• Proceedings of the KWS Conference
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• 2009.11a
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• pp.100-100
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• 2009

This paper is concerned with numerical analyses of residual stresses in welds and material's susceptibility to stress corrosion cracking (SCC) for the primary piping system in nuclear power plants: Both the dissimilar metal weld (DMW) for stainless steel to low alloy steel joints and the similar metal weld (SMW) for forged stainless steel to cast stainless steel joints are considered. Thermal elasto-plastic analyses using the finite element method (FEM) are performed to predict residual stresses generated in fabrication welding and its related processes for both the DMW and SMW, including effects of quenching for cast stainless steel piping, machining of the DMW root, and grinding of the SMW root. As a result, the effect of quenching should be included in the evaluation of residual stresses in the SMW for the cast stainless steel piping. It is deemed that residual stresses in both the DMW and SMW would not affect the SCC susceptibility of the welds providing that the welding processes are completed without any weld repair on the inside wall of the joint. However, the grinding process if performed on the safe-end to piping weld, would produce a high level of residual stresses in the inner surface region and thus a stress improvement process (e.g. buffing) should be considered to reduce susceptibilities to SCC.

• Journal of the Korean Wood Science and Technology
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• v.27 no.2
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• pp.15-22
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• 1999

Polymeric meterials that are used for noise and vibration damper in wood/polymer/wood sandwich composites, must have a high loss factor(tan ${\delta}$), and at the same time the storage modulus(E) of $5{\times}10^7$ to $10^9$ dyne/$cm^2$ must withstand over a wide temperature and frequency ranges. In this study, the series of epoxy resinlpolyacrylate interpenetrating polymer networks(IPNs) were synthesized by simultaneous polymerization. Their dynamic tensile properties were measured at 110Hz using Rheovibron instrument. Composite damping factor(tan ${\delta}_c$) and dynamic bending modulus($E_c,\;E_^{\prime\prime}c$) of wood/polymer/wood sandwich composites were measured at 110Hz using a Rheovibron in bending mode of vibration. These dynamic tensile studies indicated that cured epoxy resin/polyacrylates IPNs were semicompatible in the sense that both the shifting of T($E^{\prime\prime}_{max}$) or T(tan ${\delta}_{max}$) and the broadening of glass transition temperature range were observed. Especially, the cured Epikote871/P(n-BMA) IPNs of composition 70/30 to 50/50 showed a relatively high tan a and appropriate E' value over a wide temperature range; consequently the tan a e curves of wood/IPNs/wood sandwich composites was broadened over a wide temperature range.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.10
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• pp.1201-1206
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• 2013

Defects that occur during the manufacturing process or operation of a wind turbine blade have a great influence on its life and safety. Typically, defects such as delamination, pore, wrinkle and matrix crack are found in a blade. In this study, the detectability of the pores, a type of defect that frequently occur during manufacturing, was examined from the full field strain distribution determined with the image correlation technique. Pore defects were artificially introduced in four-ply laminated GFRP composites with $0^{\circ}/{\pm}45^{\circ}$ fiber direction. The artificial pores were introduced in consideration of their size and location. Three different-sized pores with diameter of 1, 2 and 3 mm were located on the top and bottom surface and embedded. By applying static loads of 0-200 MPa, the strain distributions over the specimen with the pore defects were determined using image correlation technique. It was found the pores with diameter exceeding 2 mm can be detected in diameter.

• Journal of the Korean Society for Nondestructive Testing
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• v.26 no.2
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• pp.77-83
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• 2006

Ultrasonic nonlinearity has been considered as a solution for the detection of microcracks or interfacial delamination in a layered structure. The distinguished phenomenon in nonlinear ultrasonics is the generation of higher-order harmonic waves during the propagation. Therefore, in order to quantify the nonlinearity, the conventional method measures a parameter defined as the amplitude ratio of a second-order harmonic component and a fundamental frequency component included in the propagated ultrasonic wave signal. However, its application In field inspection is not easy at the present stage because no standard methodology has yet been made to accurately estimate this parameter. Thus, the aim of this paper is to propose an advanced signal processing technique for the precise estimation of a nonlinear ultrasonic parameter, which is based on power spectral and bispectral analysis. The method of estimating power spectrum and bispectrum of the pulse-like ultrasonic wave signal used in the commercial SAM (scanning acoustic microscopy) equipment is especially considered in this study The usefulness of the proposed method Is confirmed by experiments for a Newton ring with a continuous air gap between two glasses and a real semiconductor sample with local delaminations. The results show that the nonlinear parameter obtained tv the proposed method had a good correlation with the delamination.

