• Journal of the Korean Society of Manufacturing Process Engineers
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• v.20 no.7
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• pp.8-14
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• 2021

Even welds that have passed non-destructive testing in the case of brittle crack arrest steel materials will actually have very fine weld defects. Based on studies showing that these defects adversely affect the structure if subjected to a certain period of load, the following conclusions were obtained by conducting CTOD tests on welding joints of high-strength BCA materials, structures comprising the upper decks of a large container vessel. First of all, the fatigue pre-cracking in the weld metal and heat affected areas was tested and the behavior was identified. Both parts of the welding joint are allowable range for the class regulations. In addition, CTOD results showed that the CTOD value in the heat affected area was more than 0.5 times higher than in the weld metal area.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.11 s.242
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• pp.1472-1479
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• 2005

Multiple surface crack distributed randomly along a weld toe influences strongly on the fatigue crack propagation life of welded joint. It is investigated by using statistical approaches based on series of systematic experiments. From the statistical results, initial crack numbers and its locations follow the normal distribution, and the probability of initial crack depths and lengths can be described well by tile Weibull distribution. These characteristics are used to calculate the fatigue crack propagation life, in which the mechanisms of mutual interaction and coalescence of the multiple cracks are considered as well as the Mk-factors obtained from a parametric study on the crack depths and lengths. The automatic calculation is achieved by the NESUSS, where the parameters such as the number, location and size of the cracks are all treated as random variables. The random variables are dealt through the Monte-Carlo simulation with sampling random numbers of 2,000. The simulation results show that the multiple cracks lead to much shorter crack propagation life compared with those in single crack situation. The sum of the simulation and tile fatigue crack initiation life derived by the notch strain approach agrees well with the experiments.

• Journal of Mechanical Science and Technology
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• v.14 no.1
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• pp.30-38
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• 2000

This paper presents a framework how to estimate crack driving forces in terms of crack-tip opening displacement and J-integral for mismatched dissimilar joints with interface cracks. The mismatch in elastic, thermal, and plastic hardening properties is not considered, but the mismatch in plastic yield strengths is emphasized here. The main outcome of the present work is that the existing methods to estimate crack driving forces for homogeneous materials can be used with slight modification. Such modification includes (i) mismatch- corrected limit load solutions, and (ii) evaluating the contribution of each material in dissimilar joints to the total crack driving force, which depends on the strength mismatch of the dissimilar joints.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2008.04a
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• pp.50-55
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• 2008

In order to investigate and estimate the cause of fatigue crack occurred to curved girder bridge that is used during 20 years, in this study, filed tests to obtain the characteristic of stress hysteresis were performed under the real traffic flows. From these test results, we analyzed the cause of fatigue crack for various fatigue crack patterns. Also, the characteristic of structural behavior for the curved girder bridge were examined from the FE analysis. In addition, to retrofit various fatigue cracks occurred in the bridge, FE analyses considering the characteristics of crack patterns were performed and retrofitting methods were suggested.

• Proceedings of the KSR Conference
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• 2007.11a
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• pp.581-584
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• 2007

The subway concrete box structure can`t establish expansion joint because of animal power delivery of the subway rail. In this case, As increase of structure volume, it is subjected to cause temperature crack. The temperature crack due to the heat of hydration classified a nonstructural crack. but it has a bad effect on durability of concrete structures. especially, in case of a subway concrete box structure, when a water-proof facilities is beaked on an outer-wall, the water leakage occurs through a penetration crack generated from a wall of the concrete structure too. This paper, for the subway concrete box structure, examined a condition of temperature crack occurrence by a heat of hydration concerned external temperature from analysing by a three dimensional finite element method.

