• Proceedings of the KWS Conference
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• 2009.11a
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• pp.93-93
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• 2009

본 연구에서는 EGW, FCAW 공정 적용에 따른 고강도 극후판 EH36-TMCP강 용접부의 역학적 거동 및 파괴인성 $K_{IC}$ 을 규명하기 위해, 먼저 열분포, 열탄소성 수치해석을 통하여 용접부의 역학적 거동(용접잔류응력, 소성변형율 등의 크기, 분포, 발생기구)을 고찰하였다. 그리고 이때 얻어진 잔류응력을 초기응력으로 하여, 잔류응력과 외력의 복합하중에 대한 파괴인성 $K_{Ic}$ 특성을 해석하였다. 용접공정별 균열이 존재하는 용접부의 파괴기준을 살펴보면, EGW용접부의 경우가 FCAW용접부의 경우에 비해 균열의 성장이 다소 용이하여 $K_{IC}$ 값이 다소 낮게 나타났다. EGW용접부의 파괴인성 $K_{IC}$ 경우 중첩된 경우(복합하중)가 순수 외력만 작용하는 경우보다 파괴 인성치가 다소 감소하는 경향을 보이고, a/W가 작을 경우 중첩의 경우가 순수 외력만의 경우보다 파괴인성치 차이가 크나, a/W가 증가함에 따라 그 차이가 점차 없어지는 것으로 나타났다. 반면, FCAW용접부의 경우 균열길이가 작은 범위에서는 중첩된 경우가 순수 외력만 작용 할 경우보다 파괴 인성치가 다소 증가함을 보이지만, a/W가 증가함에 따라 순수 외력만의 작용의 경우와 중첩의 경우의 파괴인성 차이가 없는 것으로 나타났다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.22 no.6
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• pp.565-572
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• 2009

This work intends to establish the reliability and fracture toughness $K_{IC}$ criterion of welded joints by EGW for high strength EH36-TMCP ultra thick plate. For this, firstly thermo elasto-plastic analysis has been carried out on two pass X-groove butt joint model to clarify the thermal and mechanical behaviour(residual stress, plastic strain, magnitude of stress and their distribution and production mechanism). Moreover, to establish fracture criterion, analysis of fracture toughness $K_{IC}$ has been performed under the notch machined and residual stress with the load condition on EGW welded joints. A quantitative fracture criterion for EGW welded joints is suggested by using $K_{IC}$.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.1
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• pp.25-37
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• 1993

This paper describes the use of the J-integral, a one parameter of the non-linear fracture mechanics(NLFM), as a means to measure toughness of steel fiber reinforced concrete. This parameter can be conveniently evaluated from experimentally determined load-deflection curves from flexural tests when a maximum-load failure criterion is employed. And, for high strength concrete which was reinforced steel fiber, with two different fiber length in the form of notched beams, were tested under 3-point bending, and $J_{IC}$, as well as the linear elastic fracture mechanics(LEFM) parameters $K_{IC}$ and $G_{IC}$ were evaluated. The results suggest that $J_{IC}$ is a promising fracture criterion for all of these. while $K_{IC}$(or $G_{IC}$) almost certainly are not. Also it was found that a fiber addition of less than 0.5% did not improve the fracture toughness of the high strength concrete. However, at more than 1.0% in fiber contents, $J_{IC}$ showed significant increases. reflecting the changed character of the concrete; $K_{IC}$ and $G_{IC}$ did not.

• Tunnel and Underground Space
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• v.11 no.4
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• pp.352-361
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• 2001

Mode I fracture toughness ( $K_{IC}$) of the frozen rocks and that of the frozen-thawed rocks were obtained by using BDT and CCNBD specimens. The test temperatures ranged from +$25^{\circ}C$ to -16$0^{\circ}C$. Wet and air-dry specimens of granite and sandstone were used in order to investigate the effect of water and porosity on fracture toughness. The SEM images of the frozen-thawed rocks were also analysed to check the density of thermal cracks. The $K_{IC}$ of the frozen rocks increased as the test temperature went down. The rate of increase was higher in wet condition than in dry condition and the rate of increase for wet granite was higher than that for wet sandstone. The $K_{IC}$ of the frozen-thawed rocks varied within 15% from the $K_{IC}$ of the rocks at room temperature. After one freeze-thaw process, thermal crack occurred in granite but no thermal cracks occurred in sandstone. And the crack density was increased as the temperature went down.n.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2000.04a
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• pp.34-34
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• 2000

재료에 따라 기계적 특성들은 하중속도에 의존하는 경우가 많다. 이런 기계적 특성들 중 파괴인성은 기계구조물을 파괴 역학적으로 안전하게 설계하는 경우뿐만 아니라, 운전되고 있는 기계 건전성의 측면에서 매우 중요한 파라미터이다. 또한 파괴인성은 작용하는 하중의 속도에 따라 정적파괴인성($K_{IC}$)과 동적파괴인성($K_{ID}$)으로 구분하고 이들의 측정 방법과 인성의 크기 또한 매우 상이하다. 동적파괴인성의 평가방법으로는 광탄성법, 모아레법 및 스트레인게이법을 이용한 충격실험방법들이 이용되고 있다.

