Analysis of the Spb method for geometries where ηpl depends on a/W.

Since its proposal, the simplified Spb method has been successfully applied to the fracture toughness evaluation of metallic and polymer materials. However, some points of this methodology remain unclear, like the applicability on standardized geometries in which ηpl depends on the a/W ratio. In order to discuss this and other aspects, theoretical analyses of the Spb method were made and some experimental tests were performed. The theoretical analysis revealed that considerable differences in C(T) and SE(T) geometries could be present when the same ηpl factor for both blunt notched and pre-cracked specimens is used. To minimize these differences, the use of the most general expression of the Spb method in addition to ηpl factors provided by the standards for geometries where ηpl change with a/W is proposed. The proposed experimental methodology, based on the load separation and on ηpl factors provided by the standards, proved to be suitable for C(T) geometry, whereas for SE(T) geometry the results indicate that more research is still needed.