• Proceedings of the KSME Conference
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• 2000.04a
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• pp.165-169
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• 2000

A simple method was suggested to calculate the stress intensity factor for a one-sided patched crack with finite thickness. To consider out-of-plane bending effect resulting from the load-path eccentricity, the spring constant as a function of the through-thickness coordinate z was calculated from the stress distribution in the un-cracked plate, ${\sigma}_{yy}(y=0,\;z)$, and the displacement for the representative single strip Joint, $u_y(y=0,\;z)$. The stress Intensity factors were obtained using Rose's asymptotic solution approach and compared with the finite element results. In short crack region, two results had a little difference. However, two results were almost same in long crack region. On the other hand, the stress intensity factor using plane stress assumption was more similar to finite element result than plane strain condition.

• Transactions of the Korean Society of Automotive Engineers
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• v.4 no.3
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• pp.112-121
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• 1996

Applications of bonded dissimilar materials such as metal/ceramics and resin/metal joints, are very increasing in various industry fields. It is required to find crack propagation direction and path applying to the fracture mechanics on the bonded joint of dissimilar meterials. In this paper, crack propagation direction and path were simulated numerically by using boundary element method. Crack propagation angle is able to easily determine based on the maximum stress concept. Fracture tests of Al/Epoxy dissimilar materials with an interface crack are carried out under various mixed mode conditions by using the specimens of bonded scarf joints. It is found that the experimental results are well coincide with the analysis results of boundary element method.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.5 no.4
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• pp.53-62
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• 1996

Recently, ceramic / metal bonded joints have led to inccreasing use of structural materials such as automobile, heat engine in various industries. In this paper, a method to analyze an interface crack under both residual stresses and applied loading was proposed. and some results of boundary element method(BEM) analysis Were presented, Fracture thoughness tests of ceramic/metals bonded joints with an interface crack Were carried out, and the stress intensity factors of these joints Ware analyzed by BEM. Also crack propagtion direction was simulated numerically by using BEM. Crack propagation angle was able to easily determine based on the maximum stress concept. The prediction of fracture strength by the fracture thoughness of the ceramics/metals bonded joints was proposed.

• Journal of Welding and Joining
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• v.35 no.2
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• pp.23-29
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• 2017

Mechanical properties and hardness distributions in arc brazed joints of Dual phase steel using Cu-Al insert metal were investigated. The maximum tensile shear load was 10.4kN at the highest brazing current. It was about 54% compared to tensile load of base metal. This joint efficiency is higher than that of joint of DP steel using Cu-based filler metals which are Cu-Si, Cu-Sn. Fracture positions can be divided into two types. Crack initiation commonly occurred at three point junction among upper sheet, lower sheet and the fusion zone. However crack propagations were different with increasing the brazing current. In case of the lower current, it instantaneously propagated along with the interface between fusion zone and upper base material. On the other hand, in case of higher current, a crack propagation occurred through fusion zone. When the brazing current is low (60, 70A), the interface shape is flat type. However the interface shape is rough type, when the brazing current is high (80A). It is thought that the interface shapes were the reason why the crack propagations were different with brazing current. The interface was the intermetallic compounds which consisted of $(Fe,Al)_{0.85}Cu_{0.15}$ IMC formed by crystallization at $1200^{\circ}C$during cooling. Therefore the maximum tensile shear load and the fracture behavior were determined by a interface shape and effective sheet thickness of the fracture position.

• Journal of Welding and Joining
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• v.30 no.6
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• pp.74-79
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• 2012

It depends on the joint configuration, dimensions and constraints of the joint whether the residual stress at the root of single-sided butt weld is tensile or not. Therefore, recommendation is generally made that high R ratio should be used in the fatigue test of welded joint in order to prevent excessively long life caused by compressive residual stress. In this research, the residual stress profile in butt weld joint was obtained through compliance method, using successive extension of a slot and measurement of the variation of strain during the slot extension. The residual stress profile was firstly assumed to be the linear summation of Legendre polynomials up to 9th order excluding 0th and 1st order. Strain variation on the surface was measured while the slot was being extended by cutting to find out the 8 unknown coefficients of each polynomial term. The cut was made by the electric discharge machine. It was concluded that the residual stress near the surface is positive valued, however, it turned into the negative value as soon as it passed through 2 or 3 mm of the depth.