• Transactions of the Korean Society of Automotive Engineers
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• v.13 no.6
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• pp.63-69
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• 2005

For the case that center crack is surrounded by four small cracks which are symmetrically distributed around center crack, the same values of normalized stress intensity factor of center crack according to the position of the tip of small cracks are located on the smooth curve. And the stress intensity factor according to any position of small cracks can be sufficiently obtained from this curve. The plastic zones between distributed cracks are also investigated by changing the positions of nearly small cracks. The occurrence of plastic zone due to the interaction between center crack and small cracks are analyzed by finite element method. The mechanical behavior at the vicinity of crack tips is investigated by plastic areas. The changes of plastic zones according to positions of distributed cracks are drawn schematically. The safety of materials is also analyzed.

• Journal of the Korean Society of Safety
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• v.15 no.3
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• pp.1-6
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• 2000

In fatigue crack growth test, it is important not only to analyze characteristics of fatigue crack growth but also to determine the threshold stress intensity factor, ${\Delta}K_{th}$. which is the threshold value of fatigue crack growth. Linear regression analysis using fatigue test data near the threshold is suggested to determine the ${\Delta}K_{th}$ in the standard test method but the ${\Delta}K_{th}$ can be affected by a fitting method. And there are some limitations on the linear regression analysis in the case of small number of test data near the threshold. The objective of this study is to investigate differences of the ${\Delta}K_{th}$ due to regression analysis method and to evaluate the relative error range of the ${\Delta}K_{th}$ in same fatigue crack growth test data.

• Honam Mathematical Journal
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• v.40 no.4
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• pp.785-794
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• 2018

In [8] they introduced a new finite element method for accurate numerical solutions of Poisson equations with corner singularities. They consider the Poisson equations with homogeneous Dirichlet boundary condition with one corner singularity at the origin, and compute the finite element solution using standard FEM and use the extraction formula to compute the stress intensity factor, then pose a PDE with a regular solution by imposing the nonhomogeneous boundary condition using the computed stress intensity factor, which converges with optimal speed. From the solution they could get an accurate solution just by adding the singular part. This approach uses the polar coordinate and the cut-off function to control the singularity and the boundary condition. In this paper we consider Poisson equations with multiple singular points, which involves different cut-off functions which might overlaps together and shows the way of cording in FreeFEM++ to control the singular functions and cut-off functions with numerical experiments.

• East Asian mathematical journal
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• v.38 no.5
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• pp.603-610
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• 2022

In [6, 7] they introduced a new finite element method for accurate numerical solutions of Poisson equations with corner singularities. They consider the Poisson equations with homogeneous boundary conditions, compute the finite element solutions using standard FEM and use the extraction formula to compute the stress intensity factor(s), then they posed new PDE with a regular solution by imposing the nonhomogeneous boundary condition using the computed stress intensity factor(s), which converges with optimal speed. From the solution they could get an accurate solution just by adding the singular part. They considered a partial differential equation with the input function f ∈ L²(Ω). In this paper we consider a PDE with the input function f ∈ H¹(Ω) and find the corresponding singular and dual singular functions. We also induce the corresponding extraction formula which are the basic element for the approach.

• Journal of the Korean Society of Safety
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• v.33 no.5
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• pp.1-8
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• 2018

A fuel cell is an energy conversion device that converts a chemical energy directly into an electrical energy and has higher energy efficiency than an internal combustion engine, but solid oxide fuel cell (SOFC) consisting of brittle ceramic material remains as a major issue regarding the mechanical properties as the crack formation and propagation. In this study, the stress distribution and crack behavior around the crack tip were evaluated, due to investigated the effects of the surface crack at the operating condition of high temperature. As a result, the difference of the generated stress was insignificant at operating conditions of high temperature according to the surface crack length changes. This is because, the high stiffness interconnect has a closed structure to suppress cell deformation about thermal expansion. The stress intensity factor ratio $K_{II}/K_I$ increased as the crack depth increased, at that time the effect of $K_{II}$ is larger than that of $K_I$. Also the maximum stress intensity factor increased as the crack depth increased, but the location of crack was generated at the electrolyte/anode interface, not at the crack tip.

