• Proceedings of the KSME Conference
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• 2000.11a
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• pp.268-273
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• 2000

Mechanical properties of the materials used for transportations and industrial machinery under high strain rate loading conditions are required to provide appropriate safety assessment to these mechanical structures. The Split Hopkinson Pressure Bar(SHPB) technique, a special experimental apparatus, can be used to obtain the material behavior under high strain rate loading condition. In this paper, dynamic deformation behaviors of the aluminum alloys, Al2024-T4, Al6061-T6 and Al7075-T6, under high strain rate compressive and tensile loading are determined using SHPB technique.

• Magazine of the Korea Concrete Institute
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• v.9 no.5
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• pp.115-125
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• 1997

콘크리트의 변형률국소화는 콘크리트의연화거동에 수반되어 변형이 국부적으로 집중되는 현상이다. 본 연구의 목적은 인장과 압축하중상태에서 콘크리트 부재에 발생하는 콘크리트 변형률 국소화 거동을 해석적으로 재현할 수 있는 통일된 모형을 제안하는 것이다. 본 논문에서는 인장과 압축에 대하여 변형률국소화가 일어나는 콘크리트 부재를 변형률 연화가 일어나는 국소화영역과 탄성제하가 발생하는 비국소화영역으로 구분하여 모델링하는 통일된 모형을 제안하였다. 또한 제안된 모형에서 미시역학적 평균화기법을 이용해 평균등가탄성계수와 수정된 평균등가탄성계수를 구하여 시편의 크기와 국소화영역의 크기에 따는 해석을 수행하였으며 기존의 실험값과 비교하였다. 연구결과, 본 연구에서의 변형률국소화모형이 크기효과를 포함한 콘크리트의 변형률국소화거동 해석에 타당하게 적용될 수 있음을 보여주었다.

• Journal of the Korean Recycled Construction Resources Institute
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• v.7 no.3
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• pp.279-286
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• 2019

In this study, an experimental study on the tensile properties of steel fiber-reinforced ultra high strength concrete(UHSC) with a standard compressive strength of 180MPa was performed. Steel fibers with a volume ratio of 1% were mixed to prepare direct tensile strength specimens and prism specimens for the three-point bending test. The fabricated specimens were set up in the middle section of the specimen to induce cracks, and the test was carried out according to each evaluation method. First, the stress-strain curves were analyzed by performing direct tensile strength tests to investigate the behavior characteristics of concrete after cracking. In addition, the load-CMOD curve was obtained through the three-point bending test, and the inverse analysis was performed to evaluate the stress-strain curve. Tensile behavior characteristics of the direct tensile test and the three-point bending test of the indirect test were similar. In addition, the tensile stress-strain curve modeling presented in the SC structural design guidelines was performed, and the comparative analysis of the measured and predicted values was performed. When the material reduction factor of 1.0 was applied, the predicted value was similar to the measured value up to the strain of 0.02, but when the material reduction factor of 0.8 was applied, the predicted value was close to the lower limit of the measured value. In addition, when the strain was greater than 0.02, the predicted value by SC structural design guideline to underestimated the measured value.

• Korean Journal of Materials Research
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• v.8 no.8
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• pp.726-732
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• 1998

가압 경수로형 원전에 사용되는 Alloy 600 증기발생기 전열관재료의 입계응력부식균열 거동에 미치는 냉간변형의 영향을 1차 냉각수 모사조건에서 정속인장시험방법으로 조사하였다. 인장 냉간변형은 응력부식균열을 크게 가속화 시키지는 않았으며 변형량이 25%이상인 경우에는 응력부식균열이 발생하지 않았다. 이 현상은 냉간 변형량 및 형태에 따른 미소변형 및 응력의 불균질성에 영향을 받는 것으로 사려되며 응력의 크기는 직접적인 영향을 주지 않는 것으로 보인다. 국부적인 큰 응력구배가 존재하는 경우 균열의생성 및 성장이 현저히 가속화되었는데 이는 원전 1차측 응력부식균열 기구가 응력구배에 의존하는 과정과 연관되어 있다는 증거이다. Hump 시편을 이용한 정속인장시험방법은 짧은 실험기간내에 원전 1차측 응력부식균열 특성을 평가할 수 있는 방법이었다.

• Journal of the Korean Society for Nondestructive Testing
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• v.32 no.1
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• pp.20-26
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• 2012

The objective of this study is to assess plastic deformation in aluminium alloy by acoustic nonlinearity of laser-generated surface waves. A line-arrayed laser beam made by high-power pulsed laser and mask slits is utilized to generate the narrowband surface wave and the frequency characteristics of laser-generated surface waves are controlled by varying the slit opening width and slit interval of mask slits. Various degrees of tensile deformation were induced by interrupting the tensile tests so as to obtain aluminum specimens with different degrees of plastic deformation. The experimental results show that the acoustic nonlinear parameter of a laser-generated surface wave increased with the level of tensile deformation and it has a good correlation with the results of micro-Vickers hardness test and electron backscatter diffraction (EBSD) test. Consequently, acoustic nonlinearity of laser-generated surface wave could be potential to characterize plastic deformation of aluminum alloy.

