Inelastic Models and Linear Viscoelasticity

Abstract

We have seen some of the classical constitutive equations introduced in the last three centuries, and explored some of the issues in the general formulation of constitutive equations in the last chapter. There, we mention that the general constitutive principles should be taken as guidelines only; they should emerge from the physics of the constitutive model. Only when the physics are so complex that we must guess which variables to put in our continuum model, and then these principles are applied to produce something useful. In engineering, the emphasis is to produce numbers for the design process. Therefore simple models with the “right” physics tend to be favoured. “Right” physics here means accounting for the flow process to be modelled. If the flow process does not call for certain phenomena, then those may be left out in the constitutive modelling In addition, engineers do not have any qualms in using empirical data to supplement a constitutive equation, as long as the correct physical framework has already been incorporated. Remember, simplicity in the correct theoretical framework, with enough empirical inputs to ensure a quantitative prediction is for what we are striving.