• Journal of the Korean Society of Propulsion Engineers
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• v.5 no.1
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• pp.42-48
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• 2001

Over two decades, many researchers have performed studies on strength size effects in composite laminates under tensile and flexural loads. It is well known that there is a tendency for the strength of fibre-reinforced composites to decrease with increasing specimen size. Under compressive load, however, little work has been done on the effect of specimen size to failure strength. This is due to the fact that compressive testing of composite is very difficult. In this paper, the effect of the test specimen size on the compressive strength of composites containing open hole was considered using T300/924C, $>[45/-45/0/90]_{3S}$. For sizing test specimens, the in-plane scaling method is used i.e., the change of two- dimensional specimen area in specimen width and gauge length. The results clearly show that there is a hole size effect in the finite width plates. In addition, the specimens which have the same a/W(hole diameter/specimen width) exhibit a tendency of size effect. In contrast, test results of the unnotched specimens did not show a clear strength size effect.

• Composites Research
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• v.16 no.6
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• pp.1-9
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• 2003

In this paper, probabilistic failure analysis based on Weibull distribution function is proposed to predict the fiber strength of composite pressure vessel. And, experimental tests were performed using fiber strand specimens, unidirectional laminate specimens and composite pressure vessels to confirm the volumetric size effect on the fiber strength. As an analytical method, the Weibull weakest link model and the sequential multi-step failure model are considered and mutually compared. The volumetric size effect shows the clearly observed tendency towards fiber strength degradation with increasing stressed volume. Good agreement of fiber strength distribution was shown between test data and predicted results for unidirectional laminate and hoop ply in pressure vessel. The site effect on fiber strength depends on material and processing factors, the reduction of fiber strength due to the stressed volume shows different values according to the variation of material and processing conditions.

• Korean Journal of Materials Research
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• v.7 no.5
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• pp.411-416
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• 1997

수소 및 산소분위기 하에서 2Y-TZP 및 3Y-PZP 세라믹스를 소결하여 각각 제조한 다음, 각 시편의 미세구조 및 25$0^{\circ}C$에서의 등온상전이 거동을 비교하여 고찰하였다. 그 결과 수소분위기에서 소결한 모든 시편의 표면에서는 Zr$_{4+}$ 이온의 환원에 의해 산화분위기에서 소결한 시편에 비하여 색이 검게 변하였으며, 장시간 소결시 시편 표면에 조대 입자의 생성 및 입계 이완이 관찰되었다. 이에따라 수소분위기 하에서 장시간 소결된 시편의 경우 냉각 시 상전이가 일어나 다량의 단사정상이 상온에서 존재하였다. 저온 aging동안 등온상전이 속도는 산소분위기에서 소결한 시편보다 수소분위기에서 소결한 시편에서 낮게 나타났으며, 이러한 경향은 $Y_{2}$O$_{3}$의 고용량이 크고, 입자크기가 적은 시편일수록 증가하였다. 또한 2Y-TZP 시편에서는 입자크기에 상관없이 대부분의 정방정상이 단사정상으로 빨리 등온상전이를 일으켰으나, 3Y-TZP 시편의 경우, 등온상전이는 입자크기가 증가함에 따라 상전이 속도도 증가하였다.

• Journal of the Korean GEO-environmental Society
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• v.7 no.3
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• pp.31-41
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• 2006

The scale effect of specimens on the shear behavior of joints is studied by performing direct shear tests on six different sizes in Granite. The peak and residual shear stress, shear displacement, shear stiffness, and dilation angle are measured with the different normal stress(0.29~2.65MPa) and roughness parameters. It is also shown that both the joint roughness coefficient(JRC) and the joint compression strength(JCS) reduce with increasing joint length. A series of shear tests show about 56~67% reduction in peak shear stress, and about 18~44% in residual shear stress, respectively as the contact area of joint increases from 12.25 to $361cm^2$. Also the variation of dilation angle is $27^{\circ}$ at normal stress of 0.29 MPa and $6^{\circ}$ at normal stress of 2.65 MPa, respectively. The envelopes considering scale effect for JRC are made for the peak shear strength of rock joint in comparison with the Barton's equation.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1991.04a
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• pp.133-138
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• 1991

일반적으로 고무를 비롯한 점탄성재료는 형상 및 크기를 적절히 조절함으로 써 한 방향 이상으로의 원하는 스프링상수를 얻을 수 있으며, 금속에 비하여 내부 마찰에 의한 에너지 발산이 매우 크기 때문에 강제 진동시의 진폭저감 및 충격에 따른 자유진동의 감쇠에 널리 이용되고 있다. 이와 같은 진동감쇠 에 점탄성재료를 효과적으로 사용하기 위해서는 복소탄성계수 즉, 탄성계수 와 손실계수를 정확하게 알아내는 것이 필요하다. 점탄성재료의 복소탄성계 수는 주파수, 온도 및 변형률등에 따라 변하므로 이와 같은 사용조건의 함수 로 구해야 한다. 복소탄성계수를 실험적으로 구하는 방법은 여러가지가 있으 며 실험의 용이성과 관심대상에 따라 적절한 방법을 선택하게 된다. 본 연구 에서는 주파수변화에 따른 복소탄성계수를 임피던스법으로 집중질량 모형을 이용하여 구하려고 할 때, 실험데이타로부터 보다 정확한 결과를 얻기 위하 여 적절한 시편의 크기를 결정하는 방법을 제시하고자 한다. 이를 위해서 시 편내의 파동전달효과와 포아송비와 관련된 양단제한효과 그리고 정하중시 압축변형에 대한 시편의 좌굴등을 고려하여 이론적으로 해석하였으며 실험 적으로도 검증하였다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.10
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• pp.1463-1470
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• 2010

