• Journal of the Korean Society of Industry Convergence
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• v.7 no.4
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• pp.355-361
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• 2004

The finite element method were used to determine the stress intensity factor of cracked plate. The stress method, displacement method and J Integral are most popular finte element method. ANSYS proposed another a kind of displacement method. In this paper, it was examined that the accuracy and utility of the ANSYS method could believable to determine the stress intensity factors of centered inclined crack. Generally, inclined crack has two portion of stress intensity factors, tensile mode F1 and shear mode F2. For the purpose of increasing the accuracy of stress intensity factors, examined the effect of the numbers of nodes and elements, crack tip element size and number of partition of the crack tip vicinity. It was found that the method proposed by ANSYS is useful and has high accuracy. Accuracy of calculated stress intensity factors was increased by increase of the number of nodes and elements, and at the small size of crack tip elements can get more highly accuracy.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1993.10a
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• pp.644-649
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• 1993

Practical structures are subject not only to tension but also to shear and torsional loading. In this study, the mode 1 and 2 stress intensity factors of specimens were calculated by using elastic finite element mothod. The stress fields at the crack tip subjected to mixed-mode loading were also studied by usingf eleatic finite element method and were compared with theoretical results. The three-point-bending, four-point-bending, and mixed-mode-loading experiment were carried out. And, crack propagation rate da/dN and crack growth direction were examined. Also, the elastic finite element method was applied to calculate the stress intensity factors of branch crack tip and we relate the stress intenity factor range of branch crack tip(the result of FEM) to crack propagation rate(the experimental result). The .DELTA. -da/dN relation corelated with that of mode 1.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.5
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• pp.74-83
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• 2001

In this study, internal fatigue crack initiation and propagation behavior were investigated by triple piece spot welded specimen. To estimate fatigue life of the specimen varied with shape and thickness, Crack tip opening angle(CTOA) correlated with stress intensity factor was used as the stiffness parameter. The relation between fatigue life and CTOA can be arranged by the quantitative equation for each specimen by experiment. In addition, the variation of stress distribution was solved and the effect on fatigue crack behavior was examined by finite element method(FEM).

• Korean Journal of Metals and Materials
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• v.46 no.6
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• pp.345-350
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• 2008

The magnitude of constraint effect $A_2$ value was experimentally estimated by using crack tip opening displacement(CTOD) between elastic and plastic regions near crack tip front for CT specimen with $25.4t{\ss}{\AE}$ SS400 steel. The constraint effect, $A_2$ was dependent on specimen configuration and on the measured positions of CTOD near crack front. $A_2$ should be estimated using the opening displacement calculated within crack front plastic region. If not, it's not reliable to evaluate of constraint effect at crack growth initiation in this paper.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.3
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• pp.15-22
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• 2003

The fatigue crack growth model is derived and the retardation model is proposed. The fatigue crack growth model considers the residual plastic stretch on the crack surface which results from the plastic deformation at the tip of fatigue crack. The fatigue crack growth rate is calculated by using the cumulative fatigue damage and plastic strain energy in the material elements at the crack tip. This model gives the crack growth rate in reasonable agreement with test data for aluminum alloy AL6061-T651 and 17-4PH casting steel. The fatigue crack growth retardation model is based on the residual plastic stretch produced from a tensile overload which reduced the plastic strain range of the following load cycles. A strip-yield model of a crack tip plasticity is used for the calculation of a plastic zone size. The proposed retardation model characterized the observed features and delayed retardation of the fatigue crack growth under tensile overload.

