• 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.

• 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.

• 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.

• 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.

• 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.

• Journal of the Korean Society of Safety
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• v.7 no.1
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• pp.5-12
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• 1992

Disc specimen with the center crack and edge crack simulated by two-dimensional static method is used to analyze the stress field around the crack tip in terms of the stress intensity factor, K. A simple and convenient method of testing to realize the mifed mode stress intensity factor of the cracked body is used, The conclusions obtatined in this photoelastlc analysis are as follows ; 1. According to this experiment, cracked disc specimen can be used to demonstrate the mixed mode stress intensity factor analysis by simply changing the crack angle from the loading line. 2. Despite the simplicity and continuous data reading, the photoelastic method shows the slightly lower strain reading comparing to the FEM analysis method. 3. In this photoelastic analysis, $K_{I}$ of center cracked disc specimen under a pair of compressive load shows negative value as the crack angle increases over 30$^{\circ}$.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.3
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• pp.511-518
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• 1997

The technique of fretting fatigue test was developed and fretting fatigue tests of A12024-T4 were conducted under several conditions. The newly developed calibration methods for measuring surface contact tractions showed good linearity and repeatability. The plate type specimen to which tow bridge type pads were attached and vision system was used to observe the crack behaviour. The oblieque cracks appeared in the early stage of crack growth and they became mode I cracks as they grow about 1 mm. The mode I transition points were found to be longer when surface tractions are higher or bulk stress is lower. Before the crack becomes mode I crack, 'well point' where crack grow about rate is minimum, was detected under every experimental condition. The crack behaviour was found to be affected by surface tractions, contact area, bulk stress. It was also found that partial slip and stick condition is most detrimental and the crack starts from the boundary of stick and slip. For gross slip crack started at the outside edge of pad. After crack mode transition, fretting fatigue cracks showed almost same behaviour of plain mode I fatigue cracks. Equivalent stress intensity factor was used to analyze the behaviour of fretting fatigue cracks and it was found that stress intensity factors can be applied to fretting fatigue cracks.

• Bulletin of the Society of Naval Architects of Korea
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• v.25 no.1
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• pp.21-32
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• 1988

An experimental study was carried out to identify the fatigue fracture behavior of steel for merchant ships. The bending and shear loads were applied simultaneously on the specimens to simulate of real load condition for a ship. The effects of the stress intensity factor under mode I with mode II loading condition on the initiation and the propagation of a crack were investigated, with particular emphasis on mode II. When the $K_{II}$ stress intensity factor in mode II was applied under mode I loading condition, the propagation behavior of a crack is to be affected mainly by the anisotropic characteristic of materials.

• Journal of the korean Society of Automotive Engineers
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• v.15 no.2
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• pp.112-120
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• 1993

Variable thickness plates are commonly encountered in the majority of mechanical/structural components of industrial applications. And, as a result of the unsymmetry of the structure or the load and the anisoptropy of the materials, the cracks in engineering structures are generally subjected to combined stresses. In spite of considerable practical interest, however, a few fracture mechanics study on combined mode crack in a variable thickness plate have carried out. In this respect, combined mode 1/3 stress intensity factors $K_{1}$ and $K_{3}$ at the crack tip for a variable thickness plate were obtained by 3-dimensional finite element analysis. Variable thickness plates containing a central slant crack were chosen. the parameters used in this study were dimensionless crack length .lambda. crack slant angle .alpha, thickness ratio .betha. and width ratio .omega. Stress intensity factors were calculated by crack opening displacement(COD) and crack tearing displacement(CTD) method proposed by Ingraffea and Manu. The effect of thickness ratio .betha. on $K_{1}$ is relatively great in comparison to $K_{3}$.