• 콘크리트학회논문집
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• 제18권3호
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• pp.303-312
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• 2006

본 연구에서는 GFRP 보강근의 인장특성치 시험을 위한 그립 시스템의 적합성을 검증하기 위하여 캐나다 규준에서 제안하는 그립(CSA 그립), ASTM에서 제안하는 그립(ASTM 그립) 및 프리스트레싱 강연선의 정착에 일반적으로 사용되는 쐐기형 그립 등을 사용하여 GFRP 보강근에 대한 인장특성치 시험을 실시하였다. 또한, 현재 외국에서 상용화되고 있는 대표적인 2종류의 GFRP 보강근(나선형 GFRP 보강근, 모래분사형 GFRP 보강근) 및 국내에서 자체 제작한 원형 GFRP 보강근을 대상으로 하여 인장특성치 분석을 위한 시험을 실시하고 각각의 제안된 그립의 적용성 여부를 검토하였다. 본 시험에 사용된 시험편의 제작, 가력 및 측정장치의 설치 등은 CSA S806-02에서 제안하는 권고사항에 따라 실시하였다. 외국의 상용화된 GFRP 보강근에 대하여 그립의 종류를 달리하여 실시된 본 시험결과에 의하면, CSA 그립을 사용하여 시험된 GFRP 보강근의 인장강도가 가장 높은 값을 보이는 것으로 나타났다. 그러나 ASTM 그립을 사용한 시험편에서 관측되는 강도저하 현상은 CSA 그립을 사용한 시험체에 비하여 약 10% 미만인 것으로 관측되었다. 한편, CSA 그립은 제작공정이 까다로울 뿐만 아니라 재사용이 불가능하여 경제성 측면에서도 불리한 것으로 파악되었다. 따라서, 실용적인 측면에서 판단하면 GFRF 보강근의 인장시험에는 ASTM 그립이 적절할 것으로 판단된다.

• Journal of Welding and Joining
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• 제18권1호
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• pp.52-58
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• 2000

Spot welding, namely a kind of electric resisting welding has been used widely in field of automobile and aircraft industries because of easiness to apply. Specimens used in this study was a mild steel of 1.2mm thickness and the electrode was a Cu-Cr alloy of 6mm diameter. The surface sheared of specimens after testing of tensile shear was observed by SEM(scanning electron microscope) after ultrasonic cleaning for 10min., and microstructures and grain size of all specimens were measured with using of O.M.(Optical microscope). By the means of measurement and observations of tensile shear load, fatigue strength and share surface, the weldability of spot welding was evaluated. When tensile shearing testing, fracture starting point in all specimens was took place at the bond between HAZ(Heat affected zone) and nugget. With increasing in number of layers, fatigue strength was decreased. With increasing in electric current, grain size in the HAZ became more fine.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.45-48
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• 2008

The mechanical behavior of small-sized materials has been investigated for many industrial applications, including MEMS and semiconductors. It is challenging to obtain accurate mechanical properties measurements for thin films due to several technical difficulties, including measurement of strain, specimen alignment, and fabrication. In this work, we used the micro-tensile testing unit with the real-time DIC (Digital Image Correlation) strain measurement system. This system has advantages of real time strain monitoring up to 50 nm resolution during the micro-tensile test, and ability to measure the young's modulus and Poisson's ratio at the same time. The mechanical properties of SCS (Single Crystal Silicon) are measured by uniaxial tension test from freestanding SCS which are $2.5{\mu}m$ thick, $200-500{\mu}m$ wide specimens on the (100) plane. Young's modulus, Poisson's ratio and tensile strength in the <110> direction are measured by micro-tensile testing system.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2007년도 추계학술대회 논문집
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• pp.360-363
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• 2007

This paper deals with the dynamic tensile characteristics of the steel sheets for structural members of a train. Train accidents occurs rarely but lead to many casualties and economical loss. Therefore the safety of the train becomes important during the train crash. The dynamic tensile characteristics of the steel sheets are indispensable to analyze the structural crashworthiness. Current research reports the stress-strain curves, fracture elongation and strain rate sensitivities evaluated at the various strain rates especially for SUS304L-ST and SUS304L-LT steel sheets. The results include the difference in the dynamic tensile characteristics of both rolling and transverse directions. Dynamic tensile tests were performed at the strain rates ranging from 0.003/sec to 200/sec using High Speed Material Testing Machine. The materials tested in this research shows interesting behavior at the low strain rates. The strain hardening exponent decreases remarkably while the yield strength increases.

• 한국기계가공학회지
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• 제5권1호
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• pp.45-50
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• 2006

This paper shows a new precision actuator of MUTM(miniature universal testing machine) for the testing of compression and tensile load on the MEMS materials and structures. The MUTM consists of a sample holder, an ultraprecision precision actuator(tranlation stage) and load sensor. The precision actuator has been developed for generating displacements with nanometer accuracy and a dynamic range of 1mm simultaneously. In this paper, it can be made by using the displacement property of bi-morph type PZT, which is able to extend the long range(stroke) according to cantilever size. However, it is not enough to be generated for compression and tensile load in miniature universal testing machine. Therefore, three dozen bi-morph type PZTs are used for generating the load. The load and displacement of the precision actuator are 35g and 0.4mm respectively.

