• Journal of the Korea Concrete Institute
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• v.13 no.2
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• pp.161-167
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• 2001

It is difficult to obtain accurate fracture toughness values using three point bending test(TPB) proposed by RILEM committees because the shape of load-deflection curve is irregular and final crack propagation occurs after some slow stable cracking. However, fracture toughness is easily obtained from crack initiation load in the disk test. In this paper, the fracture properties of high strength concrete disks with center-crack was investigated. For this purpose, the experimental results were compared with the results by finite element analysis(FEA). And the experimental fracture locus was compared with theoretical fracture locus. Also, the results of fracture properties for the degree of concrete strength are presented. It is concluded from this study that results from FEA with maximum stress theory were compared well with the results from experiment. And the degree of concrete strength was contributed to the crack initiation load and fracture toughness, but was not contributed to the failure angle. Also, The discrepancy of fracture locus between the maximum stress theory and the experiment for concrete is considered to depend upon a large energy requirement for inducing the mixed-mode and sliding mode fractures.

• Magazine of the Korea Concrete Institute
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• v.6 no.1
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• pp.131-141
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• 1994

This experimental study was performed to lnvestigate the effects of the lergths dnd volume contents of glued hooked steel fiber for the fracture toughness and strength of c oncretc. The notched steel fiber reinforced concrete beams with different flber length(30, 60mm) and fiber volume content(O.0, 0.5, 1.0, 1.5, 2.0%) were tested under 3-point benclmg, md 1 he flexural strengths, fracture energy and CMOD were obtained from the experimental data. The fracture energy v~ds used as d means to evaluate the fracture toughness ot concrete. The results showed that the frdcture toughness and 5trength of conuett. were generally increased ds the content of steel fiber was inc~edsed, arid the length of steel ilber had a great efiect on the flexural strength but little on the compressive itrength and fractule toughness. And also, considering the distributions of steel fiber, workablity and the maxinium size of coarse dqgregates, the optimum content of steel fiber seemed to be about 1.0 '0, and when lts length uias longer the results were somewhat tavorable.

• Magazine of the Korea Concrete Institute
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• v.9 no.3
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• pp.179-187
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• 1997

콘크리트는 여러 구성 성분들이 불규칙적인 배열을 이루어 형성된 복합재료이지만, 과거에는 이 재료를 하나의 단종재료로 간주하여 해석하였기 때문에, LEFM에서 사용되는 파괴인성계수만으로는 콘크리트의 파괴역학적 접근이 어렵다는 것 이외에는 파괴인성계수들의 크기의존성에 대한 이유라든가, 실험을 통해서 관측된 구조물 두께 방향으로의 서로 다른 깊이의 균열 진행 현상에 대해서는 설명하기가 어려웠다. 따라서 본 연구는 콘크리트를 하나의 복합재료로써 각각의 구성요소들이 차지하고 있는 체적비 및 배열상의 효과를 고려하여 복합재료의 파괴거동을 해석하고, 구성재료의 수와 파괴인성계수와의 상관관계를 분석하였다. 각각의 구성요소들을 연립변형모드( SD mode)로 배열시킨 조건에서 복합재료역학개념에 입각하여 해석한 결과, 일반적으로 실험이나 비선형파괴역학 해석과 같이 하중-변위곡선 상단부에서 비선형 거동이 관측되었다. 또한 임계응력확대계수( $K_IC$)나 파괴에너지($G_r$)는 구성원의 수나 보의 크기에 대해서 거의 무관한 값을 나타내지만, 임계군열선단개구변위 ($CTOD_c$)는 크기에 영향을 받음을 보여 주었다. 균열의 진행속도는 균열이 진행될수록 감소하며, 파괴인성이 작은 구성원에서부터 균열이 발생되어 결과적으로 보의 두께 방향으로 서로 다른 크기의 균열길이가 생성됨이 관측되었다.

• 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.

• Magazine of the Korea Concrete Institute
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• v.2 no.3
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• pp.89-95
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• 1990

Possibility for the evaluation of fracture properties of mortar and concrete by splitting tensile test was stud¬ied. Splitting tensile tests were conducted to obtain the fracture loads for several sizes of cylindrical specimens of mortar and concrete with initial notch. From the results, fracture energy and fracture toughness by SEL were obtained and compared with the values by Rooke and Cartwright, and r.E.Moo The values by SEL method converged effectively. SEL method was shown to be a good method to obtain fracture properties of mortar and concrete.

• 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.

