• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.7
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• pp.1241-1249
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• 2002

The extent of materials deterioration can be evaluated accurately by mechanical test such as impact test or creep test. But it is almost impossible to extract a large test specimen from in-service components. Thus material degradation evaluation by non-destructive method is earnestly required. In this paper, the material degradation for virgin and several aged materials of a Cr-Mo-V steel, which is an candidated as structural material of the turbine casing components for electric power plant, is nondestructively evaluated by reactivation polarization testing method. And, the results obtained from the test are compared with those in small punch(SP) tests recommended as a semi-nondestructive testing method using miniaturized specimen. In contrast to the aged materials up to 1,000hrs which exhibit the degradation behaviors with increased ${\Delta}[DBTT]_{SP}$, the improvement of mechanical property can be observed on the 2,000hrs and 3,000hrs aged materials. This is because of the softening of material due to the carbide precipitation, the increase of ferritic structures and the recovery of dislocation microstructure by long-time heat treatment. The reactivation rates($I_R/I_{Crit},\;Q_R/Q_{Crit}$) calculated by reactivation current densityt ($I_R$) and charge($Q_R$) in the polarization curves exhibit a good correlation with ${\Delta}[DBTT]_{SP}$ behaviors.

• Journal of Applied Reliability
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• v.17 no.2
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• pp.129-135
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• 2017

Purpose: This article provides step-stress accelerated degradation test (ADT) plans based on the Wiener process. Method: Step-stress levels and the stress change times are determined based on the D-optimality criteria to develop test plans. Further, a simple grid search method is provided for obtaining the optimal test plan. Results: Based on the solution procedure, ADT plans which include the stress levels and change times are developed for conducting the reliability test. Conclusion: Optimal step-stress ADT plans are provided for the case where the number of measurements is small.

• Corrosion Science and Technology
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• v.5 no.5
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• pp.177-180
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• 2006

The anticorrosive performance of epoxy coating was examined by using the hygrothermal cyclic test and the degradation mechanism of the coating was investigated by using the AC impedance method. The relationship between the results obtained from different tests was studied. It was revealed that the hygrothermal cyclic test can be used as an effective acceleration test for the degradation of organic coating. It was also found in hygrothermal cyclic test that the epoxy coatings have the resistance to stresses at some extent. The degradation of organic coating seems to be caused by the decrease of resistance of coating and the increase of both capacitance and free volume in the organic coating.

• Current Photovoltaic Research
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• v.6 no.3
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• pp.69-73
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• 2018

PV system is consisted with PV module, inverter and BOS(balance of system). To have robustic operation more than 20 years, the expected and guaranteed durability and reliability of products should be met. Almost components of PV system are qualified through IEC standards at test laboratory. But the qualification certificate of product does not ensure long-term nondefective operation. PV module's expected life time is nowadays more than 20 years and annual maximum power degradation ratio would be less than -1%. But the power degradation ratio is basically based on real data more than several years' record. Developing test method for ensuring annual maximum power degradation ratio is very need because there are many new products every month with new materials. In this paper, we have suggested new test method under continuous artificial light irradiation test condition for analyze expected maximum power drop ratio.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.10b
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• pp.351-352
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• 2002

In this paper, studies were made on the palm oil methyl ester (POME) added lubricants using FT-IR for monitoring oil degradation. In order to assess the degradation characteristics of POME added lubricant by FT-IR, static oxidation test was conducted using three different blended lubricants (viz, zero percent POME, five percent POME and ten percent POME with mineral-based oil) for 280 hrs. The oxidation temperature was set at $140^{\circ}C$. FT-IR quantitative data indicate an increased in oxidation products which was formed from 10% POME added lubricants after 280 hrs of oxidation test. The 5% POME added lubricant and mineral-based lubricant (without POME) showed less oxidation product after the test. From the FT-IR spectrum analysis of the oxidized oils it could be concluded that 5% POME can improve the performance of mineral-based oil by forming protective films.