• Korean Journal of Soil Science and Fertilizer
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• v.33 no.6
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• pp.377-383
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• 2000

The composition of primary minerals of sand fractions and secondary minerals of clay fractions were investigated on the polder soils developed from alluvio-marine deposits near to Sapgyo-lake, constructed a sea dike across river estuary located in the west coast. The effects of a topographical sequence on the physico-chemical properties and mineralogical characteristics were evaluated using XRD, DTA, and TG with the chemical composition of $H^+$ saturated clays. Soils located on the seashore side were more silt fraction, higher pH and exchangeable cations than the others. The dominant minerals of soil parent materials are in the order of quartz, feldspars, micas, chlorite and amphibole. According to the greater distance from the lake, the amount of 1:1 minerals increased, but 2:1 minerals decreased. The dominant clay minerals of polder soils are kaolinite, vermiculite and illite. Hydroxy interlayer minerals are abundant in the clay fractions derived from the soil parent materials which have relatively low soil pH.

• Journal of the Korean Wood Science and Technology
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• v.36 no.4
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• pp.93-101
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• 2008

Bearing strength test was investigated to determine the bearing properties of domestic larix glulam according to the load direction (in parallel to grain and in perpendicular to grain), the fastener (bolt and drift-pin), and the direction of laminae. The specimen was 5 ply glulam. The diameters of fastener are 12, 16 and 20 mm. The results were as follows. 1) In according to the diameter of bolt and drift-pin, the average of maximum bearing strength in parallel to grain loading was similar to that in perpendicular to grain loading. The average of maximum bearing strength was 1.50~2.31 times higher in parallel to grain loading than in perpendicular to grain loading. The average of maximum bearing strength in parallel to grain loading was lowered by 20% with increasing the diameter from 16 mm to 20 mm, but that in perpendicular to grain loading didn't show a clear tendency. 2) The average of bearing stiffness in parallel to grain loading was the highest at 16 mm in diameter. The average of bearing stiffness is similar to the shearing stiffness in drift-pin connection with increasing diameter. 3) In parallel to grain loading, the failure mode of specimens was the splitting along the grain in decreasing diameter. The failure mode in perpendicular to grain loading was the splitting along the grain. In this case, split occured more in specimens using bolt than in those using drift-pin. 4) The 5% offset yield strength in parallel to grain loading was similar to the predicted bearing strength of KBCS, NDS. In perpendicular to grain loading, the NDS's equation can be applied to predict the bearing strength.

• Journal of the Korean Wood Science and Technology
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• v.36 no.4
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• pp.19-25
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• 2008

This study was carried out to investigate the bending strength properties of the unreinforced glulam beams and the GFRP laminated glulam beams according to the volume ratio of GFRP. The 7-layer glulam beams ($10cm(b){\times}14cm(h){\times}180cm(l)$) were manufactured, using Larch (Larix kaempferi Carr.) laminae ($2cm(h){\times}10cm(b){\times}360cm(l)$), which were dried to the moisture content of 8% and specific gravity of 0.54. GPRP of 0.1 and 0.3 cm was reinforced between the outmost layer of bottom and next layer. When the glulam beams were reinforced with GFRP at the volume ratio of 0.7% and 2.1%, respectively, the bending strength was increased by 12% and 28%, respectively, in the reinforced beams than in control glulam beams. Also, the GFRP reinforced layer of the glulam beams with GFRP laminations blocked the progression of rupture, and the unbroken part held about 90% of the bending strength. In the results of glue joints test, the block shear strength is higher than $7.1N/mm^2$, the standard of KS F3021, and in the result of delamination, the adhesive strength is good as the water soaking and boiling delamination was less than 5%.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.161-162
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• 2011

