• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
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• pp.714-719
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• 2002

In The Great Hanshin-Awaji Earthquake, the general yield brittle fractures were observed in beam-column connections of steel building frames. Among many influencing factors which affect the general yield brittle fracture, it can be considered that fracture toughness has substantial effects. Some studies are making clear the required toughness for the base metal and the weld metal, but general values are not proposed. Moreover, it seems that it is also important to pay attention to the toughness decrease in the weld heat affected zone (weld HAZ), because the toughness decrease occurs in the HAZs of mild steel. In this paper, the relationship between toughness of simulated HAZs of "the rolled steels for building structures (SN)" and the weld heat-input limit of the SN steel are investigated, in an attempt to provide the required toughness for HAZs. The relationships between the increase of the hardness value and toughness, and changes of microstructure after weld heat-input are also discussed. The main results are summarized as follows. 1) The SN400B can keep its toughness at higher heat-inputs compare to the SN490Bs. 2) The steel grade, which becomes harder than other steel grades at the same heat-input, has smaller absorbed energy and smaller limit of heat-input. 3) The weld heat-input limit of the SN400B and the SN490B are proposed separately for some required toughness values.

• Nuclear Engineering and Technology
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• 제33권5호
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• pp.498-513
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• 2001

Performed here is a comparative assessment study for the generation of the pressure- temperature (P/T) limit curve of the reactor vessel. Using the cooling or heating rate and vessel material properties, the stress distribution is obtained to calculate stress intensity factors, which are compared with the material fracture toughness to determine the relations between operating pressure and temperature during cool-down and heat-up. P/T limit curves are generated with respect to crack direction, clad thickness, toughness curve, cooling or heating rate and neutron fluence, and their results are compared.

• Structural Engineering and Mechanics
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• 제14권2호
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• pp.191-208
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• 2002

A comparative assessment study for a generation of the pressure-temperature (P-T) limit curve of a reactor vessel is performed in accordance with ASME code. Using cooling or heating rate and vessel material properties, stress distribution is obtained to calculate stress intensity factors, which are compared with the material fracture toughness to determine the relations between operating pressure and temperature during reactor cool-down and heat-up. P-T limit curves are analyzed with respect to defect orientation, clad thickness, toughness curve, cooling or heating rate and neutron fluence. The resulting P-T curves are compared each other.

• Journal of Mechanical Science and Technology
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• 제15권8호
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• pp.1079-1089
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• 2001

This paper proposes J and CTOD estimation schemes applied to fracture toughness testing, covering typical homogeneous and bi-material specimens. Recommendations are based on the plastic limit analysis (either slip line field or finite element limit analyses), assuming the rigid plastic material behavior. The main outcome of the present study is that the J and CTOD estimation schemes (both codified and non-codified), recommended for homogeneous specimens, can be equally used for bi-material specimens with interface cracks. The effect of yield strength mismatch in bi-material specimens on the J-integral CTOD is discussed.

• Structural Engineering and Mechanics
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• 제53권6호
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• pp.1271-1286
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• 2015

Recently, US NRC revised fracture toughness requirements as 10CFR50.61a to reduce the conservatism of 10CFR50.61. However, unlike previous studies relating to the initial regulation, structural integrity evaluations based on the alternative regulation are not sufficient. In the present study, PTS and P-T limit curve evaluations were carried out by using both regulations and resulting data were compared. With regard to the PTS evaluation, the results obtained from the alternative requirements were satisfied with the criterion whereas those obtained from the initial requirements did not meet the criterion. Also, with regard to the P-T limit curve evaluation, operating margin by 10CFR50.61a was greater than that by 10CFR50.61.

• Geomechanics and Engineering
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• 제37권4호
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• pp.371-382
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• 2024

Measurement or prediction of compression index (C_c) of soils is essential for assessment of total and differential settlement of structures. It is a well-known fact that this parameter is controlled by several index identifiers of soil including initial void ratio, Atterberg limits, overconsolidation ratio, specific gravity, etc. Many studies in the past proposed relationships for prediction of C_c based on different index properties. Therefore, this study aims to present a comparison of previously proposed equations for estimation of C_c. Data from literature was compiled, and a total of 90 and 623 test results on remolded and undisturbed specimens were used to question the validity of previously proposed equations. Nevertheless, the modeling ability of 7 and 12 equations for estimation of C_c of remolded and undisturbed soils were questioned by use of compiled data. Moreover, new empirical relationships based on initial void ratio and toughness limit for prediction of C_c was proposed by use of nonlinear multivariable regression and evolutionary based regression analyses. The results are promising-the performances of models established are quite acceptable, which are verified by statistical analyses.

