• 한국생산제조학회지
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• 제7권5호
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• pp.46-52
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• 1998

In fracture problems, stress intensity factors obtained theoretically and experimentally have been effectively utilized in the analytical evolution of the cracks effect. The effect of surface crack of a cylindrical and a hollow cylindrical bar is investigated, as well as the effect of the thickness of a hollow cylindrical bar and inclined crack of a hollow cylinder subjected to torsion moment. In this study, stress intensity factor Km of mode III which expresses the stress state in the neighborhood of a crack tip is used. stress analysis was conducted on the inside of hollow cylinder inthe axial direction of three dimensional crack tip subjected to torsion moment by combining the caustics method and the stress freezing method.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1991년도 가을 학술발표회 논문집
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• pp.124-128
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• 1991

Wood, laminates, reinforced concrete, and some special types of metals systems with controlled grain orientation are often orthotropic and at least rectilinearly anisotropic from point to point, if regarded as homogeneous media. Orthotropic bodies where a crack is not associated with a plane of elastic symmetry may be conveniently treated as a crack problem in a generally anisotropic body. At this work, approach for the determination of the stress intensity factors (SIF) of anisotropic body using crack tip singular elements is presented. Caculated values are in good agreement with the others.

• 대한기계학회논문집
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• 제7권3호
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• pp.270-277
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• 1983

Plastic plane stress solutions are given for a center cracked strip, characterized by the Ramberg-Osgood plastic index, under bi-axial tension. Using a power law hardening stress-strain relation, an incremental plasticity finite element formulation is developed, and simple formulation is given for computing J-integral with nodal displacements. The near tip angular distribution of von Mises effective stress doesn't differ significantly in magnitude according to the change of loading stress and bi-axial load combination factor. But, for smaller plastic index, the location of its maximum value moves vertically at a head of crack. J-integral value, in the plastic zone near crack tip, decreases with load combination factor for large and small plastic index.

• Structural Engineering and Mechanics
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• 제36권5호
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• pp.575-598
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• 2010

The shape and size of the plastic zone around the crack tip are analyzed under pure mode I, pure mode II and mixed mode (I+II) loading for small scale yielding and for both plane stress and plane strain conditions. A new analytical formulation is presented to determine the radius of the plastic zone in a non-dimensional form. In particular, the effect of T-stress on the plastic zone around the crack tip is studied. The results of this investigation indicate that the stress field with a T-stress always yields a larger plastic zone than the field without a T-stress. It is found that under predominantly mode I loading, the effect of a negative T-stress on the size of the plastic zone is more dramatic than a positive T-stress. However, when mode II portion of loading is dominating the effect of both positive and negative T-stresses on the size of the plastic zone is almost equal. For validating the analytical results, several finite element analyses were performed. It is shown that the results obtained by the proposed analytical formulation are in very good agreements with those obtained from the finite element analyses.

• 대한기계학회논문집A
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• 제26권9호
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• pp.1753-1763
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• 2002

Stress and displacement fields for a propagating crack in a functionally gradient material (FGM) which has shear modulus as $\mu$=$\mu$$\_$0/(1＋ζX) are derived. The equations of motion in FGM which is nonhomogeneous material are different from those of homogeneous material. The stress intensity factors in stress fields have influence on odd terms of γ$\^$n/2-1/(n=1,3,5,...,) but stress at crack tip only retains term of γ$\^$-1/2/, where the γ is a radius of cylindrical coordinates centered at crack tip. When the FGM constant ζ is zero or γ→0, the fields for FGM are almost same as the those for isotropic material.

• 한국자동차공학회논문집
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• 제13권6호
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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.

• 대한기계학회논문집
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• 제19권1호
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• pp.79-86
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• 1995

The structural materials for cryogenic technology have been recently developed to support the many modern large-scale application from superconducting magnets for nuclear fusion reactor, magnetic levitation railway to LNG tankers. However it is pointed out that quenching phenomenon is one of the serious problems for the integrity of these applications, which is mainly attributed to the rapid temperature rising in the material due to some extrinsic factors of structures. From the viewpoint of fracture mechanics, it is therefore very important to clarify the mechanism of temperature rising of structural material due to cyclic loading at cryogenic temperature. From this purpose, fatigue test was carried out for high manganese steel at liquid helium temperature(4.2K) using triangular stress waveform to identify both the mechanism of temperature rising near crack tip and the effect of loading stress waveform on temperature rising near crack tip and the effect of loading stress waveforms on temperature rising. As the results, two types of temperature rising, that is, regular and burst types were observed. And a periodical temperature rising corresponding to the stress waveforms was also found. The peaks of the temperature rising were recorded near both the maximum and the minimum values of the applied stress. The sudden temperature rises, which indicated the higher values than those of periodical temperature rises under the repetition of stress, were observed at the final region of crack growth. It was shown that the peak values of the temperature rising increased with stress intensity factor range.

• Journal of Advanced Marine Engineering and Technology
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• 제33권4호
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• pp.539-544
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• 2009

The constraint effect $A_2$ has to be evaluated within plastic region near crack tip front using opening displacement. Plastic boundary and stress or strain conditions in the vicinity of the crack tip using recrystallization heat treatment was represented. It was found that the plastic deformation boundary by recrystallization heat treatment method was the true strain of ${\epsilon}t$ = 0.05mm/mm. With the estimation of constraint effects $A_2$, the region of proper displacement measurement point near crack tip was between 0mm and 1mm distance toward direction of crack propagation, and was between 1mm to 3mm distance toward direction of load line.

• 대한기계학회논문집A
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• 제21권1호
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• pp.124-132
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• 1997

This paper describes an experimental and numerical study on growing ductile crack-tip behaviors. The hybrid experimental and numerical method by means of a computer image processign technique, was applied to the analysis of both base metal and weld metal CT specimens. In the weld metal specimen, the initial crack-tip was placed in front of fusion line, and the crack orientation was perpendicular to it. Finite element analysis of crack growth behaviors in both base and weld matal specimens made of A533B Class 1 steel were also performed to examine the effects of weldment on near crack-tip fields. a series of experimental studies on crack-tip behaviors have clearly shown the qualitative effects of material properties, especially a hardening exponent. The experimental and numerical results have also shown that weldment does not affect displacement and strain fields near a crack-tip while a stress field is influenced by the difference between yield stresses of both base and weld metals.

• 대한기계학회논문집
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• 제17권2호
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• pp.331-341
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• 1993

The propagating crack problems under dynamic antiplane mode in orthotropic material is studied in this paper. To analyze the dynamic fracture problems by theoretical method or experimental method in orthotropic material, it is important to know the dynamic stress intensity factor in the vicinity of crack tip. Therefore the dynamic stress field and dynamic displacement field with dynamic stress intensity factor of orthotropic material in mode III were derived. When the crack propagation speed approachs to zero, the dynamic stress components and dynamic displacement components derived in this paper are identical to the those of static state. In addition, the relationships between dynamic stress intensity factor and dynamic energy release rate are determined by using the concept of crack closure energy with the dynamic stresses and dynamic displacements derived in this paper. Finally, the characteristics of crack propagation are studied with the properties of orthotropic material and crack speed. The variation of angle .alpha. between fiber direction and crack propagating direction and crack propagation speed fairly effect on stress component and displacement component in crack tip. The influence of crack propagation speed on the speed on the stress and displacement is greater in the case of .alpha.=90.deg. than in the case of .alpha.=0.deg. and the faster the crack propagation speed, the greater the stress value and displacement value.