• Corrosion Science and Technology
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• v.5 no.4
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• pp.123-128
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• 2006

It was analyzed the causes of boiler tube rupture due to a degradation and corrosion on the boiler tubes in fossil power plant. The experiments were carried out among samples taken from the operating facilities. The result were analyzed based on experimental results from mechanical strength, microstructure observation, and hardness measurement in order to determine the cause of local rupture on boiler tubes. In general, 2.25Cr-1Mo steel generates carbides, it is coarsened, its ductility and strength abruptly decreased as degradation is in progress, In order to confirm this phenomenon, we observed changes of the mount of Cr and Mo of carbide by carrying out EDX chemical composition analysis. The amount of Cr and Mo in the degraded material or service exposed material gradually increased the amount of Mo but initially they were almost maintained at the same amount. Furthermore, we observed that the carbide become coarsened both in the grain and at the grain boundary. Tensile test was carried out to measure a material hardness and to recognize a drop-off of hardness. Overall result for tensile strength and hardness turned out to be lower than new material and mechanical strength and hardness was degraded as the material degradation was in progress.

• Journal of the Korean Society for Nondestructive Testing
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• v.19 no.4
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• pp.288-293
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• 1999

The integrity of the turbine rotors can be assessed by the coercive force and Vickers hardness of the aged rotors at service temperature. The coercive force measurement system was constructed in order to evaluate material degradation nondestructively. The test specimen was 1Cr-1Mo-0.25V steel used widely for turbine rotor material, and then the seven kinds of specimens with different degradation levels were prepared by the isothermal heat treatment at $630^{\circ}C$. The coercive force of the test materials was measured at room temperature. Vickers hardness and coercive force decreased with the increase of degradation. The relationship between Vickers hardness and coercive force was investigated. The degradation of test material may be determined nondestructively by the relationship between Vickers hardness and coercive force.

• Journal of the Korea Concrete Institute
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• v.17 no.3 s.87
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• pp.313-322
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• 2005

Recently, as the remodeling market gradually substitute for new construction market and safety diagnosis for reconstruction apartment become a matter of principal Interest, it is demanded that scientific diagnosis and evaluation for existing concrete structure state. And it is increasing that the significance for reliability of data which is used for estimating the concrete compressive strength by nondestructive test. As a result, it is found that different proposal to material age and hitting angle is good to improving the reliability of presumption of concrete compressive strength in the linear hitting rebound test hammer. And for the reason that mutual relation between the compressive strength and rebound degree is highest in linear hitting rebound test hammer 25mm in all portion according to early md middle material age and hitting angle except the early material age $-45^{\circ}$, analysis showed that linear hitting rebound test hammer is more reliable than existing schmidt hammer in presumption of concrete compressive strength.

• Journal of the Korean Society for Nondestructive Testing
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• v.33 no.2
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• pp.147-153
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• 2013

Recently the primary water stress corrosion cracking(PWSCC) has occurred in the dissimilar metal weld region between pressurizer nozzle and safe-end in nuclear power plants(NPPs). As material of the pressurizer nozzle, SA508 Gr. 3 low alloy steel was used. F316L stainless steel and Alloy 82/182 were used as safe-end and weld metal, respectively. Although mechanical properties are needed for evaluation of the structural integrity against flaw in the material, material specification and standard don't supply those properties. Therefore, the present study conducted tensile and fracture toughness tests on SA508 Gr.3 and F316L stainless steel at ambient temperature and operating temperature of NPPs and reported the tested results.

• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.5
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• pp.445-450
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• 2000

The integrity of the turbine rotors can be assessed by measuring reversible permeability and Vickers hardness of the aged rotors at service temperature. The measurement system of reversible permeability, which measured by applied alternating perturbing magnetic field, was constructed in order to evaluate material degradation, nondestructively. The test specimen was 1Cr-1Mo-0.25V steel used widely for turbine rotor material, and the specimens were prepared by the isothermal heat treatment at $630\;^{\circ}C$. The reversible permeability of the test materials were measured at room temperature. The peak interval of reversible permeability and Vickers hardness decreased with the increase of degradation. The degradation of test material may be determined nondestructively by the lineality of Vickers hardness and the peak interval of reversible permeability.

• Journal of Welding and Joining
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• v.23 no.2
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• pp.59-65
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• 2005

A leaky surface acoustic wave (LSAW) velocity was measured using a scanning acoustic microscope on the ceramic/metal interface in order to investigate material properties. The inverse Fourier transform (IFFT) of the V(z) curve contains the reflectance function of a liquid-specimen interface. So, the longitudinal, transverse, and Rayleigh wave velocities for each layer are obtained by the inversion of the V(z) curve at the same time. This paper contains mainly the experimental procedure for measurements of the LSAW velocity, and the results obtained for the velocity variation of individual layer after the thermal shock. It is shown that this method is useful in measuring the material properties under external stress.

• 연구논문집
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• s.31
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• pp.157-163
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• 2001

Evolution of microstructure due to service exposure to high temperature has a strong effect performance of heat resistant steels. In case of modified 9Cr-1Mo steels, precipitation of $Fe_2Mo$-type laves phases and coarcening of $M_23C_6$-type carbides is the primary cause of degradation of mechanical properties such as creep resistance, tensile strength and toughness. Creep tests have been carried out on pre-aging mod. 9Cr-1Mo steels to examine the effect of pre-aging and stress on the creep strength. Based on the results, a nondestructive procedure, where electrochemical technique that quantitatively detect laves phases and $M_23C_6$-type carbides in a material is used, has been proposed to evaluate a residual creep life of mod. 9Cr-1Mo steels.

• Journal of the Korean Society for Nondestructive Testing
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• v.31 no.5
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• pp.494-499
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• 2011

This paper presents the biomechanical analysis and evaluation technology of musculoskeletal system by multi-body human dynamic model and 3-D motion capture data. First, medical image based geometric model and material properties of tissue were used to develop the human dynamic model and 3-D motion capture data based motion analysis techniques were develop to quantify the in-vivo joint kinematics, joint moment, joint force, and muscle force. Walking and push-up motion was investigated using the developed model. The present model and technologies would be useful to apply the biomechanical analysis and evaluation of human activities.

• 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 Ocean Engineering and Technology
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• v.15 no.3
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• pp.87-92
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• 2001

In this studies, joint time-frequency analysis techniques were applied to analyze ultrasonic signals in the degraded austenitic 316 stainless steels, to study the evolution of damage in these materials. It was demonstrated that the nonstationary characteristics of ultrasonic signals could be analyzed effectively by these methods. The WVD was more effective for analyzing the attenuation and frequency characteristics of the degraded materials through ultrasonic. It is indicated that the joint time-frequency analysis, WVD method, should also be useful in evaluating various damages and defects in structural members.