• Tunnel and Underground Space
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• v.10 no.3
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• pp.320-328
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• 2000

The numerical simulation of Brazilian fracture toughness test is carried out using PFC code and the influence parameters are analyzed such as shape of loading plane, size of Brazilian disc and unit particle of model, loading angle and loading rate. The flattened Brazilian disc is adopted for applying uniform load. The range of loading angle(2$\alpha$) necessary to induce the tensile crack at disc center and to obtain the load-displacement curve giving the critical load for the stable crack propagation is shown as 20°∼40°. In condition that the loading angle is 20°, the mode-I fracture toughness is evaluated almost constant in the range of particle size less than 1 mm and loading rate less than 0.01㎜/s. This range of influence parameters seems appropriate condition for the tensile crack initiation at disc center and the control of stable crack propagation, which can give the reliance in evaluation of fracture toughness by Brazilian test.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.917-920
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• 2008

ECC is a special kind of high performance cementititous composite which exhibits typically more than 2% tensile strain capacity by bridging microcracks at a crack section. Therefore, micromechanics should be adopted to obtain multiple cracking and strain hardening behavior. This paper propose a linear elastic analysis method to simulate the multiple cracking and strain hardening behavior of ECC. In an analysis, the stress-crack opening relation modified considering the orientation of fibers and the number of effective fibers is adopted. Furthermore, to account for uncertainty of materials and interface between materials, the randomness is assigned to the tensile strength(${\sigma}_{fci}$), elastic modulus($E_{ci}$), peak bridging stress(${\sigma}_{Bi}$) and crack opening at peak bridging stress(${\delta}_{Bi}$), initial stress at a crack section due to chemical bonding, (${\sigma}_{0i}$), and crack spacing(${\alpha}_cX_d$). Test results shows the number of cracking and stiffness of cracked section are important parameters and strain hardening behavior and maximum strain capacity can be simulated using the proposed method.

• Journal of Welding and Joining
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• v.15 no.3
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• pp.20-28
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• 1997

용접부에는 많은 취약조건들이 존재하며 파괴의 주 원인이 되고 있어 이들에 대한 많은 연구가 진행되고 있다. 따라서, 현재 용접재료, 용접 조건 및 용접방법 등 을 개선함으로써 여러 방면에서 좋은 결과를 얻고 있다. 그러나 아직도 용접시의 열소 성변형과 구속조건에 따라 분포하는 잔류응력에 의한 피로균열거동에 대한 연구는 정확한 잔류응력 측정의 어려움으로 미흡한 상태이다. 특히 잔류응력의 측정기술과 반복하중에 의한 피로균열 진전시 잔류응력의 이완 등은 이들을 해석하는데 많은 어 려움을 주고 있다. 용접시 높은 열에 의한 재료의 팽창과 냉각시의 수축변형은 용접 부재에 인장 및 압축 잔류응력을 유발시키고, 인장잔류응력은 균열 진전될 때 잔류 응력은 오히려 균열을 지연시키기도 한다. 또한 잔류응력장에서 피로 균열이 진전될 때 잔류응력은 일반적으로 작용하중의 크기와 반복 수 그리고 균열 진전 등으로 인하 여 이완되고 재분포된다. 본 해설에서는 용접재의 피로거동중에 발생하는 잔류응력의 재분포 현상을 하중의 범위, 하중 반복수, 균열 진전의 영향으로 구분하여 각각의 영향에 대해서 기술하고자 한다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.24 no.3
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• pp.237-248
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• 2011

Tensile softening characteristics play an important role in the structural behavior of steel fiber-reinforced ultra high performance concrete. Tension softening modeling and numerical analysis method are necessary for the prediction of structural performance of steel fiber-reinforced concrete. The numerical method to predict the flexural behavior is proposed in this study. Tension softening modeling is carried out by using crack equation based on fictitious crack and inverse analysis in which load-crack opening displacement relationship is considered. Thereafter material modeling is performed considering tension softening. The comparison of moment-curvature curves of the numerical analysis results with the test results indicates a reasonable agreement. Therefore, the present numerical results prove that good prediction of flexural behavior of steel fiber-reinforced ultra high performance concrete beams can be achieved by employing the proposed method.

