• Journal of Welding and Joining
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• v.21 no.6
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• pp.71-76
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• 2003

For the purpose of clarifying the influence of welding residual stress to the fatigue crack propagations behaviour, an analytical investigation based on finite element method is performed to examine the opening behaviour of tip-closed crack in the compressive residual stress. A finite element model comprised of contact elements for the crack plane and plane stress elements for the base material is used to evaluate crack opening stress of the crack existing in the residual stress field. Also an analytical method based on the superposition principle to estimate the length of opened part of tip closed crack and the stress distribution adjacent to the crack during uploading is applied to the finite element model. The software for the analysis is ABAQUS, which is a general purpose finite element package. The results show that stresses distributed on the crack surfaces are reduced and approached to zero as the applied stresses are increased up to crack tip opening stress and no mechanical discontinuity is found at the boundary of contact elements and plane stress elements. It is verified that the opening behavior of the fatigue crack in the residual stress can be predicted by finite element method with the proposed analytical method.

• Journal of Welding and Joining
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• v.21 no.6
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• pp.77-83
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• 2003

The finite element analysis was performed for the cracks existing in residual stress fields in order to investigate the effects of configuration of residual stress distribution to the fatigue crack opening behaviour. And the variation of stress distributions adjacent to the crack caused by uploading was examined. The finite element model with contact elements for the crack plane and plane stress elements for the base material and the analytical method based on the superposition principle to estimate crack opening behaviour and the stress distribution adjacent to the crack subjected to uploading were used. The results of the analysis showed that crack opening behaviors and variations of stress distribution caused by uploading were changed depending on the configuration of residual stress distribution. When the crack existed in the region of compressive residual stress and the configuration of compressive residual stress distribution were inclined, a partial crack opening just behind of a crack tip occurred during uploading. Based on the above results, it was clarified that the crack opening behaviour in the residual stress field could be predicted accurately by the finite element analysis using these analytical method and model.

• Computational Structural Engineering
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• v.8 no.4
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• pp.189-198
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• 1995

The conventional finite element formulations for incompressible materials show pressure oscillations or pressure modes in four-node quadrilateral elements of commonly used displacement and pressure interpolations. The criterion for the stability in the pressure solution is the so-called Babugka-Brezzi stability condition, and the above elements do not satisfy this condition. In this study, a pressure continuity residual based on the pressure discontinuity at element interfaces is used to study the stabilization of pressure solutions in bilinear displacement-constant pressure four-node quadrilateral elements. This pressure residual is implemented in Q1P0 element derived from the conventional incompressible elasticity. The pressure solutions can be stable with the pressure residual though they exhibit sensitivity to the stabilization parameters. Parametric study for the solution stabilization is also discussed.

• Journal of Ocean Engineering and Technology
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• v.9 no.2
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• pp.20-29
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• 1995

When structures are constructed by welding, structural elements are always accompained by welding residual stress and deformation. Therefore, when the rigidity and strength of the welded structures is considered, it is very important to have sufficient information about the effect of initial deflection and welding residual stress on them. In this paper, the square plates with welding residual stress under compression are dealt with; First, heat conduction and thermal elastic-plastic problems are analyzed by finite element method using 4-node isoparametric elements for assessment on the ultimate strength of welding joint. Later, the ultimate strength of welding joint is assessed by examining the effect of changed type of loading. The specimens are 500{\times}$500mm(a/b=1) and 750{\times}$500mm(a/b=1.5) rectangular plates of whichthicknesses is 9.0mm and simply supported plates getting axiul load in each direction.

• Journal of Korean Port Research
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• v.14 no.4
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• pp.441-450
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• 2000

In order to improve the water quality in semi-enclosed bays, Gug et al. (1997) have proposed a new method to activate the tidal exchange by creation and control of tidal residual current through the addition of artificial elements to creation and control of tidal residual current through the addition of artificial elements to create bottom roughness, so, ot is advisable to arrange as few of these as possible from a point of cost-benefit view. This paper attempts to develop the most suitable shape of artificial bottom roughness units with which to create and control an optimal tidal residual current. Several simple shapes were examined as fundamental cases. Subsequently 38 types of artificial bottom roughness units based on a few simple effective shapes, were examined experimentally. As a result of this research, two types to create artificial roughness.

