New endochronic plasticity model for soils. Interim report

A new endochronic theory of plasticity is developed which is free of several undesirable features inherent in earlier versions of the theory, and provides increased modeling capability with substantially fewer material parameters. This new constitutive theory is fully three-dimensional, and has the ability to describe the important features of soil response to seismic loading, including hysteresis, densification/dilatancy, strain hardening/softening, and creep under cyclic loading (ratcheting). It predicts elastic response at points where loading, or unloading begin and, for one-dimensional unload-reload processes, produces hysteresis loops that close, no matter how small the magnitude of the unloading. The theory, therefore, does not exhibit the peculiar small unload-reload response feature of the original theory, and consequently it can be used with confidence in the numerical solution of wave propagation problems