Application of instrumented impact test in polymer testing

Advanced methods of conducting and analyzing instrumented Charpy impact tests are described and used in measuring the initiation fracture toughness K_1c at a range of impact velocities and temperatures. Improvements developed in the impact testing of metals are discussed and applied in the toughness evaluation of polymers. In lower-speed impact tests where load–displacement records are nearly linear, the maximum recorded load may be used to evaluate K_1c by stress analysis K calibration formula. In high-speed impact tests, where the load trace is highly oscillatory, the fracture load to be used in the calculation must be derived indirectly. The indirect derivation of fracture load for this purpose from a “low blow” stiffness measurement and specimen deflection has been studied in detail, and the use of the periodic time of the “low blow” test has been found to offer a reliable method of calculating the system stiffness.