Embrittlement of Semicrystalline Polymers: A Dynamic Fracture Analysis

The fracture properties of polymers are complex to estimate because they strongly depend on the viscoplastic behavior of the polymer. This is especially true for semicrystalline thermoplastic polymers used for the transport or storage of fluids under pressure. The methodology presented in this work allows the construction of a part of the kinetic law of fracture of polymers, the one that reveals the brittleness of the polymer. The fracture energy of the material is estimated by taking into account the cracking regime and thus the potential inertial effects induced during the rapid propagation of cracks in the case of brittle behavior. Polyamide-11, a polymer used for the manufacture of hydrogen tank liners, is studied. A decrease in fracture energy is observed between the initiation resistance and the fast propagation resistance. This is referred to as polymer embrittlement. Electron microscopy analysis of fracture surfaces in three different zones (initiation, propagation, arrest) has revealed the mechanisms responsible for the ductility of the polymer in quasi-static regime and its brittleness in dynamic regime.