of 3% showed grade 5 and these were good enough in feeling.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2006년도 하계학술대회 논문집 Vol.7
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• pp.220-221
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• 2006

We investigated the electrical properties of polymer-carbon composite materials for temperature sensitive resistor applications. Cu/polymer/Cu sheets were fabricated by laminating low density polyethylene(LDPE) containing carbon powders. Weight ratio of carbon powder to LDPE was varied in a range of 0.9~2. With increasing the carbon concentration, the electrical resistance of the composite material was decreased from 0.75 to $0.08\;{\Omega}cm$. The composite layer showed a abrupt increase in the electrical resistance at $115^{\circ}C$ because of the softening of the polymer.

• 한국응용과학기술학회지
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• 제19권2호
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• pp.117-122
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• 2002

A silicone softner (SS-5), a permanent press (PP) finish, was prepared by blending silicone oil KF-96 (as a lubricating component) and beef tallow hardened oil (as a softening component) which was synthesized from fatty polyamide salts. The prepared SS-5 and the PP finishing resin were applied to PP finishing cotton cloth and P/C gingham sample by one-bath method. The properties such as crease recovery, tear strength, and bending resistance were tested. The samples treated with SS-5 and PP finishing resin showed improved properties when comparing with the untreated ones, with the ones treated only with PP finishing resin, with ones treated with commercial PP finishing softners and PP finishing resin. The grades of fabric samples treated with 3% SS-5 were fifth grade in the bending resistance test.

• 대한기계학회논문집A
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• 제26권5호
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• pp.896-903
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• 2002

The susceptibility of SCC for the weldment and PWHT specimens of HT-60 steel was evaluated using a slow strain rate method under applied potential by means of the potentiostat in synthetic seawater. In case of the parent, anodic polarization voltage was inappropriate in elongating the time to failure(TTF). -0.8V corresponding to cathodic protection range is most effective in improving the SCC resistance against corrosive environment. In case of the weldment, the values of reduction of area(ROA) and TTF at -0.68V corresponding to cathodic polarization value were 45.2% and 715,809sec which were the largest and longest life among other applied potentials. Those were vise versa at -1.1V. In case of the PWHT specimens, TTF and ROA at -0.68V was longest and largest like the weldment. Besides, PWHT is effective in prolonging the time to failure of the welded off-shore structure due to softening of effect. Regardless of the weldment and PWHT specimen, as corrosion rate gets higher, TTF becomes shorter and deformation behaviour for the weldment and PWHT specimen at -1.1V was shown to be irregular. Finally, it was found that specimens showed brittle fracture at -1.1V, but more ductile fracture accompanying the micro-cracks at applied potential of -0.68V.

• 열처리공학회지
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• 제7권1호
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• pp.44-52
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• 1994

In order to investigate the effect of tempring treatment on the mechanical properties of ausformed martensite in Fe-30%Ni-0.35%C alloy, the hardness, yield strength and elongation were examined by tensile test. 1. The strength of deformed austenite in Fe-30%Ni-0.35%C alloy was increased due to the work hardening induced from the dislocation density increased during deformation. The strength of ausformed martensite was increased because of defects inherited from deformed austenite by martensitic transformation. 2. The ductility of ausformed martensite was shown a nearly constant values independent of deformation degrees because of the interaction of multiple factors such as increased retained austenite, formation of void and decrement of twin in ausformed martensite. 3. The strength of ausformed martensite by tempering treatment was shown a little decrement up to $340^{\circ}C$, especially showed remarkable softening resistance in higher deformation degrees. 4. Virgin martensite and ausformed martensite were shown a maximum yield strength by clustering in tempering at $100^{\circ}C$ and above $100^{\circ}C$, yield strength was very small decreased due to the decrement of solute carbon by the destruction of clustering. 5. The decomposition of retained austenite was not shown up to $450^{\circ}C$ in ausformed martensite with tempering treatment, and the matrix was rapidly softening because of the decomposition of martensite and the formation of reversed austenite with tempering above $400^{\circ}C$.