• 터널과지하공간
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• 제13권2호
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• pp.117-124
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• 2003

암석의 불균질성이 정적 인장강도에 미치는 영향을 평가하기 위해, 유한요소해석법과 파괴역학에 기초하여 제안된 수치해석기법을 사용하여 정적 일축인장시험을 가정한 암석 파쇄 과정을 해석하였다 정적 인장강도 는 미시적 인장강도를 가진 모델 시험편의 파쇄 과정으로부터 평가되었으며, 평가된 공시체 강도는 미시적 인장 강도의 최소치보다 약간 큰 값에 일치하였으며, 그 강도의 흩어짐은 균질성 계수가 증가합에 따라 감소하였다. 본 해석 결과들로부터 암석 불균질성이 정적 인장강도에 미치는 중요한 요인임을 지적할 수 있었다.

• International Journal of Naval Architecture and Ocean Engineering
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• 제9권1호
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• pp.66-76
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• 2017

This paper is concerned with investigating the plastic material properties of steel plate formed by line heating method, and is aimed at implementing more rational design considering the accidental limit states such as collision or grounding. For the present study, line heating test for marine grade steel plate has been carried out with varying plate thickness and heating speed, and then microscopic examination and tensile test have been carried out. From the microscopic, it is found that the grain refined zones like ferrite and pearlite are formed all around the heat affected zone. From the tensile test results, it is seen that yield strength, tensile strength, fracture strain, hardening exponent and strength coefficient vary with plate thickness and heat input quantity. The formulae relating the material properties and heat input parameter should be, therefore, derived for the design purpose considering the accidental impact loading. This paper ends with describing the extension of the present study.

• 터널과지하공간
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• 제13권3호
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• pp.180-186
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• 2003

동적 인장강도를 평가하기 위해 수치해석기법을 이용하여 홉킨슨효과를 가정한 동적 인장시험의 암석 파쇄 과정을 해석하였다. 동적 인장 파쇄 과정과 정적 인장 파쇄 과정에 명확한 차이가 있음을 밝혔으며, 동적 인장강도와 정적 인장강도의 상위는 응력집중현상과 응력재분배에 의해 발생된다는 것을 지적하였다. 그러나 정적파쇄와 동적파쇄 과정에 큰 차이가 있음에도 불구하고 정적 인장강도와 동적 인장강도는 미시적 인장강도의 균질성 계수가 증가함에 따라 미시적 인장강도의 평균치에 근접하였다. 본 연구로부터 암석의 불균질성은 동적 인장강도에 영향을 미치는 요인이며, 동적 인장강도와 정적 인장강도의 상위를 발생시키는 중요한 요인임을 지적하였다.

• Advances in materials Research
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• 제3권1호
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• pp.283-295
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• 2014

In this paper, the microstructure, hardness, tensile deformation and fracture behavior of high strength alloy steel X2M is presented anddiscussed. The influence of both composition and processing on microstructure of the as-provided material and resultant influence of microstructure, as a function of orientation, on hardness, tensile properties and final fracture behavior is highlighted. The macroscopic mode and intrinsic microscopic features that result from fracture of the steel specimens machined from the two orientations, longitudinal and transverse is discussed. The intrinsic microscopic mechanisms governing quasi-static deformation and final fracture behavior of this high strength steel are outlined in light of the effects oftest specimen orientation, intrinsic microstructural effects and nature of loading.

• Journal of Chest Surgery
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• 제22권3호
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• pp.373-383
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• 1989

Glutaraldehyde is known as an ideal preservatives for pericardial heterograft, and many laboratories used this chemicals for preparing tissue valves, pericardial patches and MVOP [monocusp ventricular outflow patch] so we tried to find out the appropriate concentration and ingredients of the Glutaraldehyde for the preparing bovine pericardium. We selected 50 calves, aged about 2 years, and procured their pericardia. These were divided 6 groups such as fresh group, treated with only antibiotics, treated with Glutaraldehyde 0,5%, 0.625 %, 0.75 %, and 0.875 %, and our experiments included microbial culture test, tensile strength measurement and microscopic examination. On microbial culture, there were no growth on 1 week and 4 weeks after preparation with all kind of Glutaraldehyde, but on 4 weeks after only antibiotics treatment [Penicillin, Streptomycin, Kanamycin, Amphotericin -B] E.coli and candida albicans were observed. On tensile strength test, 0.625 % and 0.75 % Glutaraldehyde were revealed as the best preservatives for bovine pericardium and compared to other commercial products they kept more desirable tensile strength. On light and electron microscopic examinations, Glutaraldehyde treated pericardia had much regular and compact collagen fibers and preserved more normal structures, but there were no difference between the different concentration of the Glutaraldehyde. We concluded that 0.625% and 0.75 % Glutaraldehyde were the best concentration for preservation of bovine pericardium in our experiment.

