• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.1085-1090
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• 2003

An iterative modal analysis approach is developed to determine the effect of transverse open cracks on the dynamic behavior of simply supported Euler-Bernoulli beams with the moving masses. The influences of the velocities of moving masses, the distance between the moving masses and a crack have been studied on the dynamic behavior or a simply supported beam system by numerical method. no presence or crack results in large deflection of beam. The crack section is represented by a local flexibility matrix connecting two undamaged beam segments i.e. the crack is modelled as a rotational spring. This flexibility matrix defines the relationship between the displacements and forces across the crack section and is derived by applying fundamental fracture mechanics theory. Totally, as the velocity of the moving masses and the distance between the moving masses are increased, the mid-span deflection of simply supported beam with the crack is decreased.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.10
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• pp.1157-1162
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• 2014

Two acceleration methods, an effective force method (or inertia method) and a large mass method, have been applied for performing time history seismic analysis. The acceleration methods for uncracked structures have been verified via previous studies. However, no study has identified the validity of these acceleration methods for cracked piping. In this study, the validity of the acceleration methods for through-wall cracked piping is assessed via time history implicit dynamic elastic seismic analysis from the viewpoint of linear elastic fracture mechanics. As a result, it is identified that both acceleration methods show the same results for cracked piping if a large mass magnitude and maximum time increment are adequately selected.

• Journal of the Korean Society for Railway
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• v.12 no.1
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• pp.16-24
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• 2009

In this study, fatigue crack growth rate of a cracked railway bogie frame under variable amplitude loading is predicted by applying linear elastic fracture mechanics. For this purpose, we find the critical points by reference surveying on cracked railway bogie frames. And we make an effective load history by synthesizing the dynamic load measured from the critical points of railway bogie frame during commercial line operation and the static load calculated from structural analysis. Crack growth analyses are performed at the 3 critical points under the commercial operation loading condition by assuming an initial crack size as 40 mm. and the results are compared with the experimental results from Japanese railway bogie frame crack growth case. From the analysis results, we find that around 500,000 km operating distance is necessary to bring crack growth from the initial crack to unstable crack. And it takes around 3.8 normal operating years. We conclude that it is enough time to detect the crack between normal maintenance period.

• Structural Engineering and Mechanics
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• v.39 no.1
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• pp.77-91
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• 2011

A simply structural damage detection software is developed to identification damage in beams. According to linear fracture mechanics theory, the localized additional flexibility in damage vicinity can be represented by a lumped parameter element. The damaged beam is modeled by wavelet-based elements to gain the first three frequencies precisely. The first three frequencies influencing functions of damage location and depth are approximated by means of surface-fitting techniques to gain damage detection database of forward problem. Then the first three measured natural frequencies are employed as inputs to solve inverse problem and the intersection of the three frequencies contour lines predict the damage location and depth. The DLL (Dynamic Linkable Library) file of damage detection method is coded by C++ and the corresponding interface of software is coded by virtual instrument software LabVIEW. Finally, the software is tested on beams and shafts in engineering. It is shown that the presented software can be used in actual engineering structures.

• Journal of the Korean Society for Nondestructive Testing
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• v.8 no.1
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• pp.22-29
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• 1988

The optical method of reflected and transmitted caustics has been utilized in mechanics investigations. This relatively new experimental technique has been successfully applied on various fracture analysis such as static and dynamic c rack propagation studies, some elasticity problems and contact stress, etc, In this study, the stress intensity factors in thin polycarbonate specimens, a kind of optically anisotropic material, under Mode I loading condition are estimated by the method of caustics. The values of stress intensity factors obtained from theoretical caustics shape are compared by the experiment. It is confirmed that the two stress intensity factors agree well with Srawley's solution.

• Structural Engineering and Mechanics
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• v.25 no.2
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• pp.131-146
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• 2007

This paper presents the results of a study to show how the development of a crack alters the structural behavior of I-shaped steel beams and how this can be used to evaluate nondestructive evaluation techniques. The approach is based on changes in the dynamic behavior. An approximate finite element model for a cracked beam with I-shaped cross-section is developed based on a simplified fracture model. The model is then used to review different damage cases. Damage detection techniques are studied to determine their ability to identify the existence of the crack and to identify its location. The techniques studied are the coordinate modal assurance criterion, the modal flexibility, and the state and the slope arrays.

• Structural Engineering and Mechanics
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• v.31 no.3
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• pp.241-264
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• 2009

In this paper, the dynamic behavior for a group of transmission towers linked together through electrical wires and subjected to a strong ground motion will be investigated in detail. In performing the seismic analysis, the wires and the towers concerned are modeled, respectively, by using the efficient cable elements and the 3-D beam elements both considering geometric nonlinearities. In addition, to enhance the reliability and applicability of analytical outcome, a sophisticated soil-structure interaction model will be utilized in analyses. The strength capacities and the fracture occurrences for the main members of the tower are examined with the employment of the appropriate strength interaction equations. It is expected that by aid of this investigation, those who are engaged in code constitution or in practical designing of transmission towers may gain a better insight into the roles played by the interaction force between towers and wires and by the configurations of transmission lines under strong earthquake.

• Proceedings of the KSME Conference
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• 2000.04a
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• pp.67-72
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• 2000

Demand for now nondestructive evaluation are growing to detect fatigue crack growth behavior to predict long term performance of materials and structure in aggressive environments especially when they are In non-visible area. Acoustic emission technique is well suited to these problems and has drawn a keen interests because of its dynamic detection ability, extreme sensitivity and location of growing defects. In this study, we analysed acoustic emission signals obtained in fatigue and tensile test of high strength fire resistance steel for frame structure with time-frequency analysis methods. The main frequency range is different in the noise and the fatigue crack propagation. It could be classified that it were also generated by composite fracture mechanics of cleavage, dimple, inclusion separation etc.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.7 no.2
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• pp.54-61
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• 1998

This paper examines the crack growth behavior of 7075-T651 aluminum alloy for small tensile overload under high-low block loading condition. The cantilever beam type specimen with a chevron notch is used in this study. The crack growth and closure are investigated by compliance method. The applied initial stress ratios are R=-0.5 R=0.0 and R=0.25 Crack length, effective stress intensity factor range, ratio of effective stress intensity factor range and crack growth rate etc, are inspected with fracture mechanics estimate.

• Macromolecular Research
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• v.9 no.6
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• pp.319-326
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• 2001

Fatigue crack growth (FCG) behavior of natural rubber/ethylene-propylene-diene rubber (NR/EPDM) blend vulcanizates under dynamic tearing condition was investigated by using a fracture mechanics approach. It appeared that variation of crack growth rate with blend compositions was dependent on the level of imposed tearing energy G. At low tearing energy region, the FCG rates of the blend were lower as the EPDM content was increased, while at high tearing energy region, the trend was reversed. Over the measured range of tearing energy G, all blend compositions showed the lower crack growth rates compared to the average of properties of component elastomers. When the blends were thermally aged, the fatigue resistance of the blends was deteriorated in proportion to the concentration of EPDM phase. Fatigue crack growth behavior of the blends was supposed to be associated with the inhomogeneities of the crosslink structure of the blends arising from cure incompatibility of the EPDM and NR when they are sulphur cured.