Rate dependent yield and post-yield behavior of engineering polymers

To characterize the rate dependent fracture behavior of various engineering polymers, instrumented impact tests were performed with bending and tensile type fracture specimens in the testing rate range of 10(-5) m/s up to 8 m/s. Load-time signals were recorded using an instrumented striker and a fixture equipped with a piezoelectric load cell and strain gages, respectively. Furthermore, the time-to-fracture was detected with different strain gage types applied to the specimen side surfaces in the vicinity of the crack tip. The data reduction to determine rate dependent fracture toughness values was carried out according to different procedures (conventional force based analysis and "dynamic key curve" method) taking specific local crack tip loading rates into account. In the quasi-brittle failure regime, good agreement was found between the fracture toughness values determined by force based and dynamic data reduction schemes.