Papers by Keyword: Vertical Crack

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Authors: Noriyuki Mifune, Yoshio Harada
Abstract: The applicability of 2CaO·SiO2-CaO·ZrO2 ceramic coatings as thermal barrier coatings (TBCs) was investigated. Coatings consisting of various ratios of 2CaO·SiO2-CaO·ZrO2 bond-coated with NiCrAlY were prepared using the plasma spray process. The structure of the coatings was characterized by scanning electron microscopy and X-ray diffraction analysis. The resistance of the coatings to thermal shock was evaluated with acoustic emission techniques under a thermal cycle from 1273 K to room temperature, and the hot corrosion resistance of the coatings was investigated with V2O5 and Na2SO4 at 1273 K for 3 h. The 2CaO·SiO2-10~30mass%CaO·ZrO2 coatings had excellent thermal shock resistance, because the coatings contained a vertical micro-crack in a single flattened ceramic particle. These coatings possessed excellent corrosion protection preventing direct contact between the corrosive ashes and a NiCrAlY bond coating. The CaO in the coating reacted with vanadium compounds and inhibited the penetration of corrosive ashes to the bond coating. The developed 2CaO·SiO2-20mass%CaO·ZrO2 thermal barrier coating on stationary vanes was evaluated in an actual gas turbine. The ceramic coating did not separate from the bond coating and reacted with SOx in combustion gas to produce a stable sulfate (CaSO4), which fixed in the coating. The TBC effectively protected the metal substrate of the vanes in practical operating condition for 25,000 h.
Authors: Ji Liang Liu, Hui Chen Cui, Ming Jin Chu, Jian Qun Hou
Abstract: The shear wall built with precast two-way hollow slab is an innovated precast concrete shear wall suitable for housing industrialization. Two shear walls built with precast two-way hollow slabs were tested pseudo-statically under low cyclic lateral loads to acquire their failure process and modes. The effect of the axial compression load was investigated. The study proved that vertical cracks along the vertical holes of the new type shear wall have been appeared to avoid brittle shear failure, and the shear wall developed integral section wall to walls-columns combination. As the results, the shear walls have the adequate deformability. The test results showed that with the increase of axial compressive ratio, crack development has been limited and the energy dissipation capacity has been improved. It also can be found that with the increase of the axial compressive load, shear capacity of the new type shear walls have been improved.
Authors: Ya Zhe Xing, Yong Li, Chang Jiu Li, Cheng Xin Li, Guan Jun Yang
Abstract: YSZ molten droplets created by plasma spraying were deposited on the YSZ substrate preheated to different temperature from 75oC to 1000oC. The results showed that there is little change in crack spacing when substrate temperature is less than about 740oC, and a significant increase in crack spacing from 3.54 μm at 740oC to 10.91 μm at 1000oC was observed. A simple qualitative model was proposed on the basis of the origin of thermal stresses to explain the influence of substrate initial temperature on crack density characterized by crack spacing. The analysis indicates that the results can be ascribed to the changes in tensile stress and splat/substrate adhesion resulting from changes of substrate initial temperature.
Authors: Zhe Lu, Sang Won Myoung, Tae Sik Jang, Kang Hyeon Lee, Je Hyun Lee, Yeon Gil Jung, Ung Yu Paik
Abstract: The effects of intrinsic feature of feedstock in air plasma-sprayed (APS) coatings on the microstructure and mechanical properties of vertical-cracked thermal barrier coatings (TBCs) were investigated in thermal exposure. The microstructure after the thermal exposure for 400 h is densified, while after the thermal exposure for 800 h various defects such as interlamellar cracks and the vertical and horizontal cracks are newly developed, even though the total porosity is decreased. The microstructure of the TBC prepared with 204 C-NS is more porous than that of the TBC with 204NS, showing higher mechanical properties and better thermal stability in the TBC with 204 NS.
Authors: Cheol Jun Park, Ji Woong Kang, Oh Heon Kwon
Abstract: The crack formation and propagation remain as major issues regarding the mechanical crack behavior of solid oxide fuel cell (SOFC), due to the thermomechanical mismatch and the porous nature of the SOFC components. The SOFC consisting of brittle ceramic materials can be damaged by the cracking due to high-temperature during the manufacturing and operation. The crack generated during the manufacturing were can cause the cell performance degradation during operation. For crack evaluation because the SOFC products the required power density through the stack considering the interconnector is required. The purpose of this study is to investigate the effect of the vertical crack at the cathode electrode, and also the effects of the crack on the interconnect channel position in operation for the crack behavior and stress field.
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