• Proceedings of the Korea Concrete Institute Conference
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• 2010.05a
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• pp.3-4
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• 2010

Strength of PC walls with diagonal reinforcements can be obtained by using the section analysis. Deformation of the diagonal reinforcements is related to that of flexural reinforcement and makes the another tensile strength on the PC wall. Another tensile strength due to diagonal reinforcements is assumed to be 1/3 point of the distance between the flexural reinforcements.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.395-400
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• 2001

The Split Hopkinson Pressure Bar(SHPB) technique, a special experimental apparatus, has been used to obtain the material behavior under high strain rate loading condition. In this paper, dynamic deformation behaviors of the PMMA under high strain rate tensile loading are determined using SHPB technique.

• Magazine of the Korea Concrete Institute
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• v.5 no.3
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• pp.187-194
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• 1993

본 논문에서는 유리섬유의 적층수, 유리섬유의 배향각도에 대한 유리섬유 강화 플라스틱(Glass Fiber Reinforced Plastics ; GFRP)의 인장거동 변화를 고찰하고, 이들의 상관관계를 규명하기 위하여 일련의 GFRP 시험체에 대하여 인장실험을 수행하였다. 시험체는 폭12.5mm, 길이 60mm크기로 일정하게 제작하였으며, 시험체에 대하여 인장실험을 수행하였다. 시험체 제작시 유리섬유로 적층수는 14, 22, 30층, 유리섬유의 배향각도는 0$^{\circ}$, 30$^{\circ}$, 45$^{\circ}$로 하였다. 인장실험시 각 시험체의 파괴양상, 극한하중 및 하중변화에 대한 인장변형율을 조사하였고, 이들 결과를 토대로 유리섬유의 적층수와 배향각도에 따른 GFRP의 극한하중, 응력-변형율 선도 및 탄성계수 등을 비교 분석하였다. 한편 본 논문에서는 유리섬유의 적층수, 직경 변화에 따른 GFRP관의 파괴거동을 고찰하기 위하여 4점 재하법에 의한 GFRP관의 휨파괴실험을 수행하였다. 실험에 사용된 시험체는 길이 1200mm로 하였으며, 유리섬유의 적층수를 30, 35, 40층, 관의 직경을 50, 100, 150mm로 하였다. 파괴실험시 각 시험체의 하중변화에 대한 휨 변형율, 중앙점 처짐량 및 항복하중을 측정하였고, 이들 결과를 토대로 유리섬유으 적층수와 관의 직경에 따라 GFRP관의 항복하중 및 파괴에너지를 비교 분석 하였으며, 항복시 파괴에너지를 추정할 수 있는 제안식을 유도하였다.

• Journal of Aerospace System Engineering
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• v.12 no.4
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• pp.106-111
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• 2018

Hydrodynamic ram phenomenon could be generated by external threats such as impact and blast in the aircraft. High strain rate deformation caused by the hydrodynamic ram phenomenon is one of the main factors to influence structural survivability. Mechanical properties of composite structure change rapidly under conditions of high strain rate. Therefore, it is necessary to experimentally investigate the influence of strain rates for aircraft structural survivability. In this paper, tensile tests of composite material were conducted for low and high strain rates to investigate the influence of the various strain rates. Tensile modulus increases more compared to tensile strength at high strain rate under hydrodynamic ram condition. Regression analysis was conducted to predict tensile modulus at various strain rates because it is one of the main damaging factors for composite structures under high strain rate conditions. Also, the mechanical properties of composite materials were acquired and analyzed under high strain rate conditions. It is hypothesized that the results from this study would be used for designing aircraft composite structures and evaluation considering structural survivability.

• Journal of the Korean Geotechnical Society
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• v.19 no.6
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• pp.379-385
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• 2003

In the existing method to design geosynthetic reinforced embankment, the required strength of reinforcements is determined by vertical stress only rather than strain. This strength is not in accord with tensile strength that behaves as reinforcement in earth structures. The reinforcement and adjacent soil on the failure plan behave in one unit at the initial stress phase but they make a gap in strain as stress increases. This issue may cause a big impact as a critical factor on geosynthetic reinforcement design in earth structures. The quantitative analysis on strain behavior was performed with a PET Mat reinforced embankment on soft ground. From this study, several outstanding discussions are found that tensile strength of reinforcement governs the failure of embankment when the soil stress is greater than failure stress. Also the optimum required tensile strength of geosynthetic reinforcement(Tos) should be determined by stress, displacement, displacement gap and safety factor of soil-PET Mat at the location of PET Mat.