Creep Rupture Modelling of Polymers

Damage by creep related fracture process is of primary importance in en gineering polymers and their composites. Modelling of creep rupture is useful for engi neering design especially in obtaining design stresses. Previously, the creep rupture times of polyethylene and polypropylene have been described successfully using a three element model with a critical elastic stored energy criterion. The modelling is aided by the use of computational nonlinear regression analysis. The model predicts well the lower stress limit (no fracture) and the upper stress limit (immediate fracture) both of which are depen dent only on the elastic constants and the resilience of the material. Present results show that this model also describes accurately the rupture times of more than fifteen polymers ranging from polysulphone, polycarbonate, polyacetal to reinforced polyamide. High values of the lower stress limit are obtained if the local anisotropy (elastic ratio in the model) is small. This limit is a function of the cohesive energy density. The large number of different polymers analysed allow a basis for a physical interpretation on the anelastic (time dependent) and elastic moduli of the model. A generalized local domain segment concept having an arrangement independent of the principal directions of loading could be used to describe the creep rupture model.