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과하중 및 휴식기간이 AISI 4340 강의 피로균열 성장거동에 미치는 영향
태원필,김송희 대한금속재료학회(대한금속학회) 1987 대한금속·재료학회지 Vol.25 No.9
Effects of intermittent rest period at 300℃, overload in tension and overload followed by rest period on fatigue crack growth in 4340 steel were investigated. The intermittent lest period stopped the growth of fatigue cracks completely near the threshold level of △K. The alleviation effect of rest period on the rate of crack growth was more distinct at the lower level of △K. The higher overload ratio was (i.e., OLR = 3), the more the alleviation effect. It is suggested that compressive residual stress at the ahead of crack tip was produced during overloading period, and it is enhanced roughness of the crack surface due to crack deflection after the overloading, which, in turn, ceased or retarded crack propagation during the subsequent cycling. The most retardation of fatigue crack growth was observed when overload and subsequent rest period were combined. The mechanisms are discussed.
태원필,윤여범,김송희 한국세라믹학회 1996 한국세라믹학회지 Vol.33 No.1
The aim of this study is to investigate the change of bending strength and fatigue strength in the unpoled and poled Pb(Zr, Ti)O3 ferroelectrics of tetragonal morphotropic phase boundary (MPM) and rhombohedral com-position in terms of internal stress which is measured by XRD method. Before poling treatment the highest bending strength was found in rhombohedral composition. After poling treatment the bending strength decreas-ed in all compositions but it decreased most remarkably in tetragonal composition. The most prominent de-crease of bending strength after poling treatment in tetragonal was attributed to the occurrence of microcracks due to highanisotropic internal stress around grain boundary which was induced of bending strength after poling in MPB and rhombohedral composition was not due to the occurrence of microcracks but to the increase in tensile internal stress perpendicular to the direction of crack propagation by domain alignment. Fatigue strength was higher before poling treatment than after poling treatment for various compositions.
Preparation of Lead-free (K,Na)NbO3-LiSbO3 Ceramics with High Piezoelectric Constants by FeO Doping
태원필,설정현,이재신,Han-Na Ji,Yun-Po Ok 한국물리학회 2010 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.56 No.4
Lead-free 0.95(K0.52Na0.48)NbO3-0.05LiSbO3 (KNN-LS) ceramics doped with FeO were prepared by conventional solid sintering, and their dielectric and piezoelectric properties were explored. The results indicated that FeO-doping was highly effective in densification and growth of KNN-LS ceramics, leading to significant enhancement in both the dielectric and the piezoelectric constants. The 1-mol% FeO-doped KNN-LS ceramics sintered at 1050 ℃ for 2 h exhibited a piezoelectric constant, d33, of 311 pC/N, which is higher than the value reported so far for untextured KNN ceramics.
반복응력에 따른 PZT 세라믹스의 유전 및 잔류 기계적 특성
태원필,김송희 한국세라믹학회 1994 한국세라믹학회지 Vol.31 No.8
The aim of this study is to investigate the changes in dielectric properties, Young's modulus and remnant compressive strength with compressive cyclic loading in PZT of tetragonal, MPB and rhombohedral composition. Higher relative dielectric constants appeared in the poled condition than the unpoled condition for all the compositions. After poling treatment remarkably higher relative dielectric constants were observed particularly in MPB, tetragonal compositions. Until five percent of the expected fatigue life was exhausted, the dielectric constant increased with compressive cyclic stress in MPB and rhombohedral while it remained nearly constant in tetragonal. During the subsequent compressive cyclic stress, dielectric constant decreased in all the three compositions. As the compressive cyclic stress is applied the change of Young's modulus was coincided with the change of remnant compressive strength.
태원필,김송희,조상희 한국세라믹학회 1992 한국세라믹학회지 Vol.29 No.10
The aim of this study was to investigate the change in compressive strength, freacture behavior and degradation of piezoelectric properties with compressive cyclic loading in Pb(Zr, Ti)O3 of tetragonal, morphotropic phase boundary and rhombohedral composition. The highest compressive strength was found in rhombohedral composition. After poling treatment the strength increased by 8.4% and 6.5% in tetragonal and morphotropic phase boundary compositions respectively while changed little in rhombohedral. The increase of compressive strength after poling treatment is believed to be due to the internal stress around grain boundary by domain alginment toward electric field direction in the microstructures having tetragonality and the occurrence of domain switching to the direction perpendicular to electrical field during fracture. Fracture mode relatively change from transgranular to intergranular was observed in the large grain sized tetragonal and morphotropic phase boundary compositions before and after poling but the transgranular fracture mode always remained in the rhombohedral composition. From the X-ray diffractometer analysis the domains parallel to the electric field direction is known to undergo rearrangement during the cyclic loading into random direction that is responsible for the degradation of piezoelectric property.
