Rate dependent fracture toughness of plastics

Abstract

To characterize the rate dependent fracture behavior of various engineering polymers, instrumented impact tests were performed with bending, and tensile type 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, tf, 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 curv”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 using various specimen and loading configuratons and by force based and dynamic data reduction schemes. Also, there is a clear tendency for a decrease in fracture toughness with increasing impact rate for all materials investigated. However, the rate sensitivity of fracture toughness values strongly depends on the specific polymer type.