• Transactions of the Korean Society of Mechanical Engineers
• /
• v.8 no.4
• /
• pp.305-312
• /
• 1984

본 연구에서는 STS 316강의 고온 저사이클 피로강도와 파괴거동을 고찰하고자 고온 대기중에서 변형율 제어에 의한 인장.압축 저사이클 피로시험을 실시하였다. 전 변형율축, 탄성 변형율축 및 소성 변형율축과 피로수명과의 관계를 일정 변형율 속 도하에서 응력축, 온도 및 주파수의 영향과 파괴거동을 고찰하였다.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.20 no.3
• /
• pp.753-764
• /
• 1996

The metal matrix composites(MMC) are currently receiving a great deal of attention. These composites possess exellent mechanical and physical properties such as modulus, strength, wear resistance and thermal stability, which make them very attractive for use in automotive piston. In this study, $Al/{Al_2}{O_3}$(15%) composites are fabricated by the squeeze casting method. Mechanical properties such as tensile strength and ductility are performed at room and elevated temperature($250^{\circ}C$ and $350^{\circ}C$), respectively. Through thermomechanical analyser, thermal expansion coefficient of $Al/{Al_2}{O_3}$ composites are conducted for ranging from room temperature to ($400^{\circ}C$.And bending fatigue tests are also performed by the rotary bending machine at room temperature.The tensile strength and elastic modulus have been improved up to 38% and 35% by the addition of the reinforcements, respectively. Thermal expansion coefficients of MMCs which is located normal and parralel to the applied pressure are showed slightly different less than 10%. Fatigue strengh of the composite was improved by about 20% compared with that of unreinforced Al alloy. The results of this study will be used to understand the basic fracture behavior of MMCs and eventually to expand the applocation of MMCs as a machine parts undertaken various loadings.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.34 no.7
• /
• pp.911-917
• /
• 2010

In this study, we performed structural and fatigue analyses of the engine exhaust manifold that was subjected to thermo-mechanical cyclic loading. The methodologies used in this study are based on an approach in which the techniques for modeling the exhaust system, the temperature-dependent properties of the material, and thermal cyclic loading are taken into consideration and a reliable strategy is adopted for failure prediction. An application example shows that at an elevated temperature, considerable compressive plastic deformation is observed and that at a low temperature, tensile stresses remain in those parts of the test exhaust manifold where failure is observed. In order to predict fatigue life, mechanical damage is determined on the basis of the stress.strain hysteresis loops by using the classical Coffin.Manson equation and by adopting a method in which the dissipated plastic energy is taken into consideration.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.10 no.2
• /
• pp.110-116
• /
• 2002

At elevated temperature, very complex precipitations occur in STS316. To investigate the effect of the precipitation on mechanical properties in SIS316, tensile tests and fatigue crack growth tests were carried out at $650^{\circ}C$ using artificially degraded materials. The material degradation was simulated by aging for up to 20000 hrs. at $750^{\circ}C$, which is equal to 179000hrs (about 20yrs) of service life at $650^{\circ}C$, after conducting solution treatment for 20 min. at $11300^{\circ}C$. The result of the hardness test and the tensile test showed that both properties are closely related to the mean free distance of carbides. Also, from the results of fracture tests at $650^{\circ}C$, ${\triangle}K_{th}$, after values were found to decrease as aging time and microstructure, as the volume fraction of $\sigma$ phase increased.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.18 no.11
• /
• pp.983-989
• /
• 2005

[ $PZT(Pb(Zr,Ti)O_3)$ ] thin films were deposited by multi-target reactive sputtering method on $RuO_2$ substrates. Pure perovskite phase PZT films could be obtained by introducing Ti-oxide seed layer on the $RuO_2$ substrates prior to PZT film deposition. The PZT films deposited on the $RuO_2$ substrates showed highly voltage-shifted hysteresis loop compared with the films deposited on the Pt substrates. The surface of $RuO_2$ substrate was found to be reduced to metallic Ru in vacuum at elevated temperature, which caused the formation of oxygen vacancies at the initial stage of PZT film deposition and gave rise to the voltage shift in the P-E hysteresis loop of the PZT capacitor. The fatigue characteristics of the PZT capacitors under unipolar wane electric field were different from those under bipolar wane. The fatigue test under unipolar wane showed the increase of polarization. It was thought that the ferroelectric domains which had been pinned by charged defects such as oxygen vacancies and the charged defects were reduced in number by combining with the electrons injected from the electrode under unipolar wave, resulting in the relaxation of the ferroelectric domains and the increase of polarization.

