• Proceedings of the Korea Concrete Institute Conference
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• 2001.11a
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• pp.329-334
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• 2001

In this paper, the crack properties of steel fiber reinforced concrete (SFRC) structures for environment by experimental and analytical methods are discussed. The major role played by the steel fiber occurs in the post-cracking zone, in which the fibers bridge across the cracked matrix. Because of its improved ability to break crack, SFRC has better crack properties than that of reinforced concrete (RC). Crack properties are influenced by longitudinal reinforcement ratio, volume and type of steel fiber, strength of concrete.

• International Journal of Concrete Structures and Materials
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• v.19 no.1E
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• pp.25-32
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• 2007

The fracture energy evaluated from the previous experimental results can be simulated by using the modified singular fracture process zone (S-FPZ) model. The fracture model has two fracture properties of strain energy release rate for crack extension and crack close stress versus crack width relationship $f_{ccs}(w)$ for fracture process zone (FPZ) development. The $f_{ccs}(w)$ relationship is not sensitive to specimen geometry and crack velocity. The fracture energy rate in the FPZ increases linearly with crack extension until the FPZ is fully developed. The fracture criterion of the strain energy release rate depends on specimen geometry and crack velocity as a function of crack extension. The behaviors of micro-cracking, micro-crack localization and full development of the FPZ in concrete can be explained theoretically with the variation of strain energy release rate with crack extension.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2010.04a
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• pp.459-464
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• 2010

The dynamic propagation of an interface crack between two dissimilar functionally graded layers under anti-plane shear is analyzed using the integral transform method. The properties of the functionally graded layers vary continuously along the thickness. A constant velocity Yoffe-type moving crack is considered. Fourier transform is used to reduce the problem to a dual integral equation, which is then expressed to a Fredholm integral equation of the second kind. Numerical values on the dynamic energy release rate (DERR) are presented. Followings are helpful to increase of the resistance of the interface crack propagation of FGM: a) increase of the gradient of material properties; b) increase of the material properties from the interface to the upper and lower free surface; c) increase of the thickness of FGM layer. The DERR increases or decreases with increase of the crack moving velocity.

• Geomechanics and Engineering
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• v.17 no.1
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• pp.57-67
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• 2019

Water-induced strength reduction is one of the most critical causes for rock deformation and failure. Understanding the effects of water on the strength, toughness and deformability of rocks are of a great importance in rock fracture mechanics and design of structures in rock. However, only a few studies have been conducted to understand the effects of water on fracture properties such as fracture toughness, crack propagation velocity, consumed energy, and microstructural damage. Thus, in this study, we focused on the understanding of how microscale damages induced by water saturation affect mesoscale mechanical and fracture properties compared with oven dried specimens along three notch orientations-divider, arrester, and short transverse. The mechanical properties of calcite-cemented sandstone were examined using standard uniaxial compressive strength (UCS) and Brazilian tensile strength (BTS) tests. In addition, fracture properties such as fracture toughness, consumed energy and crack propagation velocity were examined with cracked chevron notched Brazilian disk (CCNBD) tests. Digital Image Correlation (DIC), a non-contact optical measurement technique, was used for both strain and crack propagation velocity measurements along the bedding plane orientations. Finally, environmental scanning electron microscope (ESEM) was employed to investigate the microstructural damages produced in calcite-cemented sandstone specimens before and after CCNBD tests. As results, both mechanical and fracture properties reduced significantly when specimens were saturated. The effects of water on fracture properties (fracture toughness and consumed energy) were predominant in divider specimens when compared with arrester and short transverse specimens. Whereas crack propagation velocity was faster in short transverse and slower in arrester, and intermediate in divider specimens. Based on ESEM data, water in the calcite-cemented sandstone induced microstructural damages (microcracks and voids) and increased the strength disparity between cement/matrix and rock forming mineral grains, which in turn reduced the crack propagation resistance of the rock, leading to lower both consumed energy and fracture toughness ($K_{IC}$).

• Structural Engineering and Mechanics
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• v.49 no.5
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• pp.597-618
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• 2014

For the structures containing multiple discontinuities (voids, inclusions, and cracks), the simulation technologies in the framework of extended finite element method (XFEM) are discussed in details. The level set method is used for representing the location of inner discontinuous interfaces so that the mesh does not need to align with these discontinuities. Several illustrations have been given to verify that the implemented XFEM program is effective. Then, the implemented XFEM program is used to investigate the effects of the voids, inclusions, and minor cracks on the path of major crack propagation. For a plate containing cracks and voids, two possibly crack path can be observed: i) the crack propagates into the void; ii) the crack initially curves towards the void, then, the crack reorients itself and propagates along its original orientation. For a plate with a soft inclusion, the final predicted crack paths tend to close with the inclusion, and an evident difference of crack paths can be observed with different inclusion material properties. However, for a plate with a hard inclusion, the paths tend to away from the inclusion, and a slightly difference of crack paths can only be seen with different inclusion material properties. For a plate with several minor cracks, the trend of crack paths can still be described as that the crack initially curves towards these minor cracks, and then, the crack reorients itself and propagates almost horizontally along its original orientation.

