This paper describes a case in which nonstandard test configurations had to be used to assess fracture toughness, and an experimental, analytical program to support the validity of the results.

Zirconium alloy pressure tubes (103 mm inside diameter, 5 mm thick) contain the primary coolant in CANDU™ reactors. Because irradiated materials lacks ductility, the pressure tube cannot be flattened to produce flat specimens to determine fracture toughness. Therefore, a method was devised for spark eroding 17-mm compact specimens from sections of pressure tubing. These specimens retained the normal in-plane dimensions of the standard compact specimens, but possessed the curvature of the tube. By comparing results from flat and curved specimens, this paper shows experimentally that flat-plate equations can be applied to both specimen types to calculate the fracture toughness parameters with little error. A simple analytical calculation estimates that the maximum curvature-induced stress should be less than 10% of the in-plane tensile stress at the crack tip.