최근 광전자 분야에서는 미래 에너지 자원에 대한 관심과 함께 GaN 기반 태양전지 연구가 활발히 진행되고 있다. GaN 물질은 높은 전자 이동도와 높은 포화 속도 등 광전자 소자에 유리한 광, 전기적 특성들을 가지고 있다. 또한, In의 함량을 변화시켜가며, 0.7eV에서 3.4eV까지 밴드갭을 조절함으로써, 자외선부터 적외선까지 태양빛 스펙트럼의 대부분을 흡수할 수 있는 장점이 있다. InGaN 태양전지의 효율을 높이기 위해서는 In의 함량을 늘려 밴드갭을 줄이는 것이 중요하다. 하지만 GaN 와 InN 간의 격자 부정합으로 인해 In 함량이 높은 단결정 InGaN 층을 두껍게 성장 하는 것이 어렵다. 때문에 GaN 기반 태양전지 관련 연구 그룹들이 태양전지의 효율 향상을 위해 활성층에 양자우물(MQWs) 구조, Supper Lattice (SLs) 구조와 같이 얇은 InGaN/GaN 층을 주기적으로 반복하여 적층함으로써 높은 조성의 In을 함유한 상질의 InGaN/GaN 층을 성장하는 연구들을 진행해 왔다. 본 연구에서는, p-i-n 구조와 MQW 구조를 갖는 InGaN 기반 태양전지를 제작하여, 각각의 특성을 분석해 봄으로써, In0.1Ga0.9N 태양전지 활성층의 구조에 따른 장/단점에 대해 논의하였다. 먼저 MOCVD를 이용하여 200 nm의 i-In0.1Ga0.9N 활성층을 갖는 p-i-n 구조와 In0.19Ga0.81N/GaN(3 nm/8 nm) MQWs (8 periods) 구조를 갖는 태양전지 에피를 각각 성장하였고, 그 후 공정을 통해 그림 1과 같이 InGaN 태양전지 소자를 제작하였다. 그 후, 각 태양전지의 전류/전압 곡선과 외부양자효율을 측정하여 그림 2와 같은 결과를 얻었다. p-i-n과 MQW 샘플의 외부양자효율은 각각 ~70%, ~25%로 측정 되었다. MQW 샘플의 외부 양자효율이 높지 않음에도 불구하고 p-i-n 구조에 비해 높은 In 함량을 가지고 있으므로, 더 넓은 파장의 빛을 흡수하여, 높은 단락전류(0.778 mA/cm2)를 보이고 있다. 또한 p-i-n 구조에 비해 높은 개방전압(2.3V)를 가지고 있으므로, MQW 샘플이 약 17% 정도 높은 변환효율(1.4%)를 보이고 있다. 이후 추가적으로 p-i-n 과 MQW 구조의 InGaN 태양전지에 나타나는 Voc와 Jsc의 차이를 Polarization 효과를 비롯한 다양한 측면에서 분석해 보고자 한다.

• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.5
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• pp.96-106
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• 2014

The increased vibration level of the railway bridge could make significant noise and, also, cause structural damages such as fatigue cracks. Related to these subjects, a spherical elastomeric bridge bearing, which is layered by hemispherical rubber and steel plates, was investigated in terms of its vibration performance. Several different shape factors could be considered by changing the curvature of hemispherical surface and size in rubber and steel plate thicknesses in the manufacturing stage. The performance of the spherical elastomeric bearing for the reduction in vibration was compared with that of the conventional bearing by performing vibration experiments on a scale-downed model. The rubber material characteristics and spherical shape are found to be important parameters in reducing the bridge vibration.

• Journal of the Korean Ceramic Society
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• v.40 no.1
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• pp.87-92
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• 2003

$Ti_3AlC_2$was synthesized from TiCx and Al powder as a starting materials at the temperature range between$800^{circ}C;and;1500^{\circ}C$. The vacuum sintering and hot pressing methods were imployed to synthesize$Ti_3AlC_2$. The high purity$Ti_3AlC_2$was synthesized using TiCx and Al powder as starting materials without formation of Ti-Al intermetallic compound and Al-C compound.$Ti_2$AlC and$Ti_3AlC_2$were preferentially synthesized at$800^{\circ}C$and above$1200^{\circ}C$, respectively.$Ti_2$AlC formed at low temperature was transformed to$Ti_3AlC_2$by further reaction with TiC. In this study, the synthesis mechanism for$Ti_3AlC_2$was proposed. The synthesized$Ti_3AlC_2$showed the nano laminating structure consisting of$Ti_3AlC_2$crystal with the thickness of 45~120 nm.