Viscoplastic models for high temperature applications

The information speci®c to the material deformation behavior in stress analyses of structures and manufacturing processes is contained in the material model or the constitutive equation. In the past these models had to be linear and simple to perform the stress analyses economically. Large safety (ignorance) factors made up for the simplicity. The availability of inexpensive computing power and the demands of society for reliability and safety require an improvement of stress analyses by using new and realistic constitutive equations of nonlinear, inelastic behavior of metals and their alloys. Presently used nonlinear models such as plasticity and creep theory are by far the oldest link in the stress analysis package. Test results obtained with modern mechanical testing machines and theoretical developments during the past several decades suggest that viscoplastic models using state variables are much- improved models. It is recommended that these models be carefully reviewed, further developed when needed and recommended by interdisciplinary, technology speci®c committees of materials, mechanics, testing and computing experts. Rather than having databases with material constants, databases containing `the constitutive modelʹ for di€erent alloys and associated constants should be established. The analyst would call up `the modelʹ, say, for annealed stainless steel and load it into the stress analysis program