| Abstract: | The characterization of ductile polymers with ductile fracture behavior is still a controversial subject. Presently, two approaches based on fracture mechanics have been proposed for the evaluation of impact failure of plastics, i.e., the method using the concept of essential fracture work, and the crack initiation and propagation approach. This paper discusses the validity of the fracture parameters used in these approaches. Additional experimental results and evidence are presented; they indicate that the concept of essential work of fracture cannot be used to characterize the fracture property of plastics. At high loading rates, the fracture energy of plastics can decrease with crack extension, resulting in a variable essential work of fracture. It is also found that the work dissipated in the outer plastic zone as formulated in the concept does not only reflect the non-essential work but is also related to the fracture process.Instead, the approach based on two material parameters should be used to evaluate the impact fracture behavior. Crack initiation and propagation energies should be considered to account for the variation of material's fracture behavior during crack propagation so as to include time rate and size scale effects. |
