• Proceedings of the Korea Concrete Institute Conference
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• 1999.10a
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• pp.659-662
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• 1999

Ultrasonic pulse velocity method is employed for evaluation of crack depth in concrete structures. Due to the heterogeneous nature of concrete and the indirect transmission arrangement for the transit time measurement through the surface-opening cracks in concrete structures, ultrasonic pulse velocity has so many variations as crack depths and transmission lengths vary. In this study, ultrasonic pulse velocity method is investigated to evaluate the surface-opening crack depth of concrete slabs, reinforced concrete slabs, reinforced concrete flexural members. the resent study gives a modified method for deminishing errors in transit time measurements and show limitations to the evaluation of crack depth in reinforced concrete structures.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.4
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• pp.745-753
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• 2002

It is required to evaluate nondestructively the crack depth of surface-breaking cracks for the assurance of safety of structure. Optical generation of ultrasound produces well defined pulses with a repeatable frequency content, that are free of any mechanical resonances; they are broad band and are ideal for the measurement of attenuation and scattering over a wide frequency range. Self-calibrating surface signal transmission measurement is very sensitive and practical tool for surface-breaking crack depth. In this paper, the self-calibrating technique by laser-based ultrasound is used to evaluate the depth of surface-breaking crack of material. It is suggested that the relationship between the signal transmission and crack depth can be used as a practical model for predicting the surface-breaking crack depths from the signal transmission measured in structure.

• Journal of the Korean Society for Nondestructive Testing
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• v.25 no.3
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• pp.215-221
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• 2005

It is required to evaluate nondestructively depth of surface-breaking cracks in structures. In this paper, the self-compensated technique by laser-based ultrasound is used to measure the depth of surface-breaking defect. Optical generation of ultrasound produces a well defined pulse with reliable frequency content. It is broad banded and suitable for measurement of attenuation and scattering over a wide frequency range. The self-calibrated signal transmission data of surface wave shows good sensitivity as a practical tool far assessment of surface-breaking defect depth. It is suggested that the relationship between the signal transmission and crack depth can be used to predict the surface-breaking crack depths in structures.

• Journal of the Korean Society of Safety
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• v.32 no.6
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• pp.1-8
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• 2017

P-PIE is a program developed to estimate failure probability of pipes and pressure vessels considering fatigue and stress corrosion crack growth. Using the program, crack growth simulation was performed with an initially existing crack in order to examine the effects of initial crack depth distribution on the leak probability of pipes. In the simulation stress corrosion crack growth was considered and several crack depth distribution models were used. From the results it was found that the initial crack depth distribution gives great effect on the leak probability of pipes. The log-normal distribution proposed by Khaleel and Simonen gives lower leak probability compared other exponential distribution models. The effects of the number and the quality of pre-service and in-service inspections on the leak probability were also examined and it was recognized that the number and the quality of pre-service and in-service inspections are also give great effect on the leak probability. In order to reduce the leak probability of pipes in plants it is very important to improve the quality of inspections. When in-service inspection is performed every 10 years and the quality of inspection is above the very good level, the leak probability shows nearly constant value after the first inspection for an initially existing crack.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.05a
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• pp.515-518
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• 2005

A concrete is easy to happen crack. So it requires crack-repair work to solve quality deteriorations of a building because of cracks. When crack is filled with crack-repair materials, it is difficult to find out how depth it was injected. So in this study we evaluated the injection depth with using indirect and oblique methods, ultrasonic pulse measurement method of NDT. The results of this study showed that both methods are possible to evalute penetration depth of crack-repair materials and indirect methods is thought to be more useful one than obliqure one.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.4 no.4
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• pp.42-49
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• 1995

It is not clearly known how defects or inclusions of a low carbon steel affect a fatigue strength. We study this issue using SM15C materials. The investigation is carried out by a quantitative evaluation, and experimental findings are: (1) a fatigue limit of A series smooth specimen is 205MPa, and that of B, C, D series is 245MPa, 304MPa and 245MPa, respectively. (2) the fatigue limit varies with respects to the stress distribution I the vicinity of a defects and crack. (3) the micro hole creates a half-circular shape crack, while the hole depth is not critical to the fatigue strength, (4) considering the fatigue strength, the hole diameter is more significant than the hole depth, and (5) Fatigue limit of artificially defected specimen is lower than that of a flawless one (5-10%), however, there exist allowance size and depth of defect which don't get to influence at fatigue limit.

• Journal of the Korean Society of Industry Convergence
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• v.26 no.4_2
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• pp.571-576
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• 2023

In this study, the harmless crack size(a_hml) according to the residual stress depth was evaluated using the fatigue limit of SCM440 steel by quenching-tempering(QT) and induction hardening(IH), and threshold stress intensity factor of QT steel. Because the residual stress increased rapidly as the crack depth increased, a_hml was determined at the depth of all the crack aspect ratio(As) regardless of Type I-III, and a_hml also increased according to the residual stress depth. a_hml was minimal at As=1.0 and maximal at As=0.1, but was almost similar on each Type. a_hml was small the dependence on As.

• Journal of the Korean Society for Nondestructive Testing
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• v.16 no.2
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• pp.86-94
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• 1996

In the life management safety evaluation of constructs base on a fracture mechanics, the size of defect is the very important parameter. ICFPD (Induced Current Focusing Potential Drop)technique has been developed for detecting and sizing of defects that exist not only on surface but also inside and interior of structural components. The principle of this technique is to induce a focusing current at an exploration region by a straight induction wire through which an alternating current (AC)flows that has constant amplitude and frequency. The potential distributed on the surface of metallic material is measured by potential pick-up pins that are settled on the probe. In this paper, this NDI technique was applied to the evaluation of surface cracks and blind cracks in plate specimens. The results of this study show that in the case of surface crack, the distribution of potential drop is varied with the inched angle of surface crack, and the potential drops in the crack region and the crack edge region are varied with the inclined angle and depth of crack. The distribution of potential drop for the blind crack is distingulished from that for the surface crack, and the potential drop in the crack region is varied with the depth of crack.

• Journal of the Korea institute for structural maintenance and inspection
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• v.3 no.2
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• pp.141-146
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• 1999

Recently, many existing bridges has been evaluated for maintenance and protection of collapse. In this study, field measurement according to truck loads tests on the reinforce concrete T beam bridge was carried out. Comparing the results of load test and structural analysis using the moments of inertia of gross section, crack section and effective section, and the moments of inertia of section considering depth of crack, it is conclude that the evaluation of load carrying capacity using the stress modification factor from structural analysis using the moments of inertia of gross section is more rational than using the other moments of inertia of sections.

• Proceedings of the Korea Concrete Institute Conference
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• 2010.05a
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• pp.183-184
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• 2010

In this study, it suggested evaluation method of carbonation about crack to occur in an early age. And it compared penetration depth of carbonation with crack size.