• International Journal of Concrete Structures and Materials
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• 제18권3E호
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• pp.183-189
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• 2006

Many researchers have recently proposed various parameters, variables of models and experimental methods to evaluate fracture properties of concrete, and their developments allow us to analyze the non-linear and quasi-brittle fracture mechanisms. This paper presents a brief treatment of the fracture parameters. Additionally, three-point bending tests were conducted to compare J-integral($J_{Ic}$) with other parameters($K_{Ic},\;G_{Ic},\;and\;G_F$). The change in parameter values with respect to the width and notch length of concrete beam specimens was also considered. The load-displacement curves were used to measure the concrete fracture toughness experimentally. From the results of experiment, it was found that the value of $G_F\;and\;J_{Ic}$ decreased as the notch depth increased and that $G_F$ was less sensitive than $J_{Ic}$. Therefore, the former, $G_F$, is more appropriate in using it as the concrete fracture toughness parameter. The values of $G_F\;and\;J_{Ic}$ increased when the width of concrete specimens increasing from 75 mm to 150 mm. Thus, the effects of the specimen width should be considered in determining the fracture toughness of concrete.

• Journal of the Korean Wood Science and Technology
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• 제17권4호
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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.

• Steel and Composite Structures
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• 제25권6호
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• pp.639-648
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• 2017

Fracture energy values KV have been measured on cast steel, used in the container manufacture, by instrumented Charpy impact testing. This material has a large ductility on the upper transition region at $+20^{\circ}C$ and a ductile tearing with an expended plasticity before a brittle fracture on the lower transition region at $-20^{\circ}C$. To assess the fracture toughness of this material we use, the $K_{IC}$-KV correlations to measure the critical stress intensity factor $K_{IC}$ on the lower transition region and the dynamic force - displacement curves to measure the critical fracture toughness $J{\rho}_C$, the essential work of fracture ${\Gamma}_e$ on the upper transition region. It is found, using the $K_{IC}$-KV correlations, that the critical stress intensity factor $K_{IC}$ remains significant, on the lower transition region, which indicating that our testing material preserves his ductility at low temperature and it is apt to be used as a container's material. It is, also, found that the $J_{\rho}-{\rho}$ energetic criterion, used on the upper transition region, gives a good evaluation of the fracture toughness closest to those found in the literature. Finally, we show, by using the ${\Gamma}_e-K_{IC}$ relation, on the lower transition region, that the essential work of fracture is not suitable for the toughness measurement because the strong scatter of the experimental data. To complete this study by a numerical approach we used the ANSYS code to determine the critical fracture toughness $J_{ANSYS}$ on the upper transition region.

• 한국전산구조공학회논문집
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• 제22권6호
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• pp.565-572
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• 2009

본 연구에서는 EGW공정 적용에 따른 고강도 극후판 EH36-TMCP강 용접부의 역학적 거동 및 파괴인성 $K_{IC}$ 특성을 고찰하기 위해 먼저 자체 개발한 열분포, 열탄소성 프로그램을 이용한 유한요소해석을 통하여 용접부의 역학적 거동(용접잔류응력, 소성변형율 등의 크기, 분포, 발생기구)을 규명하였다. 그리고 이때 얻어진 잔류응력을 초기응력으로 하여 상용프로그램 ANSYS에서 노치가공으로 인한 응력 재분포 특성 및 잔류응력과 외력의 복합하중에 대한 파괴인성 KIC를 계산하였다. 균열이 존재하는 EGW용접부의 파괴기준$K_{IC}$를 살펴보면, 중첩된 경우가 순수 외부하중(굽힘하중)만 작용하는 경우 보다 파괴 인성치가 다소 감소하는 경향을 보였다. a/W가 작을 경우 중첩의 경우가 순수 외부하중(굽힘하중)만의 경우보다 파괴인성치 차이가 크나, a/W가 증가함에 따라 그 차이가 점차 없어지는 것으로 나타났다.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2003년도 춘계학술대회 논문집
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• pp.300-305
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• 2003

Reduced activation ferritic (JLF-1) steel is leading candidates for blanket/first-wall structures of the D-T fusion reactor. In fusion application, structural materials will suffer effects of repeated changes of temperature. Therefore, the data base of tensile strength and fracture toughness at operated temperature $400^{\circ}C$ are very important. Fracture toughness ($J_{IC}$) and tensile tests were carried out at room temperature and elevated temperature ($400^{\circ}C$). Fracture toughness tests were performed with two type size to investigate the relationship between the constraint effect of a size and the fracture toughness resistance curve. As the results, the tensile strength and the fracture toughness values of the JLF-1 steel are slightly decreased with increasing temperature. The fracture resistance curve increased with increasing plane size and decreased with increasing thickness. The fracture toughness values of JLF-1 steel at room temperature and at $400^{\circ}C$ shows an excellent fracture toughness ($J_{IC}$) of about $530kJ/m^2\;and\;340kJ/m^2$, respectively.

