• 대한기계학회논문집A
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• 제30권1호
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• pp.60-65
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• 2006

The present paper provides experimental J estimation equation for the circumferential through-wall cracked pipe under four-point bending, based on the load-crack opening displacement (COD) record. Based on the limit analysis and the kinematically admissible rigid-body rotation field, the plastic ${\eta}$-factor for the load-COD record is derived and is compared with that for the load-load line displacement record. Comparison with the J results from detailed elastic-plastic finite element (FE) analysis shows that the proposed method based on the load-COD record provides reliable J estimates even for shallow cracks, whereas the conventional approach based on the load-load line displacement record gives erroneous results for shallow cracks. Thus, the proposed J estimation method could be recommended for testing the circumferential through-wall cracked pipe, particularly with shallow cracks.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1999년도 봄 학술발표회 논문집
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• pp.295-302
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• 1999

This paper is the experimental and analytic of reinforced concrete hemisphere dome under vertical load. It is described that when the reinforced concrete hemispherical dome supported on cylindrical wall is loaded vertically, how the opening part of dome will behave mechanically The experimental and analytic model is a Hemispherical dome with opening and the meridian angle of opening is 76$^{\circ}$at the center of sphere under concentrated load around the opening, but this is reinforced by a ring is sufficient stiffness. The diagrams of crack development are represented to understand the behavior of the reinforced concrete hemispherical dome. The method of crack analysis will be applied the rigid element spring model. The rigid element spring model is a new discrete element analysis, each divided element is assumed by rigid elements without deformation which is interconnected with elasto-plastic spring system.

• International Journal of Precision Engineering and Manufacturing
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• 제1권2호
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• pp.84-93
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• 2000

Computer simulations of the mechanical behavior of 3 point bend specimens with a quarter notch under impact load are performed. This validity is found to be identified by the experimental proof. The cases with various loading rates applied at the side of the specimen are considered. An elastoplastic von Mises material model is chosen. Gap opening displacement, reaction force, crack tip opening displacement and strain rate are also compared with rate dependent material(visco-plastic material). The stability during various dynamic load can be seen by using the simulation of this study. These differences of the cases with various loading rates are also investigated.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2001년도 봄 학술발표회 논문집
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• pp.215-220
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• 2001

The objective of this study is to examine the fracture characteristics of concrete at early ages such as critical stress intensity factor, critical crack-tip opening displacement, fracture energy based on the concepts of the effective-elastic crack model and the cohesive crack model. A wedge splitting test for Mode I was performed on cubic wedge specimens with a notch at the edge. By varying strength and age, load-crack mouth opening displacement curves were obtained and the results were analyzed by linear elastic fracture mechanics. The results from the test and analysis showed that critical stress intensity factor and fracture energy increased, and critical crack-tip opening displacement decreased with concrete age from 1 day to 28 days. The obtained fracture parameters at early ages may be used as a fracture criterion and an input data for finite element analysis of concrete at early ages.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1995년도 춘계학술대회 논문집
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• pp.28-32
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• 1995

This effective way for repairing a fatigue crack is making indetations around fatigue crack tip. In this paper, we performed fatigue test to investigate the optimal position of the indentations, and observed crack opening behavior at the same time. The indentation positions of specimens were on the crack tip, front and back of the crack tip. The results of the experiment showed taht it was veryeffective way to increase fatigue life that making indentations on the crack tip, and it was the optimal position that making indentations on the crack tip.

• International Journal of Concrete Structures and Materials
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• 제18권3E호
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• pp.191-198
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• 2006

The objective of this study is to examine fracture characteristics of concrete at early ages, i.g. critical stress intensity factor, critical crack-tip opening displacement, fracture energy, and bilinear softening curve based on the concepts of effective-elastic crack model and cohesive crack model. A wedge splitting test for Mode I was performed on cubic wedge specimens with a notch at the edge. By experimenting with various strengths and ages, load-crack mouth opening curves were obtained, and the results were analyzed by linear elastic fracture mechanics and FEM(finite element method). The results from the test and analysis showed that critical stress intensity factor and facture energy increased while critical crack-tip opening displacement decreased with concrete aging from 1 day to 28 days. Four parameters of bilinear softening curve from 1 day to 28 days were obtained from a numerical analysis. The obtained fracture parameters and bilinear softening curves at early ages from this study are to be used as a fracture criterion and an input data for the finite element analysis of concrete at early ages.

• Structural Engineering and Mechanics
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• 제19권3호
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• pp.347-359
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• 2005

This paper attempts to develop the analytical model of estimating the fatigue damage using a linear elastic fracture mechanics method. The stress history on a welding member, when a truck passed over a bridge, was defined as a block loading and the crack closure theory was used. These theories explain the influence of a load on a structure. This study undertook an analysis of the stress range frequency considering both dead load stress and crack opening stress. A probability method applied to stress range frequency distribution and the probability distribution parameters of it was obtained by Maximum likelihood Method and Determinant. Monte Carlo Simulation which generates a probability variants (stress range) output failure block loadings. The probability distribution of failure block loadings was acquired by Maximum likelihood Method and Determinant. This can calculate the fatigue reliability preventing the fatigue failure of a welding member. The failure block loading divided by the average daily truck traffic is a predictive remaining life by a day. Fatigue reliability analysis was carried out for the welding member of the bottom flange of a cross beam and the vertical stiffener of a steel box bridge by the proposed model. Results showed that the primary factor effecting failure time was crack opening stress. It was important to decide the crack opening stress for using the proposed model. Also according to the 50% reliability and 90%, 99.9% failure times were indicated.

• 한국구조물진단유지관리공학회 논문집
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• 제17권1호
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• pp.46-54
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• 2013

실제 교량의 바닥판에 적용할 목적으로 섬유의 길이 및 혼입량을 달리한 두 가지 초고성능 시멘트 복합체를 고려하고 있다. 이 연구의 목적은 이 두 재료의 균열저항성을 평가하는 것이다. 두 재료에 대한 휨인장 파괴실험을 수행하였고, 실험으로부터 얻은 하중-균열개구변위 관계를 최적으로 모사하는 인장응력-균열개구 관계를 역해석을 통해 파악하였다. 역해석결과 13 mm 길이의 섬유를 2% 함유한 UHPCC는 16.3 mm와 19.5 mm 길이의 섬유를 각각 0.5%와 1.0% 함유한 UHPCC에 비해 파괴에너지가 작은 것으로 나타났다. 균열을 보다 분산시키고 균열폭을 감소시키기 위해서는 길이가 긴 두 종류의 섬유를 혼용한 UHPCC를 사용하는 것이 바람직할 것으로 판단된다.

• 대한기계학회논문집
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• 제14권1호
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• pp.103-111
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• 1990

본 연구에서는 성장하는 균열선단에서 열림변위의 임계증분에 대한 균열성장 조건에 기본을 두고 계산된 파단하중을 실험결과와 비교하여 균열성장저항을 특성 지 을수 있는 새로운 재료상수를 제안한 것이다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집A
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• pp.80-86
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• 2001

An engineering estimation equation for the crack opening displacement (COD) is proposed for a complex cracked pipe, based on the reference stress approach. To define the reference stress, a simple plastic limit load analysis for the complex cracked pipe subjected to combined bending and tension is performed considering the crack closure effect in the compressive-stressed region. Comparison with ten published test data and the results from existing method shows that the present method not only reduces non-conservatism associated with the existing method, but also provides consistent and overall satisfactory results.