ABSTRACT
The constitutive modelling of engineering materials has been the objective of numerous works during the recent years, primarily because of the increasing complexity of the loading conditions to which modern structures are subjected and the corresponding need for more accurate analysis and response predictions. The presentation will be rather descriptive emphasizing the concepts more than the exact analytical formulation, but proper reference to the corresponding works will allow the interested reader to obtain further information. The choice of using a rate-dependent or rate-independent formulation depends on the material and the loading conditions and can be decided on the basis of the corresponding experimental data. The delayed deformation becomes much more pronounced if clusters form. In reference to subsequent notation when two juxtaposed tensors with subscripts n appear in a term which is a scalar, the repetition and summation of the corresponding trace operation over all n are implied.
