• Journal of the Korean Society of Industry Convergence
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• v.10 no.3
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• pp.165-169
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• 2007

Prediction of fatigue duration is attainable from the analysis of the growth rate of the fatigue crack, and the property of the fatigue crack growth is determined by the calculation of the stress intensity factor. And the evaluation of the stress intensity factor, K comes from the stress analysis of the vicinity of crack tip of the continuum. This study describes a simple method to decide the stress intensity factor for the small crack at the sharp edge notches. The proposed method is based on the similarities between elastic stress fields of the notch tip described by two parameters, the stress concentration factor K, the radius of arc of the notch. And it is applicable to the analysis of the semi-elliptical penetration cracks and the edge notches.

• KSTLE International Journal
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• v.1 no.1
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• pp.8-11
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• 2000

A surface crack in a semi-infinite body under Hertzian contact was considered. The simplified method used to estimate stress intensity factor K for specimen was extended to the model which is chosen in this paper. Very satisfactory results are obtained comparing with those known and it is proved that the method is more convenient than other methods. The results of the analysis show that due to the presence of $K_I$ for unlubricated condition, mode I fracture is active in the field below the surface and the maximum $K_{I}$ is obtained when the trailing edge of Hertzian contact reaches a position over the crack. The magnitudes of stress intensity factors $K_I$ and $K_Il$ increase with increasing friction forces. For a surface crack perpendicular to the contact surface, the stress intensity factor $K_I$ reaches its maximum value at a depth very close to the surface. Driving forve fer crack initiation and propagation is $K_I$ for unlubricated condition and $K_Il$ for both fluid and boundary lubricated condition.n.

• Transactions of the Korean Society of Automotive Engineers
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• v.4 no.2
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• pp.69-79
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• 1996

Dynamic stress intensity factors are derives when the crack is propagating with constant velocity under longitudinal shear stress in orthotropic disk plate. General stress fields of crack tip propagating with constant velocity and least square method are used to obtain the dynamic stress intensity factor. The dynamic stress intensity factors of GLV/GTV=1(=isotropic material or transversely isotropic material) which is obtained in out study nearly coincides with Chiang's results when mode Ⅲ stress is applied to boundary of isotropic disk. The D.S.I.F. of mode Ⅲ stress is greater when α(=angle of crack propagation direction with fiber direction) is 90° than that when α is 0°. In case of a/D(a:crack length, D:disk diameter)<0. 58, the faster crack propagation velocity, the less D.S.I.F. but when crack propagation velocity arrive on ghear stress wave velocity, the D.S.I.F. but when crack propagation velocity arrive on shear stress wave velocity, the D.S.I.F. unexpectedly increases and decreases to zero.

• Proceedings of the KSME Conference
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• 2000.11a
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• pp.304-309
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• 2000

Strain gage method is used to evaluate the mode I dynamic stress intensity factor of marging steel(18Ni) and titanium alloy(Ti-6A1-4V). To decide the best strain gage position on specimen, static fracture toughness test was performed. Then instrumented charpy impact test and dynamic tensile test was performed by using strain gage method for evlauating dynamic stress intensity factor. Strain gage signals on the crack tip region are used to calculate the stress intensity factors. It is found that strain gage method is more useful than method by using load which is obtained from impact tup to assess dynamic characteristics such as dynamic stress intensity factor.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.1
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• pp.7-11
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• 2017

In this study, we develop the exact field of mode I in an infinitely deep crack in a half-plane. Using this field, we obtain the exact stress intensity factor $K_{I}$. From the tractions on the crack faces induced by exact field, we calculate the stress intensity factor of this field. We compare the results with the stress intensity factor calculated using Bueckner's weight function formula and that calculated by using Tada's formula listed in "The Stress Analysis of Cracks Handbook" It was found that Bueckner's formula yields accurate results. However, the results obtained using Tada's formula exhibit inaccurate behavior.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2007.11a
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• pp.89-90
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• 2007

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.9 s.240
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• pp.1225-1234
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• 2005

Mode I stress intensity factor $(K_I)$ of Notched Ring Test(NRT) specimen for measuring slow crack growth resistance was found using finite-element method. The theoretical $K_I$ value of NRT was not available in any references and could not be solved analytically. At first, in order to verify the accuracy of the finite-element approach, published $K_I$ values of several cracks were calculated and compared with finite-element results. The results were in good agreement within inherent errors of theoretical $K_I$. Finally the mode I stress intensity factor of NRT was found using 2- and 3-dimensional finite-element methods and expressed as a function of the applied load. This enabled direct comparison of resistance to slow crack growth between NRT and Notched Pipe Test(NPT), which employ different loading regime.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.19-24
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• 2004

The mode I stress intensity factor ($K_I$) of a newly proposed slow-crack-growth-test (Notched Ring Test, NRT) specimen was found using finite-element method. The theoretical $K_I$ value of NRT was not available in any references and could not be solved analytically. At first, in order to verify the accuracy of the finite-element approach, published $K_I$ values of several cracks were calculated and compared with finite-element results. The results were in excellent agreement within inherent errors of theoretical $K_I$. Finally the $K_I$ of NRT was found using 2- and 3-dimensional finite-element methods and expressed as a function of the applied load.

• Journal of the Korean Society for Nondestructive Testing
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• v.27 no.6
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• pp.550-555
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• 2007

Stress intensity factor is one of the most important parameters in fracture mechanics. Both the stress field distribution and the crack propagation are closely related to these parameters. Due to the complexity of actual engineering problems, it is difficult to calculate the stress intensity factor by theoretical formulation, so photoelasticity method is a good choice. In this paper, modified two parameter method is employed to calculate stress intensity factor for opening mode by using data from more than one photoelastic fringe loop. For getting accurate experiment results, the initial fringes are doubled and sharpened by digital image programs from the fringe patterns obtained by a CCD camera. Photoelastic results are compared with those obtained by the use of empirical equation and FEM. Good agreement shows that the methods utilized in experiments are considerably reliable. The photoelastic experiment can be used for bench mark in theoretical study and other experiments.

• Journal of the Korean Wood Science and Technology
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• v.27 no.4
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• pp.51-56
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• 1999

Finite element method was utilized to analyze crack tip stress and displacement field under drying stress case as stepwise loading. Opening mode of single-edge-notched model was employed and analyzed by linear elastic fracture mechanics of plane stress case. The drying stresses were applied as stepwise loads at the boundary elements of the model with 10 steps of time serial. The stress intensity factor($K_I$) for opening mode reached to its maximum just prior to the stress reversal. The $K_I$ from the displacement fields revealed 1.7 times higher than those from stress fields. By comparing the two sets of $K_I$ from displacement and stress fields, single parameter $K_I$ showed its validity to characterize displacement fields around the crack tip front while stress field could not be characterized due to large variations between two sets of data.