• Nuclear Engineering and Technology
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• 제48권1호
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• pp.259-267
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• 2016

Most manufacturing processes, including welding, create residual stresses. Residual stresses can reduce material strength and cause fractures. For estimating the reliability and aging of a welded structure, residual stresses should be evaluated as precisely as possible. Optical techniques such as holographic interferometry, electronic speckle pattern interferometry (ESPI), Moire interferometry, and shearography are noncontact means of measuring residual stresses. Among optical techniques, ESPI is typically used as a nondestructive measurement technique of in-plane displacement, such as stress and strain, and out-of-plane displacement, such as vibration and bending. In this study, ESPI was used to measure the residual stress on the welded part of butt-welded American Society for Testing and Materials (ASTM) A36 specimens with $CO_2$ welding. Four types of specimens, base metal specimen (BSP), tensile specimen including welded part (TSP), compression specimen including welded part (CSP), and annealed tensile specimen including welded part (ATSP), were tested. BSP was used to obtain the elastic modulus of a base metal. TSP and CSP were used to compare residual stresses under tensile and compressive loading conditions. ATSP was used to confirm the effect of heat treatment. Residual stresses on the welded parts of specimens were obtained from the phase map images obtained by ESPI. The results confirmed that residual stresses of welded parts can be measured by ESPI.

• 지구물리
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• 제6권2호
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• pp.71-77
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• 2003

Generally the dynamic characteristics of stone wall structures depend on several factors such as contact, the type of interlocking bonding stones, and the filling materials. This paper describes a non-destructive technique for diagnosis of historic masonry stone structures using the measurement of natural frequency technique. For this purpose, the castle wall of Nag-An Folk Town located in Sunchon, Korea was selected as a model. The Nag-An Town Castle is one of the well maintained historical remains constructed in the Chosun Kingdom of Korea. The construction started in 1397 A.D and was finished in 1626 A.D. The non-mortar castle wall is 1470m long and the average height is 4m with a width of 3 4m. The exterior of the wall is bonded with 1 2 m rectangular rough-faced stone and the inside of the wall is filled with gravel. The traditional village still remains inside the Nag-An Town Castle, and they have a regional food festival every October. Transverse vibrations were measured at 8 points around the castle. The measured natural frequency of the first mode was 26Hz 41Hz, and the shear modulus of filling material was 2.142 x $10^3$ ~ 8.915 x $10^3$kgf/$cm^2$ . With these results, it may be assumed that the filling material is gravel or a sand-gravel mixture. It is expected that the information provided by this paper will be useful for addressing the maintenance problems of the old castle walls.

• 한국염색가공학회지
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• 제24권4호
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• pp.281-287
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• 2012

Poly(phenylene sulfide) films containing acetophenone as a photoinitiator were photocrosslinked under UV irradiation using a continuous UV irradiator. The gel fraction of the irradiated PPS in 1-Chloro naphthalene reached 94.7% with increasing UV energy and the photoinitiator concentration in the film upto $200J/cm^2$ and 12wt% respectively. Solid state $^1C$ NMR analysis suggested that the crosslinking occurred between the phenylene chains in PPS, indicating that the acetophenone may the phenylene hydrogens and subsequently adjacent polymer radicals could be recombined to form the crosslinked structure. The crosslinking improved the thermal behavior of PPS such as loss of $T_g$ and $T_c$, higher melting point and lower melting enthalphy as well as significantly higher peak pyrolysis temperature as much as $63.5^{\circ}C$. Surprisingly the tensile toughness of the most crosslinked PPS increased by 842%, resulting from the substantial enhancements in tensile modulus, strength and strain as much as 76%, 236% and 240% respectively. Also dynamic mechanical measurement indicated that the distance between crosslinks in the crosslinked PPS reached 85.3 g/mol corresponing to a crosslink density of 0.012 mol/g.

