Recently the endochronic theory in plasticity has been proposed, which seems to rationally describe the general behavior of concrete or soils under complicated multi-axial loading states. It is based on sound thermodynamic arguments, and does not require the notion of yield surface nor specification of unloading-re-loading criteria. This unique features make the theory particularly attractive for describing the behavior of concrete or soils.
The endochronic theory was originally developed by Valanis and has been applied with remarkable success to various problem of metal plasticity, which is called the integral endochronic theory (the endochronic theory with kernels).
On the other hand, the other endochronic theory was developed by Bazant et al. to describe the behavior of concrete, which is called the incremental endochronic theory. It is derived from the integral endochronic theory by replacing the kernel function with a single exponential term, and it is requires a large number of functions and material parameters.
In this paper, thermodynamic foundations for the integral endochronic theory are considered, and mechanical explanations of the theory are given by means of physical models. Moreover, the features in plasicity which were derived from the theory are examined thoroughly.