• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.3
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• pp.457-463
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• 2016

The newly developed super ductile duplex stainless steel (SDSS) has good strength and ductility, and it can be used to reduce weight and improve the fabrication efficiency of a carbody of a rolling stock. In this study, spot weldability tests were conducted to take advantage of SDDSS in a carbody for an intermodal tram. Specimens of various thickness (0.4 to 5.0 mm) were prepared to find the proper welding conditions, and tensile load tests were conducted to evaluate the tensile-shear strength of spot welded joints. Then, nugget diameters were measured to verify the quality. The tensile-shear strength was found to be proportional to the heat parameter. It was verified that the tensile-shear strengths and nugget sizes of the joints satisfy the standard requirements. The overall weldability tests confirmed that SDDSS can be used effectively for the carbody of an intermodal tram.

• Journal of the Korea Concrete Institute
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• v.13 no.2
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• pp.161-167
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• 2001

It is difficult to obtain accurate fracture toughness values using three point bending test(TPB) proposed by RILEM committees because the shape of load-deflection curve is irregular and final crack propagation occurs after some slow stable cracking. However, fracture toughness is easily obtained from crack initiation load in the disk test. In this paper, the fracture properties of high strength concrete disks with center-crack was investigated. For this purpose, the experimental results were compared with the results by finite element analysis(FEA). And the experimental fracture locus was compared with theoretical fracture locus. Also, the results of fracture properties for the degree of concrete strength are presented. It is concluded from this study that results from FEA with maximum stress theory were compared well with the results from experiment. And the degree of concrete strength was contributed to the crack initiation load and fracture toughness, but was not contributed to the failure angle. Also, The discrepancy of fracture locus between the maximum stress theory and the experiment for concrete is considered to depend upon a large energy requirement for inducing the mixed-mode and sliding mode fractures.

• Magazine of the Korea Concrete Institute
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• v.4 no.2
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• pp.103-110
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• 1992

본 연구는 인성지수에 의하여 섬유보강 콘크리트의 인성을 평가하는 기존의 여러 가지 방법을 검토하는, 하중-처짐곡선에서 초기균열시까지의 여러 가지 다른 곱으로 나타내어지는 방법의 불합리성을 지적하였다. 이를 위하여 본 연구에서는 유효인성이라고 부르는 새로운 방법을 강섬유 보강콘크리트의 인성을 평가하는데 제안하였다. 이는 초기균열을 가진 3점 휨강도 시험에 의한 하중-처짐곡선에서 지간의 1/150까지의 면적을 ligament면적으로 나눈값으로 나타낸다. 이 방법을 사용하여 강섬유 보강 고강도 콘크리트 인성특성을 검토한 결과 기존의 방법보다 더 효과적으로 인성을 평가할 수 있었다.

• Journal of the Korea Concrete Institute
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• v.17 no.2 s.86
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• pp.255-261
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• 2005

Immense quantities of coal combustion by-products are produced every year, and only a small fraction of them are currently utilized. The purpose of this study is to investigate reused techniques of coal ash in the construction field, which may contribute to the savings of building materials and conservation of environment. From the results of the compressive strength test, the elastic modulus was experimentally proposed. Also, based on the three- point-bending test, the fracture parameters - notch sensitivity, fracture energy, and initial compliance were experimentally proposed. As a result, the strength and fracture characteristics were lower than those of concrete or mortar. Also, the study showed that the deflection at a fracture decreased as the age increased and as the notch depth rate decreased. However, it was judged that its use as a building material could be expected if further research is carried out.

• Journal of the Korean GEO-environmental Society
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• v.8 no.6
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• pp.85-95
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• 2007

It is difficult for seismic survey to get hold of characteristic of coal shale fractured zone and if coal shale zone did not come into contact with underground water, coal shale zone has characteristic of good strength. But in case coal shale zone is exposed by excavation or blasting to the air, strength of coal shale zone decreases in short term and weathering of coal shale zone progresses rapidly. Therefore, the prediction of tunnel collapse is not easy in the coal shale zone and the great portion of tunnel collapse takes place in a moment. From a view point of strength, after twelve hours form result of point load test strength of coal shale decreases by fifty six percent when coal shale zone come into contact with ground water. The standard reinforcement design of coal shale fractured zone was presented in the paper.