• Journal of the Korea Concrete Institute
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• v.28 no.2
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• pp.223-234
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• 2016

In this study, direct tension test for hybrid steel fiber reinforced ultra-high performance concrete (UHPC) containing two different steel fibers with a length of 16 and 19 mm was performed to investigate the fracture behavior of UHPC. Test results showed that crack strength and tensile strength, and fracture energy increased with increasing the fiber volume ratio. Based on the test results, the peak cohesive stress at the crack tip, tensile strength, and fracture energy depending on the fiber volume ratio were proposed. The proposed tensile strength of UHPC was suggested as a function of the fiber volume ratio and compressive strength. The peak cohesive stress at the crack tip and fracture energy were also proposed as a function of the tensile strength. The predicted values were relatively agree well with the test results. Thus, the proposed equations is expected to be applicable to UHPC with a compressive strength of 140~170 MPa and a fiber volume ratio of less than 2%.

• International Journal of Highway Engineering
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• v.4 no.3 s.13
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• pp.35-42
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• 2002

Many temperature-related problems are created in asphalt pavement due to the low temperature. In particular, loss of tensile strength due to low temperature is known to be responsible for thermal failure of pavements in cold regions under $-20^{\circ}C$. The objective of this study is to evaluate characteristics of resistance against low-temperature cracking of polymer asphalt concrete mixtures modified with LDPE and SBS. The test results showed that the mixtures had the maximum indirect tensile strength(ITS) at low temperature ranging from $-10^{\circ}C. It was proved through ITS test that the stress due to differential thermal contraction over the tensile strength did generate internal damage at the temperature below $-20^{\circ}C$. It was shown that the asphalt mixtures modified with polymer had better ITS than the normal asphalt mixture at the temperature below $-20^{\circ}C$. Thus the effect of modification was revealed as tensile strength improvement. From the results of this study, it was recommended that polymer-modified asphalt should be used in order to prevent low-temperature cracking in cold region.

• Journal of the Korean Ceramic Society
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• v.28 no.1
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• pp.19-19
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• 1991

Fracture of Al2O3 tubes for different loading path under combined tension/torsion was investigated. Macroscopic directions of crack propagation agreed well with the maximum principal stress criterion, independent of the loading path. However, fracture strength from the proportional loading test(τ/σ= constant) showed either strengthening or weakening compared to that from uniaxial tension, depending on the ratio τ/σ. The Weibull theory was capable to predict the strengthening of fracture strength in pure torsion, but not the weakening in the proportional loading condition. The strengthening or weakening of fracture strength in the proportional loading condition was explained by the effect of shear stresses in the plane of randomly oriented microdefects. Finally, a new empirical fracture criterion was proposed. This criterion is based on a mixed mode fracture criterion and experimental data for fracture of Al2O3 tubes under combined tension/torsion. The proposed fracture criterion agreed well with experimental data for both macroscopic directions of crack propagation and fracture strengths.

• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.5
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• pp.121-128
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• 2012

In this paper, nonlinear analysis for reinforced concrete structure for power transmission line is performed by considering the characteristics of the failure, which are depend on loading conditions and concrete material models. On the numerical evaluation for the failure behavior, the finite element analysis is applied. For the concrete material model, microplane model based on concrete damage is introduced. However, to describe the crack bridging effect of long and short fiber of steel fiber reinforced concrete (SFRC), tensile softening model is suggested and applied for SFRC. An numerical results by finite element technique are compared with the experiment results for box culvert specimen. Comparing on the experimental and analytical results, validity and reliability of numerical analysis are investigated.

• Journal of the Korea Concrete Institute
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• v.22 no.3
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• pp.427-435
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• 2010

One of the most vulnerable properties in concrete is tensile cracking, which usually happens at early ages due to hydration heat and shrinkage. In order to accurately predict the early age cracking, it needs to find out how stress-crack opening relation is varying over time. In this study, inverse analyses were performed with the existing experimental data for wedge-splitting tests, and the parameters of the softening curve for the stress-crack opening relation were determined from the best fits of the measured load-CMOD curves. Based on the optimized softening curve, variation of fracture energy over time was first examined, and a model for the stress-crack opening relation at early ages was suggested considering the found feature of the fracture energy. The model was verified by comparisons of the peak loads, CMODs at peak loads, and fracture energies obtained from the experiments and the inverse analysis.

• Journal of the Microelectronics and Packaging Society
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• v.8 no.3
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• pp.25-30
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• 2001

The stress intensity factors for edge cracks located at the bonding interface between the semiconductor chip and the adhesive layer subjected to a uniform transverse tensile strain are investigated. Such cracks might be generated due to a stress singularity in the vicinity of the free surface. The boundary element method (BEM) is employed to investigate the behavior of interface stresses. The amplitude of complex stress intensity factor depends on the crack length, but it has a constant value at large crack lengths. The rapid propagation of interface crack is expected if the transverse tensile strain reaches a critical value.