Novel fracture toughness test using a notchless triangular prism (NTP) specimen.

The aim of this study was to develop and validate a new method for determining the fracture toughness of materials and adhesive interfaces. The new test specimen is a notchless triangular prism (NTP) which, when placed in the testing holder, achieves a configuration similar to that of the standard chevron-notched short rod (CNSR) specimen. It can be cast, ground, or simply machined easily and reproducibly without cutting an initial notch. Finite element analysis of a modeled NTP specimen loaded in tension showed a stress distribution similar to a CNSR specimen. A very good correlation was obtained between the NTP and CNSR fracture toughness values of poly(methyl methacrylate) during a calibration study. Fracture toughness values similar to those reported in the literature were obtained for several dental materials and one adhesive interface using the NTP test. The fracture patterns were indicative of plane strain conditions during testing. All bulk specimens and most of the adhesive specimens showed crack arrest, which suggested a stable, well-controlled testing procedure. These results suggest that the NTP fracture toughness test can be used to determine the fracture mechanics of bulk materials and adhesive interfaces.