• Computers and Concrete
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• v.22 no.1
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• pp.39-51
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• 2018

This study introduces a new algorithm to determine size independent values of fracture energy, fracture toughness, and fracture process zone length in three-point bending specimens with shallow to deep notches. By using the exact beam theory, a concept of equivalent notch length is introduced for specimens with no notches in order to predict the peak loads with acceptable precisions. Moreover, the method considers the variations of fracture process zone length and effects of higher order terms of stress field in each specimen size. In this paper, it was demonstrated that the use of some recently developed size effect laws raises some concerns due to the use of nonlinear regression analysis. By using a comprehensive fracture test data, provided by Hoover and Bazant, the algorithm has been assessed. It could be concluded that the proposed algorithm can facilitate a powerful tool for size effect study of three-point bending specimens with different notch lengths.

• Laser Solutions
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• v.3 no.3
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• pp.31-37
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• 2000

In this paper, the possibilities of the laser overlap spot welding were studied to utilize the advantageous properties of amorphous metal foils. In order to estimate the usage of amorphous metals foils as structural members, the tensile shear strength and the fracture features were investigated. Although the crystalline zone on the surface was formed, it was not the direct cause of the fracture of the weld. The fracture of the weld resulted from the geometry discontinuity between the workpiece and the protrusion zone, which was formed during the weld process. The vein pattern - the typical feature of the fracture of the amorphous metal - was formed on the fracture surface. The tensile shear stress was reached to 1200 N/㎟ (2-foils overlap welding) and 900 N/㎟ (10-foils overlap welding), whereas the tensile strength of the workpiece was 1500-2000 N/㎟.

• Journal of the Korea Concrete Institute
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• v.12 no.3
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• pp.31-37
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• 2000

When a crack is produced in a concrete structure, a micro crack zone of fracture process zone (FPZ) appears at the crack tip. To investigate the behaviour of this the micro crack zone, nonlinear fracture mechanics (NLFM) must be applied. However, when a massive concrete structure such as a concrete gravity dam is considered, the micro crack zone can be neglected and the structure can be assumed to have linear elastic fracture mechanics (LEFM) behaviour. This study is divided into two main topics : (1) Calculating stress intensity factor (SIF) at the crack tip by surface integral method and (2) Investigating the propagation of the initial crack. If the initial crack propagates, the angle of the propagation is calculated by using maximum circumferential tensile strength theory. This study, also, contains the effects of body forces and water pressures on the crack face.

• Nuclear Engineering and Technology
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• v.53 no.4
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• pp.1250-1258
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• 2021

In this paper, the mechanical performance of cracked surface-coated Zircaloy cladding, which has different coating materials, coating thicknesses and initial crack lengths, has been investigated. By analyzing the stress field near the crack tip, the safety zone range of initial crack length has been decided. In order to determine whether the crack can propagate along the radial (r) or axial (z) directions, the energy release rate has been calculated. By comparing the energy release rate with fracture toughness of materials, we can divide the initial crack lengths into three zones: safety zone, discussion zone and danger zone. The results show that Cr is suitable coating material for the cladding with a thin coating while Fe-Cr-Al have a better fracture mechanical performance in the cladding with thick coating. The Si-coated and SiC-coated claddings are suitable for reactors with low power fuel elements. Conclusions in this paper can provide reference and guidance for the cladding design of nuclear fuel elements.

