• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.7
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• pp.1021-1029
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• 1997

In metalforming, ductile fracture criteria have been used for the purpose of predicting fracture occurrence in the stage of process design prior to manufacturing. In the present investigation, some of popular criteria are reviewed to find the most suitable one among them. As a result, it is found that the modified Cockroft and Latham criterion is better than others. The reasons are: it agrees with Roy's and McClintock's void growth models, it is more general than Oyane's and Kuhn's criteria, and it predicts fractures in compression as well as in tension well. However, it is also found that the criterion is incapable of predicting fractures in torsion.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.8 no.1
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• pp.35-44
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• 1999

In a view point of earth environmental protection and social requirement, adhesively bonded structures of aluminum alloys have become to be employed for the purpose of decreasing fuel ratio by weight reduction and to improve performance in various engineering fields such as aircrafts, automobiles, rolling stocks and so on. In spite of such wide applications in adhesively bonded structures of aluminum alloys, the quantitative fracture criterion and evolution method of its bonded strength have not been established yet. The objective of this paper is to establish fracture criterion considering stress singularity at interface edges in adhesively bonded structures of aluminum alloys. Through the analyses of boundary element method and static fracture experiments with three different types of specimens in the adhesively bonded joints of aluminum alloys, its fracture criterion was proposed and discussed about strength evolution of adhesively bonded structures.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.4
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• pp.761-769
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• 1994

Actual load acting on rail surface in the track is the combined mode loading due to the contact rolling load of the wheels. To investigate the fracture behavior on rail steel under combined modes I and II, fracture tests were performed by using the test jigs and fracture specimen which were designed by Richard. The analysis results of experimental fracture data were compared with various fracture criteria that have been introduced for determination of the crack propagation direction and the critical stress of fracture of a crack submitted to a mixed mode loading. From the results, it was shown that the actual crack propagation direction of rail steel agree with the crack propagation directions predicted by maximum tangential stress criterion and strain energy density criterion, and that fracture criterion follows principal strain criterion.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1-6
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• 2004

In this study, the intrinsic static/dynamic fracture toughness of Al 7175=T74 is evaluated from the apparent static/ dynamic toughness of notched specimen, The critical average stress fracture model is suggested to establish the relationship to predict the intrinsic fracture toughness from the apparent fracture toughness of a notched specimen. The critical average stress fracture model is established using the relation between the notch root radius and the effective distance calculated by finite element analysis. Also, effective distance is applied to estimate the failure criterion for the combustion pipe with notch. It is conclude that the true fracture toughness can be estimated from test results of apparent fracture toughness measured by using a notched specimen. Also, the effective In this study, the intrinsic static/dynamic fracture toughness of Al 7175=T74 is evaluated from the apparent static/ dynamic toughness of notched specimen, The critical average stress fracture model is suggested to establish the relationship to predict the intrinsic fracture toughness from the apparent fracture toughness of a notched specimen. The critical average stress fracture model is established using the relation between the notch root radius and the effective distance calculated by finite element analysis. Also, effective distance is applied to estimate the failure criterion for the combustion pipe with notch. It is conclude that the true fracture toughness can be estimated from test results of apparent fracture toughness measured by using a notched specimen. Also, the effective distance can be used to evaluate the failure criterion of structure with notch.

• Journal of the Korean Ceramic Society
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• v.28 no.1
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• pp.19-19
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• 1991

Fracture of Al2O3 tubes for different loading path under combined tension/torsion was investigated. Macroscopic directions of crack propagation agreed well with the maximum principal stress criterion, independent of the loading path. However, fracture strength from the proportional loading test(τ/σ= constant) showed either strengthening or weakening compared to that from uniaxial tension, depending on the ratio τ/σ. The Weibull theory was capable to predict the strengthening of fracture strength in pure torsion, but not the weakening in the proportional loading condition. The strengthening or weakening of fracture strength in the proportional loading condition was explained by the effect of shear stresses in the plane of randomly oriented microdefects. Finally, a new empirical fracture criterion was proposed. This criterion is based on a mixed mode fracture criterion and experimental data for fracture of Al2O3 tubes under combined tension/torsion. The proposed fracture criterion agreed well with experimental data for both macroscopic directions of crack propagation and fracture strengths.

• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.5
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• pp.740-745
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• 1987

For the prediction of the crack growth initiation from a blunt notch or a precrack in a prestrained material under plane strain tension and small-scale yielding conditions, a microscopic fracture criterion is proposed in terms of the crack tip opening displacement(COD) needed for the attainment of fracture strain at a microstructural distance. Smooth blunting of a crack tip with an initial root radius is assumed, and strain distributions on the crack-line axis are calculated at each deformation stage until the distributions against an original distance normalized to the COD are insensitive to an initial root radius. This case of no initial-root-radius effect is taken as for a sharp crack tip, on which the criterion is applied to determine the characteristic length of material from a critical COD for a fatigue-precracked specimen. The predicted COD at the fracture initiation from a crack with an initial root radius or a prestraining shows reasonable agreement with experimental values.

• Transactions of Materials Processing
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• v.21 no.5
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• pp.298-304
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• 2012

The shielded slot plates for a molten carbonate fuel cell(MCFC) have a sheared corrugated trapezoidal pattern. In the FEM simulations for the production of the shielded slot plate, the user material subroutine VUMAT in the commercial FEM software ABAQUS was used to implement a ductile fracture criterion. The critical damage value for the ductile fracture criterion was determined by comparing the experimental results of the shearing process with the simulation results. Using the ductile fracture criterion, the FEM simulation of the three-dimensional forming process of the shielded slot plate was conducted. The effects of the shearing process on the forming process were examined through FEM simulation and experiments. The forming simulation of nine unit cells was conducted. Using the simulation results of the forming process, the deformed shape after springback was calculated. The experimental result shows good agreement with the simulation.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.8 no.2
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• pp.86-93
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• 1999

Ceramic/metal bonded joints have led to increasing use of structural materials such as automobiles and heat engines. A method of strength evaluation focussing on fracture criterion of mixed mode was investigated in {{{{ {Si }_{3 } {N }_{4 } }}}}/metal bonded joint, Also Fracture toughness tests of {{{{ {Si }_{3 } {N }_{4 } }}}}/metal bonded joints with an interface crack were carried out and the stress intensity factors of these joints were analyzed by boundary element method. Form the results the fracture criterion and method of strength evaluation by the fracture toughness were proposed in {{{{ {Si }_{3 } {N }_{4 } }}}}/Metal bonded joints

• Journal of Mechanical Science and Technology
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• v.18 no.1
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• pp.55-64
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• 2004

Many researchers have made a lot of progress in studying the evaluation of fracture probability of brittle materials. However, studies of fracture probability for elastic-plasticity have not been made yet. An evaluation method for fracture probability which is grafted onto a 2-parameter criterion and statistical probability analysis is not only introduced in this study, but also applied to the simple 2-dimensional model and carbon steel piping to vealuate the effect of statistical variables.

• Transactions of the Korean Society of Automotive Engineers
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• v.9 no.6
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• pp.160-169
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• 2001

To predict busting failure in tubular hydroforming, the criteria for ductile fracture proposed by Oyane is combined with the finite element method. From the histories of stress and strain in each element obtained from finite element analysis, the fracture initiation site is predicted by mean of the criterion. The prediction by the ductile fracture criterion is applied to three hydroforming processes such as a tee extrusion, an automobile rear axle housing and lower am. For these products, the ductile fracture integral I is not only affected by the process parameters, but also by preforming processes. All the simulation results show the combination of the finite element analysis and the ductile fracture criteria is useful in the prediction of farming limit in hydroforming processes.