• 한국압력기기공학회 논문집
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• 제14권1호
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• pp.15-23
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• 2018

A compact heat exchanger is one of critical components in a very high temperature gas-cooled reactor (VHTR). Alloy 617 (Ni-Cr-Co-Mo) is considered as one of leading candidates for this application due to its excellent thermal stability and strengths in anticipated operating conditions. On the basis of current ASME code requirements, sixty sheets of this alloy are prepared for diffusion welding, which is the key technology to have a reliable compact heat exchanger. Optical microscopic analysis show that there are no cracks, incomplete bond, and porosity at/near the interface of diffusion weldment, but Cr-rich carbides and Al-rich oxides are identified through high resolution electron microscopic analysis. In high-temperature tensile testing, superior yield strengths of the diffusion weldment compared to the code requirement are obtained up to 1223 K ($950^{\circ}C$). However, both tensile strength and ductility drop rapidly at higher temperature due to the insufficient grain boundary migration across the interface of diffusion weldment. Best fit curves for minimum yield strength and average tensile strength are drawn from the experimental tensile results of this study.

• Computers and Concrete
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• 제18권1호
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• pp.39-51
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• 2016

This paper considers the tensile strength of concrete samples in direct, CTT, modified tension, splitting and ring tests using both of the experimental tests and numerical simulation (particle flow code 2D). It determined that which one of indirect tensile strength is close to direct tensile strength. Initially calibration of PFC was undertaken with respect to the data obtained from Brazilian laboratory tests to ensure the conformity of the simulated numerical models response. Furthermore, validation of the simulated models in four introduced tests was also cross checked with the results from experimental tests. By using numerical testing, the failure process was visually observed and failure patterns were watched to be reasonable in accordance with experimental results. Discrete element simulations demonstrated that the macro fractures in models are caused by microscopic tensile breakages on large numbers of bonded discs. Tensile strength of concrete in direct test was less than other tests results. Tensile strength resulted from modified tension test was close to direct test results. So modified tension test can be a proper test for determination of tensile strength of concrete in absence of direct test. Other advantages shown by modified tension tests are: (1) sample preparation is easy and (2) the use of a simple conventional compression press controlled by displacement compared with complicate device in other tests.

• Advances in materials Research
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• 제1권3호
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• pp.169-182
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• 2012

In this paper the intrinsic influence of micron-sized nickel particle reinforcements on microstructure, micro-hardness tensile properties and tensile fracture behavior of nano-alumina particle reinforced magnesium alloy AZ31 composite is presented and discussed. The unreinforced magnesium alloy (AZ31) and the reinforced nanocomposite counterpart (AZ31/1.5 vol.% $Al_2O_3$/1.5 vol.% Ni] were manufactured by solidification processing followed by hot extrusion. The elastic modulus and yield strength of the nickel particle-reinforced magnesium alloy nano-composite was higher than both the unreinforced magnesium alloy and the unreinforced magnesium alloy nanocomposite (AZ31/1.5 vol.% $Al_2O_3$). The ultimate tensile strength of the nickel particle reinforced composite was noticeably lower than both the unreinforced nano-composite and the monolithic alloy (AZ31). The ductility, quantified by elongation-to-failure, of the reinforced nanocomposite was noticeably higher than both the unreinforced nano-composite and the monolithic alloy. Tensile fracture behavior of this novel material was essentially normal to the far-field stress axis and revealed microscopic features reminiscent of the occurrence of locally ductile failure mechanisms at the fine microscopic level.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1993년도 추계학술대회 논문집
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• pp.650-655
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• 1993

Carbon/epoxy composite(CFRP) coupons previously damaged by low velocity impact were tested under static tensile loading and microscope progress of damage was characterized by ultrasonic C-scan, Scanning Acoustic Microscopy (SAM) and Acoustic Emission(AE) techniques which were based on the application of elastic waves. The degress of impact damage has been correlated with the AE activity during monotonic or loading/unloading tensile testing as well as the result of ultrasonic test. The coupons were subjected to impact velocities ranged from 0.71 to 2.17 m/sec, which introduced the amount of damage rated as 0%, 10%, 30%, and 50% with reference to the total absorbed energy at fracture. Special attention was paid to determine optimal AE parameters to characterize the microscopic fracture process and to predict the residual strength of composite laminates. AE RMS voltage during the early stage of tensile loading was found an effective parameter to quantify the degree of impact damage. It was also found that the Felicity ratio is closely related to the stacking sequence and the residual strength of the CFRP laminates.

• Composites Research
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• 제26권4호
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• pp.218-222
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• 2013

본 연구에서는 제강 과정의 부산물로 발생하는 슬래그의 구조용 충전제로써의 사용 가능성을 검토하였다. 고분자 기지 슬래그 복합재료를 제작하여 슬래그 입자의 크기(8~12 ${\mu}m$ and 12~16 ${\mu}m$), 체적 비(0-30 vol.%)에 따른 슬래그 복합재료의 기계적 특성에 대한 실험적 연구를 수행하였다. 복합재료 물성에 영향을 주는 요인인 입자 분산 도와 계면상태를 고찰하기 위해 각각 시편에 대하여 조직사진을 촬영하였다. 인장 시험 결과 슬래그 복합재료의 재료강성은 슬래그 체적비가 증가할수록 증가하였고 인장 강도는 체적비가 증가할수록 감소하였다. 슬래그 복합재료의 재료강성은 슬래그 입자의 크기의 변화에 따른 뚜렷한 경향성을 띄지 않았고 인장강도는 입자의 크기가 작을수록 높은 값을 가졌다. 조직 사진 촬영 결과 슬래그 복합재료가 양호한 계면상태를 보였고, 낮은 체적 비에서는 좋은 분산 도를 나타냈지만 체적비가 높아지면 입자들의 뭉침 현상이 발생하는 것을 알 수 있었다.