• 한국조경학회지
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• 제25권2호
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• pp.94-103
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• 1997

The purpose of this study is to find out the effects of brick paved under-surface soil physical properties which are changed by fixed trampling. Thus, a sandy loam which is known as a profitable soil for plants is used an experimental soil to study the changes of the soil physical properties. It is related to sand bed's thickness & particle size which are settled by experimental variable factors. According to the variation of sand bed's particle size, bulk density and soil hardness at natural dryed soilcondition result in 0.075~2.00mm>2.00~5.00mm>2.00~8.00mm>5.00~8.00mm, and water content at natural dryed soil condition are observed being insensible change rate from the point that sand thickness is 30~40mm and more sand bed's thickness constructed by the variation of sand bed's thickness.

• Journal of Welding and Joining
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• 제30권4호
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• pp.49-54
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• 2012

The microstructure and mechanical properties of the high-strength low-alloy steel weld metals with a variation of nickel content were investigated. The weld metals with a variation of nickel content from 2.3 to 3.3 wt% were prepared using Gas Metal Arc Welding process. The amount of acicular ferrite decreased with increasing nickel content; this is accompanied with an increase in the region of bainite and martensite, hence the hardness and tensile strengths were increased with the increase in nickel content, whereas the impact energy was deteriorated.

• 열처리공학회지
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• 제35권5호
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• pp.239-245
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• 2022

The purpose of this study is to evaluate the degree of microstructural change of materials using ultrasonic nonlinear parameters. For microstructure change, isothermal heat-treated ferritic 2.25Cr steel and low-cycle fatigue-damage copper alloy were prepared. The variation in ultrasonic nonlinearity was analyzed and evaluated through changes in hardness, ductile-brittle transition temperature, electron microscopy, and X-ray diffraction tests. Ultrasonic nonlinearity of 2.25Cr steel increased rapidly during the first 1,000 hours of deterioration and then gradually increased thereafter. The variation in non-linear parameters was shown to be coarsening of carbides and an increase in the volume fraction of stable M6C carbides during heat treatment. Due to the low-cycle fatigue deformation of oxygen-free copper, the dislocation that causes lattice deformation developed in the material, distorting the propagating ultrasonic waves, and causing an increase in the ultrasonic nonlinear parameters.

• 한국조경학회지
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• 제33권6호
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• pp.40-50
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• 2006

This study was carried out to examine the tree-ring growth characteristics of Zelkova serrata Makino after replanting, for the built-up planting founds for stability of landscaped trees in the reclaimed land from the sea. the factors, many affecting the growths of Zelkova serrata Makino, were the replanting stress and drought. The growth reduction due to replanting and drought occurred in the replanting year and the following year. The mean sensitivity(year-to-year variation) and the coefficient of variation(tree-to-tree variation in a certain year) in tree rings of Zelkova serrate Makino, were higher in the poor soil sites than in the favourable soil ones. And the poor soil sites were the filled ground of improve soil and the covered ground of improve soil and the top ground of big mounding than mounding ground sites, especially soil hardness, alkali soil, high $Na^+\;and\;K^+,\;low\;Ca^{++}\;and\;Mg^{++}$ and T-C were the most crucial. We suggest technique development of the built-up planting ground for stability in the reclaimed land from the sea. The built-up planting grounds in reclaimed land from the sea, should be considered for the use of fair soil with the physical and chemical soil properties, -high level foundation of planting ground, and the prevention of disturbed soil-.

• Transactions on Electrical and Electronic Materials
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• 제5권2호
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• pp.71-75
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• 2004

This paper proposes a new bandgap reference (BGR) circuit which takes advantage of a cascode current mirror biasing to reduce the V$\_$ref/ variation, and sizing technique, which utilizes two related ratio numbers k and N, to reduce the PNP BJT area. The proposed BGR is designed and fabricated on a test chip with a goal to provide a reference voltage to the 10 bit A/D(4-4-4 pipeline architecture) converter of the CMOS Active Pixel Sensor (APS) imager to be used in X-ray imaging. The basic temperature variation effect on V$\_$ref/ of the BGR has a maximum delta of 6 mV over the temperature range of 25$^{\circ}C$ to 70$^{\circ}C$. To verify that the proposed BGR has radiation hardness for the X-ray imaging application, total ionization dose (TID) effect under Co-60 exposure conditions has been evaluated. The measured V$\_$ref/ variation under the radiation condition has a maximum delta of 33 mV over the range of 0 krad to 100 krad. For the given voltage, temperature, and radiation, the BGR has been satisfied well within the requirement of the target 10 bit A/D converter.

• 열처리공학회지
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• 제20권6호
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• pp.311-317
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• 2007

This study examined the phase changes, nitride precipitation and variation in mechanical properties of STS 304, STS 321 and STS 316L austenitic stainless steels after high temperature gas nitriding (HTGN) at temperature ranges from $1050^{\circ}C\;to\;1150^{\circ}C$. Fine round type of $Cr_2N$ nitrides were observed in the surface layers of 304 and 316L steels, even more in STS 321. Additionally, square type of TiN was found in STS 321 austenitic matrix too. As a result of many precipitates in the surface layer of the STS 321, it was seen $370{\sim}470Hv$ hardness variation depending on the HTGN treatment conditions, and interior region of austenite represented 150Hv. The surface hardness value of STS 304 and STS 316L showed $255{\sim}320Hv$, respectively. The nitrogen content was shown 0.27, 1.7 and 0.4% respectively at the surface layers of the STS 304, STS 321 and STS 316L. After the HTGN it was shown the improvement of corrosion resistance of the STS 321 and STS 316L compared with solution annealed steels in the solution of 1N $H_2SO_4$ whereas the STS 304 was not.

