The experimental
K-value evaluation method proposed in the previous paper was applied to a pressurized cylinder with an internal surface crack. A partially-embedded circular crack was introduced in the longitudinal or circumferential direction inside the tubular specimen using a grinding disk 0.47mm in thick for dental cure use. The measured
K-values were compared with those numerically analyzed by Newman and Raju. The results obtained are summarized as follows:
(1) The fracture toughness of the material tested (Acrylite
®) was found isotropic in the longitudinal and the circumferential directions.
(2) The experimentally determined relationship between the non-dimensional stress intensity factor
Me and the crack depth ratio
a/t indicated the same trend as that numerically calculated for both longitudinal and circumferential surface cracks under a constant crack aspect ratio
a/c. The measured values of
Me, all of which were larger than the calculated values, agreed with the numerical values within 10% accuracy.
(3) The initial slit introduction technique employed gave a valid
K-value for a surface crack with the crack depth ratio larger than 0.5. In the case of a shallow crack,
i. e., a/t<0.5, it was judged that the initial slit should rather be regarded as a notch.
(4) In the case of a longitudinal crack,
Me was independent of the curvature of the specimen.
(5) The circumferential crack rapidly changed its propagation path into the longitudinal direction from the early stage of crack growth at fracture. This phenomenon was explained sufficiently by the simulation analysis of crack growth path.
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