COMPUTATION OF CREEP-BEHAVIOR OF THERMOPLASTICS

The dimensioning of structural parts made of plastics requires the knowledge of the material parameters which depend on the processing and, loading conditions. In this paper, the possibility of describing the stress‐, temperature‐, and time‐dependent deformation behavior of thermoplastics below the linear viscoelastic limit is presented, using simple exponential functions. The formal relationship of the systems of equations have been ascertained based on a large number of experimental results. They enable a mathematical description of the deformation behavior of the material considered with sufficient accuracy for engineering requirements. This is based on parameters for creep experiments with three different stresses, at constant temperature, extending to 102 h. One experimental series extended to 103 h. As shown in examples, based on these experimental results, the computation makes possible a predetermination of the deformations obtained with the time‐factors of 102 to 103. The temperature can vary within the nearly linear region of the semi‐logarithmic shear modulus‐temperature curve. Within the variation of the stress, cyclic changes of the loading can also very simply be taken into account using Boltzmann's superposition principle. Principally, the computation can be carried out using any auxiliary means which contains the exponential function xy. Simple programmable pocket computers allow an automatic calculation. Copyright © 1978 Society of Plastics Engineers, Inc.