Microforming, which exploits the advantages of metal forming technology, appears very promising in manufacturing microparts since it enables the production of parts using various materials at a high production rate, it has high material utilization efficiency, and it facilitates the production of parts with excellent mechanical properties. However, the conventional macroscale forming process cannot be simply scaled down to the micro-scale process on the basis of the extensive results and know-how on the macroscale process. This is because a so-called "size effect" occurs as the part size decreases to the microscale. In this paper, we attempt to develop an effective analytical and experimental modeling technique for explaining the effects of the grain size and the specimen size on the behavior of metals in microscale deformation processes. Copper sheet specimens of different thicknesses were prepared and heat-treated to obtain various grain sizes for the experiments. Tensile tests were conducted to investigate the influence of specimen thickness and grain size on the flow stress of the material. In addition, an analytical model was developed on the basis of phenomenological experimental findings to quantify the effects of the grain size and the specimen size on the flow stress of the material in microscale and macroscale forming.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.12
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• pp.1435-1440
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• 2014

The effects of the specimen size and temperature on the compressive strength of ATJ graphite were investigated. Compressive tests were conducted in accordance with ASTM C 965 at room temperature, $700^{\circ}C$ and $900^{\circ}C$. Three types of cylindrical specimen at room temperature were used in uniaxial tests, where the diameter-to - length ratios were one to two for the ASTM standard specimen, one to one for the Type I specimen, and one to 0.5 for the Type II specimen. Two kinds of cylindrical specimens, with and without antioxidant coating, were tested at elevated temperature. The Compressive strength of the expanded specimens(Type I, II) were slightly higher than that of standard specimen at room temperature. The compressive strength of a specimen with antioxidant coating increased as the temperature increased to $900^{\circ}C$. In contrast, that of the non-coated specimen decreases sharply due to the oxidation of the specimen.

• International Journal of Highway Engineering
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• v.14 no.1
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• pp.25-34
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• 2012

The rapid economic development induced the massive road constructions, becoming bigger and high-speed of the vehicles. However, it brings lots of social problems, such as air pollutions, traffic noise and vibration. Special concrete block for the base course of asphalt pavement is needed to decrease traffic noise such as tire's explosive and vehicles sound, applying Helmholtz Resonators theory to asphalt pavement. If it is applied to the area where it happens considerable noise such as a junction, the street of a housing complex and a residential street, it is one of alternative methods to solve the social requirements of noise problems. This research examines couple of laboratory tests for the sound absorption effect of the concrete block and the base concrete block for quiet pavement. The specimens, which is fixed hall-size, space, depth as the condition of this research, are analysed of noise reduction effect using different noise levels of vehicles. Judging from the analysis of test results with vehicle noise volume, measurement distance, a form and size of the hall using the base concrete block, the use of special concrete base and quiet asphalt surface showed a good alternative solution for decreasing traffic noise level, from 4dB to 9dB.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.03a
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• pp.184-184
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• 2003

고성능 전자부품 개발이 진행되면서 나노크기의 분말에 대한 합성연구가 활발히 진행되고 있는 추세이다. 실제 나노크기의 입자는 그 기능이 기존 fm크기의 입자에 비해 뛰어나 많은 연구자들의 관심이 되어 있음에도 불구하고 제품으로 응용된 예는 거의 없는 실정인데 이는 나노크기의 입자라 할지라도 응집이 되어 있거나 작업하기 어렵기 때문이다. 따라서 본 연구에서는 응집된 BaTiO$_3$분말에 분산제와 함께 고속볼밀을 하여 이에 따른 분산 효과와 tape casting을 위한 최적 분산 안정성에 대하여 연구하였다. 분산제의 종류와 볼밀시간에 따른 분산효과를 확인하기 위하여 zeta potential 값을 비교하였으며 이러한 분산제의 종류와 볼밀시간에 따라 분산효과가 변하는 것을 확인할 수 있었다. 또한 분산된 분말에 대해 다른 분자량을 가지는 PVB와 상용바인더를 사용하여 tape casting하였다. 결합제의 종류에 따라 슬러리의 특성이 변화하였으며 분자량이 다른 PVB를 사용하여 성형한 시편을 소결하여 미세구조에 미치는 영향을 확인하였다.

• Journal of the Society of Disaster Information
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• v.15 no.4
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• pp.590-596
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• 2019

Purpose: An experimental study was conducted on the sand samples for the size effect of the test specimens, one of the problems of the direct shear test. Method: Jumunjin standard sand, a representative sand of Korea, was used as sand sample. The large direct shear test was performed to analyze the shear strength at 50%, 60%, 70%, and 80% relative density, and then the comparative results were compared with the test results of the small direct shear test. Result: It was analyzed that the internal friction angle of the small shear tester tended to be relatively large in the dense region. It was analyzed that the results of the large shear tester tend to be relatively large in the region of medium relative density. Conclusion: The size effect on the samples in the direct shear test on sandy soil was analyzed to be relatively small.