The present work is the initial part of a basic investigation on the assessment of embedded defects, where attention is focussed on the development of a practical and convenient assessing method combined with non-destructive inspection. Specimens with embedded cracks were produced by using the diffusion welding method. The mechanical properties and microstructure of the bond region in the embedded crack specimen were almost equivalent to those of the base metal. The KIc-value obtained by using the embedded circular crack specimen was equal to that of the base metal specimen with a circumferential crack. It is clear from these results that the present method using the diffusion welding is effective in producing specimens with shape- and size-controlled embedded cracks. From the result of fracture toughness tests on the specimens with embedded elliptical cracks, it was found that the K-value of an embedded elliptical crack could be estimated by using a reduced circular crack with an area equivalent to that of an elliptical crack. This fact suggests that a convenient method of assessment of embedded defects can be developed when incorporated with ultrasonic inspection which gives the area of crack easily. The effect of the eccentricity of an embedded circular crack on K-estimation was also investigated and a convenient method for evaluating the K-value, combined with ultrasonic inspection, was developed.
