• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.11a
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• pp.429-432
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• 2000

The dynamic photoelasticity with the aid of Cranz-Shardin type high speed camera system is utilized to record the dynamically propagating behavior of the interface crack. This paper investigates the effects of the hole (existed along the path of the crack propagation) shape on the dynamic interface crack propagation behavior by comparing the experimental isochromatic fringes to the theoretical stress fields.

• Journal of Ocean Engineering and Technology
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• v.1 no.2
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• pp.113-122
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• 1987

Ships and offshore strrctures are exposed to the corrosive surroundings, and the extablishment of the design criteria and the elucidation on the influence by this environment are requested to maintain the safety and to demonstrate the function of the structure. In this paper, the fatigue-crack-growth behavior on the compact tension specimens of quenched, tempered HT80 grade steels and RA36 high tensile steels having a single edge fatigue cracked notch respectively, were investigated under the repeated tensile stress with constant stroke in sea water for the welded parts by shielded metal arc welding. Main results obtained are summerized as follows; 1. The fatigue-crack-growth rates da/dN in sea water appeared to be greater behavior than those in air environment at the same stress intensisy factor range $\DeltaK$. 2. The correlation data of da/dN$\DeltaK$ of the two kinds of high tensile steels in sea water showed no great difference, however, the correlation data of da/dN$\DeltaK/\sigma_y$($\sigma_y$ stands for yield strength of the material) showed that the fatigue-crack-growth behavior of RA36 plate is affected by active path corrosion(APC) mechanism, while that of HT80 grade plate is mainly affected by hydrogen embrittlement mechanism.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.17 no.4
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• pp.423-431
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• 2004

For the fracture mechanics analysis of cracks in welds of dissimilar steels, residual stress analysis and fracture analysis must be performed simultaneously. The standard definition of the J -integral leads to a path dependent value in the presence of a residual stress field. And unlike cracks in homogeneous materials, a bimaterial interface crack always induces both opening and shearing modes of stress in the vicinity of the crack tip. Therefore, it is necessary to develope a path independent J-integral definition for a crack in a residual stress field generated by welding of dissimilar steels. This paper addresses the modification of the Rice-J-integral to produce a path independent J -integral when residual stresses due to welding of dissimilar steels and external forces are present. The residual stress problem is treated as an initial strain problem and the J-integral proposed for this class of problems is used. And a program which can evaluate the J -integral for a crack in a weld of dissimialr steels is developed using proposed J integral definition.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.487-490
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• 2004

In this paper, we investigated the characteristics of initiation and propagation behavior for fatigue crack observed by changing various shapes of initial crack and magnitudes of loading in modified compact tension shear(CTS) specimen subjected to shear loading. In the low-loading condition, the secondary fatigue crack was created in the notch root due to friction on the pre-crack face grew to a main crack. In the high-loading condition, fatigue crack under shear loading propagated branching from the pre-crack tip. Influenced by the shear loading condition, fatigue crack propagation retardation appeared in the initial propagation region due to the reduction of crack driving force and friction on crack face. In both cases, however, fatigue cracks grew in tensile mode type. The propagation path of fatigue crack under the Mode II loading was 70 degree angle from the initial crack regardless of its shape and load magnitude.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.302-307
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• 2004

This paper reviewed characteristics of fatigue crack behavior observed by changing various shapes of initial crack and magnitudes of loading in compact tension shear(CTS) specimen subjected to shear loading. In the high-loading condition, fatigue crack under shear loading propagated branching from the pre-crack tip. Meanwhile, the secondary fatigue crack in the low-loading condition which was created in the notch root due to friction on the pre-crack face grew to a main crack. Influenced by the mode II loading condition, fatigue crack propagation retardation appeared in the initial propagation region due to the reduction of crack driving force and friction on crack face. In both cases, however, fatigue cracks grew in tensile mode type. Propagation path of fatigue crack under the shear loading was 70 degree angle from the initial crack regardless of its shape and load magnitude.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.5
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• pp.158-165
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• 2004

Up to now, many crack repair techniques have been developed for inhibiting crack growth in structural components. However, the simplest way for inhibiting crack growth is to apply a indentation at the crack tip or at some distance ahead of the expected crack growth path so as to produce residual compressive stresses that can reduce the effective stresses around the crack tip. In spite of its importance to the aerospace industry, little attention has been devoted to evaluation of the indentation residual stress effect on the fatigue crack initiation life quantitatively. Therefore, in the present work, the magnitude and distribution of the indentation residual stresses were investigated in order to estimate the beneficial effect on fatigue crack initiation by using finite element method. Furthermore, to examine the validity of finite element analysis results, residual stress distribution in the indented specimen was measured by using X-ray diffraction technique, and fatigue crack behavior at fastener hole in aluminum alloy 7075-T6 before and after indentation processes was investigated.

• Journal of Mechanical Science and Technology
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• v.16 no.10
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• pp.1246-1252
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• 2002

Ultrafine grained (UFG) low carbon (0.15 wt.% C) steel produced by equal channel angula. pressing (ECAP) was tested for investigating the effect of load ratio on the fatigue crack growth rate. Fatigue crack growth resistance and threshold of UFG steel were lower than that of asreceived coarse grained steel. It was attributed to the less tortuous crack path. The UFG steel exhibited slightly higher crack growth rates and a lower △Kth with an increase of R ratio. The R ratio effect on crack growth rates and △Kth was basically indistinguishable at lower load ratio (R >0.3), compared to other alloys, which indicates that contribution of the crack closure vanishes. The crack growth rate curve for UFG steel exhibited a longer linear extension to the lower growth rate regime than that for the coarse grained as-received steel.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.187-192
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• 2001

Cracks in mechanical joints is generally under mixed-mode and there is the critical inclined angle at which mode I stress intensity factor becomes maximum. In order to evaluate the fatigue life of cracks in mechanical joints, horizontal crack normal to the applied load and located on minimum cross section is major concern but critical inclined crack must also be considered. In this paper mixed-mode fatigue crack growth test is performed for horizontal crack and critical inclined crack in mechanical joints. Fatigue crack growth path is predicted by maximum tangential stress criterion using mode I and mode II stress intensity factors obtained from weight function method, and fatigue crack growth rates of horizontal and inclined crack are compared.

• Journal of the Korean Society for Precision Engineering
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• v.7 no.2
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• pp.39-46
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• 1990

In this study, the mechanical behavious of a center crack which propagates between two holes in a panel are investigated. It is confirmed experimentally and analytically that a center crack stops and a small crack initiates from holes and propagates to fracture because of the compressive stress arising along the path of the fatigue crack propagation. Futhermore, it is noted that regardless of the configuration of the crack and the structure, Paris' law can be applied to the fatigue crack propagation.

• Journal of the Korean Society for Nondestructive Testing
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• v.9 no.1
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• pp.39-47
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• 1989

As the necessity of the safety diagnosis of the concrete structure, more reliable ultrasonic technique to qualify the concrete is required. In this study, the artificial surface crack depth is measured using several types of the ultrasonic probes. As results, the horizontal shear wave probe is most useful to determine the crack depth compared to the other probes. For the surface wave probe, the ultrasonic wave path is changed with the surface crack depth.