• Proceedings of the KSR Conference
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• 2005.05a
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• pp.385-390
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• 2005

A specimen with residual stress due to welding was analyzed by three-dimensional cohesive zone model. The residual stress distribution was calculated by simulating welding process, and cohesive elements were located along crack propagation planes. Crack growth is possible since two planes of the cohesive element are separated beyond a maximum load carrying capacity. Stress fields around a crack tip are compared for specimens with and without residual stresses. Load-displacement curves and crack growth behaviors are also examined.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.8
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• pp.767-772
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• 2009

Laser shock peening(LSP) is proving to be better surface treatment than conventional one such as shot peening. The LSP process has a compressive residual stress into a metal alloy and a significant improvement in fatigue life. Our research is focused on applying finite element method to the prediction of residual stress through the LSP processing in some LSP conditions such as pressure and spot size induced by laser. Two analysis methods are considered to calculating the compressive residual stress. But the explicit solution and the static one after partially explicit solving are almost same. In LSP, because of very high strain rate($10^6s^{-1}$), HEL(Hugoniot Elastic Limit) is the most important parameter in material behavior modeling. As the circular laser spot is considered, 2-D axisymmetric elements are used and the infinite elements are applied to boundaries for no reflection. The relations of material properties and the LSP are also important parts in this study.

• Journal of Ocean Engineering and Technology
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• v.17 no.6
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• pp.65-71
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• 2003

Since the preflex beam is fabricated through welding, the pre-compressive stresses that should occur over the concrete pier are diminished by the welding residual stresses. Therefore welding residual stresses must be relieved during the fabrication. Therefore, the analysis and examination of the accurate welding residual stress distribution characteristics are necessary. In this study, accurate distribution of welding residual stress of the preflex beam is analyzed by the finite element method, using 2 dimensional and 3 dimensional elements. Further, the thermo-mechanical behavior of the preflex beam is also studied. After the finite element analysis, real distribution of welding residual stress is measured using the sectioning method, and then is compared with the simulation results. The distribution of welding residual stress by finite analysis agreed well with the experimental results.

• Proceedings of the KIEE Conference
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• 1999.07d
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• pp.1529-1531
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• 1999

The main functions of AC railroad vehicles arresters is to protect the main transformer from lightening impulse or switching impulse surge, then the MOV(metal oxide varistor) elements rated of 10kA is applied. The residual voltage and surge energy absorption are important parameters in designing arrester, these must be carefully decided with considering protecting level of impulse environment of system. The purpose of this study is to discuss the residual voltages and the energy absorption capability by impulse currents on MOV elements for railroad vehicles, and to introduce design factors which act as optimal protecting condition against impulse currents.

• Journal of computational fluids engineering
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• v.9 no.3
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• pp.57-65
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• 2004

The incompressible Navier-Stokes equations in two dimensions are stabilized by a modified residual method, and then discretized by hierarchical elements. The stabilization is necessary to escape from the Ladyzhenskaya-Babuska-Brezzi(LBB) constraint and hence to achieve an equal order formulation. To expedite a standard iterative method such as the conjugate gradient squared(CGS) method, a preconditioning technique called the Hierarchical Iterative Procedure(HIP) has been applied. In this paper, we increased the order of interpolation within an element up to cubic. The hierarchical elements have been used to achieve a higher order accuracy in fluid flow analyses, but a proper efficient iterative procedure for higher order finite element formulation has not been available so far The numerical results by the present HIP for the lid driven cavity flow and others showed the present procedure to be stable, very efficient and useful in flow analyses in conjunction with hierarchical elements.