On the use of NURBS plasticity for geomaterials

Abstract

There are a huge number of plasticity models available in the literature to represent the behaviour of geomaterials and the majority include the concept of a yield surface which bounds the allowable stress in the material. However, each surface is distinct and requires a specific equation describing the shape of the surface to be formulated in each case. Recently Coombs et al. (2016) proposed a non-uniform rational basis spline (NURBS) plasticity framework where any isotropic yield surface can be represented and integrated using the same numerical algorithm. However, the NURBS plasticity framework is currently restricted the to case of associated plastic flow which will lead to an overly dilative response for most geomaterials. This paper extends the approach to include a non-associated plastic flow rule whilst guaranteeing the recovery of associated plastic flow if required. The algorithm's performance is demonstrated at both material point (stress-strain) and boundary value problem levels.