COMBINED STRESS CREEP OF NON-LINEAR VISCOELASTIC MATERIAL.

The multiple integral representation for creep behavior of viscoelastic material is reviewed, together with the modified superposition principle and the product form assumption for the kernels of the multiple integrals. Creep experiments under combined tension and torsion are employed to determine the material constants. Other experiments involving abrupt changes in states of stress and constant rates of stressing are employed to evaluate the usefulness of the theories by comparing the theoretical predictions with the experimental results.