Thermal barrier coating (TBC) systems which are used for insulating the substrates of gas turbine blades from high temperature can be made by thermal spraying. The TBC system has residual stresses because of high temperature deposition and the thermal expansion mismatch in the system. In this study, how the residual stress occurs in TBC system was examined by both experimental measurement and FEM analysis. The Yttria-stabilized zirconia (YSZ) top coating was deposited by atmospheric plasma spraying (APS). CoNiCrAlY bond coatings were deposited by high velocity oxygen-fuel (HVOF) spraying and APS. The temperatures of YSZ, CoNiCrAlYs and substrates were measured during thermal spraying. The temperature of YSZ was the highest and that of CoNiCrAlY(HVOF) was the lowest among the three types of spray processes. The residual stresses were elastically calculated by FEM based on the measured temperature histories. The residual stress of YSZ and CoNiCrAlYs on two types of substrates were also measured by X-ray diffraction method. It was confirmed from FEM analysis that residual stress consisted of primary quench stress and secondary thermal mismatch stress. The quench stress was caused by the quenching of coating particles during deposition which occurs due to the huge thermal capacity of the substrate. The thermal mismatch stress was caused by the difference in linear expansion coefficients between coating and substrate. It was found that not only these two mechanisms but also microcrack formation caused by quench played an important role in the residual stress. The temperatures at which residual stresses might begin to occur in the coatings were shown based on the stress relaxation by microcrack formation. It was also found that peening effect played an important role in the residual stress of HVOF sprayed coating.
An intelligent structure of concrete reinforced by CFRP which can detect and repair the delamination of CFRP from the surface of concrete has been proposed and the performance has been evaluated in this paper. In order to investigate the effect of repair, three-point bending test has been performed on the test piece. When the optical fiber sensor detects the delamination during the test, the processor judges the damage to be repaired. The embedded Ni-Cr wire is heated to release the epoxy resin in the capsule, it spreads into the delamination to adhere the damage. The result of three-point bending test after repair showed better performance than that of a specimen of non-repaired. In case the repair was delayed, however, reasonable repairing cannot be expected. Therefore, delamination must be detected and repaired in the early stage of fracture. As a result, it was recognized that the delamination of CFRP on mortar concrete can be repaired with the proposed system.
When CFRP lamina is applied for the reinforcement of concrete structures, the lamina has a possibility to delamin ate from the surface of concrete. The delamination must be detected and be repaired as soon as possible for the reliability of structures. In pursuit of this, an intelligent structure was proposed in this paper. Both sensor and actuator are required to detect and to repair the delamination, respectively. As the intelligent structure, optical fiber was used to detect the delamination of CFRP as a sensor. Epoxy resin adhesive in a capsule was used to repair the delamination as an actuator.In the first paper, characteristics of both sensor and actuator were investigated. The brightness of transmitted light in the optical fiber was decreased at bended point caused by delamination of CFRP. On the other hand, the capsuled epoxy resin has been spreaded widely into delaminated interface. As a result, it was recognized that the proposed sensor and actuator can be used to detect and repair the delamination of CFRP.
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