Essential Concepts of Neohypoplasticity

Abstract

The neohypoplastic model [12] eliminates several shortcomings of the hypoplastic vW-HP model [17]. The most important improvements are presented here. The general form of the constitutive equation $\dot{\sigma } = {\bar{\mathsf {E}}}:(\dot{\varepsilon } + \mathbf{m}Y \Vert \dot{\varepsilon }\Vert )$ is slightly modified by two additional terms in brackets. The functions $\mathsf{E}(\sigma ,e), \mathbf{m}(\sigma ,e)$ and $Y(\sigma ,e)$ are completely reformulated in order to deal with numerous problems of the old model: perpetuum mobile of the second kind, too small dilatancy during triaxial tension paths, poor predictions of peak stress and inconsistent behaviour of the model at the upper density limit. A new state variable $\mathbf{z}$ similar to the one from the Sanisand model [3] is introduced. The hitherto used state variables: the stress and the void ratio are preserved, of course. Moreover, a new kind of nonlinearity is proposed: the rotation of the deviatoric stress response. The problems connected to the extension intergranular-strain extension are not discussed here.