• Tunnel and Underground Space
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• v.7 no.4
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• pp.284-292
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• 1997

본 연구에서는 파괴형상의 특성을 이용하여 암석인장강도 측정실험법의 적용성을 평가하여Tekl. 이를 위해 화강암 및 석회암 시료를 대상으로 하여 점하중 시험법, Brazilian 시험법을 통해 인장파괴를 유도하였다. 각 파괴면의 형상을 분석하였고, Hoop 시험법의 경우 이론적인 응력분포와 함께 해석하였다. 파괴면 형상의 특징은 향후 시추코어의 파괴면 해석, 야외조사시 절리면의 파괴 해석 등에 이용될 수 있다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.1
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• pp.25-37
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• 1993

This paper describes the use of the J-integral, a one parameter of the non-linear fracture mechanics(NLFM), as a means to measure toughness of steel fiber reinforced concrete. This parameter can be conveniently evaluated from experimentally determined load-deflection curves from flexural tests when a maximum-load failure criterion is employed. And, for high strength concrete which was reinforced steel fiber, with two different fiber length in the form of notched beams, were tested under 3-point bending, and $J_{IC}$, as well as the linear elastic fracture mechanics(LEFM) parameters $K_{IC}$ and $G_{IC}$ were evaluated. The results suggest that $J_{IC}$ is a promising fracture criterion for all of these. while $K_{IC}$(or $G_{IC}$) almost certainly are not. Also it was found that a fiber addition of less than 0.5% did not improve the fracture toughness of the high strength concrete. However, at more than 1.0% in fiber contents, $J_{IC}$ showed significant increases. reflecting the changed character of the concrete; $K_{IC}$ and $G_{IC}$ did not.

• Journal of the Korean Geographical Society
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• v.43 no.6
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• pp.808-823
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• 2008

Sediment abrasion in rivers is caused by the interaction between bedrock channel bed and sediment particles transported through the river. Abrasion rate of sediment particles in rivers is controlled by two major factors; Sediment transport conditions including hydraulic conditions form the erosive forces and physical and chemical strengths of the particles form a resistance force against abrasion and other erosional processes. Physical experiments were performed to find the role of each variable on sediment abrasion process. Total 266 sediment particles were used in this experiment. All sediment particles were divided into 11 independent sediment groups with sediment particle size and sediment loads. Each sediment groups were abraded in tumbling mill for up to 8 hours. Changes in weight were recorded by run and total: 2,128 cases of abrasion rate were recoded. Physical strength of rock particles was measured with point load strength index. It is found that sediment abrasion rate has a negative functional relationship point load strength index ($I_{a(50)}$) ($R^2=0.22$). It was suggested that physical strength of sediment particles set the "maximum possible abrasion rate'. As sediment flux increases, abrasion rates of sediment particles with similar point load strength index were changed. It could be concluded that not only physical characteristics of sediment particles, but also sediment transport conditions control sediment abrasion rates.

• Journal of the Korean Geotechnical Society
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• v.25 no.8
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• pp.65-76
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• 2009

Little attention has been paid to Brazilian test for the estimation of uniaxial compressive strength and elastic modulus of rocks as an indirect method despite high availability of civil engineering parameters. This paper employed Brazilian test value to estimate two parameters of igneous rocks (granite, andesite, rhyolite) of Korea. High reliability of Brazilian test has been supported by the conclusions drawn from point load test and Schmidt hammer strike values. It has also been found that this method can be applied easily and rapidly to the estimation of uniaxial compressive strength and elastic modulus of rock cores when direct tests are not available.

• Proceedings of the KWS Conference
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• 2010.05a
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• pp.64-64
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• 2010

최근 그린 친환경, 지구온난화방지와 환경 부하물질저감, 기기 고효율화, 연비향상 등의 관점에서 항공기, 자동차 등 운송기계와 휴대용 전자제품 등 경량화가 요구되는 분야에서 경량합금의 사용이 급증하고 있다. 특히, 경량합금 중 가장 가벼운 마그네슘 합금은 최근 주목을 받고 있는 금속재료이다. 그러나 마그네슘합금은 알루미늄합금과는 달리 상온 성형성 및 접합성이 양호하지 않은 관계로 판재를 이용한 구조부품의 제작을 위해서는 많은 연구가 필요하다. 이러한 관점에서 본 연구는 마그네슘합금 판재의 마찰 교반 점용접을 시도하였다. CNC 밀링머신을 사용하여 프로브의 회전 및 삽입 속도에 변화를 주어 접합 특성을 평가하였고, 각 변수의 영향을 조사하였다. 적외선 열화상기와 로드셀을 사용하여 마찰 교반 점용접 중에 발생하는 교반부 온도와 접합부에 가해지는 수직부가하중의 거동을 측정하였다. 마찰 교반 점용접 후, 시험편의 접합 상태와 접합부 단면 관찰을 통해 접합 상태를 조사하였다. 그리고 인장전단 실험을 실시하여 마찰 교반 점용접된 시혐편의 접합강도를 평가하였고, 파단된 시험편의 파면을 관찰하였다.