Comparative study of models for nonlinear viscoelastic creep of polycarbonate

The creep behavior of a commercial grade polycarbonate is investigated. Ten different constant stresses ranging from 8 MPa to 50 MPa were applied to the specimen, and the resultant creep strains were measured at room temperature. It is found that the creep could be modeled linearly below 15 MPa, and nonlinearly above 15 Mpa. Different nonlinear viscoelastic models have been briefly reviewed and used to fit the test data. It is shown that the Schapery model represents a generalization of the modified superposition principle, and both the Findley model and the Struik representation are suitable for properly describing the creep behavior of the polycarbonate investigated in this paper; however, the Findley model fit the data better than the Struik representation at high stress.