Test MethodTensile fracture testing and energy evaluation of a light-cured composite resin

The brittle fracture of a light-cured composite resin used in dental restoration was examined using a high-speed extensometer consisting of an optical fiber and a position-sensing detector (PSD). Single-edge-cracked specimens for tensile testing were fabricated by packing the composite between two rectangular plates of polymethyl methacrylate (PMMA). In order to study the dynamic effect of brittle fracture and the nonelastic effect of the material, the specimens were pin-loaded with a special jig so that they could split and fly apart in the loading direction after fracture. The flying height and residual deformation of the split specimen were measured to estimate the elastic energy Ee and nonelastic energy En, respectively. The fracture energy Ef required to create a new fracture surface was obtained by subtracting Ee and En from the external work Uex applied to the specimen. The results showed that the ratio Ef/Uex was about 32% for the composite specimen over a wide range of the fracture load, while it was about 45% for the PMMA specimen. The energy release rate Gf was also estimated using Ef. The results indicated that, although Gf increased with the fracture load, the increasing slope for the composite specimen was smaller than that of the PMMA specimen.