• Transactions of the Korean Society of Pressure Vessels and Piping
• /
• v.12 no.1
• /
• pp.126-133
• /
• 2016

Recently, the research and development of Sodium-cooled Fast Reactors (SFRs) have made progresses. However, liquid sodium, the coolant of an SFR, is chemically unstable and sodium fire can be occurred when liquid sodium leaks from sodium pipe. To reduce the damage by the sodium fire, many fire walls and fire extinguishers are needed for SFRs. LBB concept in SFR might reduce the scale of sodium fire and decrease or eliminate fire walls and fire extinguishers. Therefore, LBB concept can contribute to improve economic efficiency and to strengthen defense-in depth safety. The LBB assessment procedure has been well established, and has been used significantly in light water reactors (LWRs). However, an LBB assessment of an SFR is more complicated because SFRs are operated in elevated temperature regions. In such a region, because creep damage may occur in a material, thereby growing defects, an LBB assessment of an SFR should consider elevated temperature effects. The procedure and method for this purpose are provided in RCC-MRx A16, which is a French code. In this study, LBB assessment was performed for PGSFR IHTS hot-leg pipe according to RCC-MRx A16 and the applicability of the code was discussed.

• Transactions of Materials Processing
• /
• v.7 no.3
• /
• pp.274-281
• /
• 1998

The service life of tools in metal forming process is to a large extent limited by wear, fatigue fracture and plastic deformation. In elevated temperature forming processes wear is the predominant factor for tool operating life. To predict tool life by wear Achard's model is generally applied. Usually hardness of die is considered to be a function of temperature. But hardness of die is a function of not only tem-perature but also operating time of die. To consider softening of die by repeated operation it is necessary to express hardness of die by a function of a function of temperature and time. By experiment of reheating of die softening curve was obtained and applied to suggest modified Archard's Model in which hardness is a function of main tempering curve.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.41 no.8
• /
• pp.751-758
• /
• 2017

The behavior of fatigue crack growth of nickel-based powder metallurgy superalloy that could be used in aircraft turbine disc is investigated at room temperature, and $650^{\circ}C$ considering real operating conditions. The direct current potential drop(DCPD) method was used to measure the crack length of material in real time according to ASTM E647. Tests were performed with various stress ratios (0.1 and 0.5). Experimental results show that stress ratio, and temperature all affect the behavior of fatigue crack growth. As the stress ratio and temperature increase, the fatigue crack growth rate of nickel-based powder metallurgy superalloy also increases. Results were compared and reviewed with fatigue crack growth rates of other nickel-based superalloy materials (Inconel-100) that were studied in previous papers. Fractography analysis of the fractured specimens was performed using as SEM.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.15 no.2
• /
• pp.44-49
• /
• 2011

A study of the fatigue life of copper alloy which was used in inner jacket of regenerative cooling chamber of liquid rocket engine has been performed. Generally used life prediction methods -original universal slopes method, modified universal slopes method, Mitchell's method, B$\"{a}$umel and Seeger's method, and Ong's method- have been used for predicting the fatigue data. It was found that the novel life prediction method which was modified from Ong's method was suggested since almost all data have not been predicted well with the widely used methods. The suggested modified Ong's method predicted well within 3X scatterbands.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2010.11a
• /
• pp.89-92
• /
• 2010

A study about the fatigue life of copper alloy which is used in inner jacket of regenerative cooling chamber of liquid rocket engine has been performed. Generally used life prediction methods-original universal slopes method, modified universal slopes method, Mitchell's method, Baumel and Seeger's method, and Ong's method-have been used for predicting the fatigue data. It was found that the novel life prediction method which is modified from Ong's method was suggested since almost all data have not been predicted well with the widely used methods. The suggested modified Ong's method predicted well within 3X scatterbands.