• Nuclear Engineering and Technology
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• v.54 no.6
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• pp.2188-2197
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• 2022

To ensure the safety margin of a reactor pressure vessel (RPV) under normal operating conditions, it is regulated through the pressure-temperature (P-T) limit curve. The stress intensity factor (SIF) obtained by the internal pressure and thermal load should be obtained through crack analysis of the nozzle corner crack in advance to generate the P-T limit curve for the nozzle. In the ASME code Section XI, Appendix G, the SIF via the internal pressure for the nozzle corner crack is expressed as a function of the cooling or heating rate, and the wall thickness, however, the SIF via the thermal load is presented as a polynomial format based on the stress linearization analysis results. Inevitably, the SIF can only be obtained through finite element (FE) analysis. In this paper, simple prediction equations of the SIF via the thermal load under, cool-down and heat-up conditions are presented. For the Korean standard nuclear power plant, three geometric variables were set and 72 cases of RPV models were made, and then the heat transfer analysis and thermal stress analysis were performed sequentially. Based on the FE results, simple engineering solutions predicting the value of thermal SIF under cool-down and heat-up conditions are suggested.

• Journal of Ocean Engineering and Technology
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• v.10 no.1
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• pp.53-64
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• 1996

In this paper, rotating bending fatigue tests have been carried out to investigate the growth behabiors of surface fatigue crack initiated from a small artificial surface defect, that might exist in real structures, on 2024-T3 and 6:4 brass. The test results are analysed in the viewpoints of both strength of materials and fracture mechanics, it can be concluded as follows. The effect of a small artificial surface defect upon the fatigue strength is very large. The sensitivity of 2024-T3 on the defect is higher than that of 6:4 brass. The growth behavior of the surface fatigue crack of 2024-T3 is different from that of 6:4 brass. The growth rate of the surface fatigue crack of 2024-T3 is considerably rapid in the early stage of the fatigue life and apt to decrease in the later stage. It was impossible to establish a unifying approach in the analysis of crack growth begabior of 2024-T3 and 6:4 brass using the maximum stress intensity factor because of their dependence on stress level. But if the elastic strain and cyclic total strain intensity factor range were applied to obtain the growth rate of surface fatigue cracks of the materials, the data were found to be nearly coincided.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.10
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• pp.2398-2406
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• 1993

Abdi's numerical method(ref.13) for representing a stress singularity by shifting the mid-side nodes of isoparametric elements is reviewed. A simple technique to obtain the optimal position of the mid-side nodes in quadratic isoparametric finite element is presented. From this technique we can directly obtain the position of the side-nodes adjacent to the crack tip. It is also observed that the present technique provides good accuracy for the expression of the opening displacement and the determination of the mid-side nodes for more wide range of material properties than that obtained by Abdicant the finite element method is applied to determine stress intensity factors for pressurized crack perpendicular to and terminating at the interface of two bonded dissimilar materials. A proper definition for stress intensity factors of a crack perpendicular to bimaterial interface is provided. It is based upon a near-tip displacement solutions on the crack surface for interface crack between two dissimilar materials. Numerical testing is carried out with the eight-node and six-node elements. The results obtained are compared with the previous solutions.

• Journal of the Korean Society for Precision Engineering
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• v.12 no.8
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• pp.147-155
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• 1995

Recent experimental studies have been shown that strain gages can be employed to determine either static or dynamic stress intensity factors $K_{I}$ wiht relatively simple experiments. However, it does not usually provide a reliable value of stress intensity factor because of local yielding and limited regions for strain gage placement at the vicinity of the crack tip. This paper attempted to define a valid region and to indicate procedures for locating and orienting the strain gage to determine static toughness $K_{Is}$ accurately form one strain gage readings with respect to varying loadings. The strain gage methods was used for compact tension specimens made of Polycarbonate and PMMA(polymethyl methacrylate). Series expansions of the static and dynamic strain fields are applied. Strain gage orientation and location are then studied to optimize the strain response. Especially, in the dynamic experiment, the specimen employed is an oversized Charpy V-notch specimen which has been modified to provide significant constraint with a large elevation of the flow stress. The impact behavior of the specimen is monitored by placing strain gage near the crack tip. The dynamic toughness $K_{Id}$ is determined from the strain time traces of this gage.e.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.8 no.1
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• pp.21-27
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• 1999

In this study, stress intensity factors KI, KII, KIII are existing at the same time to a hollow cylindrical bar of three dimension inclination crack. In order to investigate by experimentally the effect of the inclination angle $\psi$ of crack, artificial inclination cracks in the circumferential direction are put in the surface of a hollow cylindrical bar made by the epoxy-resin. Experimentally, stress analysis methods of stress intensity factors were proposed. But, suitable method are the caustic method and the photoelastic stress freezing method. The mixed mode of KI, and KII, were determined by the photoelastic method of the classical approach method and the FORTRAN language program of the used smallest square method.