• 한국정밀공학회지
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• 제9권2호
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• pp.122-127
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• 1992

In this study, we investigated defects of graphite by three NDT methods which are ultrasonic testing at 5 MHz, micro-forused X-ray testing and AE testing. As the detection of AE signals generated from graphite tensile specimens, we calculated location of AE sources and compared them with UT and X-ray test results in detecting defects of several specimens, Acoustic emission testing could be applied to some graphites which have fine grains of a few tens of micrometer, but it was difficult to those in lager grain of few fo milimeter. Also, we could understand what kind of defects has affected on tensile fracture of graphite.

• 한국정밀공학회지
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• 제21권8호
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• pp.89-96
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• 2004

Micro-tensile testing system, consisting of a micro tensile loading system and micro-ESPI(Electronic Speckle Pattern Interferometry) system, has been developed for measurement of micro-tensile properties of thin micro-materials. Micro-tensile loading system had a load cell with the maximum capacity of 50N and micro actuator with resolution of 4.5nm in stroke. The system was used to apply a tensile load to the micro-sized specimen. During tensile loading, the micro-ESPI system acquired interferornetric speckle patterns in the deformed specimen and measured the in-plane tensile strain. The ESPI system consisted of a CCD-camera with a lens and the window-based program developed for this experiment. Using this system, stress-strain curves for 4 kinds of electrolytic copper foil 18$\square$m thick were obtained. From these curves, tensile properties, including the elastic modulus. yielding strength and tensile strength, were determined and also values of the plastic exponent and coefficient based on Ramberg-Osgood relationship were evaluated.

• 소성∙가공
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• 제31권2호
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• pp.89-95
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• 2022

3D printing products manufactured by material extrusion are used in many industrial fields recently. However, these products are difficult to use in the field due to their low tensile strengths. In order to solve this problem, research on improving the tensile strength of the output using a 3D printer has been continuously conducted. In this study, we performed a tensile test using Universal Testing Machine according to infill pattern, nozzle temperature, bed temperature, and printing speed conditions. Results revealed that tensile specimen of concentric shape had the highest tensile strength in infill pattern condition and that the tensile strength increased linearly with increasing nozzle and bed temperatures. However, the tensile strength decreased with increasing printing speed. Consequently, we confirmed that tensile strength could be increased and decreased depending on output conditions of 3D printing.

• 한국정밀공학회지
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• 제18권12호
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• pp.167-176
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• 2001

The effects of heat treatments and testing temperatures on the mechanical properties of Invar materials were investigated through experiments, which call influence the formability in metal forming fields. Annealing temperatures were changed from $900^{\circ}C$ to $1200^{\circ}C$ with an increment of $100^{\circ}C$ under two different furnace atmosphere(vacuum and H$_2$gas). Microstructure and hardness tests were performed for annealed specimens at room temperature(RT) and tensile tests were also performed by changing annealing temperatures as well as testing temperatures from RT to $300^{\circ}C$. The grain size of annealed materials increased with increasing annealing temperature, while micro-hardness distributions showed almost same hardness values regardless of annealing temperatures. Strength ratio (tensile/yield strength), which influences the forming characteristics of sheet metal, remained almost constant for various experimental conditions in case of unannealed specimens. However, it showed increasing tendency with increasing both annealing and testing temperatures, particularly at the testing temperature higher than $200^{\circ}C$. Therefore it can be concluded that press formability of fully-annealed Invar material can be improved by warm forming technique.

• 소성∙가공
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• 제27권6호
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• pp.370-378
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• 2018

Cold forging, carried out at room temperature, leads to high dimensional accuracy and excellent surface integrity as compared to other forging methods such as warm and hot forgings. In the cold forging process, WC-Co (Tungsten Carbide-Cobalt) alloy is the mainly used material as a core dies because of its superior hardness and strength as compared to other structural materials. For cold forging, die life is the most significant factor because it is directly related to the manufacturing cost due to periodic die replacement in mass production. To investigate die life of WC-Co alloy for cold forging, mechanical properties such as strength and fatigue are essentially necessary. Generally, uniaxial tensile test and fatigue test are the most efficient and simplest testing method. However, uniaxial tension is not efficiently application to WC-Co alloy because of its sensitivity to alignment of the specimen due to its brittleness and difficulty in thread machining. In this study, shape of specimen, tools, and testing methods, which are appropriate for uniaxial tensile test for WC-Co alloy, are proposed. The test results such as Young's modulus, tensile strength and stress-strain curves are compared to those in previous literature to validate the proposed testing methods. Based on the validation of test results it was concluded that the newly developed testing method is applicable to other cemented carbides like Titanium carbides with high strength and brittleness, and also can be utilized to carry out fatigue tests for further investigation on die life of cold forging.