• 한국농업기계학회:학술대회논문집
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• 한국농업기계학회 2002년도 동계 학술대회 논문집
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• pp.471-478
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• 2002

초음파를 사과의 비파괴 품질판정에 이용하기 위한 기초연구로서 계측된 저장기간에 따른 사과의 초음파 특성과 본 연구에서 계측된 사과의 기계적 특성을 이용하여 초음파에 의한 사과의 탄성계수 및 생물체항복강도 예측모델을 개발하고자 하였으며, 결론은 다음과 같다. 1. UTM을 이용하여 사과의 기계적 특성치를 분석하여 생물체항복점, 생물체항복변형량, 생물체항복강도, 파괴점, 극한변형량, 극한강도 및 탄성계수 등을 구하였다. 2. 사과의 기본 물성, 초음파 특성과 기계적 특성값 들을 분석한 결과 사과의 질량, 체적, 시간영역의 진폭(PTP), 제3영역 에너지 스펙트럼 밀도함수가 기계적 특성 중 생물체항복강도, 탄성계수와 높은 상관성이 있는 것으로 나타났다. 3. 사과의 저장 기간, 질량, 체적, Peak-to-peak, 제3영역의 에너지값 등 5개의 독립변수를 가지는 다중선형회귀모형으로 사과의 탄성계수 및 생물체 항복강도 예측모형을 개발하였다.

• Geomechanics and Engineering
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• 제13권6호
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• pp.1027-1044
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• 2017

Membrane penetration is the most important factor influencing the measurement of volume change for triaxial consolidated-drained shear test for coarse-grained soil. The effective pressure p, average particle size $d_{50}$, thickness $t_m$ and elastic modulus $E_m$ of membrane, contact area between membrane and soil $A_m$ as well as the initial void ratio e are the major factors influencing membrane penetration. According to the membrane deformation model given by Kramer and Sivaneswaran, an analytical solution of the membrane penetration considering the initial void ratio is deduced using the energy conservation law. The basic equations from theory of plates and shells and the elastic mechanics are employed during the derivation. To verify the presented solution, isotropic consolidation tests of a coarse-grained soil are performed by using the method of embedding different diameter of iron rods in the triaxial samples, and volume changes due to membrane penetration are obtained. The predictions from presented solution and previous analytical solutions are compared with the test results. It is found that the prediction from presented analytical solution agrees well with the test results.

• Metals and materials international
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• 제24권6호
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• pp.1285-1292
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• 2018

Microstructural properties of as-grown and annealed CoCrFeMnNi high entropy alloy (HEA) oxynitride thin films were investigated. The CoCrFeMnNi HEA oxynitride thin film was grown by magnetron sputtering method using an air gas, and annealed under the argon plus air flow for 5 h at $800^{\circ}C$. The as-grown film was homogeneous and uniform composed of nanometer-sized crystalline regions mixed with amorphous-like phase. The crystalline phase in the as-grown film was face centered cubic structure with the lattice constant of 0.4242 nm. Significant microstructural changes were observed after the annealing process. First, it was fully recrystallized and grain growth happened. Second, Ni-rich region was observed in nanometer-scale range. Third, phase change happened and it was determined to be $Fe_3O_4$ spinel structure with the lattice constant of 0.8326 nm. Hardness and Young's modulus of the as-grown film were 4.1 and 150.5 GPa, while those were 9.4 and 156.4 GPa for the annealed film, respectively.

• Tribology and Lubricants
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• 제37권2호
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• pp.54-61
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• 2021

The effect of the sand blasting before TiAlN coating in the manufacture of WC hard metal alloy tips have been studied. For four different tips, according to the status of processing of the sand blasting and the coating, residual stress measurement by X-ray diffraction and several tests for mechanical properties have been conducted. The results suggest that there was no difference in static mechanical properties, such as hardness, surface roughness and elastic modulus, between two coatings. Furthermore, compressive residual stress was generated equally on their surfaces. Additionally, the compressive residual stress in substrate WC was found to increase greatly when subjected to sand blasting treatment. However, the compressive residual stress decrease after coating regardless of sand blasting treatment. Nevertheless, it is confirmed that the compressive residual stress generated in the coating after sand blasting is less than that in the non-sandblasting coating. This was attributed to the plastic deformation occurring in the WC substrate during coating after sand blasting. In contrast to the scratch test results, sand blasting was assumed to have a negative effect on the adhesion between the coating and substrate. This is because there is a high possibility of microcracks due to plastic deformation in the WC substrate under the coating after sand blasting.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2003년도 추계학술발표회초록집
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• pp.54-54
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• 2003

