2019 年 68 巻 9 号 p. 686-692
This paper aims to clarify a crack length on W-EDMed (Wired Electric Discharge Machined) surface and show an estimation method for the surface crack length of an electric conductive zirconia ZrO2-WC.The surface crack length was estimated based on experimental fracture strength of ZrO2-WC specimens with the W-EDMed surface and the fracture dynamics model. Two other estimation methods were used in this study to validate the crack length. One of them gave a practical crack length defined by removing thickness of the W-EDMed surface that fracture strength recovers. The other method also gave practical crack length evaluated by adding residual crack length on the ground surface to the ground removal length. Both practical lengths were evaluated by clarifying effects of the ground removal length on the fracture strength. The estimated crack lengths were compared each other. It provided the surface crack length ranged over from 45.6μm to 55.6μm. An effectiveness method for prediction of the crack length was considered based on the experimental results. The results showed that the estimated crack length as W-EDMed surface was different from both practical crack lengths. This reason why the difference occurred is because the tensile residual stress may be generated and distributed on the W-EDMed surface. W-EDM process can make zirconia ceramics induce large stresses with repetition of cooling from high temperature and changing its volume caused by structural transitions. Removing the W-EDMed surface over 10-15µm length can disappear the tensile residual stress and to provide an accurate crack length on the W-EDMed surface. It can bring a useful estimation method for an accurate crack length.