• 폴리머
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• 제27권3호
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• pp.249-254
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• 2003

가교 폴리에틸렌을 열을 가하여 노화시킨 후 구조 및 물성의 변화를 조사하였다. 가교 폴리에틸렌의 열적 산화 반응으로 카보닐 그룹이 형성됨을 X-선 광전자 분광법과 근적외선 분광법을 이용하여 확인하였다. 노화 시간이 길어질수록 1715 nm에서 관찰되는 카보닐 피이크가 정량적으로 증가하는 것을 근적외선 분광법을 이용하여 관찰하였다. 열화 시간에 따른 흡수 피이크의 선형적인 관계로부터 근적외선 분광법이 고분자 재료의 열화 과정을 감시하는데 적합한 방법임을 확인할 수 있었다. 또한 노화에 의한 가교 결합의 발생과 그에 따른 물리적 성질의 변화를 TMA, 응력-변형 시험, 쇼어 경도 측정 방법을 이용하여 관찰하였다. 노화가 진행됨에 따라 유리 전이 온도가 110에서 132$^{\circ}C$로 증가함을 관찰하였으며, 인장률은 265에서 110%로 점차 감소하고 쇼어 D 경도는 32에서 50으로 크게 증가하는 것을 관찰할 수 있었다.

• 한국세라믹학회지
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• 제30권4호
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• pp.289-298
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• 1993

Properties in terms of the variation of the glass compositions, which were density (p), molar volume(Vm), atom/ion packing density (Dp), refractive index (nD), transformation temperature (Tg), dilatometric softening point (Td), thermal expansion coefficient (α), Young's modulus (E), and knoop hardness (KHN) were investigated in CaO-SiO2 glasses and CaO-P2O5-SiO2 glasses containing less than 10mole% of P2O5. Those properties were measured by density measurement kit, Abbe refractometer, dilatometer, ultrasonic pulse echo equipment, and micro hardness tester. When CaO content was increased in CaO-SiO2 glasses, p, Dp, nD, Tg, Td, α, E and KHN were increased, while Vm was decreased. When P2O5 was added to the CaO-SiO2 glasses with constant CaO/SiO2 ratio as 1.07, p, Dp, nD, Tg, Td, α, E and KHN were decreased, while Vm was increased. When the amount of P2O5 in glasses was kept constant, the changes of the properties with variation of CaO content in the CaO-P2O5-SiO2 glasses were very similar to those of CaO-SiO2 glasses. These phenomena could be explained by the structural role of P2O5 in the CaO-P2O5-SiO2 glasses, which was polymerization of siicate structures and resulted in [PO4] monomer structure in glasses. Due to this structural characteristics, the bond strength and packing density were changed with compositions. Proportional relationships between 1) np and Dp, 2) Tg, Td, α and CaO content, 3) E and Vm-1, and 4) KHN and P2O5 content were evaluated in this investigation.

• 한국주조공학회지
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• 제3권1호
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• pp.13-21
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• 1983

In order to determine the feeding distance of aluminiun alloys (Alsi7Mg and AlCu4Ti) bar castings in the sand mold, the distance of the sound castings has been observed by radiograph for various risers, melt treatment, and casting design. Variation of porosity and hardness with the distance from the riser were also measured in order to determine the casting soundness. The results obained were as follows; 1) The modulus of riser should be 1.4 times of the casting`s 2) The maximum distance which can be made sound is greatly dependent on chemical composition and ingate location, and follows the rules given by the formula; a) When the melt flows into the casting first, and the riser afterward, D = 37.7 ${\sqrt{T}}$ for AlSi7Mg D = 31.2 ${\sqrt{T}}$ for pure aluminium D ${\ge}$ 54.8 ${\sqrt{T}}$ for AlCu4Ti Where T = casting thickness in mm Of this maximum distance, $aa{\sqrt{T}}$ for AlSi7Mg and 7.5 ${\sqrt{T}}$ for pure aluminium is made sound by the chilling effect of the casting edge. b) When the melt flows into the casting passing through the riser, $30{\times}30{\times}600mm$ bars can be made sound in all cases 3) Percentage of porosity is higer in AlCu4Ti than AlSi7Mg. And it is increased gradually by moving closer to the riser in case of $30{\times}30{\times}600mm$ bars, but for the $30{\times}30{\times}600mm$ bars it is increased gradually by moving closer to the center of bars. 4) Hardness variation is similar to the tendency of porosity. And it decreased gradually with approaching to the center in case of $30{\times}30{\times}600mm$ bars.

• 열처리공학회지
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• 제10권2호
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• pp.93-100
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• 1997

Effect of austenite grain size on starting temperature of ${\gamma}{\rightarrow}{\varepsilon}$ martensitic transformation($M_s$) has been studied in an Fe-18%Mn alloy. Particular attention was paid on the variation of stacking fault energy with austenite grain size, which is considered to be a important factor affecting ${\gamma}{\rightarrow}{\varepsilon}$ martensitic transformation. Austenite grain size was increased in a wide range from $13{\mu}m$ to $185{\mu}m$ with increasing solution treatment temperature from $700^{\circ}C$ to $1100^{\circ}C$. Hardness was decreased with increasing austenite grain size while the volume fraction of ${\varepsilon}$ martensite showed a reverse tendency, which indicates that the hardness is more dependent on austenite grain size than ${\varepsilon}$ martensite content. No significant change was found in $M_s$ temperature when the grain size was larger than about $30{\mu}m$. In case that, the austenite grain size was smaller than about $30{\mu}m$, however, $M_s$ temperature was marlkedly decreased with decreasing austenite grain size. A linear relationship between $M_s$ temperature and the stacking fault formation probability, i.e. the reciprocal of the stacking fault energy was obtained, which suggests that the variation of $M_s$ temperature with austenite grain size is closely related to the change in stacking fault energy.