• 한국항공우주학회지
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• 제46권7호
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• pp.535-541
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• 2018

본 연구에서는 입자강화 복합재료의 파괴거동을 평가하기 위해 쐐기분열시험을 수행하였다. 균열 저항성을 분석하기 위해 균열선단열림변위(CTOD)와 균열선단열림각도(CTOA)를 이용하였다. 사용된 입자강화 복합재료는 특성상 온도와 하중속도에 영향을 많이 받기 때문에 다양한 온도($-60^{\circ}C{\sim}50^{\circ}C$)와 하중속도(5~500mm/min)조건에서 시험을 수행하였다. 또한 균열선단에 대한 변형률장을 분석하기 위해 디지털 이미지 상관법(DIC)을 이용하였다. 시험결과 파괴에너지는 온도가 감소할수록 증가하였으며, 하중속도가 증가할수록 균열저항성이 증가하였다.

• International Journal of Naval Architecture and Ocean Engineering
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• 제5권4호
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• pp.580-597
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• 2013

Three materials SUS304, 9% Ni steel and Al 5083-O alloy, which are considered possible candidate for International Maritime Organization (IMO) type B Cargo Containment System, were studied. Monotonic tensile, fatigue, fatigue crack growth rate and Crack Tip Opening Displacement tests were carried out at room, intermediate low ($-100^{\circ}C$) and cryogenic ($-163^{\circ}C$) temperatures. The initial yield and tensile strengths of all materials tended to increase with decreasing temperature, whereas the change in elastic modulus was not as remarkable. The largest and smallest improvement ratio of the initial yield strengths due to a temperature reduction were observed in the SUS304 and Al 5083-O alloy, respectively. The fatigue strengths of the three materials increased with decreasing temperature. The largest increase in fatigue strength was observed in the Al 5083-O alloy, whereas the 9% Ni steel sample showed the smallest increase. In the fatigue crack growth rate test, SUS304 and Al 5083-O alloy showed a decrease in the crack propagation rate, due to decrease in temperature, but no visible improvement in da/dN was observed in the case of 9% Ni steel. In the Crack Tip Opening Displacement (CTOD) test, CTOD values were converted to critical crack length for the comparison with different thickness specimens. The critical crack length tended to decrease in the case of SUS304 and increase for the Al 5083-O alloy with decreasing temperature. In case of 9% Ni steel, change of critical crack length was not observed due to temperature decrease. In addition, the changing material properties according to the temperature of the LNG tank were analyzed according to the international code for the construction and equipment of ships carrying liquefied gases in bulk (IGC code) and the rules of classifications.

• 한국안전학회지
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• 제6권4호
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• pp.73-80
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• 1991

Interest in fracture of structure has increased significantly over the past decade. New approaches to analyze structural performance have been accompanied by the development of test methods to characterize material behavior in a manner compatible with the analysis. Several test methods have been developed as a results of advances in fracture mechanics, for example, $K_{IC}$ , $J_{IC}$, R-curve tearing instability and CTOD approaches. Among the rest, fracture toughness $K_{IC}$ and $J_{IC}$ can be used as an effective design criterion in fracture mechanics. Generally, the determintion of $J_{IC}$ was performed according to ASTM E 813 or JSME S 001 and $K_{IC}$ was performed according to ASTM E 399. In this study, the test method for $K_{IC}$ and $J_{IC}$ were discussed.scussed.

• 국제강구조저널
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• 제18권5호
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• pp.1754-1760
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• 2018

The present article showcases a temperature dependent cohesive zone model (CZM)-based fi nite element simulation of drop weight tear test (DWTT), to analyse fracture behavior of pipeline steel (PS) at different temperatures. By co-relating the key CZM parameters with known mechanical properties of PS at varying temperature, a temperature dependent CZM for PS is proposed. A modified form of Johnson and Cook model has been used for the true stress-strain behavior of PS. The numerical model, using Abaqus/CAE 6.13, has been validated by comparing the predicted results with load-displacement curves obtained from test data. During steady-state crack propagation, toughness parameters (such as CTOA and CTOD) were found to remain fairly constant at a given temperature. These toughness parameters, however, show an exponential increase with increase in temperature. The present paper offers a plausible approach to numerically analyze fracture behavior of PS at varying temperature using a temperature dependent CZM.