DLC films were deposited on Si(100) substrates by inductively coupled plasma (ICP) assisted chemical vapor deposition (CVD). A mixture of acetylene (C$_2$H$_2$) and argon (Ar) gases was used as the precursor and plasma source, respectively. The structure of the films was characterized by the Raman spectroscopy. Results from the Raman spectroscopy analysis indicated that the property change of the DLC films is due to the sp$^3$ and sp$^2$ ratio in the films under various conditions such as ICP power, working pressure and RF substrate bias. The hydrogen content in the DLC films was determined by an electron recoil detector (ERB). The roughness of the films was measured by atomic force microscope (Am). A microhardness tester was used for the hardness and elastic modulus measurement. The DLC film showed a maximum hardness of 37㎬. In this work, the relationship between deposition parameters and mechanical properties were discussed.

• Geomechanics and Engineering
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• 제37권2호
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• pp.149-166
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• 2024

The acoustic emission (AE) technique is utilized to estimate the rock failure status in underground spaces. Understanding the AE characteristics under loading conditions is essential to ensure the reliability of AE monitoring. The AE characteristics depend on the material properties (p-wave velocity, density, UCS, and Young's modulus) and damage stages (stress ratio) of the target rock mass. In this study, two groups of granite specimens (based on the p-wave velocity regime) were prepared to explore the effect of material properties on AE characteristics. Uniaxial compressive loading tests with an AE measurement system were performed to investigate the effect of the rock properties using AE indices (count index, energy index, and amplitude index). The test results were analyzed according to three damage stages classified by the stress ratio of the specimens. Count index was determined to be the most suitable AE index for evaluating rock mass stability.

• 한국구조물진단유지관리공학회 논문집
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• 제22권3호
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• pp.1-7
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• 2018

본 연구에서는 동결융해 작용을 받는 콘크리트의 내구성을 현장에서 평가하기 위한 일환으로 표면 거칠기 값과 이미지 분석을 대상으로 상대동탄성계수와의 관계를 분석하였다. 배합은 물-시멘트비에 따라 40%, 50%, 60% 및 70% 총 4배합으로 수행하였으며 동해를 조기에 발현시키기 위하여 AE제를 사용하지 않았다. 실험은 물-시멘트비에 따라 상대동탄성계수 및 압축강도 등의 기본 물성 시험과 표면 거칠기 측정, 화상 이미지 및 SEM 이미지 분석을 수행하였다. 표면 거칠기 시험 결과 물-시멘트비에 상관없이 전반적으로 싸이클이 증가함에 따라 표면거칠기 값이 증가하는 경향을 보였으며 상대적으로 조밀한 40% 및 50%의 경우 상대동탄성계수가 60% 이하인 시점까지 서서히 증가하는 경향을 보였으나, 60% 및 70%의 경우 파괴 시점에서만 표면 거칠기 값이 증가하였다. 또한, 표면부 화상 이미지 분석에서도 물-시멘트비 40% 및 50%의 경우 동결융해 싸이클이 진행되는 과정에서 표면부터 서서히 열화가 진행되는 과정을 확인할 수 있었으나 60% 및 70%의 경우 표면부의 변화가 미미하다 파괴 시점에서 균열 등의 손상을 확인할 수 있었다. 따라서, 상대적으로 수밀하지 않은 시험체의 경우 화상 이미지나 표면 거칠기 등의 인자로 동결융해의 열화 정도를 판별하기에는 일부 제한이 있을 것으로 판단되며 상대적으로 수밀한 W/C 40% 및 50%의 경우 표면 거칠기 및 표면부 화상 이미지로 동해의 열화 진행 정도를 판단할 수 있었으며 향후 현장에서 표면 거칠기 및 이미지 분석을 적용할 수 있을 것으로 판단된다.