• International Journal of Highway Engineering
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• v.3 no.1 s.7
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• pp.185-197
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• 2001

This paper dealt with modification of effective crack length model (ECM) by adding Poisson's ratio term to evaluate fracture toughness of asphalt concrete which varies its material property by temperature. The original ECM model was developed for solid materials, such as cement concrete, and Poisson's ratio of materials was not considered. However, since asphalt concrete is sensitive to temperature variation and changes its Poisson's ratio by temperature, it should be taken into consideration to know exact fracture property under various temperatures. Four binders, including 3 polymer-modified asphalt (PMA) binders, were used to make a dense-grade asphalt mixture and 3-point bending test was peformed on notched beam at low temperatures, from -5oC to 35oC. Elastic modulus, flexural strength and fracture toughness were obtained from the test. The results showed that, since Poisson's ratio was considered, the more accurate test values could be obtained using modified ECM equation than original ECM. PMA mixture showed higher stiffness and fracture toughness than normal asphalt mixture under very low temperatures.

• Journal of Industrial Technology
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• v.16
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• pp.267-275
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• 1996

금속과 같은 균질한 재료의 균열파괴의 특성을 설명하기 위하여 도입된 파괴역학의 이론들은 1960년대 이후 콘크리트나 암석 등에 대하여 적용되기 시작하였다. 파괴인성계수(fracture toughness)는 균열의 성장에 대한 재료의 저항을 나타낸다. 그러나, 암석의 파괴역학적 특성은 암석이 갖는 불균질성이나 비등방성에 의하여 영향을 받는다. 즉, 암석의 파괴역학적 특성의 측정은 시험편의 크기나 초기균열의 길이, 시험편의 형상 등에 의하여 측정자료의 분산이 심하며 따라서 다른 기본 물성들의 경우에서와 마찬가지로 일정한 시험기준의 도입이 요구되었다. 1988년에 국제암반공학회(ISRM)에서 제시한 표준시험방법은 시험편의 제작이나 시험방법에 있어서 복잡한 과정을 요구하고 있다. 본 논문에서는 표준시험방법에서 사용되는 시험편의 형태에 비하여 비교적 간단한 시험방법들에 의하여 얻어진 파괴적인성계수들을 서로 비교하여 제시하고 시험편의 크기와 기타 시험조건에 따른 파괴인성계수 측정치의 변화를 나타내고 있다. 또한, 암석에 포함되어있는 자연균열들의 특성과 파괴역학실험 중 유발되는 인공균열들의 형태를 비교하여 실험실에서 얻은 파괴역학적 계수들의 현장적용에 대한 문제점들을 지적하고 있다.

• Journal of the Korea Concrete Institute
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• v.16 no.6 s.84
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• pp.851-858
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• 2004

Purpose of this paper is to determine the appropriate size of a center notched disk specimen for mode I fracture toughness $K_{IC}$. For this purpose, mode I test results with various sizes of center notched disk were compared with the RILEM three-point-bend test ones. Compressive strength of concrete used in this paper was 44.9 MPa. Diameters of 200, 300, 400 mm, thickness of 75, 100, 125 mm, and notch length ratios an of 0.3, 0.4, 0.5, 0.6 were used for the mode I disk test. Also, diameter of 300mm thickness of 100mm, and notch length ratios a/R of 0.3, 0.4, 0.5, 0.6 were used for the mixed mode disk test. Mixed mode stress intensity factors were investigated by changing notch angles for the disk specimen. Stress intensity factors of a center notched disk were calculated with the various methods for comparison. From the test results, mode I fracture toughness calculated from the disk specimen with diameter of 300 mm, thickness of Inn and notch length ratio a/R of 0.5 was very similar to the RILEM three-point-bend test ones. And it is verified that stress intensity factors for mixed mode can be easily calculated with the disk specimen.

• Magazine of the Korea Concrete Institute
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• v.8 no.6
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• pp.235-243
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• 1996

The mechanical behavior ot concrete is strongly influenced by various scenarios of crack initiation and crack propagation. Recently. the study of the interface fracture and cracking in interfacial regions is emerged as an important field, in the context of the developement of high performance concrete composites. The crack path criterion for elastically homogeneous materials is not valid when the crack advances at an interface because. in this case, the consideration of the relative magnitudes of the fracture toughnesses between the constituent materials and the interface are involved. In this paper, a numerical method is presented to obtain the values of two interfacial fracture parameters such as the energy release rate and the phase angle at the tip of an existing interface crack. Criteria based on energy release rate concepts are suggested for the prediction of crack growth at the interfaces and an hybrid experimental-numerical study is presented on the two-phase beam composite models containing interface cracks to investigate the cracking scenarios in interfacial regions. In general, good agreement between the experimental results and the prediction from the criteria is obtained.