• Computers and Concrete
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• 제4권3호
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• pp.221-241
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• 2007

Based on the experiment results, the damage and fracture behavior of concrete at the ages of 1d, 2d, 7d and 28d, in three-point bending and uniaxial tensile tests, were simulated with a finite element program, ABAQUS. The critical stress intensity factor $K_{IC}^s$ and the critical crack tip opening displacement ($CTOD_C$) of concrete were calculated with effective-elastic crack approach for the three-point bending test of grade C30 concrete. Based on the crack band model, a bilinear strain-softening curve was derived to simulate the LOAD-CMOD curves and LOAD-Displacement curves. In numerical analysis of the uniaxial tension test of concrete of grade C40, the damage and fracture mechanics were combined. The smeared cracking model coupling with damaged variable was adopted to evaluate the onset and development of microcracking of uniaxial tensile specimen. The uniaxial tension test was simulated by invoking the damage plastic model which took both damage and plasticity as inner variables with user subroutines. All the numerical simulated results show good agreement with the experimental results.

• 비파괴검사학회지
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• 제29권3호
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• pp.219-223
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• 2009

This paper prescribed the structural integrity of the API 5L X65 pipeline subjected to tensile pre-strain. The effects of pre-strain on the mechanical properties of API 5L X65 pipe were substantially investigated through a variety of the experimental procedures. Axial tensile pre-strain of 1.5, 5 and 10% was applied to plate-type tensile specimens cut from the pipe body prior to mechanical testing. Tensile test revealed that yield strength and tensile strength were increased with increasing tensile pre-strain. The increasing rate of the yield strength owing to the pre-strain is greater than that of the tensile strength. However, the pre-strain up to 5% had a little effect on the decreasing of the fracture toughness. The structural integrity of the API 5L X65 pipeline subjected to large plastic deformation was evaluated through the fitness-for service code.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2003년도 춘계학술발표대회 개요집
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• pp.32-33
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• 2003

The evaluation of HAZ toughness and cold crack susceptibility of 90mm thickness API 2W Grade 50 steel has been made in accordance with API RP 2Z as preproduction qualification test to be certified as il steel supplier from Shell International E & P. It was shown that the steel has superior HAZ toughness; CTOD value for CGHAZ more than 1.5mm at -10$^{\circ}C$, CVN absorbed energy more than 150J at -60$^{\circ}C$. Additionally, no generation of cold cracks was observed at 0.7kJ/mm even without preheating condition. These excellent results are due to the extremely low hardenability in HAZ of the steel.

• Journal of Welding and Joining
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• 제9권4호
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• pp.40-49
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• 1991

Both impact and fracture toughnesses were investigated with root gaps in FCAW weld metals at room temperature and 0.deg.C. The maximum impact value was obtained at the root gap of 16mm for 1G position weld metal, and the impact value of 3G position weld metals also showed the maximum impact value at the root gap of 12mm. However, the fracture toughnes(CTOD)values tend to decrease with increasing root gaps at both temperatures in 1G weld metal. Bending test also showed satisfactory results with all of root gaps investigated. Based on this result, it becomes possible to apply wide root gaps in real projects in both aspects of toughness and bending resistance.

• 한국기계가공학회지
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• 제18권5호
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• pp.9-16
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• 2019

Recent economic trends are worsening and becoming longer, and Korean shipbuilding is focused on high value added and high technology, especially for LNG carriers and large container ships. Both ship types increased in size in the 2010s but have requirements such as high strength, toughness at low temperatures and continuous weldability for preventing brittle fractures at service temperatures. In particular, as container ships become larger, the International Classification Society (IACS) has established a provision (IACS UR S33) that mandates the use of BCA (Brittle Crack Arrest) certified vessels for large container vessels contracted after 2014 to ensure safety. Therefore, studies on BCA 47Y.P are currently being undertaken, but BCA 40Y.P has not been actively studied yet. We will test BCA 40Y.P to verify why it can be applied to a large container ship and measure fatigue cracking.

• 한국기계가공학회지
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• 제20권3호
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• pp.24-32
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• 2021

The size of container ships is increasing to increase the cargo loading capacity. However, container ships are limited in terms of the hull longitudinal strength. To overcome this limitation, brittle crack arrest steel can be used. This study was aimed at examining the influence of the heat input on the welding procedures of flux cored arc welding and submerged arc welding. In the experiment, the crack tip opening displacement test, which pertains to a parameter of fracture mechanics, was performed, and a 3-point bending tester was adopted. Based on the results, the crack measurement method was presented, and the stress expansion coefficient value for the pre-fatigue crack length was derived according to the heat input after the pre-cracking length was measured. It was noted that the heat input affected the crack tip opening displacement of brittle crack arrest steel.