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Standardization of Fracture Toughness Testing of Ceramics in the United States
Quinn, G.D.,Jenkins, M.J.,Salem, J.,Bar-On, I. The Korean Ceramic Society 1998 The Korean journal of ceramics Vol.4 No.4
American Society for Testing and Materials (ASTM) standard test method PS 070-97 has been created for measuring fracture toughness of advanced ceramics. PS 070-97 includes three test methods which use beams in bending: chevron notch (CNB), single-edged precracked beam (SEPB), and surface crack in flexure (SCF). Supporting data has been collected through several Versailles Advanced Materials and Standards round robins. This paper discusses the evolution of the standard including the rationale for the choice of the three methods and the specifications in the standard. Progress on Standard Reference material 2100 which will have certified values of fracture toughness is presented.
Oh-Heon Kwon,Michael G.Jenkins 대한기계학회 2002 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.16 No.9
Continuous fiber ceramic composites (CFCCs) have advantages over monolithic ceramics : Silicon Nitride composites are not well used for application because of their low fracture toughness and fracture strength, but CFCCs exhibit increased toughness for damage tolerance, and relatively high stiffness in spite of low specific weight. Thus it is important to characterize the fracture resistance and properties of new CFCCs materials. Tensile and flexural tests were carried out for mechanical properties and the fracture resistance behavior of a SCS6 fiber reinforced Si₃N₄matrix CFCC was evaluated. The results indicated that CFCC composite exhibit a rising R curve behavior in flexural test. The fracture toughness was about 4.8 MPa ㆍ m^1/2 , which resulted in a higher value of the fracture toughness because of fiber bridging. Mechanical properties as like the elastic modulus, proportional limit and the ultimate strength in a flexural test are greater than those in a tensile test. Also a numerical modeling of failure process was accomplished for a flexural test. This numerical results provided a good simulation of the cumulative fracture process of the fiber and matrix in CFCCs.<br/>
Abernathy, C.R.,Gila, B.P.,Onstine, A.H.,Pearton, S.J.,Kim, Ji-Hyun,Luo, B.,Mehandru, R.,Ren, F.,Gillespie, J.K.,Fitch, R.C.,Seweel, J.,Dettmer, R.,Via, G.D.,Crespo, A.,Jenkins, T.J.,Irokawa, Y. The Institute of Electronics and Information Engin 2003 Journal of semiconductor technology and science Vol.3 No.1
Both MgO and $Sc_2O_3$ are shown to provide low interface state densities (in the $10^{11}{\;}eV^{-1}{\;}cm{\;}^{-2}$ range)on n-and p-GaN, making them useful for gate dielectrics for metal-oxide semiconductor(MOS) devices and also as surface passivation layers to mitigate current collapse in GaN/AlGaN high electron mobility transistors(HEMTs).Clear evidence of inversion has been demonstrated in gate-controlled MOS p-GaN diodes using both types of oxide. Charge pumping measurements on diodes undergoing a high temperature implant activation anneal show a total surface state density of $~3{\;}{\times}{\;}10^{12}{\;}cm^{-2}$. On HEMT structures, both oxides provide effective passivation of surface states and these devices show improved output power. The MgO/GaN structures are also found to be quite radiation-resistant, making them attractive for satellite and terrestrial communication systems requiring a high tolerance to high energy(40MeV) protons.