ISA cyclic hypoplasticity (Fuentes et al.)
Hypoplastic models alone reproduce well the behavior of soils under monotonic loading, but fails to simulate its behavior upon cyclic loading. The Intergranular Strain Anisotropy (ISA) is a mathematical extension of conventional hypoplastic models for soils, proposed originally by Fuentes and Triantafyllidis (2015) to improve simulations of cyclic loading. It can be considered as a reformulation of the conventional intergranular strain theory by Niemunis and Herle (1997). Basically, this extension reproduces the following characteristics:
a) Yield surface within the intergranular strain space for elastic strains
b) the stiffness increase upon reversal loading
c) the reduction of the plastic strain rate for same conditions.
ISA-hypoplastic models are also able to reproduce paths of repetitive cycles, and provide an extension to account for cyclic mobility effects and thus, enabling simulations of liquefaction phenomena.
More information: http://www.geo-research.info/umats-for-soils-abaqus/