A Study on High Temperature Fatigue Strength of Plasma-Sprayed Notched Members by Using Laser Speckle Measurement

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There are so many discontinuous parts in service machines that fatigue problems of notched member are to be solved. Metallic materials used at high temperature were applicable up to 1000degC. The special materials are needed for further high temperature usage. The ceramic-sprayed material was one of the useful materials for high temperature. The purpose of this study is to clarify the characteristics of high temperature fatigue in ceramic-sprayed materials. Specially, an emphasis was put on the fatigue properties of notched members. It was found that the notched sample with 1mm in notch root radius was manufactured for the fatigue test.The bi-axial strain at notch root was monitored using a laser speckle strain/displacement measurement system, consequently. While the lateral strain at notch root was too small to measure, the longitudinal strain was large enough to examine the cyclic strain properties. It was found that the notch root was put on the plane strain condition and the fatigue life of notched specimen was nearly equal to the life in smooth specimen. The reason for the similarity in fatigue life was considered that notch constraint was limited to develop the strain hardening/softening behavior. From the observation of sample sections, a crack initiated at top coatings is not the same to a crack in the substrate. It was concluded that the coating material was not affected to the fatigue life of ceramic-sprayed specimen.