• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.4
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• pp.738-746
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• 1988

Fatigue crack propagation of duplex stainless steel weldments was studied to develop further phenomenological understanding of the influences of welding heat cycle accompanying microstructural changes. Fatigue tests were carried out under constant amplitude of load in air at room temperature. The results showed that the crack propagation rate was different in base metal, heat affected zone and welding line. The crack propagation behavior in each part of duplex stainless steel was strongly dependent on phase ratio(.gamma../.alpha.) and several factors of microstructure also affected this propagation behavior. The fractographic feature in each part of steel were discussed on crack propagation behaviors.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.10
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• pp.1155-1160
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• 2011

High-strength nickel-based super alloys have been widely used in aircraft engines, vessel engines, and turbine blades because of their high strength and excellent fatigue and oxidation resistance. In this study, tests were carried out to determine the total strain range and temperature for high-strength nickel-based super alloys. Prepared specimens of IN738LC were exposed to temperatures of $871^{\circ}C$ and $982^{\circ}C$ for 1,000.10,000 h. These specimens were subjected to tests of mechanical properties and microstructure observations. The changes in mechanical properties were related to changes in ${\gamma}$ according to the thermal exposure time.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.415-419
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• 2004

Thermal barrier systems are susceptible to instability of the thermally grown oxide(TGO) at the interface between the bond coat(BC) and the thermal barrier coating(TBC). The instabilities have been linked to thermal cycling and initial geometrical imperfections, as well as to misfit strains due to oxide growth and expansion misfit. In this work, deformation of TGO near a surface groove due to thermal cycling has been observed at high temperatures, $1100^{circ}C$, $1150^{circ}C$, $1200^{circ}C$. The effect of peak temperature and the thickness of substrate are presented.

• The tire
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• s.65
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• pp.3-9
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• 1976

가유 고무에 대변형의 반복왜를 외부자극으로서 부여하면 초기에는 대폭의 응력의 변화현상이 보여져 서서히 일정응력치에 접근하여 파단에 이른다. 이 응력의 변화현상과 피로수명(파단하기까지의 회수)이 여하한 기계적 화학적 인자의 영향을 받는가를 천연고무의 순고무 가유물로 검토했다. 그 결과 실온으로 고무에 반복신장피로를 부여하면 가교구조, 망목밀도 및 신장률이 응력변화의 대소, 피로수명의 증감에 영향을 주었다. 고온으로 고무에 반복신장피로를 주면 열산화에 의하여 어느 온도로부터 현저한 응력연화(화학응력연화) 현상이 보였다. 연이나 고무에 열화방지제를 첨가하면 고온에 있어서의 산화반응이 억제되기 때문에 무첨가의 경우와 달라서 파단이나 현저한 응력연화가 일어나지 않았다. 피로수명(F)와 파괴신장(εb),반복신장률(ε)사이에 F=A(εb-ε)n 의 관계가 성립함이 인정되었다. An은 고유의 파라메에터어이며 천연고무의 순고무가유물로서 n은 4.0~4.5의 거의 일정치를 표시했다.

• Korean Journal of Materials Research
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• v.10 no.5
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• pp.354-659
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• 2000

Applications of composite materials have been in progress noticeably in manufacturing areas of automotive, aircraft and in other industries, resulting in ensuing research activities. Carbon-epoxy, one of major composite materials, is investigated for its thermal characteristics. Upon treatments of the composite material with repeated heatings and coolings variations of its elastic constants are monitored to reveal the thermal nature of the composite material. In this study, generally, changes in elastic constants are observed to occur mostly during the first 10~20 thermal cycles. Values of G(sub)13 remain almost unchanged except a minor decrease. However in the observed small changes thermal shocks produce less effect than thermal fatigues. On the other hand, values of $E_1$show gradual increases with the num-ber of applied thermal cycles and temperatures. Meanwhile, values of $E_2$ and G(sub)23 decrease to a certain extent in the early stage during the applications of thermal cycling but are not appreciable affected by frequencies of thermal cy-cles. Also, thermal shocks are observed to induce different effects depending on treatment temperatures.

• Journal of the Korean Society for Nondestructive Testing
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• v.29 no.1
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• pp.10-14
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• 2009

Heat generation mechanism of ultrasound infrared thermography is still not well understood, yet and there are two reliable assumptions of heat generation, friction and thermo-mechanical effect. This paper investigates the principal cause of heat generation at fatigue crack with experimental and numerical approach. Our results show most of heat generation is contributed by friction between crack interface and thermo-mechanical effect is a negligible quantity.

• Journal of the Korean Society of Propulsion Engineers
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• v.17 no.1
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• pp.103-115
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• 2013

Durability testing method trends of the thermal barrier coating(TBC) for the combustion chamber of the liquid-propellant rocket engine have been investigated. Many types of the durability testing method such as the mechanical tests to measure surface cohesion force, the thermal fatigue tests with laser, furnace, burner or plasma, the small scale combustion tests using injectors, and the thermo-mechanical fatigue tests were observed. The TBC with sufficient durability can be selected for the use of combustion chamber through such specimen-level tests and the durability can be verified by the tests using the real scale combustion chambers.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2012.05a
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• pp.603-615
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• 2012

Durability testing method trends of the thermal barrier coating(TBC) for the combustion chamber of the liquid-propellant rocket engine has been investigated. Many types of the durability testing method such as the mechanical tests to measure surface cohesion force, the thermal fatigue tests with laser, furnace, burner or plasma, the small scale combustion tests using injectors, and the thermo-mechanical fatigue tests were observed. The TBC with sufficient durability can be selected for the use of combustion chamber through such specimen-level tests and the durability can be verified by the tests using the real scale combustion chambers.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.4 s.235
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• pp.526-533
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• 2005

Reliability problem in inkjet printhead, one of MEMS devices, is also very important. To eject an ink drop, the temperature of heater must be high so that ink contacting with surface reaches above $280^{o}C$ on the instant. Its heater is embedded in the thin multi-layer in which several materials are deposited. MEMS processes are the main sources of residual stresses development. Residual stress is one of the factors reducing the reliability of MEMS devices. We measured residual stresses of single layers that consist of multilayer. FE analysis is performed using design of experiment(DOE). Transient analysis for heat transfer is performed to get a temperature distribution. And then static analysis is performed with the temperature distribution obtained by heat transfer analysis and the measured residual stresses to get a stress distribution in the structure. Although the residual stress is bigger than thermal stress, thermal stress is more influential on fatigue life.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.9
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• pp.1897-1904
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• 2002

Monotonic torsional and pure torsional low cycle fatigue(LCF) test with artificial degradation were performed on duplex stainless steel(CF8M). CF8M is used in pipes and valves in nuclear reactor coolant system. It was aged at 430$^{\circ}C$ for 3600hrs. Through the monotonic and LCF test, it is found that mechanical properties(i.e., yield strength, strain hardening exponent, strength coefficient etc.) increase and fatigue life(N$\sub$f/) decreases with degradation of material. The relationship between shear strain amplitude(${\gamma}$$\sub$a/)and N$\sub$f/ was proposed.