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권종오,김효철,류재문,오정근 대한조선학회 2017 大韓造船學會 論文集 Vol.54 No.6
A segment of the wave board has been expressed as a submerged line segment in the two dimensional wave flume. The lower end of the line segment could be extended to the bottom of the wave flume and the other opposite upper end of the board could be extended to the free surface. It is assumed that the motion of the wave board could be defined by the sinusoidal motion in horizontal direction on either end of the wave board. When the amplitude of sinusoidal motion of the wave board on lower and upper end are equal, the wave board motion could express the horizontally oscillating submerged segment of piston type wave generator. The submerged segment of flap type wave generator also could be expressed by taking the motion amplitude differently for the either end of the board. The pivot point of the segment motion could play a role of hinge point of the flap type wave generator. Simplified analytic solution of oscillating submerged wave board segment in water of finite depth has been derived through the first order perturbation method at two dimensional domain. The case study of the analytic solution has been carried out and it is found out that the solution could be utilized for the design of wave generator with arbitrary shape by linear superposition.
Poling 강도 변화에 따른 PZT 세라믹스의 역학적 특성 변화
이홍림,권종오,한봉석 연세대학교 산업기술연구소 1995 논문집 Vol.27 No.2
PZT ceramics is a piezoelectric material with the perovskite structure. The internal stress of PZT is induced by the para-to ferroelectric phase transition at the Curie point during cooling process after firing and the additional anisotropic internal stress is induced by dc field application. By this reason, the fracture toughness is increased in poling direction, on the other hand, it is decreased in perpendicular direction. Therefore, the fracture toughness of PZT exhibits the anisotropic property. The purpose of this study are to investigate the dependence of mechanical properties(fracture toughness, strength, and fracture type) on the variation of the poling strength. The PZT(Pb(Zr1/2Ti1/2)O₃) specimens were pled by the poling strengths of 0~6kV/mm and their strengths were measured by 4 point flexure system. It was observed that the fracture toughness was decreased in vertical direction to the poling direction, however, it was increased in parallel direction as the polling strength was increased. The bending strength was decreased as the poling strength was increased and the bending strength to the vertical direction was larger than that in parallel to the poling direction. The fracture type transferred to intergranular from transgranular fracture as the poling strength was increased. The mechanical breakdown happened when the poling strength higher than 4kV/mm was applied.
Poling 강도 변화에 따르는 PZT 세라믹스의 강도와 균열성장 의존성
이홍림,권종오,한봉석 한국세라믹학회 1997 한국세라믹학회지 Vol.34 No.8
The dependence of strength, crack growth, fracture mode and degree of domain rearrangement of PZT ceramics on poling strength were studied. The PZT [(Pb0.94Sr0.06)(Zr0.46Ti0.54)O3+Nb(trace)] specimens were poled at 0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0 kv/mm, and the strength of the specimens was measured by 3 point flexure system. The bending strength of the specimen decreased in different modes according to the bending directions; xz, zx and yz plane direction with x axis of the poling direction in Cartesian coordinate system. The strength differences between the directions increased as the poling strength increased. The fracture mode transferred to intergranular fracture mode from transgranular one as the poling strength increased. The mechanical breakdown occurred when the poling strength higher than 3 kV/mm was applied to the specimen. It was observed that the crack length increased in the normal direction to the poling direction, however, decreased in the parallel direction to the poling direction when the poled PZT specimen was indented by the Vickers indenter. However, the crack produced by indentation continuously was continuously increased little by little after indentation on the specimen. The domain rearrangement occurred as the poling strength increased and the domains were rearranged more effectively when the electric field was continuously increased little by little.