Structure/property relationships in highly crosslinked polyurethanes. Part II. Crack propagation and blunting

The crack propagation and yield behaviour of highly crosslinked polyurethanes, which were studied previously have been investigated using double torsion and uniaxial compression testing. A correlation has been found between the initiation fracture toughness (K_ICi) and yield stress (σ_y) and this has been interpreted using a crack blunting analysis. A fractography study has enabled the plastic deformation zone to be studied in detail. The dependence of the fracture behaviour of the materials upon the structure of the polyurethanes is also discussed. It is shown that the fracture toughness depends upon chain flexibility rather than cross-link density.