Implicit integration of incrementally non-linear, zero- elastic range, bounding surface plasticity

Artikel i vetenskaplig tidskrift, 2019

The zero elastic range, bounding surface plasticity framework is a suitable choice for modeling materials which exhibit zero purely elastic response during shearing. As a consequence of zero elastic range the plastic strain increment direction, and consequently the elastic-plastic moduli fourth order tensor depends on the direction of the stress increment, rendering the model incrementally non-linear. The system of ordinary differential equations of the elastic-plastic formulation is intrinsically implicit. Thus, an iterative algorithm based on the Backward Euler numerical integration method and the damped Newton-Raphson method with an adaptive trial step is proposed in this work. The proposed methodology is applied to the zero elastic range SANISAND-Z model for sands and a thorough verification is done for various applied strain histories. The proposed integration scheme allows the use of SANISAND-Z or any other bounding surface zero elastic range model in displacement-driven finite element analysis.