• Journal of the Korea Concrete Institute
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• v.12 no.3
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• pp.3-10
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• 2000

In this study, we compared a plain mortar with the CAS-system shrinkage compensation mortar for Ondol that is Korean traditional heating system. The Ondol mortar is necessary to have properties as non-crack, fine flatness and stability for thermal changes. especially, mortar'crack prevention is to be most important property in Ondol mortar. To develope the stable material on the crack-prevention, we used to calcium-sulfo-aluminate(CSA)system in shrinkage compensation mortar. And so, we confirmed the effects of calcium-sulfo-aluminate(CSA) system for mortar's physical properties such as setting time, compressive strength and expansion ratio for crack prevention. The initial and final setting time of the CSA mortar is faster than plain mortar about 2hours. And, Compressive strength increased about 20% that plain mortar. The crack length per unit area, plain mortar is 0.426∼0.481m/m2. The Results of apartment construction field test, the shrinkage compensation mortar is excellent about the crack-reduce effect.

• Journal of Mechanical Science and Technology
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• v.14 no.10
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• pp.1041-1050
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• 2000

In this paper the effect of specimen thickness on fatigue crack growth with the spatial distribution of material properties is presented. Basically, the material resistance to fatigue crack growth is treated as a spatial stochastic process, which varies randomly on the crack surface. The theoretical autocorrelation functions of fatigue crack growth resistance with specimen thickness are discussed for several correlation lengths. Constant ${\Delta}K$ fatigue crack growth tests were also performed on CT type specimens with three different thicknesses of BS 4360 steel. Applying the proposed stochastic model and statistical analysis procedure, the experimental data were analyzed for different specimen thicknesses for determining the autocorrelation functions and probability distributions of the fatigue crack growth resistance.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.16 no.4
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• pp.26-34
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• 2008

This article provides a comprehensive treatment of cracks in non-homogeneous structural materials such as functionally graded materials (FGMs). It is assumed that the material properties depend only on the coordinate perpendicular to the crack surfaces and vary continuously along the crack faces. By using laminated composite plate model to simulate the material non-homogeneity, we present an algorithm for solving the system based on Laplace transform and Fourier transform techniques. Unlike earlier studies that considered certain assumed property distributions and a single crack problem, the current investigation studies multiple crack problem in the FGMs with arbitrarily varying material properties. As a numerical illustration, transient thermal flow intensity factors for a metal-ceramic joint specimen with a functionally graded interlayer subjected to sudden heating on its boundary are presented. The results obtained demonstrate that the present model is an efficient tool in the fracture analysis of non-homogeneous material with properties varying in the thickness direction.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.8
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• pp.1458-1467
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• 1992

Recently, the composite materials have been researched actively by many researchers because of its useful properties. Especially, an interface crack on the dissimilar material exposes the behavior of the mixed mode crack even though under only the tension stress. In the previous papers, crack energy density(CED) was shown as the crack behavior evaluation parameter which can be expressed consistently from the onset until a final fracture. In a present paper, the basic properties of CED on the interface crack are examined because the results by CED at the homogeneous material above are also expected to be held at the dissimilar material. And we proposed that the contribution of each mode of CED can be separated and be evaluated. Furthermore, the total CED and contribution of each mode are evaluated by domain integral through a finite element analysis at the elastic crack model and the basic examination are carried out.

• Proceedings of the Korean Society of Agricultural Engineers Conference
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• 2000.10a
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• pp.284-289
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• 2000

This study is performed to evaluate an the crack properties and repair-reinforcement of concrete introduced crack. Materials used are portland cement, coarse aggregate, fine aggregate, unsaturated polyester resin and fly ash. Specimen is used beam of 76${\times}$76${\times}$412mm for measurement of pulse velocity, dynamic modulus of elasticity and bending strength and is introduced crack artificially. The following conclusions are drawn; Pulse velocity, dynamic modulus of elasticity and bending strength of concrete introduced crack is shown the lower 1.24∼11.91%, 3.42∼17.21% and 38.17∼61.0% than that of the control concrete, respectively. Pulse velocity, dynamic modulus of elasticity and bending strength of concrete repaired and reinforced crack is shown the higher 0.5∼2.60%, 1.57∼3.07% and 28.17∼47.25% than that of the concrete introduced crack and the lower than that of the control concrete, respectively.