Strength Evaluation of Alumina Spray Coating (2nd Report, Proposal for Judgment of Crack Interference and Correction Methods of Crack- Shape):(2<SUP>nd</SUP> Report, Proposal for Judgment of Crack Interference and Correction Methods of Crack- Shape)

The alumina spray coating is a material containing many pores (cracks) and there is a crack-interference in the alumina spray coating, therefore, the crack-interference leads to a decrease in the fracture strength. There are some studies that have used the elastic analysis for two or more cracks. Moreover, there are some standards for the combining of the cracks. However, in ceramics including alumina, a study of quantifying the internal spread of the crack when interfering and presuming a static fracture strength with judgment of the crack-interference after the stable crack propagation is not known. In this study, after the alumina spray coating single layer was taken out, a Vickers' indentation crack was introduced, a 4-point bending test was performed and a <I>R</I>-curve was acquired. As a result, the fracture strength characteristic of the alumina spray coating single layer was clarified. Three judgments of the crack-interference with the <I>R</I>-curve were then proposed. Moreover, a correction method of the crack-shape when the cracks interfere was proposed. The validities of the proposals were verified with bending tests after two Vickers' indentation cracks were introduced.