• Geophysics and Geophysical Exploration
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• v.2 no.1
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• pp.33-42
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• 1999

AVO and complex trace analyses mainly used to characterize natural gas reservoir were tested in this paper for a possible application to detection of major geological discontinuities such as fracture zones. The test data used in this study were calculated by utilizing a viscoelastic numerical program which was based on the generalized Maxwell body for a horizontal fracture model. In AVO analysis of a horizontal fracture zone, p-wave reflection appears to be variant depending upon the acoustic-impedence contrast and the offset distance. The fracture zone is also effectively clarified both in gradient stack and range-limited stack in which fracture zone reflection is attenuated with the increasing offset distance. In complex attribute plots (instantaneous amplitude, frequency, and phase), the top and bottom of the fracture Tone are characterized by a zone of strong amplitudes and an event of the same phase. Low frequency characteristics appear at the fracture zone and the underneath. Amplitude attenuation and waveform dispersion are dependent on Q-contrast between the fracture zone and the surrounding media. They were properly compensated by optimum inverse Q-filtering.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.3
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• pp.528-536
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• 2002

As one step for the safety performance of LNG storage tank, the change in fracture toughness within the X-grooved weld heat-affected zone (HAZ) of newly developed 9% Ni steel, which was submerged arc (SA)-welded, was investigated. Both crack initiation fracture toughness and crack arrest fracture toughness were evaluated by the crack tip opening displacement (CTOD) tests and compact crack arrest (CCA) tests. As the evaluated region approached the fusion line, each test result shorted different tendency, that is, crack initiation toughness decreased while crack arrest toughness increased. The results were discussed through the observation of the microstructural change.

• Nuclear Engineering and Technology
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• v.53 no.6
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• pp.1924-1930
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• 2021

By using miniature SENB specimens, the fracture properties of the materials in the region of welded metal, 321 stainless steel heat affected zone, 690 alloy heat affected zone of 321/690 dissimilar metal girth welded joints were tested. Both the J-resistance curves and critical fracture toughness of the three different materials are affected by the crack size because of the effect of crack tip constraint. Groups of constraint corrected J-resistance curves of the three materials are obtained according to J-Q-M approach. The welded metals exhibit the best fracture resistance but the worst fracture resistance is observed in the material of 690 alloy heat affected zone.

• Journal of the Korea Concrete Institute
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• v.16 no.4 s.82
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• pp.511-520
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• 2004

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 variation of strain energy release rate with crack extension can explain theoretically the micro-cracking, micro-crack localization and full development of the FPZ in concrete.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.05a
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• pp.230-235
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• 2003

In the micro hole punching, the size and shape of burr and burnish zone are very important factors to evaluate quality of micro holes which depend on punch-die clearance, stain rate, workpiece material and etc. To get micro holes with small burr and wide burnish zone for industrial demands, not only the parametric study but also a study on fracture behavior in shear band are necessary. In this study, 100 $\mu\textrm{m}$, 25 $\mu\textrm{m}$ micro holes in diameter were fabricated on brass (Cu63/Zn37) and SUS 316 foils as aspect ratio 1:1, and the characteristics of micro holes was investigated comparing with man holes over several mm by scanning electron microscopic views and section views. Like macro hole, micro hole is also composed of 4 portions, rollover, burnish zone, fracture zone and it shows similar fracture behavior in shear band, but？ by high strain rate (10$^2$∼ 10$^3$s$\^$-1/) unlike macro hole fabrication and increment of relative grain size several different results are shown.

• Magazine of the Korea Concrete Institute
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• v.7 no.4
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• pp.149-156
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• 1995

The fracture process zone in concrete is a region ahead of a traction-free crack, in which two major mechanisms, microcracking and bridging, play important roles. The toughness due to bridging is dominant compared to toughness induced by microcracking, so that the bridging is dominani: mechanism governing the fracture process of concrete. Fracture mechanics does work for concrete provided that the fracture process zone is being considered, so that the development of model for the fracture process zone is most important to describe fracture phenomena in concrete. In this paper the bridging zone, which is a part of extended rnacrocrack with stresses transmitted by aggregates in concrete, is modelled by a Dugdale-Barenblatt type model with linear tension-softening curve. Two finite element techniques are shown for the analysis of progressive cracking in concrete based on the discrete crack approach: one with crack element, the other without crack element. The advantage of the technique with crack element is that it dees not need to update the mesh topology to follow the progressive cracking. Numerical results by the techniques are demonstrated.