• 콘크리트학회논문집
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• 제12권3호
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• pp.31-37
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• 2000

When a crack is produced in a concrete structure, a micro crack zone of fracture process zone (FPZ) appears at the crack tip. To investigate the behaviour of this the micro crack zone, nonlinear fracture mechanics (NLFM) must be applied. However, when a massive concrete structure such as a concrete gravity dam is considered, the micro crack zone can be neglected and the structure can be assumed to have linear elastic fracture mechanics (LEFM) behaviour. This study is divided into two main topics : (1) Calculating stress intensity factor (SIF) at the crack tip by surface integral method and (2) Investigating the propagation of the initial crack. If the initial crack propagates, the angle of the propagation is calculated by using maximum circumferential tensile strength theory. This study, also, contains the effects of body forces and water pressures on the crack face.

• 한국해양공학회지
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• 제16권5호
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• pp.80-87
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• 2002

In this study, CT specimens were prepared from spring steel(SUP9) which was used in suspension of automobile for room temperature and low temperature service. We got the following characteristics from fatigue crack growth test carried out in the environment of room temperature and low temperature at $25^{\circ}C$, ­3$0^{\circ}C$, ­5$0^{\circ}C$, ­7$0^{\circ}C$ and ­10$0^{\circ}C$ in the range of stress ratio of 0.05 by means of opening mode displacement. The threshold stress intensity factor range ΔKth in the early stage of fatigue crack growth (Region I) and stress intensity factor range ΔK in the stable of fatigue crack growth (Region II) was decreased in proportion to descend temperature. It is assumed that the fatigue resistance characteristics and fracture strength at low temperature and high temperature is considerable higher than that of room temperature in the early stage and stable of fatigue crack growth region.

• 한국해양공학회지
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• 제7권2호
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• pp.103-113
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• 1993

X-ray diffraction analysis technique was used for the fatigue damage analysis and fatigue life prediction in Al 7075-T651 alloy. The tensile test, fatigue strength and fatigue crack propagation test with change of stress ratio were carried out. As a result, half-value breadth was increased with the plastic deformation in the specimen increasint at all test conditions. In particular, half-value breadth at the surface of the specimens fractured by fatigue was increased as stress intensity factor range and effective stress intensity factor range were increased. In addition, the good relationship between half-value breadty and diffraction pattern was shown.

• 한국안전학회지
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• 제24권3호
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• pp.19-24
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• 2009

Currently the technique of composite material field is developed day by day. The many kinds industrial facility and life articles are coming to make with the composite material. But still the engineering works field the building and the bridge uses the material which is old era and is making. To here there is a various problem but the biggest problem the theory of the composite material is complicated too and means that the application is been delayed about constructive structure. When the composite material is used widely from constructive field, too with difficult theory in technical expert and easily with the research for the experiment data accumulation is necessary. The tensile and fatigue test of the carbon/epoxy which is a high-class composite material led from the present paper consequently and the change of the intensity coefficient which follows in repeated load researched.

• 한국생산제조학회지
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• 제7권2호
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• pp.54-61
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• 1998

This paper examines the crack growth behavior of 7075-T651 aluminum alloy for small tensile overload under high-low block loading condition. The cantilever beam type specimen with a chevron notch is used in this study. The crack growth and closure are investigated by compliance method. The applied initial stress ratios are R=-0.5 R=0.0 and R=0.25 Crack length, effective stress intensity factor range, ratio of effective stress intensity factor range and crack growth rate etc, are inspected with fracture mechanics estimate.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집A
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• pp.389-394
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• 2001

The notched Charpy and Izod impact tests arc the most prevalent techniques used to characterize the effects of high impulse loads on ploymeric materials. An analysis method for rubber toughened PVC is suggested to evaluate critical strain energy release rates(Gc) from the Charpy impact energy measurements. An Instrumented Charpy impact tester was used to extract ancillary information concerning fracture properties in addition to total fracture properties and maximum critical loads. The stress intensity factor Kd was computed for varying amounts of rubber contents from the obtained maximum critical loads and also toughening effects were investigated as well.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집A
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• pp.585-590
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• 2001

Turbine blade is subject to torsional load by torsion-mount, centrifugal load by rotation of rotor and repeated bending load by steam pressure. Turbine with partially cracked blade has normal working condition at initial repair time but vibratory working condition at middle repair time due to crack growth. Finite element analysis on turbine blade indicates that repeated bending load out of all loads is the most important factor on fatigue strength of turbine blade. Therefore, this study shows root mean square roughness has linear relation with stress intensity factor range in 12% Cr steel and can predict loading condition of fractured turbine blade.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2016년도 추계 학술논문 발표대회
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• pp.26-27
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• 2016

This study analyzes the engineering characteristics of mortar according to admixture replacement ratios in cement mortar in a high-intensity ternary system, and changes in FA and BS combination ratios, in order to deduce the optimal combination ratio of FA and BS. Results showed that due to the characteristics of unhardened mortar, flow rate increased with the increase in admixture replacement and FA combination ratios, whereas air quantity decreased and setting time was delayed. Due to the characteristics of light mortar, compression strength decreased at early material ages as the overall combination ratio of FA increased. The FA : BS combination ratio was 2 : 3 on day 28 of material age, proving the best and potentially optimal combination ratio.

• 한국식품영양과학회지
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• 제30권2호
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• pp.239-242
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• 2001

Electron spin resonance(ESR) spectroscopy was used to investigate the effect of irradiation dose on the ESR signal intensity of irradiated spices and to identify the stability of radicals after storage. Red, white and black peppers, and garlic powders were irradiated with doses of 0, 1, 5, 10, 20 and 30 kGy at room temperature using a Co-60 irradiator. Triplet ESR signals were observed in irradiated pepper powders, while singlet ESR signals were observed in irradiated garlic powders. Those characteristic signals were not detected in non-irradiated samples. The strength of ESR signals linearly increased with the applied doses(1~3 kGy). Highly positive correlation coefficients ($R^2$=0.9757~0.9933) were obtained between the irradiation doses and the corresponding ESR signal intensities. The signal intensities of irradiated samples were stable even after 97 days of storage at room temperature.

• Journal of Welding and Joining
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• 제19권3호
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• pp.298-304
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• 2001

Turbine blade is subject to force of three types ; the torsional force by torsional mount, the centrifugal force by the rotation of rotor and the cyclic bending force by steam pressure. The cyclic bending force was a main factor on fatigue strength. SEM fractography in root of turbine blade showed micro-clack width was not dependent on stress intensity factor range. Especially, fatigue did not exist on SEM photograph in root of turbine blade. To clear out the fracture mechanism of turbine blade, nanofractography was needed on 3-dimensional crack initiation and crack growth with high magnification. Fatigue striation partially existed on AFM photograph in root of turbine blade. Therefore, to find a fracture mechanism of the torsion-mounted blade in nuclear power plant, the relation between stress intensity factor range and surface roughness measured by AFM was estimated, and then the load amplitude ΔP applied to turbine blade was predicted exactly by root mean square roughness.