• Journal of Welding and Joining
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• v.31 no.3
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• pp.22-30
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• 2013

Due to ELV banning, automotive electronics cannot use four kinds of heavy metal element (Pb, Hg, Cd, $Cr^{6+}$) from 2016. Therefore, this study was focused on degradation characteristics of Sn-3.0Ag-0.5Cu Lead-free solder joint with OSP and ENIG finsh under various reliability assessment method, as like to thermal shock test and high temeprature/high humidity test with test duration for cabin electronics. Also, we compared bonding strength degradation to other advanced research results of electronic control unit for engine room because of difference service temperature with mount location in automotive. Whisker growth phenomenon and mitigation method which were essentially consideration items for Pb-free car electronics were examined. Conformal coating is a strong candidate for mitigating whisker growth in automotive electronics. Necessary condition to adapt Pb-free in car electronics was shown.

• Journal of Ocean Engineering and Technology
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• v.14 no.4
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• pp.68-72
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• 2000

The ultrasonic method, which is well known as nondestructive test method, is widely used to evaluate the material damage due to degradation. However, this method is just used for measuring the crack size and the thickness loss of the tube. The purpose of this study is to investigate the application of the ultrasonic technique for the evaluation of marine diesel engine exhaust valve and to suggest the correlation between the ultrasonic characteristics and valve degradation. From the evaluation of the results obtained, the technique of using the ultrasonic property was founds to be a efficient method to degree of marine diesel engine exhaust valve by nondestructive test.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.07a
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• pp.152-155
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• 2000

PWM inverter-fed traction motor is able to occur problems by additive transient surge stress and harmonic loss in contrast with motor driven by 60Hz sine wave alternating source. Therefore in this paper, test method and standard of existed already were investigate, "thermal + electric" complex degradation test that considered additive degradation occurred by inverter drive carried out in order to obtain insulation reliability of traction motor driven by inverter. It seems that this test method confers large value of application at reliability estimation which the subject of complete motor not windings sample from now on.

• Journal of the Korean Society of Propulsion Engineers
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• v.23 no.4
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• pp.42-49
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• 2019

This paper presents a method to predict the storage reliability of springs for turbo engine components based on an accelerated degradation test. The reliability assessment procedure for springs is established to proceed with the accelerated degradation test. The spring constant is selected as the performance degradation characteristic, the temperature is determined to be the stress factor that deteriorates the spring constant. The storage tests are performed at three temperature test conditions. The spring constant is measured periodically to check the degradation status of the springs. Failure times of the springs are predicted by using the degradation model. Finally, the storage lifetime of the springs at normal use conditions is predicted using an accelerated model and failure times of all test conditions.

• Proceedings of the KSME Conference
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• 2000.04a
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• pp.49-54
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• 2000

Cr-Mo-V steel is widely used as a material for the turbine structural component in fossil power plants. It is well known that this material shows the various material degradation phenomenons such as temper embrittlement, carbide coarsening. and softening etc. or ins to the severe operation conditions as high temperature and high pressure. These deteriorative factors cause tile change of mechanical properties as reduction of fracture toughness. Therefor it is necessary to evaluate tile extent of degradation damage for Cr-Mo-V steel in life assessment of turbine structural components. In this paper. the electrochemical potentiokinetic reactivation(EPR) test in $50wt%-Ca(NO_3)_2$ solution is performed to develop the newly technique for degradation damage evaluation of Cr-Mo-V steel. The results obtained from the EPR test are compared with those in small punch(SP) tests recommended by semi-nondestructive testing method using miniaturized specimen. The evaluation parameters used in EPR test are tile reactivation current density$(I_R)$ and charge$(Q_{RC})$ reactivation rate$(I_R/I_{Crit},\;Q_R/Q_{Crit})$. The results suggest that $I_R/I_{Crit}$ in these parameters shows a good correlation with SP test results.