• 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.

• Advances in concrete construction
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• 제2권2호
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• pp.145-162
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• 2014

In this study, the fracture toughness $K_{IC}$ of high performance concrete (HPC) was determined by conducting three-point bending tests on eighty notched HPC beams of $500mm{\times}100mm{\times}100mm$ at high temperatures up to $450^{\circ}C$ (hot) and in cooled-down states (cold). When the concrete beams exposed to high temperatures for 16 hours, both thermal and hygric equilibriums were generally achieved. $K_{IC}$ for the hot concrete sustained a monotonic decrease tendency with the increasing temperature, with a sudden drop at $105^{\circ}C$. For the cold concrete, $K_{IC}$ sustained a two-stage decrease trend, dropping slowly with the heating temperature up to $150^{\circ}C$ and rapidly thereafter. The fracture energy-based fracture toughness $K_{IC}$' was found to follow similar decrease trends with the heating temperature. The weight loss, the fracture energy and the modulus of rapture were also evaluated.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.61-66
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• 2004

Fracture toughness database system was developed with Visual Foxpro 6.0 and operates in MS Windows environment. The database system contains 10,278 sets of $K_{IC}$ data, 7,046 sets of $K_{C}$ data, 784 sets of $J_{IC}$ data, 571 sets of CTOD data, 62 sets of $K_{a}$ data and 26 sets of $K_{Id}$ data. The data were collected from JSMS(Society of Material Science, Japan) fracture toughness data book and USAF(United States Air Force) crack growth database. In addition, the database was applied to predicting $K_{IC}$ from tensile material properties using artificial neural networks.

• 대한치과보철학회지
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• 제39권6호
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• pp.682-697
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• 2001

This investigation evaluated the fracture toughness($K_{IC}$) of eight currently available core materials, and relate the fracture toughness value to fractography analysis and surface characteristics using a atomic force microscope (AFM). Single-edge notched (SEN) test specimens (n=10) and compact tension (CT) test specimens (n=10) were prepared conforming to the ASTM Standard E-399 for a high copper amalgam, three composite core materials (Core-Max II, Core Paste, Bisfil Core), two reinforced composite core materials (Ti-Core, Ti-Core Natural), a resin-modified glass ionomer core material (Vitremer), and a conventional glass ionomer core material (Ketac-Molar). The specimens were tested with an Instron Universal Testing Machine. The maximum loads were measured to calculate the fracture toughness ($K_{IC}$). Thereafter, fracture surfaces of SEN specimens of each material were investigated for fractography analysis using scanning electron microscope. And, disc-shaped specimens with 1mm thickness were fabricated for each material and were investigated under AFM for surface morphology analysis. The results were as follows: 1. Bisfil Core showed the highest mean fracture toughness regardless of test methods. 2. For the tooth-colored materials, Ti-Core Natural exhibited the highest fracture toughness. 3. Ketac Molar showed a significantly low fracture toughness when compared with the amalgam and the composite resin core materials(p<0.05). 4. The fracture toughness values obtained with the single-edge notched test, except Ketac Molar, were higher than those obtained in the compact tension test. 5. SEM revealed that the fracture surface of high fracture toughness material was rougher than that of low fracture toughness material. 6. AFM revealed that the surface particles of the composite resins were smaller in size, with a lower surface roughness than the glass ionomer core materials.

• Composites Research
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• 제28권6호
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• pp.361-365
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• 2015

The influence of MWCNTs on fracture toughness properties of MWCNTs/Nickel-Pitch Fibers/epoxy composites (MWCNTs/Ni-PFs/epoxy) was investigated according to MWCNTs content. Nickel-Pitch-based carbon fibers (Ni-PFs) were prepared by electroless nickel-plating. The surface properties of Ni-PFs were determined by scanning electron microscopy (SEM) and X-ray photoelectron spectrometry (XPS). The fracture toughness of MWCNTs/Ni-PFs/epoxy was assessed by critical stress intensity factor ($K_{IC}$) and critical strain energy release rate ($G_{IC}$). From the results, it was found that the fracture toughness properties of MWCNTs/Ni-PFs/epoxy were enhanced with increasing MWCNTs content, whereas the value decreased above 5 wt.%. MWCNTs content. This was probably considered that the MWCNTs entangled with each other in epoxy due to an excess of MWCNTs.