• Journal of the Korea Concrete Institute
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• v.13 no.4
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• pp.371-378
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• 2001

Recently, the parameters, models, and experimentations, which evaluate the fracture properties of concrete, have been proposed by many researchers, and their developments allow us to analyze the non-linear and quasi-brittle fracture mechanisms. In this paper, a brief treatment of the fracture parameters was presented and the experiments of 3-point bending tests were conducted to compare J-integral($J_{Ic}$ /) with other parameters($K_{Ic}$ , $G_{v}$ , and $G_{F}$ ). The change of parameter values according to the width and notch length of concrete beam specimens was also considered. The load-displacement curves are used to experimentally measure concrete fracture toughness. From the results of experiment, it is noted that the value of $GF$ and tic decreases as the notch depth increases and $G_{F}$ is less sensitive than $J_{Ic}$ . Therefore, the former is more appropriate to use as the concrete fracture toughness parameter. The values of $v_{v}$ and $J_{Ic}$ increase when the width of concrete specimens increase from 75 mm to 150 mm. Therefore, the effects of specimen width need to be considered in determining the concrete fracture toughness.

• Journal of the Korean Institute of Gas
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• v.15 no.4
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• pp.21-26
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• 2011

Type-3 cylinder liner has a limitation of machining the standard specimen for fracture toughness test because it has approximately 5 mm in thickness as well as a curvature. Hence, it needs to be employed a miniature specimen test technique to evaluate fracture toughness of the cylinder liner. In this study, small punch (SP) test method was employed to evaluate fracture toughness of the cylinder liner. Load-displacement curve result measured from the SP test showed that the liner material was failed during membrane stretching in the general SP load-displacement curve. Additionally, it was shown that liner material was isotropic although the amount of plastic deformation was different depending on the direction due to manufacturing process characteristics. Fracture toughness, $J_{Ic}$, was evaluated using the SP test data. The value of fracture toughness obtained was $13.0kJ/m^2$. This value was similar to that of the same kind of materials. Therefore, the fracture toughness evaluated using the SP test data was reasonable.

• Journal of the Korean Wood Science and Technology
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• v.17 no.4
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• pp.70-76
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• 1989

The fracture toughness of two species, Pinus rigida MILL and Pinus koraiensis S. et Z. grown in Korea, was investigated by means of single edge notch beam specimen for the six principal systems of crack propagation in wood. The values of the fracture toughness for the LR and the LT systems ($K_{IC}$LR and $K_{IC}$LT) were found to be similar to each other and about 8 times greater than those for the other systems ($K_{IC}$RL, $K_{IC}$TL and $K_{IC}$TR) in both species. The results indicate that the characteristics of fracture toughness in three principal directions of wood (L, R, T direction) are quite different from those of bending strength for the responsible direction. To predict $K_{IC}$ value based on the variation of specific gravity, the experimental values of $K_{IC}$LT and $K_{IC}$TL were compared to the predicted values by published relationship between $K_{IC}$ and specific gravity. However, there were 10 to 25% differences between the former and the latter.

• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.5
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• pp.424-430
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• 2000

In order to develop an ultrasonic evaluation method for properties degradation of high temperature materials, a number of Cr-Mo-V steel samples were heat-treated and their damage mechanism was examined. Ultrasonic parameters such as velocity, attenuation, and more recently developed nonlinear acoustic parameter were measured. The nonlinear acoustic parameter was found to be most sensitive to material degradation mainly attributed to the precipitation of impurities in grain boundaries. When compared to the electrical resistivity results, the nonlinear parameters showed similar behavior. There existed a relatively good correlation between the nonlinear parameter and the fracture appearance transition temperature (FATT) obtained by Charpy V-notch impact test. Based on the relationship between the FATT and the fracture toughness ($K_{IC}$), correlation between the nonlinear parameter and $K_{IC}$ was established.

• Elastomers and Composites
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• v.39 no.1
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• pp.42-50
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• 2004

In this work, the diglycidylether of bisphenol A (DGEBA) and modified polyurethane (PU) blends were initiated by N-benzylpyrazinium hexafluoroantimonate (BPH). The cure and fracture toughness of neat DGEBA with the addition of PU were investigated. The cure properties of DGEBA/PU blend system were examined by DSC and near-IR measurements. The fracture touhtness were investigated by measuring the critical stress intensity factor ($K_{IC}$) and the critical strain energy release rate ($G_{IC}$). According to the results, the maximum values of owe activation energy ($E_a$) and conversion (${\alpha}$) were found at 10 phr of PU. Also the $K_{IC}$ showed a similar behavior with the results of conversion. These results were probably due to increase of crosslinking density in the blends resulted from increase of the hydrogen bonding between the hydroxyl groups of DGEBA and isocyanate groups of PU.