Fracture mechanics of thermoplastic elastomers: applicability of the load separation criterion

Initially proposed for metals and then extended to polymeric materials, the Load Separation Criterion, LSC, is the theoretical basis of several laboratory test methods for the fracture characterisation of materials exhibiting plasticity. In this work, the applicability of the LSC to the fracture characterisation of thermoplastic elastomers, TPEs, was analysed and discussed for the first time. Due to their peculiar nature, TPEs combine melt state processability with a high compliance and elasticity typical of rubbers. At a macroscopic scale, their mechanical response appears generally complex, with an evident viscoelastic character coupled with clear signs of plasticity (behaviour often referred to as of the elastoviscoplastic type). Three industrially relevant TPEs, differing for the chemical nature, were examined. First, their stress-strain behaviour was studied by uniaxial tensile tests, carried out on dumbbell specimens. Then, to verify the load separability, single-edge notched in tension, SENT, tests were carried out on blunt-notched specimens (stationary crack tests under plane stress conditions). Specimens with different crack-length/width ratios were tested at room temperature and with a fixed crosshead speed (low rate). The LSC proved to be valid for all three TPEs studied.