• Corrosion Science and Technology
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• v.11 no.4
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• pp.141-150
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• 2012

Stress corrosion cracks in Alloy 600 compact tension specimens tested at $325^{\circ}C$ in a simulated primary water environment of pressurized water reactor were analyzed by analytical transmission electron microscopy and secondary ion mass spectroscopy (SIMS). From a fine-probe chemical analysis, oxygen was found on the grain boundary just ahead of the crack tip, and chromium oxides were precipitated on the crack tip and the grain boundary attacked by the oxygen diffusion, leaving a Cr/Fe depletion (or Ni enrichment) zone. The oxide layer inside the crack was revealed to consist of a double (inner and outer) layer. Chromium oxides existed in the inner layer, with NiO and (Ni,Cr) spinels in the outer layer. From the nano-SIMS analysis, oxygen was detected at the locations of intergranular chromium carbides ahead of the crack tip, which means that oxygen diffused into the grain boundary and oxidized the surfaces of the chromium carbides. The intergranular chromium carbide blunted the crack tip, thereby suppressing the crack propagation.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.6
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• pp.1839-1851
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• 1991

Fatigue crack behavior is studied through the two-level rotary bending test with the deep non-through radial holed notch specimens of low carbon steels(SM22C). The main factors investigated are the effects of the damage zone size around crack tip and phenomena of closing or opening of the crack tip. Obtained results are summarized as follows. Fatigue crack behavior in second level stressing slightly lower than fatigue limit is closely related to the size of damage zone produced by the first level stress higher than fatigue limit and to the phenomena of crack closing and opening for the second level stress. The non-propagating crack limit condition depends upon the crack length l$_{1}$ propagated under the first level stress and the magnitude of second level stress .sigma.$_{2}$ lower than the fatigue limit. The non-propagating crack limit condition is expressed by following eq. $\sigma_2^{6.1}{\times}l_{1}=7.35{\times}10^{6}[(kg_{f}mm^{6.1}(mm)]$

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.7
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• pp.1373-1380
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• 1992

The local cyclic strain distribution near the crack tip has been investigated by the fine Dot Grid Strain Measurement Method, which had been suggested strain measurement method to resolve experimental difficulties by authors. It has been found that the magnitude of the local cyclic strain distribution(.DELTA..epsilon.$_{eq}$ )near a crack tip has been varied by the applied cyclic load level and material, but the shape of the local cyclic strain distribution near the crack tip has been experimentally scrarcely altered : that is .DELTA..epsilon.$_{eq}$ = .DELTA.A.f(.theta.). $r^{-1}$ . Consequently, the local cyclic strain field near the crack tip could be favorably characterized by a single parameter fatigue strain intensity factor .DELTA.A. In addition, with the viewpoint that .DELTA.A depends on material and load level, .DELTA.A has been applied to evaluate the fatigue crack propagation rate and usefulness of the result has been considered. As a result, it has been ascertained that .DELTA.A has been a useful parameter to evaluate the fatigue crack propagation rate.

• Journal of the Korean Society of Safety
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• v.14 no.4
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• pp.43-52
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• 1999

In this study, theoretical stress field analysis near the crack tip under tension-compression loading was performed. The results of the theoretical stress analysis were compared to the results of Finite Element Method(FEM). From this study, generation of tensile residual stress at crack tip was proved after 1-cycle of tension-compression loading, and the fracture toughness and the fracture load of a structure can be decreased by the residual stress.

• Journal of Welding and Joining
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• v.21 no.7
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• pp.71-77
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• 2003

In this study, an investigation based on the superposition principle to predict residual stress redistribution caused by crack propagation itself initially through residual tensile stress field was performed by finite element method. The tendency in residual stress redistribution caused by crack propagation recognized both from the analytical results and experimental result was the residual stress concentration consecutively occurred in the vicinity of crack tip even the situation that the crack propagated to the region initially residual compressive stress existed. The software for the analysis is ABAQUS, which is a general purpose finite element package. The analytical method that attempt to take the plastic deformation at the crack tip due to tensile residual stress into the consideration of residual stress redistribution caused by crack propagation was proposed. The plastic zone size at the tip of fatigue crack and redistributed residual stresses were calculated by finite element method on the bases of the concept of Dugdale model. Comparing these analytical results with experimental results, it is verified that the residual stress redistribution caused by crack propagation can be predicted by finite element method with the proposed analytical method.