• 대한기계학회논문집A
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• 제26권3호
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• pp.505-513
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• 2002

During heatup and cooldown of pressurized water reactor, thermal stress was generated in the reactor pressure vessel (RPV) because of the temperature gradient. To prevent potential failure of RPV, pressure was required to be maintained below the P-T limit curves. In this paper, several methods for constructing the P-T limit curves including the ASME Sec. XI, App. G method were explained and the results were compared. Then, the effects of the various parameters such as flaw size, flaw orientation, cooldown rate, existence of chad, and reference fracture toughness, were evaluated. It was found that the current ASME Sec. XI App. G method resulted in the most conservative P-T limit curve. As the more accurate fracture mechanics analysis results were used, some of the conservatism can be removed. Among the parameters analysed, reference flaw orientation and reference fracture toughness curve had the greatest effect on the resulting P-T limit curves.

• 대한기계학회논문집A
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• 제38권7호
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• pp.757-764
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• 2014

본 연구에서는 한계하중법을 이용하여 Curved CT 시험편의 J-적분에 미치는 형상변수 영향을 평가하였다. 주요 형상변수인 시험편의 길이와 폭의 비(L/W), 평균곡률반경과 두께의 비($R_m/t$)에 대한 파괴인성시험 후, ASTM 시험법에서 제시한 표준시험편의 J-적분과 한계하중법으로 구한 J-적분을 각각 적용하여 구한 파괴저항곡선을 평가하였다. 또한 배관의 파괴저항곡선을 잘 모사한다고 알려진 휨 광폭평판(CWP) 및 표준시험편의 파괴저항곡선과 비교 고찰하여 최종적으로 Curved CT 시험편의 파괴저항곡선에 대한 유효성을 평가하였다. 본 논문의 결과는 향후 실배관의 정확한 파괴인성을 평가하는 데 있어 Curved CT 시험편의 적용가능성을 평가하는 데에 활용할 수 있다.

• 전산구조공학
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• 제10권4호
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• pp.155-164
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• 1997

핵분열로 인한 고온, 고압의 냉각수를 유지하는 원자로 용기는 원자로의 냉각 또는 가열시 압력에 의한 응력과 함께 열응력이 가해지고 원자로 벽의 온도변화에 따라 파괴인성치가 변화하기 때문에 임의의 결함이 존재할 경우 건전성 확보가 쉽지 않다. 따라서 가상결함이 성장하지 않도록 압력과 온도를 조정하면서 냉각 및 가열시킬 필요가 있다. 본 연구에서는 원자로 운전 중 냉각 및 가열시 안전하게 운전하기 위한 압력/온도 한계곡선을 구하는 절차에 필요한 이론을 조사하였고 이의 도출을 위한 해석과정을 전산화하였다. 국내원전 중 가장 오래된 고리 1호기에 대한 압력/온도 한계곡선을 다양한 냉각 및 가열률에 따라 설정하였고 이들 결과를 검토하였다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1998년도 봄 학술발표회 논문집(I)
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• pp.359-364
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• 1998

The interfacial zone in concrete materials is extensive, geometrically complex, and constitutes inherently weak zones that limit the concrete performance. Motar-aggregate interfaces play a major role in the fracture processing in concrete composites. Also, the interfacial bond considerably influence mechanical properties of concrete such as modulus of elasticity, strength, and fracture energy, Characterization of the interfacial properties is, therefore, essential to overcome the limitations associated with the interfaces. an objective of this paper is to investigate the corelationship between the fracture toughness of mortar-aggregate interface and the concrete properties such as strengths and elastic moduli. It is observed from the test results that interface fracture toughness is closely related with the compressive strength rather than other properties. At early ages, the development of both tensile strength and elastic modulus are much greater thatn that of both interface fracture toughness and compressive strength.