분극처리 전후의 Pb(Zr, Ti)$O_3$ 세라믹스의 파괴인성의 변화
태원필,김송희,Tae, Won-Pil,Kim, Song-Lee 한국재료학회 1993 한국재료학회지 Vol.3 No.5
본 연구에서는 입계의 성질을 이용한 PTCR 재료에 입계 modifier로서 $Bi_{2}$$O_{3}$와 BN을 첨가하고 입계의 미세구조와 결함농도를 변화시켜 이에 따른 소결 및 전기적 특성변화를 TMA, XRD, 복합 임피던스방법 등을 이용하여 해석하였다. 실험 결과 Y이 도우핑된 BaT$iO_{3}$ PTCR 재료에 $Bi_{2}$$O_{3}$를 첨가하였을때 약 0.1mol%까지 고용이 되는 것으로 밝혀졌다. $Bi_{2}$$O_{3}$를 고용한계 이하로 첨가시에는 생성되는 vacancy등의 결함으로 말미암아 Y-BaT$iO_{3}$의 치밀화가 촉진되었으나, 그 이상 첨가하면 치밀화 뿐만 아니라 결정립 성장도 억제되었다.$Bi_{2}$$O_{3}$ 결정립 내부에 Ba와 Ti vacancy가 동시에 생길 수 있어 고온저항이 높아짐을 알 수 있었다. BN은 BaT$iO_{3}$에 고용이 되지 않는 것으로 밝혀졌으며 $B_{2}$O/wub/3를 주성분으로한 액상형성으로 인하여 저온에서의 급격한 치밀화가 관찰되었다. 또 Ba-Y-Ti-B-O의 비정질 상이 tripie junction에 존재함으로서 상온저항이 크게 변화하였으며, PTCR jump도 높아졌다.
Sol-Gel 법으로 제작한 Zn<sub>1-x</sub>Co<sub>x</sub>O 박박의 미세조직 및 자기적 특성
고윤덕,태원필,김응권,김기출,최춘기,김종민,송준태,박태석,서수정,김용성,Ko, Yoon-Duk,Tai, Weon-Pil,Kim, Eung-Kwon,Kim, Ki-Chul,Choi, Choon-Gi,Kim, Jong-Min,Song, Joon-Tae,Park, Tae-Seok,Suh, Su-Jeung,Kim, Young-Sung 한국세라믹학회 2005 한국세라믹학회지 Vol.42 No.7
Zn$_{l-x}$Co$_{x}$O (x = 0.05 - 0.20) films were grown on Coming 7059 glass by sol-gel process. A homogeneous and stable Zn$_{l-x}$Co$_{x}$O sol was prepared by dissolving zinc acetate dihydrate (Zn(CH$_{3}$COO)$_{2}$$\cdot$2H$_{2}$O), cobalt acetate tetrahydrate ((CH$_{3}$)$_{2}$$\cdot$CHOH) and aluminium chloride hexahydrate (AlCl$_{3}$ $\cdot$ 6H$_{2}$O) as solute in solution of isopropanol ((CH$_{3}$)$_{2}$$\cdot$CHOH) and monoethanolamine (MEA:H$_{2}$NCH$_{2}$CH$_{2}$OH). The films grown by spin coating method were postheated in air at 650°C for 1 h and annealed in the condition of vacuum (5 $\times$ 10$^{-6}$ Torr) at 300$^{\circ}C$ for 30 min and investigated the nature of c-axis preferred orientation and physical properties with different Co concentrations. Znl_xCOxO thin films with different Co concentrations were well oriented along the c-axis, but especially a highly c-axis oriented Zn$_{l-x}$Co$_{x}$O thin film was grown at 10 at$\%$ Co concentration. The transmittance spectra showed that Zn$_{l-x}$Co$_{x}$O thin films occur typical d-d transitions and sp-d exchange interaction became activated with increasing Co concentration. The electrical resistivity of the films at 10 at$\%$ Co had the lowest value due to the highest c-axis orientation. X-ray photoelectron spectroscopy and alternating gradient magnetometer analyses indicated that no Co metal cluster was formed, and the ferromagnetic properties appeared, respectively. The characteristics of the electrical resistivity and room temperature ferromagnetism of Zn$_{l-x}$Co$_{x}$O thin films suggested the possibility for the application to dilute magnetic semiconductors.
증착온도를 달리하여 제조한 Zn0.8Co0.2O 박막의 미세조직 및 자기 특성
강영훈,태원필,서수정,김봉석,김기출,박태석,김용성 한국세라믹학회 2006 한국세라믹학회지 Vol.43 No.2
We studied the microstructure and magnetic property of the pulsed DC magnetron sputtered Zn0.8Co0.2O film as a function of substrate temperatures. The X-ray patterns of the Zn0.8Co0.2O film showed a strong (002) preferential orientation at 500℃. The films with a crystallite size of 23-35 nm were grown in the form of nano-sized structure and this tendency was remarkable with increasing substrate temperature. The UV-visible result showed that the Zn0.8Co0.2O film prepared above 300℃ has a high optical transmittance of over 80% in the visible region. The absorption bands were observed due to sp-d interchange action by Co2+ complex ion and d-d transition in the region from 500 to 700 nm. The resistivity of the film was below 10-1 Ωcm above 300℃. The AGM analyses results for the all films showed the magnetic hysteresis curves of ferromagnetic nature. The low electrical resistivity and room temperature ferromagnetism of ZnCoO thin films deposited above 300℃ suggested the possibility for the application to diluted magnetic semiconductors(DMSs).