Measuring Fracture Energy in a Brittle Polymeric Material: Application of a High-Speed Optical Extensometer

The brittle fracture of polymethyl methacrylate (PMMA) was studied using a high-speed extensometer, which consisted of an optical fiber and a position-sensing detector (PSD). Single-edge-cracked tensile specimens were pin-loaded with a special jig so that they could split and fly in the loading direction after fracture. The flying height and residual deformation of the split specimen were measured to estimate the elastic energy E _e and non-elastic energy E _n, respectively. By subtracting E _e and E _n from the external work U _ex applied to the specimen, the fracture energy E _f for creating a new fracture surface was evaluated. The results showed that E _e, E _n, and E _f increased with U _ex, and the ratio E _f/U _ex was about 45% over a wide range of U _ex. Energy release rate was also estimated using U _ex or E _f, and the results suggested that it was overestimated if E _e and E _n were included.