Classical and Non-Classical Creep Models

The following paper gives a short introduction into classical and non—classical creep models and their application to structural mechanics calculations. The analysis of creep processes is becoming more and more important in engineering practice. This development is connected with extended exploitation conditions and increasing safety standards. The quality of the predictions is influenced by the reliability of the material and structural models. In other words, it depends strongly on the possibilities to describe the creep problem, which should be analysed with the help of an adequate mathematical model.In solid mechanics two types of equations are generally used — material independent and material dependent equations. The latter one should contain relations, which are able to reflect the individual response of the materials to external loadings. One goal in mechanics is to formulate suitable constitutive and, if necessary, evolution equations describing the material behaviour phenomenologically. Such an approach should be adopted for the material behaviour by an identification procedure which allows to find relations between the parameters in the equations and the experimentally determined characteristics of the material. The following considerations are related to these questions.Classical creep equations are insensitive to the kind of loading. They describe, for example, identical behaviour under tension and compression (only the sign of the creep deformations is opposite). In addition, constitutive equations, which are able to reflect differences in the material behaviour with respect to the kind of loading, are discussed.